Burning fossil fuels release gases, notably carbon dioxide (CO2) to the atmosphere; this extra CO2 absorbs infra-red radiation that would otherwise escape into space, thereby heating the atmosphere – the greenhouse effect – and possibly causing changes in climate. The following are likely effects of any doubling of CO2 concentration: average earth temperature would increase by 2 to 3 degrees C; precipitation would increase in some regions, though the change in rainfall patterns is uncertain (some scientists suggest that regions between middle and high latitudes would be affected, which is where most developing countries are located); and evaporative tendencies would increase in parts of the world, perhaps more than rainfall.
Carbon dioxide or CO2 (carbon with two oxygen atoms) is a clean, natural, common gas which is not strictly pollution; it cannot harm ordinary life, unlike carbon monoxide, which kills you if you breathe enough of it). For generations, in fact, engineers said that an engine burned clean if it produced only water vapour and carbon dioxide. CO2 emissions into the atmosphere have become a pollution problem only in recent years, due to their sheer quantity as a result of the burning of fossil fuels. They matter because the molecular structure of CO2 traps heat in the atmosphere that would otherwise radiate back out to space.
CO2 is not the only greenhouse gas produced by human activity, but it is the main one, accounting for about half of all human sources of global warming. CO2 had a pre-industrial level in the atmosphere of 280 parts per million (ppm); the 1986 level was 346 ppm, and the 1992 level 357 ppm. The current annual increase is 1.5 ppm. At current rates, it will be more than 500 parts per million by the middle of the 21st century.
Historically the level has fluctuated, but at no time in the previous 100,000 years did concentrations reach 300 ppm. Most of the pre-industrial changes in atmospheric CO2 concentration are believed to involve changing ocean fluxes such as outgassing processes, biological productivity, ocean circulation, ice cover and coral reefs. Anthropogenic emission, particularly those from fossil fuel combustion for energy, are the primary cause for the more than 25 percent increase in the concentration of carbon dioxide during the past two centuries.
One of the strongest indicators that the theories of global warming are correct comes from a monitoring station based atop the Mauna Loa observatory in Hawaii, which has been measuring the concentration of carbon dioxide in the atmosphere since 1958. It is the longest continuous record of atmospheric carbon dioxide levels in the world and has been moving relentlessly upwards every year.
Offsetting this drift to higher carbon emissions, is a long-term trend toward decarbonization of energy. However, these improvements in the carbon intensity of the world economy, historically about 1.3% per year during the last century, have been overwhelmed by growth in economic output of roughly 3.0% per year. The difference of 1.7% parallels the annual increases in CO2 emissions. According to IIASA, in 1990 the projected reduction of energy intensity by year 2020 was 36% in OECD countries, in reforming economies 42%, and in developing countries 11%. This means an average of 24% reduction in global emissions of CO2 per unit of economic activity during the 30-year period, from 290 grams of carbon per dollar to 220 grams. These improvements, while significant, would not be enough to offset the near-doubling in global economic activity over the period, estimated from US$ 24 trillion to US$ 46 trillion (in constant dollars). Global emissions of carbon in the form of CO2 would rise from 5.5 gigatonnes of carbon in 1990 to an estimated 8.0 gigatonnes in 2020. Alternative estimates of carbon emissions in 2020 are 10.2 gigatonnes made by the USA EPA, and 9.8 gigatonnes used in the reference scenario of the Intergovernmental Panel on Climate Change (IPCC).
Trends documented by the the World Bank and Worldwatch Institute, and reported to the Rio+5 conference in 1997, at that emissions of CO2, the main contributor to global warming, have increased by 10 to 40 percent in many developing countries since 1990. In 1993, the rapidly expanding economy of China already ranked third in CO2 emissions, behind the USA and the former Soviet Union (when Soviet emissions are split among the newly independent republics, China may well be second). Chinese energy and environmental officials expect coal consumption to rise from the current level of 1.1 billion tonnes a years to more than 1.4 billion tonnes by the year 2000, despite the fact that energy growth has been held to half the rate of economic growth. One projection even suggests that China would pass the USA in carbon emissions by the year 2025.
In 1990, Canadians emitted 461 megatonnes of CO2, most of it from the combustion of fossil fuels. The transport sector accounted for the largest part of the CO2 emissions (34%), followed by: electricity production (20%), industrial sources (17%) and miscellaneous heating and industrial processes.
Research revealed that on the basis of bubbles of atmospheric gass contained in ice cores extracted from the Antarctic ice sheet, the levels of Carbon Dioxide in the atmosphere is higher in 1998 than at any other time in the last 420,000 years. at 360 parts per million, the levels are 20% higher than in any previous warm period between the ice ages, and double the particular concentrations during an ice age.
In the late 1990s, annual emissions of carbon dioxide were almost four times the 1950 level and atmospheric concentrations of carbon dioxide had reached their highest level in 160,000 years.
Annual global emissions of carbon dioxide from the burning of fossil fuels, cement manufacture and gas flaring reached a new high of nearly 23 900 million tonnes in 1996 (CDIAC 1999). This was some 400 million tonnes more than in 1995 and nearly four times the 1950 total. Only in some countries in Europe and Central Asia has there been a significant drop in emissions during the past decade, mainly as a result of the economic crises in Eastern and Central Europe. Atmospheric concentrations of CO2 in 1997 reached more than 360 parts per million (ppm), the highest level in 160 000 years (Keeling and Whorf 1998).
The annual increase will go higher, because the population will double and perhaps nearly triple again in the next century and the world economy will grow five to ten times larger. CO2 levels will double from their level prior to the Industrial Revolution by about 2040, latest by 2070.
The largest source of greenhouse gas may be termites, whose digestive activities are responsible for about 50 billion tonnes of CO2 and methane each year. That is ten times more than the present world production of CO2 from burning fossil fuels.
Any attempt to cut CO2 emissions from cars and power plants would place intolerable restrictions and demand unwanted sacrifices on society.
The long term forcing of greenhouse gas emissions on the climate system depends on both the atmospheric lifetime of the gas and its instantaneous radiative properties. For CO2, the instantaneous climate response to emissions may decrease significantly as its ambient concentration increases. However, this effect may be largely offset by an expected increase in CO2 atmospheric lifetime due to reduced rate of CO2 uptake in oceans, making the net effect of CO2 emissions on climate largely independent of its atmospheric concentration level.