Climate Change Primer
Human Impacts on Climate Change
While the concentrations of almost all greenhouse gases have been increasing since the Industrial Revolution, carbon dioxide has had the greatest effect on changing the climate. During the 1980s, humans released 5.5 billion tons of carbon dioxide into the atmosphere annually by burning fossil fuels (coal, oil, natural gas) for heat, transportation, and electricity. An additional 1.6 billion tons was released from anthropogenic (human-induced) changes in land-use (i.e. clearing land for agriculture, pastures, etc.) mostly through deforestation in the tropics. By the 1990s the average release of carbon dioxide from fossil fuels was 6.6 billion tons of carbon per year; and in the period 2000-2008, it was 7.7 billion tons carbon per year. In 2008, 8.7 billion tons carbon dioxide were released to the atmosphere from the combustion of fossil fuels. Emissions of carbon from deforestation have not increased since the 1980s, and may have decreased slightly.
Where does that annual release of carbon go? Approximately 4 billion tons of carbon dioxide per year are accumulated in the atmosphere. Ocean modelers find that the oceans take up approximately 25% of emissions per year (2.3 billion tons), and the land takes up about 3 billion tons (or 33% of total emissions). These flows or "fluxes" within the Global Carbon Cycle may be summarized using the formula:
Atmospheric increase = Emissions from fossil fuels + Net emissions from changes in land use - Oceanic uptake - Terrestrial carbon sink
Human beings are causing the release of carbon dioxide and other greenhouse gases to the atmosphere at rates much faster than the earth can cycle them. Fossil fuels - oil, coal, natural gas, and their derivatives - were formed through the compression of organic (once living) material for millions of years, yet billions of tons of these fuels are now being burned per year. The CO2 expelled into the atmosphere through these activities will remain in the atmosphere on the order of decades to centuries. This means that the CO2 emitted today will likely be affecting the climate for generations.
Despite the widespread recognition of this fact, worldwide emissions of fossil fuels have continued to grow at an ever increasing rate (Le Quéré et al., 2009). Emissions will increase even further as the developing world moves towards greater industrialization. In 2007, China passed the United States in being the number one emitter of carbon dioxide, though the United States still leads in terms of per capita emissions. Based on existing demographic, economic, social, and political conditions and trends, energy-related emissions of carbon dioxide are projected to increase from 7.9 billion tons carbon in 2006 to 11.0 billion tons carbon in 2030. Under business-as-usual scenarios, energy-related emissions of carbon from OECD countries are predicted to increase by 7 percent during this period, while the increase in emissions from non-OECD countries are predicted to increase by 68 percent (EIA, 2009). These emissions trajectories could be altered drastically, however, with changes to the drivers of emissions, such as economic growth and climate change mitigation strategies.