'Science will have to drive decisions at both ends of the social ladder'From the Copenhagen summit on climate change, Rajendra Pachauri, chair of the IPCC, talks about the need for people to tell their elected leaders that they expect firm and forward-looking action on climate change
Rajendra Pachauri
guardian.co.uk, Thursday 17 December 2009
Showing posts with label Intergovernmental Panel on Climate Change (IPCC). Show all posts
Showing posts with label Intergovernmental Panel on Climate Change (IPCC). Show all posts
Friday, 18 December 2009
Tuesday, 20 January 2009
Sense and Nonsense in Climate Change - David Warden at Dorset Humanists
On 10th January 2009 at Dorset Humanists (Bournemouth, Dorset UK) David Warden gave his views on the Climate Change debate. My comments in green. David Wardens answers in yellow.
- Man made emissions of CO2 - 30 Billion Tonnes v x Quadrillion Tonnes gases in the atmosphere.
- Total atmosphere NOT Carbon is 99.9% at current CO2 levels of 380ppm. The reason David turned "380ppm" into "99.9% carbon free" was really to highlight the fact that we are so easily swayed by the way data is presented.
- If CO2 levels double the figure will be 99.4%. cf homeopathy. Crabsallover: 'No explanation why CO2 / Methane /NO2 are such potent green house gasses was discussed.' David: "The potency of CO2 is believed to be enhanced by a secondary effect: global warming leads to evaporation which adds the greenhouse effect of water vapour. Sooner or later water vapour gets washed out as rain, so this theory is highly debateable. Methane is a potent greenhouse gas but there’s very little of it in the atmosphere. There’s also a tiny amount of NO2 in the atmosphere."
- "the most surprising fact about global warming is that it is not, at the present time, happening." Nigel Lawson
- compared arguements of Catastrophist (the Cats) with Moderates (the Mods)
- IPCC - remit is to assess understanding of human-induced climate change - but not climate change in general. Crabsallover 'IPCC brief is much wider than David Warden suggested and includes a full overview of Climate Change. Twenty one years ago UNEP and WMO established the Intergovernmental Panel on Climate Change (IPCC) to provide independent scientific advice on the complex and important issue of climate change. The Panel was asked to prepare a report on all aspects relevant to climate change and its impacts and to formulate realistic response strategies. I told David Warden that greater attention should have given in this talk to the findings of the 4 reports in 1990, 1995, 2001 and 2007 - with each IPPC report the probability of man made climate change through increasing CO2, has increased." David"I think we would have got totally bogged down if I had attempted to appraise 4 massive IPCC reports. I was making the more general point that the IPCC has been criticised by the sceptical scientists, particularly its summaries for policymakers which iron out a lot of the scientific uncertainties, rather like Blair’s ‘dodgy dossier’ on Iraqi WMD." I say "I would expect the 22 page Summaries for Policymakers to simplify some of the science presented in the 52 page Synthesis report, Which scientific uncertainties were 'ironed out'? Did this mean that Policymakers were somehow misled?
- Joseph Fourier discovered greenhouse gases in 1824
- Average greenhouse emmsission per person: 11T - UK, 2T India, 20T USA
- 2% of global CO2 emmissions are from the UK
- 99.9% of atmosphere is C free, 0.8 degree C rise in global temperatures since 1850
- NIPCC - Fred Singer (Nature, not Humans, rules the Climate). Crabsallover 'some scientists have dismissed Singer's most recent report on global warming as "fabricated nonsense".'
- Kyoto cost $150Bn pa - would money be better spent on reducing poverty worldwide?
- in Cretaceous the sea level was 650' higher than today (twice height of St Pauls Cathedral!)
- Sawtooth graph: annual changes in temperature levels due to plant growth/decay - mostly fluctuating - whilst CO2 levels rise
- Hockey stick graph (IPCC)
- IPCC - a doubling of CO2 will give a temperature rise of 1.1-6.4 degrees - IPCC (6 Scenarios, Table 3.1, http://www.ipcc.ch/pdf/assessment-report/ar4/syr/ar4_syr.pdf )
- David said in this posts 5th comment "A large part of the sceptical case is discontent with the whole IPCC process - described by Nigel Lawson as science by committee - leading to a politically manufactured consensus from which few are brave enough to dissent.
- David Warden said 'you can prove anything with graphs'
- Gaia Hypothesis - James Lovelocke
- CO2 levels - 350ppm levels (= 350*100%/1,000,000) = 0.35%
- Russian Scientist - a big freeze by 2050?
- Hole in greenhouse blancket discovered in Pacific Ocean in 2001
- Sea Level rises in 21st Century: IPCC estimate 2', Al Gore 20', James Hansen 80'
- Sea Level rises if ALL of these land mass melted: Greenland 23', Antarctica 200' (West Antarctica 16')
- Geological timescale eg; Eon - Phanerozic ; Era - Mesozoic; Period - Quarternary; Epoch - Eocene
- Rachel Carson book Silent Spring book led to a ban on DDT which lead to many dying from malaria
- flooding of Maldives (no mention of Bangladesh). David answers "I omitted this for reasons of time: A 2 foot sea level rise is likely to be a problem but not a catastrophe. For low-lying countries like Bangladesh, it’s likely to be a problem (about 50% of the land would be flooded if the sea level were to rise by 3 feet) but as Bangladesh gets richer, it’ll find ways to manage or mitigate the problem such as building sea defences. The Bangladesh economy has been growing at about 5-6% over recent years and poverty has fallen by 20% since the early 1990s. But even without global warming, Bangladesh will always be a geographically vulnerable place for human beings to live. Just as Florida is a geographically vulnerable place for human beings to live."
- post Kyoto costs will be $8 Trillion (Fred Pierce)
- climate change is a secular religion, Spanish Inquisition against climate change deniers!
- 'their is a fairly weak correlation between CO2 levels and temperature'
- 'global warming is not a serious threat to man'
- "At most, we may see a total rise of about 2 or 2½°C during the 21st century over and above the temperature in 1850 (and this includes the 0.8C rise between 1850-2000) ie a 1.2 or 1.7°C rise during 21st over 1850-2000 period".
- "this 2 or 2½°C temperature rise will be mostly beneficial."
- 'global cooling may happen by 2050'
- 'governments are agreeing to target of a 2 degree rise because that is what will happen naturally whether man intervenes or not to stop Climate Change'
- 'their is a fairly weak correlation between CO2 levels and temperature'. Most of the observed increase in global average temperatures since the mid-20th century is very likely due to the observed increase in anthropogenic GHG concentrations. (IPCC Synthesis summary, pg 5)
- 'global warming is not a serious threat to man'. if DW scenario (increase of 1.1-1.7C by end 21st century), IPCC say that up to 30% species at risk of extinction, most corals bleached, increased damage from floods and storms. (IPCC Synthesis Report).
- "At most, we may see a total rise of about 2 or 2½°C during the 21st century over and above the temperature in 1850 (and this includes the 0.8C rise between 1850-2000) ie a 1.2 or 1.7°C rise during 21st over 1850-2000 period". See following graphs (click for larger graph) incl. David Warden (DW) 1.2-1.7C scenario v IPCC 6 scenarios (IPCC Synthesis Report).
Comments by Audience- Sue Chapman: Iain Stewart programme - Earth: The Climate Wars; Nigel Lawson excludes CO2 levels - his book is a work of fiction, 11thhourproject,
- Harry: 30K scientists signed up to Kyoto Protocol
- I said "Stern Report - will cost 1-2% GDP to correct problem if act now vs 8% GDP if act in 2030"
- I said "vast majority of scientists agree that climate change is happening and it is man made." David answers "I don’t think this argument can be settled on a number count. We need to listen to climate scientists. All of them, including the sceptics, agree that climate change is happening and that part of it is man made."I say' Agreed, most importantly we must listen and act on what climate scientists are saying. The IPCC say Most of the observed increase in global average temperatures since the mid-20th century is very likely due to the observed increase in anthropogenic (man made) Green House Gas concentrations. (IPCC Synthesis summary, pg 5)'
- Paul Entwhistle: Royal Society (1400 members) report on Climate Change - page / pdf; ask MP to vote for Early Day Motion EDM 21; on ; albedo effect; solar power; desalination;
- a lady 'no kind of concensus amongst scientists'
- albedo effect
- Roger West: 'High voltage direct current', Solar Power / Desalination.
Thursday, 15 January 2009
Tuesday, 13 January 2009
Robust Findings and Key Uncertainties - IPCC 2007 Synthesis Report.
Reposted from: http://www.ipcc.ch/pdf/assessment-report/ar4/syr/ar4_syr.pdf
I have noted below some of the Robust Findings and Key Uncertainties in Section 6 of the IPCC 2007 Synthesis Report.
6.1 Observed changes in climate and their effects, and their causes
Robust findings
Robust findings
Robust findings
I have noted below some of the Robust Findings and Key Uncertainties in Section 6 of the IPCC 2007 Synthesis Report.
