A1 and B1. SRES scenarios and climate change initiatives While some scenarios assume a more environmentally friendly world than others, none include any climate-specific initiatives, such as the Kyoto Protocol. Atmospheric GHG concentrations The SRES scenarios have been used to project future atmospheric GHG concentrations. Under the six illustrative SRES scenarios, the IPCC Third Assessment Report (2001) projects the atmospheric concentration of carbon dioxide () in the year 2100 as between 540 and 970 parts per million (ppm). In this estimate, there are uncertainties over the future removal of carbon from the atmosphere by carbon sinks. There are also uncertainties regarding future changes in the Earth's biosphere and feedbacks in the climate system. The estimated effect of these uncertainties mean that the total projected concentration ranges from 490 to 1,260 ppm. This compares to a pre-industrial (taken as the year 1750) concentration of about 280 ppm, and a concentration of about 368 ppm in the year 2000. The United States Environmental Protection Agency has also produced projections of future atmospheric GHG concentrations using the SRES scenarios. These projections are shown opposite, and are subject to the uncertainty described earlier regarding the future role of carbon sinks and changes to the Earth's biosphere. Observed emissions rates Between the 1990s and 2000s, the growth rate in CO2 emissions from fossil fuel burning and industrial processes increased (McMullen and Jabbour, 2009, p. 8). The growth rate from 1990-1999 averaged 1.1% per year. Between the years 2000-2009, growth in emissions from fossil fuel burning was, on average, 3% per year, which exceeds the growth estimated by 35 of the 40 SRES scenarios (34 if the trend is computed with end points instead of a linear fit). Human-caused greenhouse gas emissions set a record in 2010, a 6% jump on 2009 emissions, exceeding even the "worst case" scenario cited in the IPCC Fourth Assessment Report. Views and analysis MER and PPP The SRES scenarios were criticised by Ian Castles and David Henderson. The core of their critique was the use of market exchange rates (MER) for international comparison, in lieu of the theoretically favoured PPP exchange rate which corrects for differences in purchasing power. The IPCC rebutted this criticism. The positions in the debate can be summarised as follows. Using MER, the SRES scenarios overstate income differences in past and present, and overestimate future economic growth in developing countries. This, Castles and Henderson originally argued,