The IPCC Assessment Process: Future Projections of Climate Change Ronald J StoufferGeophysical Fluid Dynamics LaboratoryNOAAThe views described here are solely those of the presenter and not of GFDL/NOAA/DOC or any other agency or institution.
What is the IPCC? http://www.ipcc.ch
Established by: World Meteorological Organization (WMO) United Nations Environment Programme (UNEP) Open to all members of the UN and WMO Started in 1988 - Full reports in 1990, 1995, 2001, 2007
From the IPCC web pages:
The role of the IPCC is to assess on a comprehensive, objective, open and transparent basis the scientific, technical and socio-economic information relevant to understanding the scientific basis of risk of human-induced climate change, its potential impacts and options for adaptation and mitigation.
What is the IPCC? Every 5-6 years, over 1000 scientists from more than 100 nations assess the published scientific literature documenting the state of scientific knowledge related to climate change issues. The IPCC reports are ratified by the ~180 member nations.
NOAA GFDL has been a prime player in the 4 major assessment reports, including the IPCC 4th Assessment Report (AR4) published in early 2007.
IPCC WGI 2007 FindingsThe planet is warming. The warming is not uniform. In fact, some small areas are cooling. Other climate and biophysical changes support the idea that the planet is warming. Sea ice and snow edges retreating; increased precipitation; more water vapor in the atmosphere; earlier river thaws; earlier spring migrations; plant blooms; etc.
Humans are the cause of increasing greenhouse gases in the atmosphere (CO2, methane, etc.). Humans also cause emissions of items that tend to cool the planet (sulfate aerosols for example).
Climate models using estimates of past forcings (GHG, aerosols, solar, volcanoes) can simulate much of the past climate variations at the global scale and many regional scales. Using estimates of future emissions, climate models project relatively large increases in warming and other associated climate impacts (precipitation, sea level, etc.) over the next century.
IPCC- How is it organized?Three Working GroupsI. Physical climate changesII. Impacts of physical climate changes on human and natural systemsIII. Mitigation (cost/benefits) of future climate changesScientists assess peer-reviewed literatureRole of consensusRole of uncertainty
IPCC- Role of consensusFinding consensus is a messy businessScientists seem much better at finding points of disagreement than points of agreementDoes a given statement reflect the scientific literature, uncertainties and a wide range of opinions?
IPCC- Role of consensusWording is a big issue2001 WGI bottom line as an example: There is new and stronger evidence that most of the warming over the last 50 years is attributable to human activities. Plenary turned much into mostPrevious disagreement over substantial resulted in muchWhat does substantial mean?Majority?Plurality?
IPCC- Role of consensus> Can I live with statement?Is statement wrong?In plenary this question can be very important
IPCC- Role of uncertainty Different ways to express uncertaintyProbability (pdf) likelihood WG1Virtually certain, Very likely, likely, etc.Confidence high confidence WG2High, medium, low confidenceAgreement high agreement WG3High, medium, low agreementEvidence much evidence WG3Much, medium, limited evidence
IPCC- Role of governmentsMust approve SPM (Summary for PolicyMakers) line by line (or word by word)Scientists must also agree to wording changesMust be consistent with underlying reportCan I live with wording? questionPossible to have footnotes saying that a given country or countries did not approve of a part of the text never used to date but often threatened
IPCC- PlenaryValencia, Spain November, 2007
IPCC- PlenaryTypically go very slowly through text in the beginningWhen progress stops on a wording/science/political issue => breakout groupsBreakout groups meet before/after meetingFocus on a subset of the textLast day(s) goes well into nightRush to get things done
IPCC- Process (Authors viewpoint)Organizational meeting Literature search and community inputWrite 1st draftLimited expert reviewSecond meetingCross cutting issues between chaptersPlan next draftWrite 2nd draftPublication deadline for referenced papers
IPCC- Process (Authors viewpoint)Deal with review comments (experts and national review)Each must be answeredReview and Comments made publicMore than 1000 comments per chapter3rd authors meetingCross cutting issuesDeal with review/commentsWrite last draft
IPCC- Process (Authors viewpoint)Deal with review comments (national and NGO review)Each must be answeredReview and Comments made publicMore than 1000 comments per chapterWrite final versionCross chapter referencesConsistency between chapter and SPM
Projections of future climate changeReviewProjectionsTime scales of responseVariabilityAbrupt climate change
Important greenhouse gases are increasing.
The largest increases are in the last 100 years or so.IPCC WGI SPMCarbonDioxideMethaneNitrousOxide
Over the last 100 years the:Surface temperature is increasing
Sea level is rising
Snow cover is decreasingIPCC WGI SPM
Human activities are very likely the cause of the warming of last 100 years.Black line: temperature observation from thermometers.Pink shade: Climate model simulations using all past radiative forcings.Blue shade: Climate model simulation using only natural forcings (solar, volcanoes).IPCC WGI SPM
Human activities are likely to be the cause of the warming over last 100 years on each continent.IPCC WGI SPM
Past IPCC Projections vs. Observations Projections very good so far.
