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A serious global threat
The scientific evidence is now overwhelming: climate change is a serious global threat, one that demands an urgent worldwide response. There is now a strong scientific consensus that recent changes in our global climate are almost certainly caused by human activity. Carbon dioxide and other greenhouse gases in the atmosphere, in particular from fossil fuel use, deforestation and agriculture, are the main contributors.
The science of climate change
The greenhouse effect is a natural process whereby gases present in the atmosphere, such as water vapour, CO2 and methane, trap enough of the sun’s energy to keep the earth warm enough to sustain the abundance of life around us.
Over the last century the amount of these greenhouse gases (GHGs) in our atmosphere has risen steadily, almost certainly as a result of human activity. For example, CO2 levels have risen from 280 parts per million (ppm) to nearly 380ppm, driven in large part by our usage of fossil fuels. Concentrations of other GHGs, like methane have also risen, mainly because of deforestation and more intensive agriculture.
There is solid evidence that the world is warming as a result - between 0.5 and 1 degree Celsius in the past 100 years. In early 2007, the scientists of the United Nations’ Intergovernmental Panel on Climate Change (IPCC) re-confirmed the scientific consensus – now with more than 90% certainty – that man-made climate change is underway.
How much more the temperature might rise, and what might happen as a result, is largely governed by the eventual concentration of GHGs in the atmosphere. The latest estimates from the IPCC about how high concentrations could go – and the range of possible increases in average temperatures as a result - are summarised below:
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See what we say about climate change in the Shell Sustainability Report 2008.