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Trends of measured climate forcing agents
1National Aeronautics and Space Administration, Goddard Institute for Space Studies, New York, NY 10025, USA. jhansen@giss.nasa.gov
Summary
Global greenhouse gas forcing growth has declined due to international cooperation. Concerted actions can further reduce climate forcing to meet alternative scenarios, but these reductions are not automatic co-benefits of slowing CO(2) emissions.
Area of Science:
- Climate science
- Atmospheric chemistry
- Environmental policy
Background:
- The growth rate of climate forcing from greenhouse gases peaked around 1980.
- International cooperation has led to a decline in this growth rate.
- Current trends in aerosol climate forcing remain highly uncertain.
Purpose of the Study:
- To analyze past trends in climate forcing growth rates.
- To propose strategies for reducing future climate forcing.
- To project near-term global warming rates.
Main Methods:
- Analysis of historical climate forcing data.
- Modeling of climate forcing trends under different action scenarios.
- Estimation of future global warming rates based on emission constraints.
Main Results:
- The growth rate of climate forcing by greenhouse gases has decreased from nearly 5 W/m(2) per century to approximately 3 W/m(2) per century.
- Concerted actions can reduce climate forcing to approximately 2 W/m(2) per century over the next 50 years.
- Global warming is projected to continue at a rate of +0.15 +/- 0.05 degrees C per decade.
Conclusions:
- Reductions in climate forcing require deliberate, concerted actions beyond simply slowing CO(2) emissions.
- Uncertainty in aerosol forcing trends highlights the need for further research.
- Near-term global warming is constrained by practical emission limits.