Global Warming - 1Global Warming - 1 An Assessment An Assessment

The balance of the evidence ...The balance of the evidence ...

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Greenhouse gases warm the earth, Greenhouse gases warm the earth, increasing evaporation.increasing evaporation.

Do you think changes in cloudiness will Do you think changes in cloudiness will cool or warm the earth? What is your cool or warm the earth? What is your reasoning?reasoning?

Key PointsKey Points Scientific assessment describes present state of Scientific assessment describes present state of

knowledgeknowledge Global temperature has increased during 20 Global temperature has increased during 20

century, continuing through the 1990s century, continuing through the 1990s – beyond reasonable doubt ( beyond reasonable doubt ( virtually certainvirtually certain))

Some of this increase is due to human activitiesSome of this increase is due to human activities– the balance of the evidence (the balance of the evidence (likelylikely))

Impacts are complex, vary with region, very Impacts are complex, vary with region, very difficult to quantify reliablydifficult to quantify reliably

Any action to limit future increases will take Any action to limit future increases will take decades to become effectivedecades to become effective– certain (certain (virtually certainvirtually certain))

Scientific AssessmentsScientific Assessments There There areare accepted standards of what accepted standards of what

constitutes scientific evidence constitutes scientific evidence Review and discussion by knowledgeable Review and discussion by knowledgeable

peers establishes consensuspeers establishes consensus– What is thoroughly establishedWhat is thoroughly established– What is plausible, but definitive evidence lackingWhat is plausible, but definitive evidence lacking– What is poorly understood or legitimately What is poorly understood or legitimately

controversialcontroversial

Scientists are paid to be skeptical. Some will Scientists are paid to be skeptical. Some will always disagreealways disagree

The Intergovernmental Panel The Intergovernmental Panel on Climate Changeon Climate Change

IPCC95 CoverIPCC95 Cover

Prediction IPPC 1990 ReportPrediction IPPC 1990 Report Latest predictions show less warmingLatest predictions show less warming Uncertainties were underestimatedUncertainties were underestimated

IPCC90 Fig 8IPCC90 Fig 8

Notes on Notes on Science AssessmentScience Assessment

Current consensus on attribution Current consensus on attribution – Balance of the evidenceBalance of the evidence

Regional predictions much less secure Regional predictions much less secure than global averagethan global average

Precipitation predictions much less Precipitation predictions much less secure than temperaturesecure than temperature

Impacts on ecosystems, agriculture, etc Impacts on ecosystems, agriculture, etc only in general terms only in general terms

Judgements of ConfidenceJudgements of ConfidenceIPCC Third Assessment Report-2001IPCC Third Assessment Report-2001

Summary for policymakers - Footnote 7Summary for policymakers - Footnote 7

Statement Statement – Virtually CertainVirtually Certain– Very LikelyVery Likely– LikelyLikely– Medium LikelihoodMedium Likelihood– UnlikelyUnlikely– Very unlikelyVery unlikely– Exceptionally Exceptionally

unlikelyunlikely

Chance TrueChance True– > 99%> 99%– 90-99%90-99%– 60-90%60-90%– 33-66%33-66%– 10-33%10-33%– 1-10%1-10%– < 1%< 1%

Key PointsKey Points Scientific assessment describes present state of Scientific assessment describes present state of

knowledgeknowledge Global temperature has increased during 20 Global temperature has increased during 20

century, continuing through the 1990s century, continuing through the 1990s – beyond reasonable doubt ( beyond reasonable doubt ( virtually certainvirtually certain))

Some of this increase is due to human activitiesSome of this increase is due to human activities– the balance of the evidence (the balance of the evidence (likelylikely))

Impacts are complex, vary with region, very Impacts are complex, vary with region, very difficult to quantify reliablydifficult to quantify reliably

Any action to limit future increases will take Any action to limit future increases will take decades to become effectivedecades to become effective– certain (certain (virtually certainvirtually certain))

Global Average TemperatureGlobal Average Temperature

Is this a natural fluctuation or attributable to Is this a natural fluctuation or attributable to human activities?human activities?

Sept 1998. Every month for past 19 has been Sept 1998. Every month for past 19 has been a record high!a record high!

