1

Global Warming:State of the Science

Richard WolfsonRichard WolfsonBenjamin F. Benjamin F. Wissler Wissler Professor of PhysicsProfessor of Physics

Professor, Environmental StudiesProfessor, Environmental StudiesMiddlebury CollegeMiddlebury College

St MichaelSt Michael’’s Colleges CollegeJanuary 25, 2007January 25, 2007

Global Warming - A Brief History 1919thth Century Century

Fourier, Tyndall, Langley:Fourier, Tyndall, Langley:greenhouse gases warm Earthgreenhouse gases warm Earth

Arrhenius Arrhenius (1896):(1896):5-65-6˚̊C rise for COC rise for CO22 doubling doubling

2

Global Warming - A Brief History

2020thth Century Century 1970s, early 80s: global cooling? nuclear winter?1970s, early 80s: global cooling? nuclear winter?

Summer of Summer of ’’8888

1991 IPCC first assessment report (FAR):1991 IPCC first assessment report (FAR):observed climate observed climate ““broadly consistentbroadly consistent”” with withanthropogenic greenhouse effectanthropogenic greenhouse effect

1996 IPCC SAR: 1996 IPCC SAR: ““discernible human influence ondiscernible human influence onglobal climateglobal climate””

2121stst Century Century 2001 IPCC TAR:2001 IPCC TAR:

““most of the warming observed over the last 50 years is attributable tomost of the warming observed over the last 50 years is attributable tohuman activitieshuman activities””

National Academy of Sciences 2001:National Academy of Sciences 2001: ““greenhouse gases are accumulating in Earthgreenhouse gases are accumulating in Earth’’s atmosphere as a result ofs atmosphere as a result ofhuman activities, causing surface air temperature and subsurface oceanhuman activities, causing surface air temperature and subsurface oceantemperature to risetemperature to rise””

U.S. Global Change Research Program,U.S. Global Change Research Program,report to Congress, August 25, 2004:report to Congress, August 25, 2004:““North American temperature changes fromNorth American temperature changes from1950 to 1999 were unlikely to be due only to1950 to 1999 were unlikely to be due only tonatural climate variationsnatural climate variations””

2007 IPCC2007 IPCC AR4 (summary due next Friday):AR4 (summary due next Friday):Will affirm and strengthenWill affirm and strengthen attribution of climate change to humanattribution of climate change to humanactivitiesactivities—— ““Look for an Look for an ‘‘iconic statementiconic statement——a simple but strong anda simple but strong andunequivocal summaryunequivocal summary’”’” (K. (K. TrenberthTrenberth, quoted in Tuesday, quoted in Tuesday’’s s Free PressFree Press))

Global Warming - A Brief History

3

What is this IPCC? Intergovernmental Panel on Climate ChangeIntergovernmental Panel on Climate Change Established 1988 byEstablished 1988 by

World Meteorological OrganizationWorld Meteorological Organization United Nations Environment ProgramUnited Nations Environment Program

Major assessment reports every ~six yearsMajor assessment reports every ~six years Summarize climate researchSummarize climate research

Three Working GroupsThree Working Groups Science, Impacts, MitigationScience, Impacts, Mitigation

Hundreds of scientists & policymakersHundreds of scientists & policymakers WG1 (Science): 637 authors, hundreds more reviewersWG1 (Science): 637 authors, hundreds more reviewers

IPCC: Synthesizing ResearchModel runs with 1%/yearequivalent CO2 increase

IPCC 2001 WG1 Fig. 9.3

4

Global Warming: Is it Happening?

Source: University of East Anglia, Climatic Research Unit, updated 1/25/07http://www.cru.uea.ac.uk/cru/data/temperature/hadcrut3vgl.txt

Year

Tem

pera

ture

dev

iatio

n, °C

20 Hottest Years on RecordUniversity of East Anglia Climatic Research Unit; Updated 1/25/07

Top 10Top 1019981998200520052003200320022002200420042006200620012001199719971999199920002000

Next 10Next 1019951995199019901991199119871987198819881983198319941994199619961981198119891989

5

Other Indicators of Recent Change Ice and snowIce and snow

40% decrease in arctic ice thickness in recent decades40% decrease in arctic ice thickness in recent decades 10-15% decrease in arctic ice extent since 195010-15% decrease in arctic ice extent since 1950 10% decrease in global snow cover area since 1960s10% decrease in global snow cover area since 1960s Widespread retreat of non-polar glaciersWidespread retreat of non-polar glaciers

El Niño eventsEl Niño events More frequent, persistent, and intense past 30 yearsMore frequent, persistent, and intense past 30 years

Biological indicatorsBiological indicators Growing season increasing 1-4 days/decadeGrowing season increasing 1-4 days/decade Plant and animal ranges shifting poleward 6 km/decadePlant and animal ranges shifting poleward 6 km/decade Coral reefs bleachingCoral reefs bleaching

The Shrinking Arctic

Sea ice minimum, 2005

Source: NASA;http://www.nasa.gov/centers/goddard/news/topstory/2005/arcticice_decline.html

Sea ice minimum, 1979

6

National Park?

