Climate change affects more than just a change in the weather, it refers to seasonal changes over a long period of time. These climate patterns play a fundamental role in shaping natural ecosystems, and the human economies and cultures that depend on them.

Successive scientific reports, notably those from the Intergovernmental Panel on Climate Change (IPCC), have come to ever firmer conclusions about human-kind's influence on the modern-day climate, and about the impact of rising temperatures. According to the latest report, it is more than 90 per cent probable that human-kind is largely responsible for modern-day climate change.

The principal cause is burning fossil fuels - coal, oil and gas. Deforestation and processes that release other greenhouse gases such as methane also contribute.

Although the initial impact is a rise in average temperatures around the world - global warming - this also produces changes in rainfall patterns, rising sea levels, changes to the difference in temperatures between night and day, and so on.

Last June, the G8 and a number of large developing countries agreed that the average temperature rise since pre-industrial times should be limited to 2˚C.

But sceptics question whether this is necessary. They argue that the Earth's climate has always changed naturally over time. Some scientists argue that that rising temperatures result from the influence of the sun. For example, variability in our planet's orbit alters its distance from the sun, which has given rise to major Ice Ages and intervening warmer periods.

Antonio Zichichi, Emeritus Professor of Advanced Physics at the University of Bologna, said at a climate change conference at Vatican City last year that "models used by the IPCC are incoherent and invalid from a scientific point of view".

Research by various international organisations into the funding of climate sceptics revealed support by the oil industry. For example, Greenpeace analysed the tax returns of Exxon Mobil and discovered that the oil giant had funded the climate change denial industry to the tune of US$23 million since 1998.

The climate sceptics' arguments still gained ground because of recent events, dubbed 'climategate'. Britain's Climate Research Unit suffered a data breach in recent days when a hacker apparently broke into their system and made away with thousands of e-mails and documents. The stolen data was then posted to a Russian server and quickly made the rounds.

The occurrence, so close to the start of the summit, has raised questions of attempted sabotage. Climategate has been denounced by scientists and global leaders - the Obama administration dismissed it, vowing to press forward with negotiations for a climate deal.

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