6.1 Observed changes in climate and their effects, and their causes
Robust findings
- Warming of the climate system is unequivocal
- Global total annual anthropogenic GHG emissions have grown by 70% between 1970 and
2004 - Most of the global average warming over the past 50 years is very likely due to anthropogenic GHG increases
- Analysing and monitoring changes in extreme events, including drought, tropical cyclones, extreme temperatures and the frequency and intensity of precipitation, is more difficult than for climatic averages
Robust findings
- With current climate change mitigation policies and related sustainable development practices, global GHG emissions will continue to grow over the next few decades.
- For the next two decades a warming of about 0.2°C per decade is projected for a range of SRES emissions scenarios.
- Continued GHG emissions at or above current rates would cause further warming and induce many changes in the global climate system during the 21st century that would very likely be larger than those observed during the 20th century.
- Models differ considerably in their estimates of the strength of different feedbacks in the climate system, particularly cloud feedbacks, oceanic heat uptake and carbon cycle feedbacks
- Future changes in the Greenland and Antarctic ice sheet mass, particularly due to changes in ice flow, are a major source of uncertainty that could increase sea level rise projections.
- Decisions about macro-economic and other policies that seem unrelated to climate change can significantly affect emissions.
Robust findings
- Some planned adaptation (of human activities) is occurring now; more extensive adaptation is required to reduce vulnerability to climate change.
- Unmitigated climate change would, in the long term, be likely to exceed the capacity of natural, managed and human systems to adapt.
- The economic mitigation potential is sufficient to offset the projected growth of global
emissions or to reduce emissions to below current levels in 2030. - Many impacts can be reduced, delayed or avoided by mitigation.
- Delayed emissions reductions significantly constrain the opportunities to achieve lower stabilisation levels and increase the risk of more severe climate change impacts.
- The range of stabilisation levels for GHG concentrations that have been assessed can be achieved by deployment of a portfolio of technologies that are currently available
- Barriers, limits and costs of adaptation are not fully understood
- Estimates of mitigation costs and potentials depend on assumptions about future socio-economic growth, technological change and consumption patterns.
Monday, 12 January 2009
IPCC - Report Procedures
Reposted from: http://www.ipcc.ch/ipccreports/index.htm
The main activity of the IPCC is to provide in regular intervals Assessment Reports of the state of knowledge on climate change. The latest one is "Climate Change 2007", the Fourth IPCC Assessment Report.
The IPCC produces also Special Reports; Methodology Reports; Technical Papers; and Supporting Material, often in response to requests from the Conference of the Parties to the UNFCCC, or from other environmental Conventions.
The preparation of all IPCC reports and publications follows strict procedures agreed by the Panel. The work is guided by the IPCC Chair and the Working Group and Task Force Co-chairs. Hundreds of experts from all over the world are contributing to the preparation of IPCC reports as authors, contributors and reviewers. The composition of author teams shall reflect a range of views, expertise and geographical representation. Review by governments and experts are essential elements of the preparation of IPCC reports.
The IPCC is honored with the Nobel Peace Prize
Reposted from: http://www.ipcc.ch/index.htm
Oslo, 10 December 07
The Intergovernmental Panel on Climate Change and Albert Arnold (Al) Gore Jr. were awarded of the Nobel Peace Prize "for their efforts to build up and disseminate greater knowledge about man-made climate change, and to lay the foundations for the measures that are needed to counteract such change".
IPCC - Links
Reposted from: http://www.ipcc.ch/links/index.htm
Selected Links.
Selected Links.
Canada
Taking Action on Climate Change
New Zealand
United States
Sunday, 11 January 2009
Glossary of Terms used in the IPCC Fourth Assessment Report
Reposted from: http://www.ipcc.ch/glossary/index.htm
Glossary of Terms used in the IPCC Fourth Assessment Report
IPCC - Press Information
Information for the Press (2007-2008): http://www.ipcc.ch/press/index.htm
Press Releases: http://www.ipcc.ch/press/press-releases.htm
Press Releases: http://www.ipcc.ch/press/press-releases.htm
IPCC FOURTH ASSESSMENT REPORT, CLIMATE CHANGE 2007 (AR4) - Graphics
Reposted from: http://www.ipcc.ch/graphics/graphics.htm
IPPC - Speeches
Reposted from: http://www.ipcc.ch/graphics/speeches.htm
selected IPCC speeches
1 December 2008: Speech of the IPCC Chairman, Mr Rajendra Pachauri at the Openning Ceremony of the UNFCCC COP 14, Poznán, Poland
selected IPCC speeches
1 December 2008: Speech of the IPCC Chairman, Mr Rajendra Pachauri at the Openning Ceremony of the UNFCCC COP 14, Poznán, Poland
23 January 2008 : Speech of the IPCC Chairman, Mr Rajendra Pachauri, at the World Economic Forum in Davos - Opening Session
10 December 2007 : Acceptance Speech for the Nobel Peace Prize Awarded to the IPCC delivered by R K Pachauri - Oslo
24 September 2007 : Presentation by Dr R.K. Pachauri during the Opening Session of the UN High Level Event on Climate Change - New York
The Physical Science - IPCC - Presentations
source: http://www.ipcc.ch/graphics/presentations.htm
selected presentations
20th Anniversary of the Intergovernmental Panel on Climate Change
See also the "1988-2008 20 years IPCC" brochure
IPCC Fourth Assessment Report (AR4) "Climate Changes 2007"
Presentation of the WG I Report at the GMEF and UNEP GC-24 Nairobi, 6 February 2007 Nairobi
selected presentations
20th Anniversary of the Intergovernmental Panel on Climate Change
Presentations on the evolution of climate change science as reflected in IPCC Reports, Opening Ceremony, 31 August 2008, Geneva
Sir John Houghton's presentation on the WG 1
Mr. Bob Watson's presentation on the WG 2
Mr. Ogunlade Davidson's presentation on the WG 3See also the "1988-2008 20 years IPCC" brochure
IPCC Fourth Assessment Report (AR4) "Climate Changes 2007"
Presentation of the WG I Report at the GMEF and UNEP GC-24 Nairobi, 6 February 2007 Nairobi
IPPC 4th Assessment Reports (2007)
About IPCC
The IPCC (Intergovernmental Panel on Climate Change) was established in 1988 World by the Meteorological Organization and the United Nations Environment Programme to provide the decision-makers and others interested in climate change with an objective source of information about climate change. More...
16th Anniversary (2004) brochure - describes the history of the IPCC & major achievements.
IPPC 4th Assessment Reports (2007)
Synthesis Report (AR4)
FULL REPORT
Summary for Policymakers
The Climate Change 2007 Synthesis Report is based on the assessment carried out by the three Working Groups of the IPCC. It provides an integrated view of climate change and addresses the following topics:
• Observed changes in climate and their effects
• Causes of change
• Climate change and its impacts in the near and long term under different scenarios
• Adaptation and mitigation options and responses, and the interrelationship with sustainable development, at global and regional levels
• The long-term perspective: scientific and socio-economic aspects relevant to adaptation and mitigation, consistent with the objectives and provisions of the Convention, and in the context of sustainable development
• Robust findings, key uncertainties
Working Group I Report "The Physical Science Basis"
FULL REPORT
Summary for Policymakers & Technical Summary
The IPCC Working Group I (WG1) assesses the physical scientific aspects of the climate system and climate change. More...
WG1 Technical Support Unite web page: http://ipcc-wg1.ucar.edu
Working Group II Report "Impacts, Adaptation and Vulnerability
FULL REPORT
Summary for Policymakers & Technical Summary
The IPCC Working Group II assesses the vulnerability of socio-economic and natural systems to climate change, negative and positive consequences of climate change, and options for adapting to it. More...
WG2 Technical Support Unite web page : http://www.ipcc-wg2.org
Working Group III Report "Mitigation of Climate Change"
FULL REPORT
Summary for Policymakers & Technical Summary
The IPCC WG3 assesses options for mitigating climate change through limiting or preventing greenhouse gas emissions and enhancing activities that remove them from the atmosphere. More...
WG3 Technical Support Unit web page: http://www.mnp.nl/ipcc/
Hard copies of all above reports are available from Cambridge University Press
Saturday, 10 January 2009
Intergovernmental Panel on Climate Change (IPCC) - Background
Reposted from: http://unfccc.int/methods_and_science/other_methodological_issues/items/1077.php
The Intergovernmental Panel on Climate Change (IPCC) is an independent body founded under the auspices of the World Meteorological Organization (WMO) and the United Nations Environment Programme (UNEP). It assesses the scientific literature and provides vital scientific information to the climate change process.
The IPCC is best known for its comprehensive assessment reports, incorporating summaries for policymakers from all three Working Groups, which are widely recognized as the most credible sources of information on climate change.
The First Assessment Report in 1990 helped launch negotiations on the Convention.
The 1995 Second Assessment Report, in particular its statement that "the balance of evidence suggests … a discernible human influence on global climate", stimulated many governments into intensifying negotiations on what was to become the Kyoto Protocol.
