climate change

climate change. The earth's climate continually fluctuates as a result of the earth's elliptical orbit around the sun. When the earth is closer to the sun it receives more radiant energy. Long-term analyses of climate based on deep ocean deposits and ice cores from the Antarctic and Greenland ice caps show there are climatic cycles lasting 25,000, 40,000, and 100,000 years, which have resulted in the oscillations between glacial and interglacial periods. There are also millennial scale oscillations: the Vikings were able to colonize Greenland in their longboats during a mild climatic period about a thousand years ago, and from there visited Vinland, whereas there was a mini-ice age in the early 18th century when goose fairs were regularly held on the frozen Thames. Recently, 70-year cycles have been identified in the North Atlantic Oscillation. When pressure is high over the Azores, and low over Iceland, the flow of the Gulf Stream increases, keeping north-western Europe's climate mild. In the opposite phase the flow reduces and the climate of Europe is cooler. Similar oscillations have been identified in the North Pacific and both may be linked with El Niño events.

The gases in past atmospheres can be measured in the gas bubbles trapped deep in the ice caps. These show that as climate has oscillated so have the amounts of carbon dioxide in the atmosphere. When CO₂ concentrations are high, more of the incoming radiant heat from the sun is trapped in the atmosphere—the so-called greenhouse effect. Other gases such as methane and CFCs (chlorofluorocarbons) are many more times more effective in trapping the heat, but their concentrations are rising more slowly. This link between carbon dioxide and climate is well established, but exactly what causes it is a matter of controversy. Since the start of the Industrial Revolution in the 18th century the burning of fossil fuels has increased the carbon dioxide content of the atmosphere from pre-industrial levels of 240 parts per million (ppm) to present levels of over 370 ppm. If we continue to burn oil and coal at the present rates it will rise to 500–600 ppm by the end of the century. As more and more of the sun's energy gets trapped in the atmosphere, the earth's climate will warm, but not uniformly across the planet; polar regions will warm more than the tropics. Although some countries will benefit from such shifts most will lose out. Sea levels will rise as the polar ice caps melt and in 2003 Australian scientists produced fresh evidence showing that the area of sea ice surrounding Antarctica has shrunk by 20% in the last 50 years. Weather patterns will become less predictable with bigger and more destructive storms. Shifts in rainfall will increase flooding in some places, but cause droughts and desertification in others. The pattern of ocean currents will shift, and close links between ocean currents and local climate are contributing to the uncertainties of predicting the outcome of global climate change and are discouraging governments from taking the social and economic sacrifices needed to halt the rise in carbon dioxide emissions.

Already ocean plankton off the west coast of Britain has become more typical of warmer seas, and there have been sharp decline in the abundances of keystone species, such as the crustacean copepod (Calanus finmarchicus), which has been linked to the catastrophic decline in cod stocks. Climate will continue to fluctuate because many of the causes are planetary, but the implications of the changes will become increasingly threatening as world population grows and industralization increases globally, one of the most serious environmental issues facing us today.

M. V. Angel