Global Warming--Are We on Thin Global Warming--Are We on Thin Ice? Convergence of evidence Ice? Convergence of evidence

for anthropogenic global for anthropogenic global warmingwarming

• Climate forcing, feedback, response, committed warming

• Evidence of global warming• Projections of global warming

Compton Tucker

NASA/Goddard Space Flight Center and

Climate Change Science Program Office

Washington, D.C. USA

Climate FeedbackClimate Feedback

Given a climate forcing (e.g. COGiven a climate forcing (e.g. CO22 increase) increase) initial warming initial warming

• Amplifying loopsAmplifying loops (positive feedback) (positive feedback) magnify the warmingmagnify the warming

• Diminishing loopsDiminishing loops (negative feedback) (negative feedback)

Climate FeedbacksClimate Feedbacks

Warming

Evaporation from ocean,Increase water vapor in atmEnhance greenhouse effect

Increase cloud cover;Decrease absorption of solar energy

Decrease snow cover;Decrease reflectivity of surfaceIncrease absorption of solar energy

Measured Surface Temperature Measured Surface Temperature the past 150 yearsthe past 150 years

6 warmest years: 1998, 2002, 2003, 2004, 2005, 20066 warmest years: 1998, 2002, 2003, 2004, 2005, 2006

.

Warming Warming greatest at greatest at

high high latitudeslatitudes

Amplification of Amplification of warming due to warming due to

decrease of decrease of albedo (melting of albedo (melting of

snow and ice)snow and ice)

Bore Hole LocationsBore Hole Locationsdifferent physics (different physics (thermal diffusivity) thermal diffusivity)

& 10s of years time steps& 10s of years time steps

Bore Hole Temp. ReconstructionsBore Hole Temp. Reconstructions

~500 years

Sub-surface Annual TemperatureSub-surface Annual Temperature12.8 m depth @ Wisconsin USA12.8 m depth @ Wisconsin USA

Bore Hole Temperature Reconstructions

Proxy surface Temperature data Proxy surface Temperature data density circa 1500 ADdensity circa 1500 AD

Proxy surface Temperature data Proxy surface Temperature data density circa 1000 ADdensity circa 1000 AD

National Research Council USA National Research Council USA June 2006 ReportJune 2006 Report

Mann, Bradley, & Hughes (1998):Mann, Bradley, & Hughes (1998):The “hockey stick” surface temperatureThe “hockey stick” surface temperature

Proxy data used by Mann et al. 1998Proxy data used by Mann et al. 1998

McIntyre and McKitrick 2003McIntyre and McKitrick 2003a reanalysis with a subset of Mann et al. a reanalysis with a subset of Mann et al.

1998’s data1998’s data

15th century the warmest time 15th century the warmest time in the past 1000 to 2000 years?in the past 1000 to 2000 years?

Same result as Mann et al. 1998 when Same result as Mann et al. 1998 when 5 PCs are used for 15th century5 PCs are used for 15th century

Same result as Mann et al. 1998Same result as Mann et al. 1998

Tree Ring DendrochronologyTree Ring Dendrochronology

Some ring-width seriesSome ring-width series

Cook, 1989Four red spruce ring-width series from the same stand – different Four red spruce ring-width series from the same stand – different

trends related to competition and disturbance.trends related to competition and disturbance.

~40-50% of tree ~40-50% of tree ring data from ring data from

trees selected from trees selected from temperature- temperature-

limited areaslimited areas are are related to surface related to surface

air temperatureair temperature

Coral 18O/16O TemperatureReconstruction

Proxy Surface Temperaturesfrom corals, sediments, and

ice cores using 18O/16O18O = (18O/16O)sample - (18O/16O)SMOW x 103 ‰

(18O/16O)SMOW

SMOW = Standard Mean Ocean Water

1818O: O: 0.20%0.20%

1717O: O: 0.04%0.04%

1616O: O: 99.76%99.76%

The vapor pressure of HH221616O is > than that of O is > than that of

HH221818O; converselyO; conversely HH22

1818OO passes into the liquid state more readily. Because condensation is the result of cooling, the greater the fall in

temperature the lower the 1818O concentration O concentration in Hin H22O will be. Isotope concentration can thus O will be. Isotope concentration can thus

be considered a function of temperature.be considered a function of temperature.