Third Assessment Report of the Intergovernmental Panel on Climate Change
The Third Assessment Report, released in May 2001, confirmed the findings of the Second Assessment Report, providing new and stronger evidence of a warming world.
* Scientific, technical and socio-economic aspects of impacts of, and vulnerability and adaptation to, climate change, and
* Scientific, technical and socio-economic aspects of mitigation,
Fourth Assessment Report of the Intergovernmental Panel on Climate Change
During SBSTA 26 (Bonn, May 2007), the secretariat has organized, in cooperation with the IPCC, an in-depth briefing during the sessions of the subsidiary bodies on the contributions of the three IPCC working groups to the Fourth Assessment Report (AR4).
The Intergovernmental Panel on Climate Change (IPCC) is an independent body founded under the auspices of the World Meteorological Organization (WMO) and the United Nations Environment Programme (UNEP). It assesses the scientific literature and provides vital scientific information to the climate change process.
The IPCC is best known for its comprehensive assessment reports, incorporating summaries for policymakers from all three Working Groups, which are widely recognized as the most credible sources of information on climate change.
The First Assessment Report in 1990 helped launch negotiations on the Convention.
The 1995 Second Assessment Report, in particular its statement that "the balance of evidence suggests … a discernible human influence on global climate", stimulated many governments into intensifying negotiations on what was to become the Kyoto Protocol.
Third Assessment Report of the Intergovernmental Panel on Climate Change
The Third Assessment Report, released in May 2001, confirmed the findings of the Second Assessment Report, providing new and stronger evidence of a warming world.
* Scientific, technical and socio-economic aspects of impacts of, and vulnerability and adaptation to, climate change, and
* Scientific, technical and socio-economic aspects of mitigation,
Fourth Assessment Report of the Intergovernmental Panel on Climate Change
During SBSTA 26 (Bonn, May 2007), the secretariat has organized, in cooperation with the IPCC, an in-depth briefing during the sessions of the subsidiary bodies on the contributions of the three IPCC working groups to the Fourth Assessment Report (AR4).
Saturday, 8 September 2007
Scientific American - the Physical Science behind Climate Change
Full 10 page article - download (pdf) by Scientific American August 2007
Great summary of the IPCC recent reports.
KEY CONCEPTS
■ Scientists are confident that humans have interfered with the climate and that further human-induced climate change is on the way.
■ The principal driver of recent climate change is greenhouse gas emissions from human
activities, primarily the burning of fossil fuels.
■ The report of the Intergovernmental Panel on Climate Change places the probability that
global warming has been caused by human activities at greater than 90 percent. The previous report, published in 2001, put the probability at higher than 66 percent.
■ Although further changes in the world’s climate are now inevitable, the future, particularly in the longer term, remains largely in our hands—the magnitude of expected change depends on what humans choose to do about greenhouse gas emissions.
—The Editors
Great summary of the IPCC recent reports.
KEY CONCEPTS
■ Scientists are confident that humans have interfered with the climate and that further human-induced climate change is on the way.
■ The principal driver of recent climate change is greenhouse gas emissions from human
activities, primarily the burning of fossil fuels.
■ The report of the Intergovernmental Panel on Climate Change places the probability that
global warming has been caused by human activities at greater than 90 percent. The previous report, published in 2001, put the probability at higher than 66 percent.
■ Although further changes in the world’s climate are now inevitable, the future, particularly in the longer term, remains largely in our hands—the magnitude of expected change depends on what humans choose to do about greenhouse gas emissions.
—The Editors
Friday, 11 May 2007
Robust Findings and Key Uncertainties - IPCC - Working Group I
TS.6.1 Changes in Human and Natural Drivers of Climate
Robust Findings:
Current atmospheric concentrations of CO2 and CH4, and their associated positive radiative forcing, far exceed those determined from ice core measurements spanning the last 650,000 years. {6.4} Fossil fuel use, agriculture and land use have been the dominant cause of increases in greenhouse gases over the last 250 years. {2.3, 7.3, 7.4} Annual emissions of CO2 from fossil fuel burning, cement production and gas flaring increased from a mean of 6.4 ± 0.4 GtC yr–1 in the 1990s to 7.2 ± 0.3 GtC yr–1 for 2000 to 2005. {7.3} The sustained rate of increase in radiative forcing from CO2, CH4 and N2O over the past 40 years is larger than at any time during at least the past 2000 years. {6.4} Natural processes of CO2 uptake by the oceans and terrestrial biosphere remove about 50 to 60% of anthropogenic emissions (i.e., fossil CO2 emissions and land use change flux). Uptake by the oceans and the terrestrial biosphere are similar in magnitude over recent decades but that by the terrestrial biosphere is more variable. {7.3} It is virtually certain that anthropogenic aerosols produce a net negative radiative forcing (cooling influence) with a greater magnitude in the NH than in the SH. {2.9, 9.2} From new estimates of the combined anthropogenic forcing due to greenhouse gases, aerosols and land surface changes, it is extremely likely that human activities havev exerted a substantial net warming influence on climate since 1750. {2.9} Solar irradiance contributions to global average radiative forcing are considerably smaller than the contribution of increases in greenhouse gases over the industrial period. {2.5, 2.7}
Key Uncertainties:
The full range of processes leading to modification of cloud properties by aerosols is not well understood and the magnitudes of associated indirect radiative effects are poorly determined. {2.4, 7.5} The causes of, and radiative forcing due to stratospheric water vapour changes are not well quantified. {2.3} The geographical distribution and time evolution of the radiative forcing due to changes in aerosols during the 20th century are not well characterised. {2.4} The causes of recent changes in the growth rate of atmospheric CH4 are not well understood. {7.4} The roles of different factors increasing tropospheric ozone concentrations since pre-industrial times are not well characterised. {2.3} Land surface properties and land-atmosphere interactions that lead to radiative forcing are not well quantified. {2.5} Knowledge of the contribution of past solar changes to radiative forcing on the time scale of centuries is not based upon direct measurements and is hence strongly dependent upon physical understanding. {2.7}
TS.6.2 Observations of Changes in Climate TS.6.2.1 Atmosphere and Surface
Robust Findings:
Global mean surface temperatures continue to rise. Eleven of the last 12 years rank among the 12 warmest years on record since 1850. {3.2} Rates of surface warming increased in the mid-1970s and the global land surface has been warming at about double the rate of ocean surface warming since then. {3.2} Changes in surface temperature extremes are consistent with warming of the climate. {3.8} Estimates of mid- and lower-tropospheric temperature trends have substantially improved. Lower-tropospheric temperatures have slightly greater warming rates than the surface from 1958 to 2005. {3.4} Long-term trends from 1900 to 2005 have been observed in precipitation amount in many large regions. {3.3} Increases have occurred in the number of heavy precipitation events. {3.8} Droughts have become more common, especially in the tropics and subtropics, since the 1970s. {3.3} Tropospheric water vapour has increased, at least since the 1980s. {3.4}
Key Uncertainties:
Radiosonde records are much less complete spatially than surface records and evidence suggests a number of radiosonde records are unreliable, especially in the tropics. It is likely that all records of tropospheric temperature trends still contain residual errors. {3.4} While changes in large-scale atmospheric circulation are apparent, the quality of analyses is best only after 1979, making analysis of, and discrimination between, change and variability difficult. {3.5, 3.6} Surface and satellite observations disagree on total and low-level cloud changes over the ocean. {3.4} Multi-decadal changes in DTR are not well understood, in part because of limited observations of changes in cloudiness and aerosols. {3.2} Difficulties in the measurement of precipitation remain an area of concern in quantifying trends in global and regional precipitation. {3.3} Records of soil moisture and streamflow are often very short, and are available for only a few regions, which impedes complete analyses of changes in droughts. {3.3} The availability of observational data restricts the types of extremes that can be analysed. The rarer the event, the more difficult it is to identify long-term changes because there are fewer cases available. {3.8} Information on hurricane frequency and intensity is limited prior to the satellite era. There are questions about the interpretation of the satellite record. {3.8} There is insufficient evidence to determine whether trends exist in tornadoes, hail, lightning and dust storms at small spatial scales. {3.8}
TS.6.2.2 Snow, Ice and Frozen Ground
Robust Findings:
The amount of ice on the Earth is decreasing. There has been widespread retreat of mountain glaciers since the end of the 19th century. The rate of mass loss from glaciers and the Greenland Ice Sheet is increasing. {4.5, 4.6} The extent of NH snow cover has declined. Seasonal river and lake ice duration has decreased over the past 150 years. {4.2, 4.3} Since 1978, annual mean arctic sea ice extent has been declining and summer minimum arctic ice extent has decreased. {4.4} Ice thinning occurred in the Antarctic Peninsula and Amundsen shelf ice during the 1990s. Tributary glaciers have accelerated and complete breakup of the Larsen B Ice Shelf occurred in 2002. {4.6} Temperature at the top of the permafrost layer has increased by up to 3°C since the 1980s in the Arctic. The maximum extent of seasonally frozen ground has decreased by about 7% in the NH since 1900, and its maximum depth has decreased by about 0.3 m in Eurasia since the mid-20th century. {4.7}
Key Uncertainties:
