The Carbon Cycle

Topics: Carbon dioxide, Greenhouse gas, Global warming Pages: 9 (3147 words) Published: October 1, 2008
According to the United States Environmental Protection Agency (“EPA”), the increase in anthropogenic CO2 emissions has led to the increase in global temperatures in the past century . Because of the preponderance of evidence linking greenhouse gases and climate change, governments worldwide are developing policy to reduce CO2 emissions. CO2 can enter the atmosphere by burning fossil fuels, in manufacturing processes, and other energy-reliant activities. However, not all emitted carbon remains in the atmosphere; oceans and plant matter absorb some, and some escapes the atmosphere. It is the remaining CO2 in the atmosphere that is causing climate change. To illustrate, the following diagram depicts the cycle of carbon in the atmosphere. The effect of carbon emissions on the atmosphere can be seen by observing increasing CO2 levels. From the Intergovernmental Panel on Climate Change Working Group I (“IPCC WGI”): “The global atmospheric concentration of carbon dioxide has increased from a pre-industrial value of about 280 ppm to 379 ppm in 2005. The atmospheric concentration of carbon dioxide in 2005 exceeds by far the natural range over the last 650,000 years (180 to 300 ppm) as determined from ice cores. The annual carbon dioxide concentration growth rate was larger during the last 10 years (1995–2005 average: 1.9 ppm per year), than it has been since the beginning of continuous direct atmospheric measurements (1960–2005 average: 1.4 ppm per year) although there is year-to-year variability in growth rates .” Other greenhouse gases, such as Methane and Nitrous Oxide, have also been increasing in recent years: “Methane has increased from pre-industrial levels of 715 ppb to 1774 ppb in 2005. Nitrous oxide has increased from 270 ppb to 319 ppb over the same time period (IPCC WGI SPM).” Still, CO2 is the focus of most global warming policies because it accounts for the majority of greenhouse gas emissions. The following diagram illustrates the share of US greenhouse gases in 2005.

The US is currently the largest contributor to global CO2 emissions. Due to the US economy’s continued migration to the service sector, CO2 emissions growth within the US has slowed in recent years. However, emission growth within emerging powers such as China and India are increasing. Combined, the three countries account for over 45% of the global CO2 emissions, which amounts to 13,000MM metric tons per year; total CO2 emissions worldwide amount to approximately 27,000MM metric tons per year . Thus, the nature of global warming necessitates global cooperation, and any substantive effort to reduce emissions should seek to include the US, China, and India. PROJECTIONS

CO2 emissions are projected to be between 34,058MM tons and 51,767MM tons in future years. “The IPCC Special Report on Emission Scenarios projects an increase of global GHG emissions by 25-90% (CO2-eq) between 2000 and 2030, with fossil fuels maintaining their dominant position in the global energy mix to 2030 and beyond .”

The consequences of continued CO2 emission growth is summed up by the IPCC Fourth Assessment: “Continued GHG emissions at or above current rates would cause further warming and induce many changes in the global climate system during the 21st century that would very likely be larger than those observed during the 20th century (IPCC syr SPM).” TEMPERATURE CHANGE

The effects of global warming can be seen in the increase in the average global temperature. According to the IPCC, the rate of warming has increased over the past five years: “Eleven of the last twelve years (1995-2006) rank among the twelve warmest years in the instrumental record of global surface temperature (since 1850). The 100-year linear trend (1906-2005) of 0.74 [0.56 to 0.92]°C 1 is larger than the corresponding trend of 0.6 [0.4 to 0.8]°C (1901-2000) given in the Third Assessment Report (“TAR”). The temperature increase is widespread over...
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