Ice CoverageIce Coverage 1850: 100 km1850: 100 km22

1971: 40 km1971: 40 km22

2003: 19 km2003: 19 km22

Yellow: Permanent ice/snow, 1850Pink: Permanent ice/snow, 1995

Source: www.nrmsc.usgs.gov/research/glacier_retreat.htm

Mt Jackson, ______National Park

Going Further Back . . .

Source: Mann et al., “Northern Hemisphere Millennial Temperature Reconstruction,”Geophys. Res. Let., 26, 759, 1999 as reproduced in IPCC 2001 WG1

The “Hockey Stick”

7

Going Further Back . . .

Source: Robert A. Rhode, Global Warming Arthttp://www.globalwarmingart.com/wiki/Image:1000_Year_Temperature_Comparison.png

The “Hockey Team”

Millennial Temperature Reconstruction Uses multiple indicators to reconstructUses multiple indicators to reconstruct

1000-year1000-year temperature record temperature record Up to 112 indicators (tree rings, ice cores, ice melt, solarUp to 112 indicators (tree rings, ice cores, ice melt, solar

activity, coral reefs, etc)activity, coral reefs, etc) Recent warming unprecedentedRecent warming unprecedented in past in past millenniummillennium Solar variability and volcanism are dominant influencesSolar variability and volcanism are dominant influences

on climate before 20on climate before 20thth century century Anthropogenic greenhouse gasesAnthropogenic greenhouse gases are dominant 20 are dominant 20thth

century influencecentury influence Provides independent confirmation of Provides independent confirmation of human influencehuman influence

on climateon climate

Mann et al., “…millennial Temperature Reconstruction,” Geophys. Res. Let., 26, 759, 1999;Crowley, “Causes of Climate Change Over the Past 1000 Years,” Science, 289, 270, July 14, 2000

8

And Further Still . . ..

-10-8-6-4-20246

-160 -120 -80 -40 0

Thousands of years before present

Te

mp

era

ture

de

via

tio

n

(°C

)

Source: Carbon Dioxide Information Analysis Center

Ice Age

~6˚C

Climate Science: Quick Summary

Incoming sunlight

Outgoing infrared

9

Incoming sunlight

Outgoing infrared

Sunlight in: 240 watts/m2

Infrared out: σT4

Result: T=255 K(–18°C, 0°F)

Climate Science: Quick Summary

The Greenhouse Effect

Incoming sunlight

Outgoing infrared

Infrared re-radiatedby greenhouse gases

Result:surface warmerby 33°C(Naturalgreenhouseeffect)

Taverage=15˚C

10

A Tale of Three Planets

Planet Calc.

Temp

Actual

Temp

Venus 50 500

Earth –18 15

Mars –60 –50

Temperatures in ˚C

Earth’s Energy Balance: Details

Source: Slide from Kevin Trenberth, NCARBased on Kiehl & Trenberth 1997, Bull. Am. Met. Soc., 78, 197

11

A Human Influence?Climate Forcings, 2005 relative to 1750

Source: IPCC

Cool

ing

War

min

g

W/m2

A Human Influence?

Year

Sources: Temperature: University of East Anglia Climate Research Unit, updated 1/07; CO2: Through 1953 - Siple Station, Antarctica; Friedli et al. 1986 Nature 324, 237;1959 - Mauna Loa; Keeling & Whorf 2004 “Atmospheric CO2 records …” in Trends: A Compendium of Data on Global Change(Carbon Dioxide Information Analysis Center, Oak Ridge National Laboratory, TN)

Glo

bal a

vera

ge te

mp,

°C

275

300

325

350

CO2 c

once

ntra

tion,

ppm375

12

Ancient Climates.

-10-8-6-4-20246

-160 -120 -80 -40 0

Thousands of years before present

Te

mp

era

ture

de

via

tio

n

(°C

)

150

200

250

300

CO C

once

ntra

tion

(ppm

)2

Source: Carbon Dioxide Information Analysis Center Trends: A Compendium of Data on Global Change

Today:~382 ppm

A Human Influence on Climate?

