Greenhouse gases (GHG) can intercept solar radiation and in such a way affect the climate system. Text box 1: Greenhouse gases and their inclusion in international legislation The lower band of the uncertainty range has been exceeded already in 2010, whereas it may take more than 50 years before the upper uncertainty band is exceeded. Assuming the 2000-2011 trend of annual increase of total GHG concentrations will also continue in the coming years, the threshold value may be exceeded in less than 25 years.
Overall, assuming a concentration threshold of 450 ppm CO 2 equivalents will result in a 2 oC temperature change (see rationale), means concentrations can only increase by a further about 45 ppm before this threshold value is exceeded. Long-term data on tropospheric ozone are difficult to develop due to the scarcity of representative observing sites with long records and the large spatial heterogeneity (IPCC, 2013). The contribution of tropospheric ozone to the climate system is considered to be stable in the recent decades when comparing large annual and special variation (IPCC, 2007a, IPCC, 2013 3).
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