Climate Change
Climate change is with us．A decade ago, it was conjecture．Now the future is unfolding before our eyes．Canada's Inuit see it in disappearing Arctic ice and permafrost (永久冻结带)．The shanty town dwellers of Latin America and Southern Asia see it in lethal storms and floods．Europeans see it in disappearing glaciers, forest fires and fatal heat waves.
Scientists see it in tree rings, ancient coral and bubbles trapped in ice cores．These reveal that the world has not been as warm as it is now for a millennium or more．The three warmest years on record have all occurred since 19983 19 of the warmest 20 since 1980．And Earth has probably never warmed as fast as in the past 30 years a period when natural influences on global temperatures, such as solar cycles and volcanoes should have cooled us down.
Climatologists reporting for the UN Intergovernmental Panel on Climate Change (IPCC) say we are seeing global warming caused by human activities．The felling down of trees that largely decrease the photosynthesis (光合作用) to absorb CO2 and the burning of coal, oil and natural gas that gives out great amount of CO2 in the air all result in the increasing of temperatures．
Global Greenhouse
People are causing the change by burning nature's vast store of coal, oil and natural gas．This releases billions of tons of carbon dioxide (CO2) every year, although the changes may actually have started with the dawn of agriculture, say some scientists.
The physics of the 'greenhouse effect' has been a matter of acientific fact for a century．CO2 is a greenhouse gas that traps the sun's radiation within the troposphere(对流屋), the lower atmosphere．It has accumulated along with other man-made greenhouse gases, such as methane (沼气) and chlorfiuorocarbons (CFCs) (碳氟化合物)．Some studies suggest that cosmic rays may also be involved in warming.
If current trends continue, we will raise atmospheric CO2 concentrations to double pre-industrial levels during this century．That will probably be enough to raise global temperatures by around 2℃ to 5℃．And the trend is still going on．Some warming is certain, but the degree will be determined by cycles involving melting ice, the oceans, water vapor, clouds and changes to vegetation and plants.
Warming is bringing other unpredictable changes．Melting glaciers and precipitation are causing some rivers to overflow, while evaporation is emptying others．Diseases are spreading, especially in tropical areas．Some crops grow faster than before while others see yields slashed greatly by disease and drought．Clashes over dwindling water resources may cause conflicts in many regions.
As natural ecosystems—such as coral reefs—are disrupted, biodiversity is reduced．Most species cannot migrate fast enough to keep up, though others are already evolving in responses to warming．This has resulted to the extinction (or close extinction) of some species and put a lot of species in er．In addition, for those who have adapted to the new environment, the amount of the species is increasing in great deal.
Thermal expansion of the oceans, combined with melting ice on land, is also raising sea levels．In this century, human activity could trigger an irreversible melting of the Greenland ice sheet．This would condemn the world to a rise in sea level of six meters—enough to flood land occupied by billions of people．And this is one fear that almost all scientists hold in heart.
The global warming would be more pronounced if it were not for sulphur particles and other pollutants that shade us, and because forests and oceans absorb around half of the CO2 we produce．But the accumulation rate of atmospheric CO2 has doubled since 2001, suggesting that nature's ability to absorb the gas could now be stretched to the limit．Recent research suggests that natura