Past NH Summer TemperaturePast NH Summer Temperature tree rings, ice cores,documentstree rings, ice cores,documents

IPCC95 Fig 10IPCC95 Fig 10

IPPC 3rd Assessment Report-1IPPC 3rd Assessment Report-1 Global temperature increased over the 20th Century Global temperature increased over the 20th Century

by about 0.6by about 0.6o o C : C : virtually certainvirtually certain This increase is largest for any century within past 100 This increase is largest for any century within past 100

years: years: likelylikely Snow cover and ice extent decreasedSnow cover and ice extent decreased

– Snow by 10% since 1960sSnow by 10% since 1960s very likelyvery likely– Lakes & rivers by 2 wks since 1900 Lakes & rivers by 2 wks since 1900 very likelyvery likely– Arctic sea-ice by 40% since 1950s Arctic sea-ice by 40% since 1950s likelylikely

Global average sea level rose 10-20 cm (4-8 inches) Global average sea level rose 10-20 cm (4-8 inches) during 20th century during 20th century

Cloud cover increased 2% over mid-high latitude land Cloud cover increased 2% over mid-high latitude land during 20th century during 20th century likelylikely

Key PointsKey Points Scientific assessment describes present state of Scientific assessment describes present state of

knowledgeknowledge Global temperature has increased during 20 Global temperature has increased during 20

century, continuing through the 1990s century, continuing through the 1990s – beyond reasonable doubt ( beyond reasonable doubt ( virtually certainvirtually certain))

Some of this increase is due to human activitiesSome of this increase is due to human activities– the balance of the evidence (the balance of the evidence (likelylikely))

Impacts are complex, vary with region, very Impacts are complex, vary with region, very difficult to quantify reliablydifficult to quantify reliably

Any action to limit future increases will take Any action to limit future increases will take decades to become effectivedecades to become effective– certain (certain (virtually certainvirtually certain))

What Do the Models Say?What Do the Models Say?Partially Tuned SimulationsPartially Tuned Simulations

What happened 1940-1970?What happened 1940-1970?

IPCC95 Fig 15IPCC95 Fig 15

Model TuningModel Tuning

Models are simplified representations of realityModels are simplified representations of reality They represent what are believed to be the most They represent what are believed to be the most

significant processessignificant processes Representations sometimes involve coefficients Representations sometimes involve coefficients

which must be empirically determinedwhich must be empirically determined Tuning = adjusting coefficients within plausible Tuning = adjusting coefficients within plausible

ranges to achieve desired model output ranges to achieve desired model output

Is the Aerosol Effect Real?Is the Aerosol Effect Real?We think we understand it but could be We think we understand it but could be

surprisedsurprised Radiative forcing per unit sulfate aerosol Radiative forcing per unit sulfate aerosol

uncertain uncertain a prioria priori Good simulations of Mt. Pinatubo Good simulations of Mt. Pinatubo

– aerosol in stratosphere, not troposphereaerosol in stratosphere, not troposphere Warming in sulfate areas only at nightWarming in sulfate areas only at night

– observed and modeledobserved and modeled Better agreement for global rise for past Better agreement for global rise for past

100 years100 years– some tuningsome tuning

After Eruption of Mt. PinatuboAfter Eruption of Mt. Pinatubo

IPCC95 Fig 14IPCC95 Fig 14

Sensitivity to Aerosols -1Sensitivity to Aerosols -1for 3 values of cloud feedbackfor 3 values of cloud feedback

greenhouse gases only greenhouse gases only

IPCC95 Fig 16a IPCC95 Fig 16a

Sensitivity to Aerosols -2Sensitivity to Aerosols -2for 3 values of cloud feedbackfor 3 values of cloud feedback

greenhouse gases greenhouse gases and aerosolsand aerosols

IPCC95 Fig 16b IPCC95 Fig 16b

Estimated Current ForcingEstimated Current Forcing

IPCC IPCC 19951995

Key PointsKey Points Scientific assessment describes present state of Scientific assessment describes present state of

knowledgeknowledge Global temperature has increased during 20 Global temperature has increased during 20

century, continuing through the 1990s century, continuing through the 1990s – beyond reasonable doubt ( beyond reasonable doubt ( virtually certainvirtually certain))

Some of this increase is due to human activitiesSome of this increase is due to human activities– the balance of the evidence (the balance of the evidence (likelylikely))

Impacts are complex, vary with region, very Impacts are complex, vary with region, very difficult to quantify reliablydifficult to quantify reliably