There is no global compilation of in situ snow data prior to 1960. Well-calibrated snow water equivalent data are not available for the satellite era. {4.2} There are insufficient data to draw any conclusions about trends in the thickness of antarctic sea ice. {4.4} Uncertainties in estimates of glacier mass loss arise from limited global inventory data, incomplete area-volume relationships and imbalance in geographic coverage. {4.5} Mass balance estimates for ice shelves and ice sheets, especially for Antarctica, are limited by calibration and validation of changes detected by satellite altimetry and gravity measurements. {4.6} Limited knowledge of basal processes and of ice shelf dynamics leads to large uncertainties in the understanding of ice flow processes and ice sheet stability. {4.6}
TS.6.2.3 Oceans and Sea Level
Robust Findings:
The global temperature (or heat content) of the oceans has increased since 1955. {5.2} Large-scale regionally coherent trends in salinity have been observed over recent decades with freshening in subpolar regions and increased salinity in the shallower parts of the tropics and subtropics. These trends are consistent with changes in precipitation and inferred larger water transport in the atmosphere from low latitudes to high latitudes and from the Atlantic to the Pacific. {5.2} Global average sea level rose during the 20th century. There is high confidence that the rate of sea level rise increased between the mid-19th and mid-20th centuries. During 1993 to 2003, sea level rose more rapidly than during 1961 to 2003. {5.5} Thermal expansion of the ocean and loss of mass from glaciers and ice caps made substantial contributions to the observed sea level rise. {5.5} The observed rate of sea level rise from 1993 to 2003 is consistent with the sum of observed contributions from thermal expansion and loss of land ice. {5.5} The rate of sea level change over recent decades has not been geographically uniform. {5.5} As a result of uptake of anthropogenic CO2 since 1750, the acidity of the surface ocean has increased. {5.4, 7.3}
Key Uncertainties:
Limitations in ocean sampling imply that decadal variability in global heat content, salinity and sea level changes can only be evaluated with moderate confidence. {5.2, 5.5} There is low confidence in observations of trends in the MOC. {Box 5.1} Global average sea level rise from 1961 to 2003 appears to be larger than can be explained by thermal expansion and land ice melting. {5.5}
TS.6.2.4 Palaeoclimate
Robust Findings:
During the last interglacial, about 125,000 years ago, global sea level was likely 4 to 6 m higher than present, due primarily to retreat of polar ice. {6.4} A number of past abrupt climate changes were very likely linked to changes in Atlantic Ocean circulation and affected the climate broadly across the NH. {6.4} It is very unlikely that the Earth would naturally enter another ice age for at least 30,000 years. {6.4} Biogeochemical and biogeophysical feedbacks have amplified climatic changes in the past. {6.4} It is very likely that average NH temperatures during the second half of the 20th century were warmer than in any other 50-year period in the last 500 years and likely that this was also the warmest 50-year period in the past 1300 years. {6.6} Palaeoclimate records indicate with high confidence that droughts lasting decades or longer were a recurrent feature of climate in several regions over the last 2000 years. {6.6}
Key Uncertainties:
Mechanisms of onset and evolution of past abrupt climate change and associated climate thresholds are not well understood. This limits confidence in the ability of climate models to simulate realistic abrupt change. {6.4} The degree to which ice sheets retreated in the past, the rates of such change and the processes involved are not well known. {6.4} Knowledge of climate variability over more than the last few hundred years in the SH and tropics is limited by the lack of palaeoclimatic records. {6.6} Differing amplitudes and variability observed in available millennial-length NH temperature reconstructions, as well as the relation of these differences to choice of proxy data and statistical calibration methods, still need to be reconciled. {6.6} The lack of extensive networks of proxy data for temperature in the last 20 years limits understanding of how such proxies respond to rapid global warming and of the influence of other environmental changes. {6.6}
TS.6.3 Understanding and Attributing Climate Change
Robust Findings:
Greenhouse gas forcing has very likely caused most of the observed global warming over the last 50 years. Greenhouse gas forcing alone during the past half century would likely have resulted in greater than the observed warming if there had not been an offsetting cooling effect from aerosol and other forcings. {9.4} It is extremely unlikely (<5%)>Key Uncertainties:
Confidence in attributing some climate change phenomena to anthropogenic influences is currently limited by uncertainties in radiative forcing, as well as uncertainties in feedbacks and in observations. {9.4, 9.5} Attribution at scales smaller than continental and over time scales of less than 50 years is limited by larger climate variability on smaller scales, by uncertainties in the small-scale details of external forcing and the response simulated by models, as well as uncertainties in simulation of internal variability on small scales, including in relation to modes of variability. {9.4} There is less confidence in understanding of forced changes in precipitation and surface pressure than there is of temperature. {9.5} The range of attribution statements is limited by the absence of formal detection and attribution studies, or their very limited number, for some phenomena (e.g., some types of extreme events). {9.5} Incomplete global data sets for extremes analysis and model uncertainties still restrict the regions and types of detection studies of extremes that can be performed. {9.4, 9.5} Despite improved understanding, uncertainties in modelsimulated internal climate variability limit some aspects of attribution studies. For example, there are apparent discrepancies between estimates of ocean heat content variability from models and observations. {5.2, 9.5} Lack of studies quantifying the contributions of anthropogenic forcing to ocean heat content increase or glacier melting together with the open part of the sea level budget for 1961 to 2003 are among the uncertainties in quantifying the anthropogenic contribution to sea level rise. {9.5}
TS.6.4 Projections of Future Changes in Climate
TS.6.4.1 Model Evaluation
Robust Findings:
Climate models are based on well-established physical principles and have been demonstrated to reproduce observed features of recent climate and past climate changes. There is considerable confidence that AOGCMs provide credible quantitative estimates of future climate change, particularly at continental scales and above. Confidence in these estimates is higher for some climate variables (e.g., temperature) than for others (e.g., precipitation). {FAQ 8.1} Confidence in models has increased due to: • improvements in the simulation of many aspects of present climate, including important modes of climate variability and extreme hot and cold spells; • improved model resolution, computational methods and parametrizations and inclusion of additional processes; • more comprehensive diagnostic tests, including tests of model ability to forecast on time scales from days to a year when initialised with observed conditions; and • enhanced scrutiny of models and expanded diagnostic analysis of model behaviour facilitated by internationally coordinated efforts to collect and disseminate output from model experiments performed under common conditions. {8.4}
Key Uncertainties:
A proven set of model metrics comparing simulations with observations, that might be used to narrow the range of plausible climate projections, has yet to be developed. {8.2} Most models continue to have difficulty controlling climate drift, particularly in the deep ocean. This drift must be accounted for when assessing change in many oceanic variables. {8.2} Models differ considerably in their estimates of the strength of different feedbacks in the climate system. {8.6} Problems remain in the simulation of some modes of variability, notably the Madden-Julian Oscillation, recurrent atmospheric blocking and extreme precipitation. {8.4} Systematic biases have been found in most models’ simulations of the Southern Ocean that are linked to uncertainty in transient climate response. {8.3} Climate models remain limited by the spatial resolution that can be achieved with present computer resources, by the need for more extensive ensemble runs and by the need to include some additional processes. {8.1–8.5}
TS.6.4.2 Equilibrium and Transient Climate Sensitivity
Robust Findings:
Equilibrium climate sensitivity is likely to be in the range 2°C to 4.5°C with a most likely value of about 3°C, based upon multiple observational and modelling constraints. It is very unlikely to be less than 1.5°C. {8.6, 9.6, Box 10.2} The transient climate response is better constrained than the equilibrium climate sensitivity. It is very likely larger than 1°C and very unlikely greater than 3°C. {10.5} There is a good understanding of the origin of differences in equilibrium climate sensitivity found in different models. Cloud feedbacks are the primary source of intermodel differences in equilibrium climate sensitivity, with low cloud being the largest contributor. {8.6} New observational and modelling evidence strongly supports a combined water vapour-lapse rate feedback of a strength comparable to that found in AOGCMs. {8.6}
Key Uncertainties:
Large uncertainties remain about how clouds might respond to global climate change. {8.6}
TS.6.4.3 Global Projections
Robust Findings:
