Evidence for Global Warming..

After discussing global warming in the last post it would therefore make sense to discuss global warming in a little more depth.

Throughout history, since the humble beginnings of the Earth, the climate has continually fluctuated naturally between warm and cold periods (glacials and interglacials). Since around the 1950's however, there is evidence of a steep increase in global temperatures. It is this recent increase that is known as global warming.

Evidence for global warming comes from different sources:

1. Instrument readings - measurements made using at weather stations suggest a clear increasing trend. Figures show that temperatures have increased globally by 0.5 degrees since 1980.
2. Arctic Ice Cover - studies have shown that over the last 30 years, Arctic Ice has thinned to nearly half its previous level. As the ice retreats less solar radiation is reflected back into space. Darker ocean areas will absorb more radiation, increasing temperatures further.
3. Glacier retreat - photographic evidence has shown clear glacial retreat over the last century. Studies have estimated that up to 25% of global mountain glaciers could disappear by 2050. However, a natural reduction in snowfall could also lead to glacial retreat.
4. Ice Cores - Ice cores have provided some of the most compelling evidence for global warming. Similar to tree rings in their formation they display a a visual record of snow fall. Gas molecules trapped in the ice can also be analysed to discover the atmospheric conditions at the time of formation.

The causes of climate change

Scientists believe that the recent trend of global warming is directly related to the actions of man as opposed to natural cycles of temperature change associated with slight changes in the Earths orbit around the sun. The atmosphere allows heat from the sun (in the form of short-wave radiation) to pass through and heat the Earth. When the Earth gives off heat (in the form of long-wave radiation), gases such as carbon dioxide are able to absorb it, hence the term 'greenhouse gases'.

In recent years the levels of greenhouse gases have increased and many scientists and academics believe that this is a result of human activity such as the burning of fossil fuels. The IPCC (Intergovernmental Panel on Climate Change) has predicted that by 2100 global temperatures will have risen by between 1.8 and 4.0 degrees leading to a rise in sea level of approximately 40cm.