by Jimmy Nightingale

Created on: August 25, 2009   Last Updated: January 05, 2010

The Fourth Assessment Report(4AR) of the Intergovernmental Panel on Climate Change (IPCC), released in February 2007, provided the strongest statement yet that global warming (or climate change) is (1) real, (2) is going to lead to significant adverse impacts within the next century, and (2) is being driven by human activity. The 4AR is the latest iteration of the IPCCs flagship summary of the scientific basis of climate change and its impacts (the previous one was in 2001) and concludes:

1.) human influences on climate are 'very likely' detectable in the observational record (meaning >90 percent chance; up from 66 percent in the previous report);

2.) global temperatures are likely to rise by between 1.1 and 6.4 degrees Celsius by 2100 (1.4 to 5.8 degrees Celsius in the previous report); and

3.) sea levels are likely to rise by between 0.18 and 0.59 metres by 2100 (the upper limit reduced from 0.88m from the previous report).

What these key conclusions mean in real terms is difficult as much of the impact will depend on where you live and your capacity to adapt. The ranges in 2.) and 3.) above also depend on what action humanity takes to tackle this challenge. Much of the research to date doesn't provide a complete picture of what temperature rises of 1 or 6 degrees Celsius means.

Environmentalist and climate change author Mark Lynas has researched this to provide a holistic view of what each degree of additional warming means for life on Earth. His book "Six Degrees" paints a near apocalyptic picture of what awaits humanity unless we act very soon (preferably immediately) to move our economy away from its reliance on carbon based energy. The former chair of the IPCC, Professor Bob Watson has been championing "mitigate for two degrees, prepare for four" in his post-IPCC role in the Millenium Ecosystem Assessment, a landmark UN study, published in 2005, that looks at the total human impact on the Earth's natural systems.

Much of the political discussion revolves around the likelihood of two degrees of warming by 2100. That doesn't sound like much, however this is not the same everywhere on our planet and it does not mean that we simply add two degrees on to the temperature wherever in the world we may be. Two degrees means:

- acidification of the world's oceans, endangering much of the marine food chain;
- summer heatwaves of increasing frequency, duration and intensity. It is likely that every second summer on average will endure severe heatwaves (like the

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