Even if concentrations of radiative forcing agents were to be stabilised, further committed warming and related climate changes would be expected to occur, largely because of time lags associated with processes in the oceans. {10.7} Near-term warming projections are little affected by different scenario assumptions or different model sensitivities, and are consistent with that observed for the past few decades. The multi-model mean warming, averaged over 2011 to 2030 relative to 1980 to 1999 for all AOGCMs considered here, lies in a narrow range of 0.64°C to 0.69°C for the three different SRES emission scenarios B1, A1B and A2. {10.3} Geographic patterns of projected warming show the greatest temperature increases at high northern latitudes and over land, with less warming over the southern oceans and North Atlantic. {10.3} Changes in precipitation show robust large-scale patterns: precipitation generally increases in the tropical precipitation maxima, decreases in the subtropics and increases at high latitudes as a consequence of a general intensification of the global hydrological cycle. {10.3} As the climate warms, snow cover and sea ice extent decrease; glaciers and ice caps lose mass and contribute to sea level rise. Sea ice extent decreases in the 21st century in both the Arctic and Antarctic. Snow cover reduction is accelerated in the Arctic by positive feedbacks and widespread increases in thaw depth occur over much of the permafrost regions. {10.3} Based on current simulations, it is very likely that the Atlantic Ocean MOC will slow down by 2100. However, it is very unlikely that the MOC will undergo a large abrupt transition during the course of the 21st century. {10.3} Heat waves become more frequent and longer lasting in a future warmer climate. Decreases in frost days are projected to occur almost everywhere in the mid- and high latitudes, with an increase in growing season length. There is a tendency for summer drying of the mid-continental areas during summer, indicating a greater risk of droughts in those regions. {10.3, FAQ 10.1} Future warming would tend to reduce the capacity of the Earth system (land and ocean) to absorb anthropogenic CO2. As a result, an increasingly large fraction of anthropogenic CO2 would stay in the atmosphere under a warmer climate. This feedback requires reductions in the cumulative emissions consistent with stabilisation at a given atmospheric CO2 level compared to the hypothetical case of no such feedback. The higher the stabilisation scenario, the larger the amount of climate change and the larger the required reductions. {7.3, 10.4}
Key Uncertainties:
The likelihood of a large abrupt change in the MOC beyond the end of the 21st century cannot yet be assessed reliably. For low and medium emission scenarios with atmospheric greenhouse gas concentrations stabilised beyond 2100, the MOC recovers from initial weakening within one to several centuries. A permanent reduction in the MOC cannot be excluded if the forcing is strong and long enough. {10.7} The model projections for extremes of precipitation show larger ranges in amplitude and geographical locations than for temperature. {10.3, 11.1} The response of some major modes of climate variability such as ENSO still differs from model to model, which may be associated with differences in the spatial and temporal representation of present-day conditions. {10.3} The robustness of many model responses of tropical cyclones to climate change is still limited by the resolution of typical climate models. {10.3} Changes in key processes that drive some global and regional climate changes are poorly known (e.g., ENSO, NAO, blocking, MOC, land surface feedbacks, tropical cyclone distribution). {11.2–11.9} The magnitude of future carbon cycle feedbacks is still poorly determined. {7.3, 10.4}
TS.6.4.4 Sea Level
Robust Findings:
Sea level will continue to rise in the 21st century because of thermal expansion and loss of land ice. Sea level rise was not geographically uniform in the past and will not be in the future. {10.6} Projected warming due to emission of greenhouse gases during the 21st century will continue to contribute to sea level rise for many centuries. {10.7} Sea level rise due to thermal expansion and loss of mass from ice sheets would continue for centuries or millennia even if radiative forcing were to be stabilised. {10.7}
Key Uncertainties:
Models do not yet exist that address key processes that could contribute to large rapid dynamical changes in the Antarctic and Greenland Ice Sheets that could increase the discharge of ice into the ocean. {10.6} The sensitivity of ice sheet surface mass balance (melting and precipitation) to global climate change is not well constrained by observations and has a large spread in models. There is consequently a large uncertainty in the magnitude of global warming that, if sustained, would lead to the elimination of the Greenland Ice Sheet. {10.7}
TS.6.4.5 Regional Projections
Robust Findings:
Temperatures averaged over all habitable continents and over many sub-continental land regions will very likely rise at greater than the global average rate in the next 50 years and by an amount substantially in excess of natural variability. {10.3, 11.2–11.9} Precipitation is likely to increase in most subpolar and polar regions. The increase is considered especially robust, and very likely to occur, in annual precipitation in most of northern Europe, Canada, the northeast USA and the Arctic, and in winter precipitation in northern Asia and the Tibetan Plateau. {11.2–11.9} Precipitation is likely to decrease in many subtropical regions, especially at the poleward margins of the subtropics. The decrease is considered especially robust, and very likely to occur, in annual precipitation in European and African regions bordering the Mediterranean and in winter rainfall in south-western Australia. {11.2–11.9} Extremes of daily precipitation are likely to increase in many regions. The increase is considered as very likely in northern Europe, south Asia, East Asia, Australia and New Zealand – this list in part reflecting uneven geographic coverage in existing published research. {11.2–11.9}
Key Uncertainties:
In some regions there has been only very limited study of key aspects of regional climate change, particularly with regard to extreme events. {11.2–11.9} Atmosphere-Ocean General Circulation Models show no consistency in simulated regional precipitation change in some key regions (e.g., northern South America, northern Australia and the Sahel). {10.3, 11.2–11.9} In many regions where fine spatial scales in climate are generated by topography, there is insufficient information on how climate change will be expressed at these scales. {11.2–11.9}
Robust Findings:
Current atmospheric concentrations of CO2 and CH4, and their associated positive radiative forcing, far exceed those determined from ice core measurements spanning the last 650,000 years. {6.4} Fossil fuel use, agriculture and land use have been the dominant cause of increases in greenhouse gases over the last 250 years. {2.3, 7.3, 7.4} Annual emissions of CO2 from fossil fuel burning, cement production and gas flaring increased from a mean of 6.4 ± 0.4 GtC yr–1 in the 1990s to 7.2 ± 0.3 GtC yr–1 for 2000 to 2005. {7.3} The sustained rate of increase in radiative forcing from CO2, CH4 and N2O over the past 40 years is larger than at any time during at least the past 2000 years. {6.4} Natural processes of CO2 uptake by the oceans and terrestrial biosphere remove about 50 to 60% of anthropogenic emissions (i.e., fossil CO2 emissions and land use change flux). Uptake by the oceans and the terrestrial biosphere are similar in magnitude over recent decades but that by the terrestrial biosphere is more variable. {7.3} It is virtually certain that anthropogenic aerosols produce a net negative radiative forcing (cooling influence) with a greater magnitude in the NH than in the SH. {2.9, 9.2} From new estimates of the combined anthropogenic forcing due to greenhouse gases, aerosols and land surface changes, it is extremely likely that human activities havev exerted a substantial net warming influence on climate since 1750. {2.9} Solar irradiance contributions to global average radiative forcing are considerably smaller than the contribution of increases in greenhouse gases over the industrial period. {2.5, 2.7}
Key Uncertainties:
The full range of processes leading to modification of cloud properties by aerosols is not well understood and the magnitudes of associated indirect radiative effects are poorly determined. {2.4, 7.5} The causes of, and radiative forcing due to stratospheric water vapour changes are not well quantified. {2.3} The geographical distribution and time evolution of the radiative forcing due to changes in aerosols during the 20th century are not well characterised. {2.4} The causes of recent changes in the growth rate of atmospheric CH4 are not well understood. {7.4} The roles of different factors increasing tropospheric ozone concentrations since pre-industrial times are not well characterised. {2.3} Land surface properties and land-atmosphere interactions that lead to radiative forcing are not well quantified. {2.5} Knowledge of the contribution of past solar changes to radiative forcing on the time scale of centuries is not based upon direct measurements and is hence strongly dependent upon physical understanding. {2.7}
TS.6.2 Observations of Changes in Climate TS.6.2.1 Atmosphere and Surface
Robust Findings:
Global mean surface temperatures continue to rise. Eleven of the last 12 years rank among the 12 warmest years on record since 1850. {3.2} Rates of surface warming increased in the mid-1970s and the global land surface has been warming at about double the rate of ocean surface warming since then. {3.2} Changes in surface temperature extremes are consistent with warming of the climate. {3.8} Estimates of mid- and lower-tropospheric temperature trends have substantially improved. Lower-tropospheric temperatures have slightly greater warming rates than the surface from 1958 to 2005. {3.4} Long-term trends from 1900 to 2005 have been observed in precipitation amount in many large regions. {3.3} Increases have occurred in the number of heavy precipitation events. {3.8} Droughts have become more common, especially in the tropics and subtropics, since the 1970s. {3.3} Tropospheric water vapour has increased, at least since the 1980s. {3.4}
Key Uncertainties:
Radiosonde records are much less complete spatially than surface records and evidence suggests a number of radiosonde records are unreliable, especially in the tropics. It is likely that all records of tropospheric temperature trends still contain residual errors. {3.4} While changes in large-scale atmospheric circulation are apparent, the quality of analyses is best only after 1979, making analysis of, and discrimination between, change and variability difficult. {3.5, 3.6} Surface and satellite observations disagree on total and low-level cloud changes over the ocean. {3.4} Multi-decadal changes in DTR are not well understood, in part because of limited observations of changes in cloudiness and aerosols. {3.2} Difficulties in the measurement of precipitation remain an area of concern in quantifying trends in global and regional precipitation. {3.3} Records of soil moisture and streamflow are often very short, and are available for only a few regions, which impedes complete analyses of changes in droughts. {3.3} The availability of observational data restricts the types of extremes that can be analysed. The rarer the event, the more difficult it is to identify long-term changes because there are fewer cases available. {3.8} Information on hurricane frequency and intensity is limited prior to the satellite era. There are questions about the interpretation of the satellite record. {3.8} There is insufficient evidence to determine whether trends exist in tornadoes, hail, lightning and dust storms at small spatial scales. {3.8}
