The Carbon Cycle
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There are both anthropogenic (human-caused) and natural sources of atmospheric carbon—so they each have to be identified, measured, and taken into account. This chapter examines the global sources of carbon dioxide from buildings, transport, and industry; and the natural sinks including forests and the oceans. Land use change can go either way. In 2015, the Paris Agreement proposed that the increase in global average temperatures be limited to below 2 °C above preindustrial levels. Over 190 countries signed up to this agreement. However, in 2018 it was shown that attaining this target is virtually impossible unless stronger measures are taken to reduce the emissions of greenhouse gases. Scientists have shown that there is a limit to how much carbon dioxide can be emitted globally by the combustion of fossil fuels. Called the carbon budget, it will be used up within the next decade if emissions of carbon dioxide and methane continue at present levels. This realisation has led to the conclusion that most of the world’s reserves of fossil fuels, particularly of coal, must be left in place.