Global Warming--Are We on Thin Ice? Convergence of evidence for anthropogenic global warming 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 Feedback Given a climate forcing (e.g. CO 2 increase)  initial warming Amplifying loops (positive feedback) magnify the warmingAmplifying loops (positive feedback) magnify the warming Diminishing loops (negative feedback)Diminishing loops (negative feedback)

Climate Feedbacks Warming Evaporation from ocean, Increase water vapor in atm Enhance greenhouse effect Increase cloud cover; Decrease absorption of solar energy Decrease snow cover; Decrease reflectivity of surface Increase absorption of solar energy

Measured Surface Temperature the past 150 years 6 warmest years: 1998, 2002, 2003, 2004, 2005, 2006.

Warming greatest at high latitudes Amplification of warming due to decrease of albedo (melting of snow and ice)

Bore Hole Locations different physics ( thermal diffusivity) & 10s of years time steps

Bore Hole Temp. Reconstructions ~500 years

Sub-surface Annual Temperature 12.8 m Wisconsin USA

Bore Hole Temperature Reconstructions

Proxy surface Temperature data density circa 1500 AD

Proxy surface Temperature data density circa 1000 AD

National Research Council USA June 2006 Report

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

Proxy data used by Mann et al. 1998

McIntyre and McKitrick 2003 a reanalysis with a subset of Mann et al. 1998’s data 15th century the warmest time in the past 1000 to 2000 years? Same result as Mann et al when 5 PCs are used for 15th century Same result as Mann et al. 1998

Tree Ring Dendrochronology

Some ring-width series Cook, 1989 Four red spruce ring-width series from the same stand – different trends related to competition and disturbance. ~40-50% of tree ring data from trees selected from temperature- limited areas are related to surface air temperature

Coral  18 O/ 16 O Temperature Reconstruction

Proxy Surface Temperatures from corals, sediments, and ice cores using 18 O/ 16 O  18 O = ( 18 O/ 16 O)sample - ( 18 O/ 16 O)SMOW x 10 3 ‰ ( 18 O/ 16 O)SMOW SMOW = Standard Mean Ocean Water 18 O: 0.20% 17 O: 0.04% 16 O: 99.76% H 2 16 O is > than that of H 2 18 O; converselyH 2 18 O 18 O concentration in H 2 O will be. Isotope concentration can thus be considered a function of temperature. The vapor pressure of H 2 16 O is > than that of H 2 18 O; conversely H 2 18 O passes into the liquid state more readily. Because condensation is the result of cooling, the greater the fall in temperature the lower the 18 O concentration in H 2 O will be. Isotope concentration can thus be considered a function of temperature.

Greenland ice core: high resolution/distinct layers

Bore Hole - Hockey Stick Comparison ‘Adjusted’ by Mann et al.

Bore Hole - Hockey Stick Comparison

Bore Hole Data for Eastern & Western North America ( Huang & Pollack)

Bore Hole - Briffa et al Comparison

Bore Hole - Overpeck et al Comparison

Satellite Era 1970s ---> now

Total Solar Irradiance ~1 watt/m 2 variation out of ~1400 w/m 2 over 30 years

Tropospheric Temperature Trends Christy and Spencer were wrong

Sea Level Rise from thermal expansion & input of water from melting glaciers 20 cm (7 inches) in a century

Arctic Sea Ice Trends 2005 summer minima 1979 summer minima

Satellite Detection of Sea Ice Higher rate of microwave emission from sea ice than from open water. Emissivities indicated are for wavelength of 1.55 cm (19 GHz)

Warmer Earth Greener North Arctic Sea Ice Extent 1979 to 1999 Claire Parkinson et al. 2002

Atmospheric CO 2 measurements

Outstanding Questions Only half of the CO 2 produced by human activities is remaining in the atmosphereOnly half of the CO 2 produced by human activities is remaining in the atmosphere Where are the sinks that are absorbing over 40% of the CO 2 that we emit?Where are the sinks that are absorbing over 40% of the CO 2 that we emit? –Land or ocean? –Eurasia/North America? Why does CO 2 buildup vary dramatically with nearly uniform emissions?Why does CO 2 buildup vary dramatically with nearly uniform emissions? How will CO 2 sinks respond to climate change?How will CO 2 sinks respond to climate change?

Observed Halting of the Greening Trend  (NDVI) /  t : Summer  (NDVI) /  t : Summer Summer drying  reduced photosynthesis  Recent slowing of the land C sink Angert et al. “Drier summers cancel out the CO 2 uptake enhancement induced by warmer springs” PNAS 2005

Equilibrium Climate from Ice Core Data J. Hansen Estimate climate forcing (W/m 2 ) from atmospheric composition changesEstimate climate forcing (W/m 2 ) from atmospheric composition changes Regress Temperature anomalies against climate forcingRegress Temperature anomalies against climate forcing

Atmospheric CO 2 since 1740 Different  CO 2 slopes reflect  time techno-economic conditions

Climate Forcing: expressed as a change in radiative heating (W/m2) at surface for a given change in trace gas composition or other change external to the climate system

Colder temperatures -> more snow and ice -> colder temperatures… More snow and ice ---> higher albedo

J. Hansen

What? Me worry?

Majority of Glaciers are receding

Greenland--where the rubber hits the climate road

It’s only a matter of time… 400 km 3 ice = 1 mm sea level

> Streaming, >Earthquakes

Satellite record melt of 2002 was exceeded in 2005 Surging glaciers & melting Greenland Ice: 70 m thinning in 5 years

Greenland Mass Loss from GRACE

Gravity Recovery & Climate Experiment 500 km orbit 220 km separation Distance accuracy  mm

Summary Global warming is real and happeningGlobal warming is real and happening 21 st C: drying of tropics  reduce C uptake  accelerate global warming21 st C: drying of tropics  reduce C uptake  accelerate global warming 21 st C: stable stratification in ocean, reduce thermohaline circulation  reduce C uptake  accelerate global warming21 st C: stable stratification in ocean, reduce thermohaline circulation  reduce C uptake  accelerate global warming Fossil Fuel emission faster than land & ocean uptake bottlenecks  accelerate global warmingFossil Fuel emission faster than land & ocean uptake bottlenecks  accelerate global warming Rapid destablization of glaciers  ice-albedo feedback  accelerate global warming  raise sea levelRapid destablization of glaciers  ice-albedo feedback  accelerate global warming  raise sea level Uncertainty: how much faster? Uncertainty: how much faster?

Global Warming Skeptics Dr. S. Fred Singer “Ozone, Skin Cancer, and the SST” S. Fred Singer Aerospace America July 1994 “The hole truth about CFCs” S. Fred Singer in Chemistry and Industry March 21, 1994 “The EPA and the Science of Environmental Tobacco Smoke” S. Fred Singer and Kent Scholar Alexis de Tocqueville Institution Dr. 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 Bore Hole Data

Holgate Glacier July 24, 1909 Holgate Glacier August 13, 2004

21 st C warming depends on CO 2 increase 20 th C stabilizn: CO 2 constant at 380 ppmv for the 21 st C 21 th C “Business as usual”: CO 2 increasing 380 to 680 ppmv Meehl et al. (Science 2005)