title: Climate forcings in the industrial era.
abstract: 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.
authors.affiliation: National Aeronautics and Space Administration Goddard Institute for Space Studies, New York, NY 10025, USA. jhansen@giss.nasa.gov
authors.forename: J E
authors.initials: JE
authors.lastname: Hansen
authors.forename: M
authors.initials: M
authors.lastname: Sato
authors.forename: A
authors.initials: A
authors.lastname: Lacis
authors.forename: R
authors.initials: R
authors.lastname: Ruedy
authors.forename: I
authors.initials: I
authors.lastname: Tegen
authors.forename: E
authors.initials: E
authors.lastname: Matthews
mesh_terms: D002980:Climate; D004787:Environmental Pollution; D005740:Gases / Q000009:adverse effects; D017752:Greenhouse Effect; D006801:Humans; D007221:Industry
chemical_list: D005740:Gases