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Greenhouse Gas Emissions

Greenhouse gases such as carbon dioxide are a major cause of climate change. Carbon dioxide levels in the atmosphere are currently 30% higher than at any point in the past million years and are projected to increase.

The Intergovernmental Panel on Climate Change (IPCC) has determined that greenhouse gas emissions are very likely to have caused modern climate change occurring since the 1950s.¹² Specifically, emissions increase greenhouse gas concentrations in the atmosphere, which cause temperature levels to increase by trapping heat. The increase in temperature creates other climate changes including sea level increases, changes in precipitation patterns, desertification, flooding, and extreme weather discussed in other sections of this report. Looking at greenhouse gas emissions is therefore essential when considering climate change, its impacts, and ways to mitigate it.

CO₂ makes up 70% of total greenhouse gas emissions and thus is the primary contributor to climate change.¹³ The majority of CO₂ comes from the combustion of fossil fuels for electricity generation and transportation. CO₂ levels in the atmosphere have spiked to levels significantly higher than any measured over the last 800 millennia. Globally, CO₂ levels have risen sharply since the mid-nineteenth century as a consequence of the Industrial Revolution.

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China and the United States are the highest emitters of CO₂. Each contributes well over three times the global CO₂ emissions of Russia, the next largest emitter. However, when CO₂ emissions are measured per capita, the United States ranks 9th and China 82nd.¹⁴ Wealthy oil nations make up four of the five top emitters per capita with Qatar nearly producing more than double America's emissions on a per capita basis. These countries typically have relatively small populations and hydrocarbon intensive economies focusing on the extraction of petroleum. They also have high energy needs due to their climates. Several European states with high population density also emit significant amounts of CO₂ on a per capita basis.

CO₂ emissions increased consistently around the world between the 1960s and 1980s. A brief dip in emissions associated with the recession of the early 1980s and increased emphasis on fuel economy following the 1970s oil shocks was followed by steady renewed growth in the 1990s.¹⁵ Western Europe has for the most part stabilized its CO₂ emission rate, while China recently overtook the United States.

In addition to CO₂, methane also is a significant contributor to climate change, making up an estimated 24% of total greenhouse gas emissions.¹⁶ Slightly over half of methane emissions come from human activity, typically from the extraction of natural gas fields. But methane also comes from more mundane things, such as decaying trash in solid waste landfills. While methane makes up a significantly lower percentage of overall emissions, it is 21 times more powerful at warming the atmosphere than CO₂. Additionally, methane dissipates from the atmosphere in 12 years. In comparison, CO₂ takes nearly one hundred years to dissipate.¹⁷ As a consequence, policies to control or harness methane emissions could have a significant short-term impact, but in the long-run addressing carbon emissions will be a crucial element of managing climate change. International debate over measures to reduce CO₂ will reflect these statistics and play an important role in shaping the positions of individual governments in the debate.

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