Greenland ice core: high resolution/distinct layers

Bore Hole - Hockey Stick Bore Hole - Hockey Stick ComparisonComparison

‘‘Adjusted’ by Mann et al.Adjusted’ by Mann et al.

Bore Hole - Hockey Stick Bore Hole - Hockey Stick ComparisonComparison

Bore Hole Data for Eastern & Bore Hole Data for Eastern & Western North America Western North America

((Huang & Pollack)Huang & Pollack)

Bore Hole - Briffa et al Bore Hole - Briffa et al ComparisonComparison

Bore Hole - Overpeck et al Bore Hole - Overpeck et al ComparisonComparison

Satellite EraSatellite Era1970s ---> now1970s ---> now

Total Solar Irradiance

~1 watt/m~1 watt/m22 variation out of ~1400 w/m variation out of ~1400 w/m22 over 30 years over 30 years

Tropospheric Temperature TrendsChristy and Spencer were wrong

Sea Level Rise from thermal expansion Sea Level Rise from thermal expansion & input of water from melting glaciers& input of water from melting glaciers

20 cm (7 inches) in a century20 cm (7 inches) in a century

Arctic Sea Ice Trends

2005 summer minima

1979 summer minima

Satellite Detection of Sea IceSatellite Detection of Sea IceHigher rate of microwave Higher rate of microwave

emission from sea ice than emission from sea ice than from open water. Emissivities from open water. Emissivities indicated are for wavelength indicated are for wavelength of 1.55 cm (19 GHz)of 1.55 cm (19 GHz)

Warmer Earth Warmer Earth Greener NorthGreener North

Arctic Sea Ice Extent 1979 to 1999Arctic Sea Ice Extent 1979 to 1999

Claire Parkinson et al. 2002

Atmospheric CO2 measurements

Outstanding QuestionsOutstanding Questions

• Only half of the COOnly half of the CO22 produced produced

by human activities is by human activities is remaining in the atmosphereremaining in the atmosphere

• Where are the Where are the sinkssinks that are that are absorbing over 40% of the COabsorbing over 40% of the CO22

that we emit?that we emit?

– Land or ocean?Land or ocean?

– Eurasia/North America?Eurasia/North America?

• Why does COWhy does CO22 buildup vary buildup vary

dramatically with nearly dramatically with nearly uniform emissions? uniform emissions?

• How will COHow will CO22 sinks respond to sinks respond to

climate change?climate change?

Observed Halting of the Greening Trend

(NDVI) / t : Summer 1982-1991

(NDVI) / t : Summer 1994-2002

Summer drying reduced photosynthesis Recent slowing of the land C sink Angert et al. “Drier summers cancel out the CO2 uptake enhancement induced by warmer springs”

PNAS 2005

Equilibrium Climate from Ice Core DataEquilibrium Climate from Ice Core Data

J. HansenJ. Hansen

• Estimate Estimate climate climate

forcing (W/mforcing (W/m22) ) from from

atmospheric atmospheric composition composition

changeschanges

• Regress Regress Temperature Temperature

anomalies anomalies against against climate climate forcing forcing

Atmospheric COAtmospheric CO22 since 1740 since 1740

Different CO2 slopes reflect time

techno-economic conditions

Climate Forcing: expressed as a change in Climate Forcing: expressed as a change in radiative heating (W/m2) at surface for a given radiative heating (W/m2) at surface for a given

change in trace gas composition or other change change in trace gas composition or other change external to the climate systemexternal to the climate system

Colder temperatures -> more snow Colder temperatures -> more snow and ice -> colder temperatures…and ice -> colder temperatures…

Earth TOA actual W/m^2 1365

Total Watts Temp. (K)"Albedo" absorbed

0.20 5.58E+17 263.40.25 5.23E+17 259.20.30 4.88E+17 254.80.35 4.54E+17 250.10.40 4.19E+17 245.1

1365*(1-albedo)*4*pi*radius*radiusMore snow and ice ---> higher albedoMore snow and ice ---> higher albedo

J. Hansen

What? Me worry?

