Abstract
Abstract. In order to use knowledge of past climate change to improve our understanding of the sensitivity of the climate system, detailed knowledge about the time development of radiative forcing (RF) of the earth atmosphere system is crucial. In this study, time series of anthropogenic forcing of climate from pre-industrial times until 2010, for all well established forcing agents, are estimated. This includes presentation of RF histories of well mixed greenhouse gases, tropospheric ozone, direct- and indirect aerosol effects, surface albedo changes, stratospheric ozone and stratospheric water vapour. For long lived greenhouse gases, standard methods are used for calculating RF, based on global mean concentration changes. For short lived climate forcers, detailed chemical transport modelling and radiative transfer modelling using historical emission inventories is performed. For the direct aerosol effect, sulphate, black carbon, organic carbon, nitrate and secondary organic aerosols are considered. For aerosol indirect effects, time series of both the cloud lifetime effect and the cloud albedo effect are presented. Radiative forcing time series due to surface albedo changes are calculated based on prescribed changes in land use and radiative transfer modelling. For the stratospheric components, simple scaling methods are used. Long lived greenhouse gases (LLGHGs) are the most important radiative forcing agent with a RF of 2.83±0.28 W m−2 in year 2010 relative to 1750. The two main aerosol components contributing to the direct aerosol effect are black carbon and sulphate, but their contributions are of opposite sign. The total direct aerosol effect was −0.48±0.32 W m−2 in year 2010. Since pre-industrial times the positive RF (LLGHGs and tropospheric O3) has been offset mainly by the direct and indirect aerosol effects, especially in the second half of the 20th century, which possibly lead to a decrease in the total anthropogenic RF in the middle of the century. We find a total anthropogenic RF in year 2010 of 1.4 W m−2. However, the uncertainties in the negative RF from aerosols are large, especially for the cloud lifetime effect.
Highlights
Since the industrial revolution, anthropogenic activities have altered the concentrations of components in the atmosphere, some of which impact the radiative balance of the earth system
Using the same factors as above we find an increase in burden of organic matter in year 2000 of 2.79 mg m−2 (1.42 Tg) including secondary organic aerosols (SOA) and 2.34 mg m−2 (1.19 Tg) excluding SOA, a larger increase than in the AeroCom simulations but in agreement with other previous published studies summarized in Schulz et al (2006)
We have presented radiative forcing time series of what are currently believed to be the main anthropogenic components
Summary
Anthropogenic activities have altered the concentrations of components in the atmosphere, some of which impact the radiative balance of the earth system. Long-lived greenhouse gases, primarily carbon dioxide (CO2) and methane (CH4), nitrous oxide (N2O) and halocarbons are the most important anthropogenic climate forcing agents (Forster et al, 2007), but short lived components like tropospheric ozone and black carbon aerosols cause a significant heating of the climate system. The aerosols can alter the cloud properties, causing indirect aerosol effects (Twomey, 1977; Albrecht, 1989). Changes in stratospheric water vapour and ozone in the stratosphere as well as anthropogenic changes to the properties of the land surface give a radiative forcing on the climate system (Forster et al, 2007)
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