Global carbon dioxide (CO2) emissions from the burning of fossil fuels stood at a record 8.38 gigatons of carbon (GtC) in 2006, 20 percent above the level in 2000. Emissions grew 3.1 percent a year between 2000 and 2006, more than twice the rate of growth during the 1990s. Carbon dioxide emissions have been growing steadily for 200 years, since fossil fuel burning began on a large scale at the start of the Industrial Revolution. But the growth in emissions is now accelerating despite unambiguous evidence that carbon dioxide is warming the planet and disrupting ecosystems around the globe.
In 2000, the Intergovernmental Panel on Climate Change (IPCC) laid out projections of how greenhouse gas emissions were likely to evolve during the twenty-first century due to economic, demographic, and technological changes. The high-end scenario combined rapid economic growth and globalization with intensive fossil fuel use and was used as the IPCC's upper limit for estimates of future climate change in its recent 2007 report. Yet this upper-limit projection predicted annual emissions growth of only 2.3 percent between 2000 and 2010 -- far less than the 3.1 percent annual increase observed so far this century. With CO2 emissions currently exceeding the worst-case scenario, we can expect that temperature and sea level rise will likely do the same.
Five countries are responsible for over half of fossil-fuel-related CO2 emissions, and the United States and China alone account for more than a third. The United States has been the world's largest emitter for over a century, releasing 1.66 GtC in 2006, or 19.8 percent of global emissions. It is now closely followed by China, where growth in emissions has been driven by a rapid increase in coal consumption -- China is currently opening an average of two coal-fired power plants a week. Emissions in China have more than doubled since 1990, reaching 1.48 GtC in 2006, or 17.7 percent of the world total. Analysts expect that China will overtake the United States to become the world's largest emitter before 2009.
The other countries in the top five are Russia, India, and Japan, respectively accounting for 5.2, 4.7, and 4.1 percent of global CO2 emissions. Of these, India has had the fastest growth in emissions, which have tripled since 1981. The increase in emissions from India and China reflects the rapid industrialization and economic growth currently happening throughout Asia. Since 2000, carbon dioxide emissions in Asia have grown five times faster than emissions in the rest of the world. The region, which produced less then 10 percent of global emissions in 1970, now accounts for almost a third of the world total.
These national and regional numbers mask huge differences in per capita CO2 emissions. After the tiny nations of Qatar, the United Arab Emirates, Kuwait, and Singapore, the United States has the largest per capita emissions in the world. At 5.5 tons of carbon, per person U.S. emissions are almost five times greater than those in China, and almost 200 times greater than those in the poorest countries in the world. The United Nations calculates that an average air-conditioner in Florida is responsible for more CO2 every year than a person in Cambodia is in a lifetime, and that a dishwashing machine in Europe annually emits as much as three Ethiopians.
In general, richer countries have higher per capita emissions, but important examples show that emissions do not have to be correlated with standard of living. California, where the average income is well above the U.S. mean, still has per capita emissions just over half the national average. Many countries in Europe also have per capita emissions less than half those in the United States and yet still have a comparable standard of living.
Fossil fuel burning is not the only source of carbon dioxide emissions. Currently, roughly 2 gigatons of carbon are released every year as forests are logged for timber or burned to provide agricultural land or pasture. Deforestation is most severe in Indonesia and Brazil, countries with some of the largest remaining stands of tropical rainforest. Together, these two countries account for more than half of emissions from land-use change.
Carbon dioxide from both fossil fuel burning and deforestation is accumulating in the atmosphere. Ice core records indicate that there is more CO2 in the atmosphere now than at any point in the last 650,000 years. In 2007, the atmospheric CO2 concentration was 384 parts per million (ppm), up from 280 ppm at the start of the Industrial Revolution. Between 2000 and 2007, atmospheric CO2 concentration grew by an average of 2 ppm per year, the fastest seven-year increase since continuous monitoring began in 1959.
Only about half of the CO2 released into the atmosphere every year actually remains there, as at least 45 percent is rapidly removed by carbon sinks such as plants and the ocean. As carbon dioxide emissions grow and the planet warms, however, studies suggest that these sinks will begin to saturate and will be unable to continue taking up the same share of emissions. Carbon dioxide is less soluble in a warmer ocean, for example, and warmer soils tend to hold less carbon, so as temperatures rise, a smaller proportion of CO2 emissions will be taken up by land and ocean sinks. A detailed examination of the growth rate of atmospheric CO2 concentration published in late 2007 suggested that a slowdown in sink uptake may already be occurring -- much earlier than scientists had anticipated.
Rising concentrations of carbon dioxide, in combination with other greenhouse gases, have already raised global average temperature by 0.8 degrees Celsius, with more than two thirds of that increase coming since 1980. This warming is already affecting natural systems around the world: climate scientists have documented trends of more heat waves, longer and more-intense droughts, higher sea level, more-frequent heavy rain events, and stronger hurricanes. Increasing CO2 levels are also acidifying the ocean, making survival more difficult for organisms such as coral that use calcium carbonate to form their structure. The pH (a measure of acidity where a lower value indicates more acidic conditions) of the surface ocean has already decreased by 0.1 points and could drop a further 0.3-0.4 points by 2100 if carbon dioxide emissions are not reduced. This would threaten the existence of organisms that play key roles in the marine ecosystem.
The IPCC projects that without policy measures to address global warming, carbon dioxide emissions from fossil fuel burning could more than double between 2000 and 2030, a trajectory that would make it almost impossible to avoid a temperature increase of 3 degrees Celsius above pre-industrial temperatures. Increasing evidence suggests that even a warming of less than 2 degrees above pre-industrial temperatures would constitute "dangerous" climate change, something nations have already committed to avoid under the U.N. Framework Convention on Climate Change.
It is clear that to prevent the most serious and irreversible effects of climate change, the world must act swiftly to substantially cut emissions. Energy efficiency measures and existing technologies such as wind power and plug-in hybrid electric cars, combined with programs to protect and restore the world's forests could cut net global carbon dioxide emissions 80 percent by 2020, a goal outlined in Plan B 3.0: Mobilizing to Save Civilization by Lester R. Brown. Putting this plan into action would halt and reverse the longstanding trend of growing carbon dioxide emissions.