Climate forcings in the industrial era.
The forcings that drive long-term climate change are not known with an accuracy sufficient to define future climate change. Anthropogenic greenhouse gases (GHGs), which are well measured, cause a strong positive (warming) forcing. But other, poorly measured, anthropogenic forcings, especially changes of atmospheric aerosols, clouds, and land-use patterns, cause a negative forcing that tends to offset greenhouse warming. One consequence of this partial balance is that the natural forcing due to solar irradiance changes may play a larger role in long-term climate change than inferred from comparison with GHGs alone. Current trends in GHG climate forcings are smaller than in popular "business as usual" or 1% per year CO2 growth scenarios. The summary implication is a paradigm change for long-term climate projections: uncertainties in climate forcings have supplanted global climate sensitivity as the predominant issue.
Hansen
J E
JE
National Aeronautics and Space Administration Goddard Institute for Space Studies, New York, NY 10025, USA. jhansen@giss.nasa.gov
Sato
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M
Lacis
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A
Ruedy
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R
Tegen
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I
Matthews
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E
D002980:Climate; D004787:Environmental Pollution; D005740:Gases / Q000009:adverse effects; D017752:Greenhouse Effect; D006801:Humans; D007221:Industry
D005740:Gases