Source: Caspar Ammann, National Center for Atmospheric Research

13

Why Believe Today’s Climate Models?

Better resolution (thanks to MooreBetter resolution (thanks to Moore’’s Law!)s Law!) Horizontal: 250 kmHorizontal: 250 km Vertical: 10-30 atmospheric, ocean layersVertical: 10-30 atmospheric, ocean layers

Better treatment of sulfate aerosolBetter treatment of sulfate aerosol Elimination of flux correctionElimination of flux correction Better sub-grid parameterizationBetter sub-grid parameterization Corrections to satellite measurementsCorrections to satellite measurements Model validation experimentsModel validation experiments

Why Believe Today’s Climate Models?The Pinatubo “Experiment”

Source: IPCC 1996 WG1 p. 33

14

Why Believe Today’s Climate Models?

They reproduce observed temperature, precipitation:

LatitudeLatitude

mm/day

Source: IPCC 2001 WG1 Fig 8.2, 8.3

IPCC Climate Projections Depend on human behaviorDepend on human behavior IPCC Emissions Scenarios (SRES)IPCC Emissions Scenarios (SRES)

Economicemphasis

Environmentalemphasis

Global Regional

A1

B2

A2

B1

FI: fossil intensiveB: balancedT: new technologies

15

IPCC Climate Projections Depend on human behaviorDepend on human behavior New IPCC Emissions Scenarios (SRES)New IPCC Emissions Scenarios (SRES)

Economicemphasis

Environmentalemphasis

Global Regional

A1

B2

A2

B1

Population peaksmid 21st century

Population stillgrowing in 2100

CO2 Emissions in the IPCC Scenarios

Source: IPCC 2001 WG1 TS Fig 17

16

Temperature Scenarios

Source: IPCC 2001 WG1 Fig 9.14

Regional Variations2071-2100 relative to 1961-1990

Source: IPCC 2001 WG1 Fig 9.10d

17

What’s In Store for Vermontand New England?

Boston Boston ➞➞ Richmond, VA (3.5 Richmond, VA (3.5˚̊C); Atlanta (5.6C); Atlanta (5.6˚̊C)C) Warmer, wetter winters - greatly reduced Warmer, wetter winters - greatly reduced snowpacksnowpack?? No Vermont maple syrup?No Vermont maple syrup?

Sources: Preparing for a Changing Climate: The Potential Consequences of Climate Variability and Change,New England Region Overview, New England Regional Assessment Group, 2001;New England 20th century temperature increases from Trombulak & Wolfson, Geophys. Res. Let. 31, L19202, 2004

2.1

2.2

1.5

1.8

3.32.7 2.7

2.0˚F

twentieth century

Lyme Disease in VermontA Connection to Climate Change?

Source: Vermont Department of Health http://healthvermont.gov/prevent/lyme/lymenumbers.pdf; 2006 figure tentative

Lyme disease cases contracted within Vermont

18

Other Climate Impacts

Higher maximum temperatures; more heat wavesHigher maximum temperatures; more heat waves(very likely; 90-99%)(very likely; 90-99%)

More intense precipitation events More intense precipitation events (very likely)(very likely)

Increased tropical cyclone winds Increased tropical cyclone winds (likely; 66-90%)(likely; 66-90%)

Drier continental interiors Drier continental interiors (likely)(likely)

““SurpriseSurprise”” events events (unlikely before 2100)(unlikely before 2100) But - thermohaline circulation weakensBut - thermohaline circulation weakens Probability of surprises rises after 2100Probability of surprises rises after 2100

http://www.thedayaftertomorrow.com/

Hurricanes!

Source: Data from Kerry Emanuel, MIT: http://wind.mit.edu/~emanuel/Papers_data_graphics.htmbased on K. Emanuel, Nature 436, 4 August 2005; Data for North Atlantic

19

It Doesn’t Stop at 2100

Source: IPCC 2001 Synthesis Report Fig SPM-5

Is Global Warming Real?The Millennial Perspective

3.5˚C

2100

21st century temperature riseIPCC mid-range projection

20

Is Global Warming Real? Global temperature rising rapidlyGlobal temperature rising rapidly Why? Anthropogenic greenhouse gas emissionsWhy? Anthropogenic greenhouse gas emissions

COCO22 levels 30% higher than in past 20 million years levels 30% higher than in past 20 million years

The futureThe future Substantial warmingSubstantial warming Significant impactsSignificant impacts

Is global warming real?Is global warming real?

YOU DECIDEYOU DECIDE