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Once emitted, GHGs can remain in the atmosphere for 10 years to thousands of years, depending on the gas. This means that emissions that occurred long ago are still in the atmosphere and still affecting the Earth’s climate system. Rich industrialized countries have been emitting large quantities of GHGs since the start of the industrial revolution in the mid-18th Century. The United States is responsible for the largest fraction of cumulative CO2 emissions from energy use since 1850 (see figure).
Just four countries account for half and 17 countries account for 80 percent of historic energy-related emissions. Only five developing countries rank among the top 20 emitters of cumulative CO2. If we included CO2 emissions from land use change—about 20 percent of human-produced CO2 emissions are from this source—then a few developing countries like Brazil and Indonesia would move up the list but would not be at the top.
However, GHG emissions from the most rapidly developing countries in Asia, Africa, and Latin America are catching up with those of the developed world. Indeed, China’s annual GHG emissions already exceed those of the United States and the European Union. Unless future development follows a low-carbon energy path, developing countries will be responsible for most of the growth in GHG concentrations in the future. Determining responsibility for climate change necessitates consideration of these complex patterns of development, past, present, and future.
Source: Center for Climate and Energy Solutions