Burning fossil fuels (oil, gas, and coal) produces the greenhouse gas carbon dioxide (CO₂), which is released into the atmosphere. Greenhouse gases warm the atmosphere by trapping solar radiation. The more greenhouse gases, the more solar radiation is trapped in the atmosphere, and the warmer the earth gets, hence CO₂ emissions lead to global warming. Global warming leads to climate change. The climate is by far the most important regulator of earth processes and a change in climate properties will have a major impact on all living things from plants to humans.

The three main indicators of global warming are temperature, precipitation, and sea level:

1) The mean global surface temperature has increased by about 0.3 to 0.6°C since the late 19th century. The warming has not been globally uniform. The recent warming has been greatest between latitudes of 40°N and 70°N latitude and the highest expected temperature increases are most likely to be found in the Arctic due to loss of sea ice, which at present reflects much of the solar radiation. This will lead to positive feedback mechanisms and enhanced global warming. The mean global temperature is expected to increase 1.4 to 5.8°C by 2100.

2) Precipitation has increased over land at high altitudes in the northern hemisphere, especially during the cold season. The amount of rain falling during heavy rain events has increased in some areas, such as the USA, the former Soviet Union and China. Extreme weather events are expected to occur more frequently than previously.

3) Over the last 100 years the global sea level has risen by about 4 to 14 cm. The expected rise of sea level in the 20th century expands 1 to 7 m. If the entire ice cap of Greenland melts, the sea level will rise 7 m. Many researchers claim that if the temperature increase is more than 3°C, a climate tipping point is reached, and large sea level rises can be experienced.

Climate change effects in the Arctic

In the Arctic, loss of permafrost regions triggers erosion and subsidence, changes hydrologic processes, reduces the stability of slopes and thus increases incidences of slides and avalanches. This threatens oil pipelines and all structures that are built on permafrost. Already melting permafrost is causing great structural damage to roads and buildings in Alaskan and Siberian areas. Changes in weather patterns have also caused massive storms and subsequent floods, and more storms in the northern hemisphere have increased the wave height in the North Atlantic Ocean. Climate change also causes loss of sea ice habitats, which will threaten the existence of polar bears and other ice-associated animals. For example, the Barents Sea will probably be ice-free year-round by 2050, with detrimental consequences for the productive marginal ice flora and fauna.