Carbon footprints: Global emissions
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The world’s carbon footprint is made up of various components, reflecting all the processes and activities for which we burn fossil fuels. The main contributors are: electricity and heat generation, which account for about 29% of global emissions; agriculture, which accounts for about 14%; manufacturing and construction, about 12% each; and transport, also about 12%. Fuel combustion for other purposes generates about 9% of global emissions, and other activities – such as industrial processes or gases leaking out from pressurised equipment – account for a few per cent each. Changing land use and deforestation also affect the carbon content of the atmosphere, contributing around 15% of the global carbon footprint.
In order of quantity in the atmosphere, the main greenhouse gases are: watervapour, carbon dioxide, methane, nitrous oxide, ozone and chlorofluorocarbons (CFCsCFCs). Human activity doesn’t directly increase the concentrations of water vapour in the atmosphere. However, as the atmosphere warms because of the release of other greenhouse gases, levels of water vapour also rise because warmer air can hold more water vapour. Human activity releases varying quantities of all the other main greenhouse gases into the atmosphere. Carbon dioxide accounts for more than 70% of total global greenhouse gas emissions, and methane accounts for a further 15–20%. Nitrous oxide accounts for less than 10% and ozone and CFCs less than 2%.
Cutting down trees and changing the ways land is used can result in the release of greenhouse gases. It’s estimated that land use change and deforestation account for between 12 and 18% of global emissions. Scientists have concluded that there are five main drivers of deforestation around the world: population growth, rising incomes, changing diets, policy incentives and land ownership. The decay and burning of the felled trees releases carbon dioxide into the atmosphere. For forests to continue to act as effective carbon sinks, trees must be replanted and those cut down must be harvested and turned into long-lived products.