Any action to limit future increases will take Any action to limit future increases will take decades to become effectivedecades to become effective– certain (certain (virtually certainvirtually certain))

Impacts of Climate ChangeImpacts of Climate Change Regional analysis is criticalRegional analysis is critical Current climate models disagree on regional Current climate models disagree on regional

changeschanges Changes in precipitation at least as important Changes in precipitation at least as important

as changes in temperatureas changes in temperature Impacts on ecosystems, water resources, Impacts on ecosystems, water resources,

agriculture, extreme events (floods, droughts, agriculture, extreme events (floods, droughts, hurricanes,…). Some beneficial,vary with hurricanes,…). Some beneficial,vary with regionregion

Other stresses use to land use, acid rainOther stresses use to land use, acid rain Less wealthy countries more vulnerableLess wealthy countries more vulnerable Need to build resilience to multiple stressesNeed to build resilience to multiple stresses

Key PointsKey Points Scientific assessment describes present state of Scientific assessment describes present state of

knowledgeknowledge Global temperature has increased during 20 Global temperature has increased during 20

century, continuing through the 1990s century, continuing through the 1990s – beyond reasonable doubt ( beyond reasonable doubt ( virtually certainvirtually certain))

Some of this increase is due to human activitiesSome of this increase is due to human activities– the balance of the evidence (the balance of the evidence (likelylikely))

Impacts are complex, vary with region, very Impacts are complex, vary with region, very difficult to quantify reliablydifficult to quantify reliably

Any action to limit future increases will take Any action to limit future increases will take decades to become effectivedecades to become effective– certain (certain (virtually certainvirtually certain))

IPPC 3rd Assessment Report-2IPPC 3rd Assessment Report-2 Atmospheric CO2 Atmospheric CO2

– increased 31% since 1750increased 31% since 1750 virtually certain virtually certain– present concentrations largest in 420,000 yr andpresent concentrations largest in 420,000 yr and likely likely in in

20,000,000 yr20,000,000 yr

3/4 anthropogenic emissions CO2 due to fossil fuel 3/4 anthropogenic emissions CO2 due to fossil fuel burning, remainder mainly land use change burning, remainder mainly land use change

Human influences will continue to change Human influences will continue to change atmospheric composition throughout the 21st atmospheric composition throughout the 21st CenturyCentury

Global average temperatures are projected to Global average temperatures are projected to rise under all IPPC scenarios.rise under all IPPC scenarios.

Changes in Radiative ForcingChanges in Radiative ForcingBusiness as Usual ScenarioBusiness as Usual Scenario

Projected Future WarmingProjected Future WarmingIntermediate cloud feedbackIntermediate cloud feedback

For high or low feedback multiply by 1.8 or 0.6 For high or low feedback multiply by 1.8 or 0.6 Must examine credibilityMust examine credibility

IPCC95 Fig 18IPCC95 Fig 18

Emissions ScenariosEmissions ScenariosCOCO22 Gt C /y Gt C /y

Concentration ScenariosConcentration ScenariosCOCO22 ppmv ppmv

Key PointsKey Points Scientific assessment describes present state of Scientific assessment describes present state of

knowledgeknowledge Global temperature has increased during 20 Global temperature has increased during 20

century, continuing through the 1990s century, continuing through the 1990s – beyond reasonable doubt ( beyond reasonable doubt ( virtually certainvirtually certain))

Some of this increase is due to human activitiesSome of this increase is due to human activities– the balance of the evidence (the balance of the evidence (likelylikely))

Impacts are complex, vary with region, very Impacts are complex, vary with region, very difficult to quantify reliablydifficult to quantify reliably

Any action to limit future increases will take Any action to limit future increases will take decades to become effectivedecades to become effective– certain (certain (virtually certainvirtually certain))

Sources of InformationSources of Information Horel and Geisler Chapter 8Horel and Geisler Chapter 8 Climate Change 1995 - Houghton Climate Change 1995 - Houghton et al et al

Cambridge University Press Cambridge University Press IPCC (Working Group 1) “Third IPCC (Working Group 1) “Third

Assessment Report.” Summary for Assessment Report.” Summary for Policy Makers Policy Makers

IPPC “Regional Impacts of Climate IPPC “Regional Impacts of Climate Change” Change” http://www.grida.no/climate/ipcc/regional/http://www.grida.no/climate/ipcc/regional/

– Introduction Introduction