Integrated View of Climate Change and Air Quality

 Global Roundtable on Climate Change

May 11-12, 2005

 

James E. HansenNASA Goddard Institute for Space Studies,

The Earth Institute at Columbia University

Dangerous Anthropogenic Interference

What Determines Critical Global Warming Level?

► Sea Level Rise: Evidence from The Earth’s History (+5 meters eemian period; +25 meters middle pliocene)

► Arctic Environment: Avoid Demise of Summer Sea Ice(very sensitive because of positive albedo feedback)

► Regional Climate Disruptions: Avoid Drastic Changes(+1ºC may be moderate change; +3ºC is a different planet)

Conclusion: Need to Keep Global Warming ≤ 1ºC

References:►Defusing the global warming time bomb, Scientific American, March, 2004.►A slippery slope: how much global warming constitutes “dangerous anthropogenic

interference”?, Clim. Change, 68, 269, 2005.

Global Climate Forcings

Forcing Changes in the Industrial Era (1850-2000)

► CO2 Is Largest Forcing

► Air Pollutants (O3, CH4, BC) Cause Large Forcing

► Aerosol Effects (direct + on clouds) Most Uncertain

Conclusion: CO2 Largest Forcing, But Others Significant

References:►Trends of measured climate forcing agents, Proc.Natl.Acad.Sci., 98, 14778, 2001.►Efficacy of climate forcings, J. Geophys. Res., in press, 2005.

Estimated 1850-2000 climate forcings; circled forcings are prime contributors to air pollution.

An Alternative Climate Scenario

Places Equal Weight On

► Reducing Conventional Air Pollutants Causing Warming(Ozone, Ozone precursors, esp. CH4, Soot = Black Carbon)

► Flattening of CO2 Emissions Rate(declining CO2 emissions by mid-century)

Conclusion: Need Integrated Climate Assessment

References:►Global warming in the twenty-first century: an alternative scenario, Proc. Natl. Acad. Sci.,

97, 9875-9880, 2000.►A brighter future, Climatic Change, 52, 435-440, 2002.►Image Credit: Burke, Paul. First People. http://www.firstpeople.us/pictures/bear/A-Mothers-

Special-Touch-1600x1200.html

Carbon Dioxide Emissions

Flat Emissions (50 years), Declining 1.5 W/m2 in 100 yrs.

► Annual Growth Rate Declined From 4-5% to 1.4% in 1970s (price driven + efficiency regulations)

► Further Gains are Feasible, which Could Flatten Emissions (untapped efficiencies, renewables, CO2 seques., next gen. nuclear)

► Fuel Cost Too Low to Drive Greater Efficiency Gains(Iowa economist approach: gift + tax = 0 = little guy gains)

Conclusion: Flat (Uncaptured) CO2 Emissions Technically Feasible

References:► On the Road to Climate Stability, http://www.columbia.edu/~jeh1 ► Can we defuse the global warming time bomb?, NaturalSCIENCE, 2003,

http://www.naturalscience.com/ns/articles/01-16/ns_jeh.html

CO2 Trade-off w. Non-CO2 Climate

Forcings

Alternatives Achieving 1.5 W/m2 for 21st Century Forcing

► +0.5 W/m2 Non-CO2 (typ. IPCC) Max CO2 = 440 PPM(infrastructure + current trends 440 ppm implausible)

► -0.5 W/m2 Non-CO2 Max CO2 = 520 PPM(520 ppm also permits larger on-going fossil fuel use)

Conclusion: Small Forcings Make Big Difference

References:►Greenhouse gas growth rates, Proc. Natl. Acad. Sci., 101, 16109-16114, 2004.

5-year mean growth rate of climate forcing by well-mixed greenhouse gases (O3 and

stratospheric H2O not included)

21st Century Global Warming

Climate Simulations for IPCC 2007 Report

► Climate Model Sensitivity ~ 2.7ºC for 2xCO2 (consistent with paleoclimate data & other models)

► Simulations Consistent with 1880-2003 Observations(key test = ocean heat storage)

► Simulated Global Warming < 1ºC as Alternative Scenario

Conclusion: Warming < 1ºC if additional forcing ~ 1.5 W/m2

References:► Climate simulations with GISS modelE, to be submitted to J. Geophys. Res.

Global surface temperature simulations extended through 21st century.

April 4-6, 2005; Local Host: Intn’l. Center for Climate and Society, Univ. Hawaii

Workshop at East-West Center, Honolulu

“Air Pollution as Climate Forcing: A Second Workshop”

► Multiple Benefits by Controlling CH4 and O3- Precursors(benefits climate, human health, agriculture)

► Multiple Benefits from Near-Term Efficiency Emphasis (climate & health benefits, avoid undesirable infrastructure)

► Targeted Soot Reduction to Minimize Warming from Planned Reductions of Reflective Aerosols (improved diesel controls, biofuels, small scale coal use)

Conclusion: Technical Cooperation Offers Large Mutual Benefits to Developed & Developing Nations.

References:►Air Pollution as Climate Forcing: 2002 meeting:

http://www.giss.nasa.gov/meetings/pollution02/►Air Pollution as Climate Forcing: 2005 Workshop:

http://www.giss.nasa.gov/meetings/pollution2005/