TS.6.2.2 Snow, Ice and Frozen Ground
Robust Findings:
The amount of ice on the Earth is decreasing. There has been widespread retreat of mountain glaciers since the end of the 19th century. The rate of mass loss from glaciers and the Greenland Ice Sheet is increasing. {4.5, 4.6} The extent of NH snow cover has declined. Seasonal river and lake ice duration has decreased over the past 150 years. {4.2, 4.3} Since 1978, annual mean arctic sea ice extent has been declining and summer minimum arctic ice extent has decreased. {4.4} Ice thinning occurred in the Antarctic Peninsula and Amundsen shelf ice during the 1990s. Tributary glaciers have accelerated and complete breakup of the Larsen B Ice Shelf occurred in 2002. {4.6} Temperature at the top of the permafrost layer has increased by up to 3°C since the 1980s in the Arctic. The maximum extent of seasonally frozen ground has decreased by about 7% in the NH since 1900, and its maximum depth has decreased by about 0.3 m in Eurasia since the mid-20th century. {4.7}
Key Uncertainties:
There is no global compilation of in situ snow data prior to 1960. Well-calibrated snow water equivalent data are not available for the satellite era. {4.2} There are insufficient data to draw any conclusions about trends in the thickness of antarctic sea ice. {4.4} Uncertainties in estimates of glacier mass loss arise from limited global inventory data, incomplete area-volume relationships and imbalance in geographic coverage. {4.5} Mass balance estimates for ice shelves and ice sheets, especially for Antarctica, are limited by calibration and validation of changes detected by satellite altimetry and gravity measurements. {4.6} Limited knowledge of basal processes and of ice shelf dynamics leads to large uncertainties in the understanding of ice flow processes and ice sheet stability. {4.6}
TS.6.2.3 Oceans and Sea Level
Robust Findings:
The global temperature (or heat content) of the oceans has increased since 1955. {5.2} Large-scale regionally coherent trends in salinity have been observed over recent decades with freshening in subpolar regions and increased salinity in the shallower parts of the tropics and subtropics. These trends are consistent with changes in precipitation and inferred larger water transport in the atmosphere from low latitudes to high latitudes and from the Atlantic to the Pacific. {5.2} Global average sea level rose during the 20th century. There is high confidence that the rate of sea level rise increased between the mid-19th and mid-20th centuries. During 1993 to 2003, sea level rose more rapidly than during 1961 to 2003. {5.5} Thermal expansion of the ocean and loss of mass from glaciers and ice caps made substantial contributions to the observed sea level rise. {5.5} The observed rate of sea level rise from 1993 to 2003 is consistent with the sum of observed contributions from thermal expansion and loss of land ice. {5.5} The rate of sea level change over recent decades has not been geographically uniform. {5.5} As a result of uptake of anthropogenic CO2 since 1750, the acidity of the surface ocean has increased. {5.4, 7.3}
Key Uncertainties:
Limitations in ocean sampling imply that decadal variability in global heat content, salinity and sea level changes can only be evaluated with moderate confidence. {5.2, 5.5} There is low confidence in observations of trends in the MOC. {Box 5.1} Global average sea level rise from 1961 to 2003 appears to be larger than can be explained by thermal expansion and land ice melting. {5.5}
TS.6.2.4 Palaeoclimate
Robust Findings:
During the last interglacial, about 125,000 years ago, global sea level was likely 4 to 6 m higher than present, due primarily to retreat of polar ice. {6.4} A number of past abrupt climate changes were very likely linked to changes in Atlantic Ocean circulation and affected the climate broadly across the NH. {6.4} It is very unlikely that the Earth would naturally enter another ice age for at least 30,000 years. {6.4} Biogeochemical and biogeophysical feedbacks have amplified climatic changes in the past. {6.4} It is very likely that average NH temperatures during the second half of the 20th century were warmer than in any other 50-year period in the last 500 years and likely that this was also the warmest 50-year period in the past 1300 years. {6.6} Palaeoclimate records indicate with high confidence that droughts lasting decades or longer were a recurrent feature of climate in several regions over the last 2000 years. {6.6}
Key Uncertainties:
Mechanisms of onset and evolution of past abrupt climate change and associated climate thresholds are not well understood. This limits confidence in the ability of climate models to simulate realistic abrupt change. {6.4} The degree to which ice sheets retreated in the past, the rates of such change and the processes involved are not well known. {6.4} Knowledge of climate variability over more than the last few hundred years in the SH and tropics is limited by the lack of palaeoclimatic records. {6.6} Differing amplitudes and variability observed in available millennial-length NH temperature reconstructions, as well as the relation of these differences to choice of proxy data and statistical calibration methods, still need to be reconciled. {6.6} The lack of extensive networks of proxy data for temperature in the last 20 years limits understanding of how such proxies respond to rapid global warming and of the influence of other environmental changes. {6.6}
TS.6.3 Understanding and Attributing Climate Change
Robust Findings:
Greenhouse gas forcing has very likely caused most of the observed global warming over the last 50 years. Greenhouse gas forcing alone during the past half century would likely have resulted in greater than the observed warming if there had not been an offsetting cooling effect from aerosol and other forcings. {9.4} It is extremely unlikely (<5%)>Key Uncertainties:
Confidence in attributing some climate change phenomena to anthropogenic influences is currently limited by uncertainties in radiative forcing, as well as uncertainties in feedbacks and in observations. {9.4, 9.5} Attribution at scales smaller than continental and over time scales of less than 50 years is limited by larger climate variability on smaller scales, by uncertainties in the small-scale details of external forcing and the response simulated by models, as well as uncertainties in simulation of internal variability on small scales, including in relation to modes of variability. {9.4} There is less confidence in understanding of forced changes in precipitation and surface pressure than there is of temperature. {9.5} The range of attribution statements is limited by the absence of formal detection and attribution studies, or their very limited number, for some phenomena (e.g., some types of extreme events). {9.5} Incomplete global data sets for extremes analysis and model uncertainties still restrict the regions and types of detection studies of extremes that can be performed. {9.4, 9.5} Despite improved understanding, uncertainties in modelsimulated internal climate variability limit some aspects of attribution studies. For example, there are apparent discrepancies between estimates of ocean heat content variability from models and observations. {5.2, 9.5} Lack of studies quantifying the contributions of anthropogenic forcing to ocean heat content increase or glacier melting together with the open part of the sea level budget for 1961 to 2003 are among the uncertainties in quantifying the anthropogenic contribution to sea level rise. {9.5}
TS.6.4 Projections of Future Changes in Climate
TS.6.4.1 Model Evaluation
Robust Findings:
Climate models are based on well-established physical principles and have been demonstrated to reproduce observed features of recent climate and past climate changes. There is considerable confidence that AOGCMs provide credible quantitative estimates of future climate change, particularly at continental scales and above. Confidence in these estimates is higher for some climate variables (e.g., temperature) than for others (e.g., precipitation). {FAQ 8.1} Confidence in models has increased due to: • improvements in the simulation of many aspects of present climate, including important modes of climate variability and extreme hot and cold spells; • improved model resolution, computational methods and parametrizations and inclusion of additional processes; • more comprehensive diagnostic tests, including tests of model ability to forecast on time scales from days to a year when initialised with observed conditions; and • enhanced scrutiny of models and expanded diagnostic analysis of model behaviour facilitated by internationally coordinated efforts to collect and disseminate output from model experiments performed under common conditions. {8.4}
Key Uncertainties:
A proven set of model metrics comparing simulations with observations, that might be used to narrow the range of plausible climate projections, has yet to be developed. {8.2} Most models continue to have difficulty controlling climate drift, particularly in the deep ocean. This drift must be accounted for when assessing change in many oceanic variables. {8.2} Models differ considerably in their estimates of the strength of different feedbacks in the climate system. {8.6} Problems remain in the simulation of some modes of variability, notably the Madden-Julian Oscillation, recurrent atmospheric blocking and extreme precipitation. {8.4} Systematic biases have been found in most models’ simulations of the Southern Ocean that are linked to uncertainty in transient climate response. {8.3} Climate models remain limited by the spatial resolution that can be achieved with present computer resources, by the need for more extensive ensemble runs and by the need to include some additional processes. {8.1–8.5}
TS.6.4.2 Equilibrium and Transient Climate Sensitivity
Robust Findings:
Equilibrium climate sensitivity is likely to be in the range 2°C to 4.5°C with a most likely value of about 3°C, based upon multiple observational and modelling constraints. It is very unlikely to be less than 1.5°C. {8.6, 9.6, Box 10.2} The transient climate response is better constrained than the equilibrium climate sensitivity. It is very likely larger than 1°C and very unlikely greater than 3°C. {10.5} There is a good understanding of the origin of differences in equilibrium climate sensitivity found in different models. Cloud feedbacks are the primary source of intermodel differences in equilibrium climate sensitivity, with low cloud being the largest contributor. {8.6} New observational and modelling evidence strongly supports a combined water vapour-lapse rate feedback of a strength comparable to that found in AOGCMs. {8.6}
Key Uncertainties:
Large uncertainties remain about how clouds might respond to global climate change. {8.6}