280

320

360

400

440

480

520

560

600

1900 1950 2000 2050 2100 2150

Atmospheric CO

2 (ppmv)

Oil

Gas

Coal

Biosphere

Business-as-Usual(2% annual growth until 50% depletion, then 2% annual decline)

280

320

360

400

440

480

520

560

600

1900 1950 2000 2050 2100 2150

Atmospheric CO

2 (ppmv)

Oil

Gas

Coal

Biosphere

Alternative Case: Coal Phaseout(+2%/yr to 2012; +1%/yr to 2022; linear shutdown between 2025-2050)

Majority of Glaciers are recedingMajority of Glaciers are receding

Greenland--where the rubber Greenland--where the rubber hits the climate roadhits the climate road

It’s only a matter of time…

400 km3 ice = 1 mm sea level

> Streaming, >Earthquakes> Streaming, >Earthquakes

Satellite record melt of 2002 was exceeded in 2005

Surging Surging glaciers & glaciers &

meltingmelting

Greenland Ice: Greenland Ice: 70 m thinning in 5 years70 m thinning in 5 years

Greenland Mass Loss from GRACEGreenland Mass Loss from GRACE

Gravity Recovery & Gravity Recovery & Climate ExperimentClimate Experiment

500 km orbit500 km orbit

220 km separation220 km separation

Distance accuracy Distance accuracy 0.001 mm0.001 mm

SummarySummary• Global warming is real and happeningGlobal warming is real and happening• 2121stst C: drying of tropics C: drying of tropics reduce C uptake reduce C uptake

accelerate global warming accelerate global warming• 2121stst C: stable stratification in ocean, reduce C: stable stratification in ocean, reduce

thermohaline circulation thermohaline circulation reduce C uptake reduce C uptake accelerate global warming accelerate global warming

• Fossil Fuel emission faster than land & ocean uptake Fossil Fuel emission faster than land & ocean uptake bottlenecks bottlenecks accelerate global warming accelerate global warming

• Rapid destablization of glaciers Rapid destablization of glaciers ice-albedo feedback ice-albedo feedback accelerate global warming accelerate global warming raise sea level raise sea level

Uncertainty: how much faster? Uncertainty: how much faster?

Global Warming SkepticsGlobal Warming Skeptics

Dr. S. Fred SingerDr. S. Fred Singer

““Ozone, Skin Cancer, and Ozone, Skin Cancer, and the SST” S. Fred Singerthe SST” S. Fred Singer

Aerospace AmericaAerospace America July 1994 July 1994

““The hole truth about CFCs”The hole truth about CFCs”S. Fred Singer in S. Fred Singer in Chemistry Chemistry and Industryand Industry March 21, 1994 March 21, 1994

““The EPA and the Science of The EPA and the Science of Environmental Tobacco Smoke”Environmental Tobacco Smoke”

S. Fred Singer and Kent S. Fred Singer and Kent ScholarScholar

Alexis de Tocqueville Alexis de Tocqueville InstitutionInstitutionDr. Singer has a sordid history of opposition to second-hand

tobacco smoke and health, the role of chloro-floro-carbons and ozone depletion, and most recently global warming.

Pollack & Huang Pollack & Huang Bore Hole DataBore Hole Data

Holgate Glacier July 24, 1909Holgate Glacier July 24, 1909

Holgate Glacier August 13, 2004Holgate Glacier August 13, 2004

2121ststC warming depends on COC warming depends on CO2 2 increaseincrease

20thC stabilizn:CO2 constant at 380 ppmv for the 21stC

21thC “Business as usual”:CO2 increasing 380 to 680 ppmv

Meehl et al. (Science 2005)