To some, it's a massive conspiracy to con the public. To others, it's the greatest threat to the future of our world.
Over recent years, opinions about global warming have become increasingly polarised.
It came to a head late last year when hundreds of e-mails from the University of East Anglia's Climatic Research Unit were published.
The so-called "Climategate" debate was born.
Despite governments, scientists and campaigners telling us the world's climate is changing, opinion polls suggest growing uncertainty about global warming.
It hasn't helped that recent weather forecasts of a barbecue summer and a mild winter have been spectacularly wrong.
Panorama's Tom Heap has gone back to basics to ask what we really know about our climate and how it affect us.
His examination of the topic comes just ahead of the third and final report into "Climategate".
Thus far, there have been two inquiries: the Parliamentary Science and Technology Select Committee and an independent review by Lord Oxburgh.
Both found that there was no grand global conspiracy and no deliberate scientific impropriety or dishonesty.
The final report by Sir Muir Russell has looked at whether the scientists involved could have been more open with their critics.
The e-mails, which talk of hiding and deletion, gave some the impression that information had been deliberately withheld. They also appeared to lift the lid on an apparently vicious and personal conflict.
We wanted to pin down what, if anything, is broadly agreed and certain about global warming.
Top Gear may have its "Cool Wall", but we have built a "Wall of Certainty". We tested it out on some leading scientists and asked them a few key questions about climate change.
We gave them just four options - certain, likely, unlikely or no way. The answers were fascinating.
First up was Professor Bob Watson. He chaired the Intergovernmental Panel on Climate Change for five years, worked for former US Vice-President Al Gore, and is now chief scientific adviser to the Department for Environment, Food and Rural Affairs.
Second was the leading sceptic Professor John Christy, an atmospheric scientist at the University of Alabama in Huntsville.
Contrary to some of the newspaper headlines and blogs that suggest all global warming science is a con, they agreed that mankind is causing the planet to warm up.
We also hear from the scientist behind the graph which has become an icon in the climate-change debate. Professor Michael Mann regrets the way his so-called "hockey-stick graph" was put in the spotlight by politicians.
And we find out that the leading sceptic Bjorn Lomborg, author of the best-selling book The Skeptical Environmentalist, accepts much of the basic science and agrees with the critical IPCC finding that most of the recent global warming is man-made.
There is genuine uncertainty and disagreement about the exact scale and speed of human-induced global warming and crucially what we should do about it. But I was surprised to find how much agreement there is on the fundamental science.
Mike Rudin is producer of Panorama's What's Up With The Weather? You can watch it on BBC One on Monday 28 June at 2030BST and online.