TS.6.4.3 Global Projections
Robust Findings:
Even if concentrations of radiative forcing agents were to be stabilised, further committed warming and related climate changes would be expected to occur, largely because of time lags associated with processes in the oceans. {10.7} Near-term warming projections are little affected by different scenario assumptions or different model sensitivities, and are consistent with that observed for the past few decades. The multi-model mean warming, averaged over 2011 to 2030 relative to 1980 to 1999 for all AOGCMs considered here, lies in a narrow range of 0.64°C to 0.69°C for the three different SRES emission scenarios B1, A1B and A2. {10.3} Geographic patterns of projected warming show the greatest temperature increases at high northern latitudes and over land, with less warming over the southern oceans and North Atlantic. {10.3} Changes in precipitation show robust large-scale patterns: precipitation generally increases in the tropical precipitation maxima, decreases in the subtropics and increases at high latitudes as a consequence of a general intensification of the global hydrological cycle. {10.3} As the climate warms, snow cover and sea ice extent decrease; glaciers and ice caps lose mass and contribute to sea level rise. Sea ice extent decreases in the 21st century in both the Arctic and Antarctic. Snow cover reduction is accelerated in the Arctic by positive feedbacks and widespread increases in thaw depth occur over much of the permafrost regions. {10.3} Based on current simulations, it is very likely that the Atlantic Ocean MOC will slow down by 2100. However, it is very unlikely that the MOC will undergo a large abrupt transition during the course of the 21st century. {10.3} Heat waves become more frequent and longer lasting in a future warmer climate. Decreases in frost days are projected to occur almost everywhere in the mid- and high latitudes, with an increase in growing season length. There is a tendency for summer drying of the mid-continental areas during summer, indicating a greater risk of droughts in those regions. {10.3, FAQ 10.1} Future warming would tend to reduce the capacity of the Earth system (land and ocean) to absorb anthropogenic CO2. As a result, an increasingly large fraction of anthropogenic CO2 would stay in the atmosphere under a warmer climate. This feedback requires reductions in the cumulative emissions consistent with stabilisation at a given atmospheric CO2 level compared to the hypothetical case of no such feedback. The higher the stabilisation scenario, the larger the amount of climate change and the larger the required reductions. {7.3, 10.4}
Key Uncertainties:
The likelihood of a large abrupt change in the MOC beyond the end of the 21st century cannot yet be assessed reliably. For low and medium emission scenarios with atmospheric greenhouse gas concentrations stabilised beyond 2100, the MOC recovers from initial weakening within one to several centuries. A permanent reduction in the MOC cannot be excluded if the forcing is strong and long enough. {10.7} The model projections for extremes of precipitation show larger ranges in amplitude and geographical locations than for temperature. {10.3, 11.1} The response of some major modes of climate variability such as ENSO still differs from model to model, which may be associated with differences in the spatial and temporal representation of present-day conditions. {10.3} The robustness of many model responses of tropical cyclones to climate change is still limited by the resolution of typical climate models. {10.3} Changes in key processes that drive some global and regional climate changes are poorly known (e.g., ENSO, NAO, blocking, MOC, land surface feedbacks, tropical cyclone distribution). {11.2–11.9} The magnitude of future carbon cycle feedbacks is still poorly determined. {7.3, 10.4}
TS.6.4.4 Sea Level
Robust Findings:
Sea level will continue to rise in the 21st century because of thermal expansion and loss of land ice. Sea level rise was not geographically uniform in the past and will not be in the future. {10.6} Projected warming due to emission of greenhouse gases during the 21st century will continue to contribute to sea level rise for many centuries. {10.7} Sea level rise due to thermal expansion and loss of mass from ice sheets would continue for centuries or millennia even if radiative forcing were to be stabilised. {10.7}
Key Uncertainties:
Models do not yet exist that address key processes that could contribute to large rapid dynamical changes in the Antarctic and Greenland Ice Sheets that could increase the discharge of ice into the ocean. {10.6} The sensitivity of ice sheet surface mass balance (melting and precipitation) to global climate change is not well constrained by observations and has a large spread in models. There is consequently a large uncertainty in the magnitude of global warming that, if sustained, would lead to the elimination of the Greenland Ice Sheet. {10.7}
TS.6.4.5 Regional Projections
Robust Findings:
Temperatures averaged over all habitable continents and over many sub-continental land regions will very likely rise at greater than the global average rate in the next 50 years and by an amount substantially in excess of natural variability. {10.3, 11.2–11.9} Precipitation is likely to increase in most subpolar and polar regions. The increase is considered especially robust, and very likely to occur, in annual precipitation in most of northern Europe, Canada, the northeast USA and the Arctic, and in winter precipitation in northern Asia and the Tibetan Plateau. {11.2–11.9} Precipitation is likely to decrease in many subtropical regions, especially at the poleward margins of the subtropics. The decrease is considered especially robust, and very likely to occur, in annual precipitation in European and African regions bordering the Mediterranean and in winter rainfall in south-western Australia. {11.2–11.9} Extremes of daily precipitation are likely to increase in many regions. The increase is considered as very likely in northern Europe, south Asia, East Asia, Australia and New Zealand – this list in part reflecting uneven geographic coverage in existing published research. {11.2–11.9}
Key Uncertainties:
In some regions there has been only very limited study of key aspects of regional climate change, particularly with regard to extreme events. {11.2–11.9} Atmosphere-Ocean General Circulation Models show no consistency in simulated regional precipitation change in some key regions (e.g., northern South America, northern Australia and the Sahel). {10.3, 11.2–11.9} In many regions where fine spatial scales in climate are generated by topography, there is insufficient information on how climate change will be expressed at these scales. {11.2–11.9}
Working Group I - Technical Summary - Treatment of Uncertainties
Contribution of Working Group I to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change - Technical Summary
Box TS.1: Treatment of Uncertainties in the Working Group I Assessment
The importance of consistent and transparent treatment of uncertainties is clearly recognised by the IPCC in preparing its assessments of climate change. The increasing attention given to formal treatments of uncertainty in previous assessments is addressed in Section 1.6. To promote consistency in the general treatment of uncertainty across all three Working Groups,
authors of the Fourth Assessment Report have been asked to follow a brief set of guidance notes on determining and describing uncertainties in the context of an assessment.
2 This box summarises the way that Working Group I has applied those guidelines and covers some aspects of the treatment of uncertainty specific to material assessed here. Uncertainties can be classified in several different ways according to their origin. Two primary types are ‘value uncertainties’ and ‘structural uncertainties’. Value uncertainties arise from the incomplete determination of particular values or results, for example, when data are inaccurate or not fully representative of the phenomenon of interest. Structural uncertainties
arise from an incomplete understanding of the processes that control particular values or results, for example, when the conceptual framework or model used for analysis does not include all the relevant processes or relationships.
Value uncertainties are generally estimated using statistical techniques and expressed probabilistically. Structural uncertainties are generally described by giving the authors’ collective judgment of their confidence in the correctness of a result. In both cases, estimating uncertainties is intrinsically about describing the limits to knowledge and for this reason involves expert judgment about the state of that knowledge. A different type of uncertainty arises in systems that are either chaotic or not fully deterministic in nature and this also limits our ability to project all aspects of climate change.
The scientific literature assessed here uses a variety of other generic ways of categorising uncertainties. Uncertainties associated with ‘random errors’ have the characteristic of decreasing as additional measurements are accumulated, whereas those associated with ‘systematic errors’ do not. In dealing with climate records, considerable attention has been
given to the identification of systematic errors or unintended biases arising from data sampling issues and methods of analysing and combining data. Specialised statistical methods based on quantitative analysis have been developed for the detection and attribution of climate change and for producing probabilistic projections of future climate parameters. These are summarised in the relevant chapters.
The uncertainty guidance provided for the Fourth Assessment Report draws, for the first time, a careful distinction between levels of confidence in scientific understanding and the likelihoods of specific results. This allows authors to express high confidence that an event is extremely unlikely (e.g., rolling a dice twice and getting a six both times), as well as high confidence that an event is about as likely as not (e.g., a tossed coin coming up heads). Confidence and likelihood
as used here are distinct concepts but are often linked in practice.
The standard terms used to define levels of confidence in this report are as given in the IPCC Uncertainty Guidance Note, namely:
Confidence Terminology Degree of confidence in being correct
Very high confidence At least 9 out of 10 chance
High confidence About 8 out of 10 chance
Medium confidence About 5 out of 10 chance
Low confidence About 2 out of 10 chance
Very low confidence Less than 1 out of 10 chance
Note that ‘low confidence’ and ‘very low confidence’ are only used for areas of major concern and where a risk-based perspective is justified.