Lots of issues: - No aerosols in FAR - No volcanoes in all - Natural variability largeIPCC AR4 WGI Chapter 1
Special Report on Emission Scenarios (SRES, 2000) and Post-SRES scenariosEmissions depend on:PopulationTechnological developmentSocietys choicesNo mitigation assumedEmissions differ in beginning of this centuryEmissions very different by end of century
Figure from AR4 Synthesis report
Projection of future changes in climateRange of projections is broadly consistent with the TAR.Stronger climate-carbon cycle feedbacks. Projection - scenario independent over next several decades.Warming this century much larger than last century.Best estimate and likely uncertainty range at 2100IPCC WGI SPM
Warming greatest over land and at most high northern latitudes and least over Southern Ocean and parts of the North Atlantic OceanContinuing recent observed trends in contraction of snow covered area, increases in thaw depth over most permafrost regions, and decrease in sea ice extent In some projections using SRES scenarios, Arctic late-summer sea ice disappears almost entirely by the latter part of the 21st centurySurface Warming PatternA1B, 2090-2099 relative to 1980-1999IPCC WGI SPM
Projection of future changes in climate sea levelIPCC WGI SPMNote: No upper bound No likelihood No best estimate Model based estimate only, no expert judgment
meters
Sea Level Rise UncertaintyWhy so large? Understanding of some important effects that determine sea level rise is too limited
Published literature lacking Climate-carbon cycle feedbacks Changes in ice sheet flowIPCC AR4 Synthesis Report wording
Sea Level Rise UncertaintyThe projections include a contribution due to increased ice flow from Greenland and Antarctica at the rates observed for 1993-2003, but these flow rates could increase or decrease in the future. Therefore the upper values of the ranges given are not to be considered upper bounds for sea level rise. If this contribution (the observed rates) were to grow linearly with global average temperature change, the upper ranges of sea level rise for SRES scenarios would increase by 0.1 m to 0.2 m. {WGI 10.6, SPM}IPCC AR4 Synthesis Report wording
Other examples of regional changesVery likely increase in frequency of hot extremes, heat waves, and heavy precipitationLikely increase in tropical cyclone intensity; less confidence in global decrease of tropical cyclone numbersPoleward shift of extra-tropical storm tracks with consequent changes in wind, precipitation, and temperature patternsVery likely precipitation increases in high latitudes and likely decreases in most subtropical land regions, continuing observed recent trendsIPCC WGI SPM
Very likely runoff will increase in high latitudes.Likely runoff will decrease over some subtropical and tropical regions. 21st Century Water Availability (Runoff) Changes(Annually averaged)WetterDrierIPCC AR4 Synthesis
Time scales of ResponseHuman and natural systemsPhysical climate systemGreenhouse gas lifetimes in atmosphereOceanIce sheets
Response time scales Note response in 2020s very similar in spite of very different emissions.Note response in 2090s much more scenario dependent.Actions taken today only have large impacts in climate response in the future.
Response time scalesRole of Oceans
Anthropogenic warming and sea level rise would continue for centuries, even if GHG concentrations were to be stabilized at or above todays levels.
AR4 estimates 0.2 to 0.6m sea level rise per oC at equilibrium due only to thermal expansion of sea water.IPCC WGI SPMResponse time scalesRole of Oceans
What would 1 meter do?
VariabilityHow smooth is the future temperature increase?
January 2008 is a cold month Drop as large as December to January fairly common Cause? La Nina Variability over NH continents
Anthropogenic warming could lead to some impacts that are abrupt or irreversible, depending upon the rate and magnitude of the climate change.Partial loss of ice sheets on polar land could imply meters of sea level rise, major changes in coastlines and inundation of low-lying areas, with greatest effects in river deltas and low-lying islands. Such changes are projected to occur over millennial time scales, but more rapid sea level rise on century time scales cannot be excluded.IPCC WGI SPM
Based on current model simulations, the Meridional Overturning Circulation (MOC) of the Atlantic Ocean will very likely slow down during the 21st century; nevertheless temperatures over the Atlantic and Europe are projected to increase. The MOC is very unlikely to undergo a large abrupt transition during the 21st century. Longer-term MOC changes cannot be assessed with confidence. Anthropogenic warming could lead to some impacts that are abrupt or irreversible
SummaryThe IPCC is a successful mechanism communicating climate change science.The IPCC can influence policy through government actionsImportance of govt approval of SPMsThe projections of climate change for this century are larger than what has occurred in the past century.Response time scales, natural variability complicate discussion and hinder understanding.We know a lot about future climate changes, but some surprises are expected.
Thank you
More systematic understanding of the timing and magnitude of impacts related to differing amounts and rates of climate change.
WaterThere is high confidence that hundreds of millions of people will be exposed to increased water stress
EcosystemsThere is high confidence that many species are at increasing risk of extinction with increasing temperature.
FoodGlobally food production is projected to increase at local temperature increases of 1-3 oC; decreases projected above (medium confidence).
CoastsThere is high confidence that millions of people could experience more coastal flooding if global temperature increases more than 2C in this century. Sea level has very long times and will continue to rise for centuries after stabilization of GHG.
HealthThe health status of millions of people is projected to be affected through, for example: Increases in malnutrition Increased deaths, diseases and injury due to extreme weather events Increased burden of diarrhoeal diseases Increased frequency of cardio-respiratory diseases due to changes in air quality Altered spatial distribution of some infectious diseases.
Some regions are likely to be especially affectedThe Arctic, because of the impacts of high rates of projected warming on natural systems and human communitiesAfrica, because of low adaptive capacity and projected climate change impactsSmall islands, where there is high exposure of population and infrastructure to projected climate change impactsAsian and African megadeltas, due to large populations and high exposure to sea level rise, storm surges and river flooding.
There is medium confidence that approximately 20-30% of species assessed so far are likely to be at increased risk of extinction if increases in global average warming exceed 1.5-2.5oC (relative to 1980-1999).
As global average temperature increase exceeds about 3.5oC, model projections suggest significant extinctions (40-70% of species assessed) around the globe.
Anthropogenic warming could lead to some impacts that are abrupt or irreversible
