The causes of climate change, its intensity and the future effects on mankind are far from settled, say a growing number of climate scientists.

The popular "global warming" theory touted by politicians, the media, and the majority of scientists, says that the observed heating-up of the Earth is a result of increases in man-made greenhouse gases, such as carbon dioxide - the products of industrialisation.

The predicted results are more violent weather, melting of the polar ice caps and sea-level rise. Urgent action is, therefore, needed to reduce greenhouse gas emissions and stop climate change.

No debating these facts? Actually, say some high-profile experts, the science underpinning these beliefs is far from secure.

Despite the collapse of ice-shelves on the Antarctic Peninsula, there is evidence that the Antarctic ice sheet is actually growing, says Dr Duncan Wingham. Computer climate modelling is limited and unreliable, says Dr Henk Tennekes. The statistics underlying climate predictions are flawed, and trained statisticians are not usually involved in the research projects, says Dr Edward Wegman.

All agree that the actual influence of greenhouse gases on climate change is not well understood, and man's contribution is very difficult to distinguish from the natural fluctuations.

The Solar Link

One popular alternative theory links climate change to solar activity. Dr Svensmark of the Danish National Space Centre found a link between cosmic rays and low cloud formation.

As more cosmic rays hit the Earth, more low-altitude clouds form, which play a large role in cooling the planet.

However, the sun's magnetic field, which deflects cosmic rays away from the Earth, doubled in strength over the 20th century. This shields the Earth from a vast number of cosmic rays, potentially resulting in global warming, according to Dr Svensmark, as reported in Canadian National Post .

Sunspot records have also been linked with changes in Earth's temperature by Dr Weiss of the University of Cambridge - the less sunspots, the cooler the Earth.

During medieval times the Earth was warm enough to allow Vikings to colonise Greenland and wine to be grown in Britain.

However, in the 17th century, over a period of 70 years of almost no sunspot activity called the Little Ice Age, New York Harbour froze and Viking colonists abandoned Greenland for warmer climates.

According to Dr Weiss's research we may be in for a similar cool periods in future.

Science vs Politics

Government policies have been largely influenced by the scientific reports commissioned by the United Nations International Panel for Climate Change (IPCC).

The most recent policy makers' summary was released in February, but the main scientific report is not out until May.

Two-thousand five hundred of the world's leading scientists were involved in this project, including Dr Richard Tol, Dr Richard Lindzen and Dr Christopher Landsea. They claim the results of their research have been twisted or ignored to suit political aims.

In fact the IPCC guidelines clearly state that the scientific report can be amended to be consistent with the policy makers' summary that is written by bureaucrats.

Dr Landsea, a hurricane expert and one of the lead authors, has since resigned.

"I personally cannot in good faith continue to contribute to a process that I view as both being motivated by pre-conceived agendas and being scientifically unsound," he said in an open letter.