Chapter 2 of this report uses a related term ‘level of scientific understanding’ when describing uncertainties in different contributions to radiative forcing. This terminology is used for consistency with the Third Assessment Report, and the basis on which the authors have determined particular levels of scientific understanding uses a combination of approaches
consistent with the uncertainty guidance note as explained in detail in Section 2.9.2 and Table
2.11.
The standard terms used in this report to define the likelihood of an outcome or result where this can be estimated probabilistically are:
Likelihood Terminology Likelihood of the occurrence/ outcome
Virtually certain > 99% probability
Extremely likely > 95% probability
Very likely > 90% probability
Likely > 66% probability
More likely than not > 50% probability
About as likely as not 33 to 66% probability
Unlikely < 33% probability
Very unlikely < 10% probability
Extremely unlikely < 5% probability
Exceptionally unlikely < 1% probability
The terms ‘extremely likely’, ‘extremely unlikely’ and ‘more likely than not’ as defined above have been added to those given in the IPCC Uncertainty Guidance Note in order to provide a more specific assessment of aspects including attribution and radiative forcing.
Unless noted otherwise, values given in this report are assessed best estimates and their uncertainty ranges are 90% confidence intervals (i.e., there is an estimated 5% likelihood of the value being below the lower end of the range or above the upper end of the range). Note that in some cases the nature of the constraints on a value, or other information available, may indicate an asymmetric distribution of the uncertainty range around a best estimate. In such cases, the uncertainty range is given in square brackets following the best estimate.
Box TS.1: Treatment of Uncertainties in the Working Group I Assessment
The importance of consistent and transparent treatment of uncertainties is clearly recognised by the IPCC in preparing its assessments of climate change. The increasing attention given to formal treatments of uncertainty in previous assessments is addressed in Section 1.6. To promote consistency in the general treatment of uncertainty across all three Working Groups,
authors of the Fourth Assessment Report have been asked to follow a brief set of guidance notes on determining and describing uncertainties in the context of an assessment.
2 This box summarises the way that Working Group I has applied those guidelines and covers some aspects of the treatment of uncertainty specific to material assessed here. Uncertainties can be classified in several different ways according to their origin. Two primary types are ‘value uncertainties’ and ‘structural uncertainties’. Value uncertainties arise from the incomplete determination of particular values or results, for example, when data are inaccurate or not fully representative of the phenomenon of interest. Structural uncertainties
arise from an incomplete understanding of the processes that control particular values or results, for example, when the conceptual framework or model used for analysis does not include all the relevant processes or relationships.
Value uncertainties are generally estimated using statistical techniques and expressed probabilistically. Structural uncertainties are generally described by giving the authors’ collective judgment of their confidence in the correctness of a result. In both cases, estimating uncertainties is intrinsically about describing the limits to knowledge and for this reason involves expert judgment about the state of that knowledge. A different type of uncertainty arises in systems that are either chaotic or not fully deterministic in nature and this also limits our ability to project all aspects of climate change.
The scientific literature assessed here uses a variety of other generic ways of categorising uncertainties. Uncertainties associated with ‘random errors’ have the characteristic of decreasing as additional measurements are accumulated, whereas those associated with ‘systematic errors’ do not. In dealing with climate records, considerable attention has been
given to the identification of systematic errors or unintended biases arising from data sampling issues and methods of analysing and combining data. Specialised statistical methods based on quantitative analysis have been developed for the detection and attribution of climate change and for producing probabilistic projections of future climate parameters. These are summarised in the relevant chapters.
The uncertainty guidance provided for the Fourth Assessment Report draws, for the first time, a careful distinction between levels of confidence in scientific understanding and the likelihoods of specific results. This allows authors to express high confidence that an event is extremely unlikely (e.g., rolling a dice twice and getting a six both times), as well as high confidence that an event is about as likely as not (e.g., a tossed coin coming up heads). Confidence and likelihood
as used here are distinct concepts but are often linked in practice.
The standard terms used to define levels of confidence in this report are as given in the IPCC Uncertainty Guidance Note, namely:
Confidence Terminology Degree of confidence in being correct
Very high confidence At least 9 out of 10 chance
High confidence About 8 out of 10 chance
Medium confidence About 5 out of 10 chance
Low confidence About 2 out of 10 chance
Very low confidence Less than 1 out of 10 chance
Note that ‘low confidence’ and ‘very low confidence’ are only used for areas of major concern and where a risk-based perspective is justified.
Chapter 2 of this report uses a related term ‘level of scientific understanding’ when describing uncertainties in different contributions to radiative forcing. This terminology is used for consistency with the Third Assessment Report, and the basis on which the authors have determined particular levels of scientific understanding uses a combination of approaches
consistent with the uncertainty guidance note as explained in detail in Section 2.9.2 and Table
2.11.
The standard terms used in this report to define the likelihood of an outcome or result where this can be estimated probabilistically are:
Likelihood Terminology Likelihood of the occurrence/ outcome
Virtually certain > 99% probability
Extremely likely > 95% probability
Very likely > 90% probability
Likely > 66% probability
More likely than not > 50% probability
About as likely as not 33 to 66% probability
Unlikely < 33% probability
Very unlikely < 10% probability
Extremely unlikely < 5% probability
Exceptionally unlikely < 1% probability
The terms ‘extremely likely’, ‘extremely unlikely’ and ‘more likely than not’ as defined above have been added to those given in the IPCC Uncertainty Guidance Note in order to provide a more specific assessment of aspects including attribution and radiative forcing.
Unless noted otherwise, values given in this report are assessed best estimates and their uncertainty ranges are 90% confidence intervals (i.e., there is an estimated 5% likelihood of the value being below the lower end of the range or above the upper end of the range). Note that in some cases the nature of the constraints on a value, or other information available, may indicate an asymmetric distribution of the uncertainty range around a best estimate. In such cases, the uncertainty range is given in square brackets following the best estimate.
Main Activities and Products of IPCC
A main activity of the IPCC is to provide in regular intervals an assessment of the state of knowledge on climate change. The IPCC also prepares Special Reports and Technical Papers on topics where independent scientific information and advice is deemed necessary and it supports the UN Framework Convention on Climate Change (UNFCCC) through its work on methodologies for National Greenhouse Gas Inventories. A number of IPCC reports are published commercially. Summaries, CD ROMs and Technical Papers can be obtained free of charge. A limited number of full reports are avaible from the IPCC Secretariat for developing countries and countries with economies in transition.
History of IPCC to December 2004.
The First IPCC Assessment Report was completed in 1990. The Report played an important role in establishing the Intergovernmental Negotiating Committee for a UN Framework Convention on Climate Change by the UN General Assembly. The UN Framework Convention on Climate Change (UNFCCC) was adopted in 1992 and entered into force in 1994. It provides the overall policy framework for addressing the climate change issue.
The IPCC has continued to provide scientific, technical and socio-economic advice to the world community, and in particular to the Parties to the UNFCCC through its periodic assessment reports and special reports. Its Second Assessment Report, Climate Change 1995, provided key input to the negotiations, which led to the adoption of the Kyoto Protocol to the UNFCCC in 1997.
The Third Assessment Report (TAR), Climate Change 2001, was completed in 2001. It was submitted to the 7th Conference of the Parties to the UNFCCC and Parties agreed that it should be used routinely as a useful reference for providing information for deliberations on agenda items of the Conference of the Parties.
The IPCC has decided to continue to prepare comprehensive assessment reports and agreed to complete its Fourth Assessment Report in 2007.
History of IPCC to December 2004.
The First IPCC Assessment Report was completed in 1990. The Report played an important role in establishing the Intergovernmental Negotiating Committee for a UN Framework Convention on Climate Change by the UN General Assembly. The UN Framework Convention on Climate Change (UNFCCC) was adopted in 1992 and entered into force in 1994. It provides the overall policy framework for addressing the climate change issue.
The IPCC has continued to provide scientific, technical and socio-economic advice to the world community, and in particular to the Parties to the UNFCCC through its periodic assessment reports and special reports. Its Second Assessment Report, Climate Change 1995, provided key input to the negotiations, which led to the adoption of the Kyoto Protocol to the UNFCCC in 1997.
The Third Assessment Report (TAR), Climate Change 2001, was completed in 2001. It was submitted to the 7th Conference of the Parties to the UNFCCC and Parties agreed that it should be used routinely as a useful reference for providing information for deliberations on agenda items of the Conference of the Parties.
The IPCC has decided to continue to prepare comprehensive assessment reports and agreed to complete its Fourth Assessment Report in 2007.
Tuesday, 8 May 2007
CO2 gas 'must halve' by 2050 - IPCC report - Working Group III
The world needs to halve CO2 emissions by 2050 to keep global warming in check, a UN report says. Play media report.
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