A growing body of scientific research has bolstered the view that human activities, especially the burning of fossil fuels, have contributed to a recent rise in global temperature. Moreover, many of the notable sceptics among the scientific community no longer need to be convinced.
The overwhelming majority of scientists accept recent temperature changes bear the imprint of human activity, says Dr John Sweeney, senior lecturer at NUI Maynooth Department of Geography.
This view has been "considerably strengthened over the past five years. We are at the stage where we are 99 per cent sure of the human influence on recent warming, but this is not yet 100 per cent established."
The scientific evidence shows the Earth is moving towards an era of more extreme climates, with huge impacts on coastlines increasingly likely.
But it is still difficult to pin down the human influence on climate change. Dr Sweeney adds: "It's like listening to a bad radio signal trying to find a signal in all the noise."
Climate change is also caused by a range of natural causes, and human activity "may be masked or enhanced by natural changes".
But data will become more definite in coming years, he said .
A significant amount of scientists do not agree with the prevailing theory, however. They argue that the recent rise in global temperatures are completely natural and no amount of expensive controls on the greenhouse gas emissions will stop the changes.
This is the position of President Bush, but it is treated with scepticism among much of the scientific community, as much of this research is funded by influential oil and energy interests in the US.
The world's leading experts on climate change have noted a "discernable influence" of human activity on global warming, Dr Sweeney underlines. The third report by the Intergovernmental Panel on Climate Change (IPCC), officially published earlier this year, revised its earlier predictions of temperature increases, which were "too conservative", Dr Sweeney notes.
Current predictions say the average global temperature will increase by .3 degrees Celsius at least per decade over the next century. Two studies, which were published in the influential journal Science this year, compared computer projections of climate change with new records which showed that the Earth's oceans have warmed by .06 degrees in the past 40 years. They found the predictions and the actual warming closely match.
"Our results support climate modelling predictions that show increasing atmospheric greenhouse gases will have a relatively large warming influence on the Earth's atmosphere," said the lead author of one study.
The leading climate researcher, Prof Tom Crowley of Texas A&M University, said recently in response: "To me the question of whether global warming is happening is receding as the central question. In my view, it's already here and I didn't believe that two years ago. Now the question is: how will it affect us?"
(Series concluded)