File:Recent (1990-2007) and projected (2000-2100) global emissions of carbon dioxide and atmospheric concentrations under five emissions scenarios (USGCRP).png

English: The graphs show recent (1990-2007) and projected (2000-2100) global emissions of carbon dioxide in gigatons of carbon, on the left, and atmospheric concentrations on the right under four emissions scenarios. References for the graphs can be found in the cited source - US Global Change Research Program (USGCRP, 2009).

The top three projections in the key are based on scenarios from the Intergovernmental Panel on Climate Change's Special Report on Emissions Scenarios (SRES). There are a total of 40 SRES scenarios (Le Quéré et al., 2010), all of which are "baseline" scenarios, i.e., they assume no explicit climate policies. The SRES scenarios project different "storylines" of future social and economic development (see Special Report on Emissions Scenarios for details of these storylines). The graph shows projections based on three different storylines - "A1FI", "A2", and "B1". The fourth projection in the key is a "stabilization" scenario. In the stabilization scenario, emissions are reduced so that the atmospheric concentration of carbon dioxide is stabilized at 450 parts per million.

The graph of 2000-2100 emissions projections shows baseline projections varying over time, with the highest projection reaching about 25 gigatonnes per year (Gt.yr^-1) in 2050, and 30 Gt.yr^-1 in 2100. The middle baseline projection reaches about 16 Gt.yr^-1 in 2050, and just under 30 Gt.yr^-1 in 2100. The lowest baseline projection reaches about 12 Gt.yr^-1 in 2050, and about 5 Gt.yr^-1 in 2100. The 450 ppm projection reaches about 3 Gt.yr^-1 in 2050, and 2.5 Gt.yr^-1 in 2100.

The graph of 2000-2100 atmospheric concentration projections shows baseline projections increasing at various rates over time. The high baseline projection reaches about 575 ppm in 2050 and 960 ppm in 2100. The medium baseline projection reaches about 525 ppm in 2050 and 850 ppm in 2100. The low baseline projection reaches about 500 ppm in 2050 and 550 ppm in 2100. The stabilization projection reaches about 450 ppm in 2050 and remains almost stable at this level until 2100.

The inset expanded below the 2000-2100 emissions chart shows emissions for 1990-2010 under the three projections based on the SRES scenarios, along with actual emissions to 2007 (in black). This inset is potentially misleading: the SRES emissions projections shown in the inset are not based on the commonly used "illustrative" SRES scenarios (Le Quéré et al., 2010). To explain, the IPCC selected six of the forty original SRES scenarios as “illustrative” of the storylines to be used for projections of climate change. Projections shown in the inset, however, are based averages across models for A1FI, A2, and B1. The averages across models for A1FI, A2, and B1 are not equal to the illustrative scenarios for these storylines (Le Quéré et al., 2010). The inset shows that recent emissions were above all the scenario averages. However, emissions in one of the six illustrative SRES scenarios was higher than observed (Le Quéré et al., 2010).

References: Le Quéré, C., et al., 14 June 2010: Recent trends in CO₂ emissions, RealClimate, accessed 2011-12-04.