Global warming: The facts

Scientists say global warming causes rising sea levels: The map shows the effect a rise of 1.5m would have on the Nile delta

Every time severe weather strikes, global warming seems to be blamed. But what is it and should we be worried?

Is it real?

Records show that the average temperature of the planet is climbing quite rapidly.

The global average surface air temperature has risen by between 0.3 and 0.6 degrees C in the last century. For Britain, 1998 has proved the hottest year in the last thousand years.

• Although the global weather system is extremely complex and not wholly understood, experts say that such a rapid change in temperature is bound to have severe implications for future weather and climate patterns.

• Climate researchers are predicting that the Earth's average temperature will continue to increase in the next 100 years.

• If greenhouse gas emissions drop slightly, the average world temperature in 2100 could be 1 degree C warmer than in 1990.

• But if they increase a lot and the climate proves very sensitive, the rise could be 3.5 degrees C.

• Scientists think they have uncovered evidence of just such sensitivity. They believe that rainforests damaged by the results of climate change will themselves start emitting carbon, making the problem worse still.

• The global sea level has risen by between 10 and 25 cms over the last century, as glaciers melt and warming sea water expands.

• Levels could rise by between 15 and 95 cms by 2100, and they will inevitably go on rising for 500 years, because the oceans have only just begun to warm up.

• If the researchers' predictions are correct, the rate of change over the last two to three centuries will have been greater than at any other time in the last 10,000 years.

The greenhouse effect

Most scientists believe recent global warming has been generated by human influence on a naturally-occurring phenomenon called the greenhouse effect.

Under normal conditions some of the sun's heat is radiated back into space

The 'greenhouse effect' occurs when heat is trapped in the atmosphere by gases like carbon dioxide, methane and CFCs

• The Sun's energy heats the surface of the Earth, although some of that heat is radiated back into space and the planet cools.

• Some gases in the atmosphere, called the greenhouse gases, prevent this radiation and so trap the heat.

• Since the Industrial Revolution, humans have been pumping out huge quantities of greenhouse gases, most notably carbon dioxide.

• Before 1850 human activity had little influence on the amount of carbon dioxide in the atmosphere, but since the industrial revolution concentrations of carbon dioxide, methane, nitrous oxide and chlorofluorocarbons, or CFCs, have greatly increased.

• Burning fossil fuels is responsible for most of the increase in carbon dioxide.

• The upsurge in concentrations of methane is due to gas produced by livestock and rice paddies.

The consequences

General warming is expected to lead to an increase in the number of extremely hot days and decrease in the number of extremely cold days.

• Warmer temperatures will lead to more severe droughts and floods in some places, and because rapid climate changes are unpredictable may lead to some "surprises".

• And even if people are able to adapt to climate change, many animal species will not.

• For vegetation the prospect is even worse. Plants and trees will not be able to migrate fast enough to find new habitats as the heat encroaches on their existing territory

.

What can be done?

Future trends may depend on action humans take to modify their activities. Both scientists and environment campaigners say human impact on the climate can be reduced by a number of measures:

• We could reduce energy consumption by making fewer journeys and using better insulation in our homes. This would lessen the need to burn coal and oil, and lead to reduced emissions of carbon dioxide and nitrous oxide.

• Advances in technology could result in fossil fuels being burned more efficiently.

• Emissions could be reduced by making wider use of low carbon fossil fuels like natural gas, and decarbonising exhaust gases from power plants.

• Environmental groups like Greenpeace and Friends of the Earth would like to see a switch to renewable and clean sources of energy such as solar, wind and hydro-electric power.

• Sustaining existing forest cover, planting new trees and better management of land use is also suggested as a means to slow global warming.

• More controversial is the use of nuclear power. Nuclear fission avoids using large quantities of fossil fuel for energy but is very contentious because it produces radioactive waste.

• Nuclear fusion, a theoretical way of harnessing power by fusing atoms which is still under development, may one day provide a cleaner alternative to the world's energy problem.

What we are seeing now is the result of the greenhouse gases emitted up till 1968, because the climate takes about 30 years to catch up with extra pollution already emitted.

The damage our pollution today is causing will not become apparent till about 2030.

And analysis of ancient ice rings drilled from miles down on the Greenland ice cap shows that the climate can cool down or heat up quite dramatically in less than three decades.