By Bjorn LomborgThis week, the United Nations' climate scientists will release a major report synthesising the world's best global warming research. It will be the first time we've heard from the Intergovernmental Panel on Climate Change (IPCC) since its scientists won the Nobel Peace Prize with former US vice-president Al Gore.
The IPCC's Assessment Report will tell policy-makers what to expect from man-made climate change. It is the result of rigorous and painstaking labour: more than can be said for the other Nobel Prize winner. The difference between Gore's claims and IPCC research is instructive.
While Gore was creating alarm with his belief that a 20-foot-high wall of water would inundate low-lying cities, the IPCC showed us we should realistically prepare for a rise of one foot or so by the end of the century. Beyond the dramatic difference, it is also worth putting that one foot in perspective. Over the last 150 years, sea levels rose about one foot - yet, did we notice?
Most tellingly, while Gore was raising fears about the Gulf Stream halting and a new Ice Age starting, the scientists discounted the prospect entirely. The Gulf Stream takes warm water from around Mexico and pushes it toward Europe. Around 8,000 years ago, a melting lake in the region of the present-day Canadian Great Lakes broke through and a massive torrent of cold, fresh water flooded into the North Atlantic, significantly slowing the Gulf Stream for around 400 years. Gore worries that Greenland's ice shelves could melt and do the same thing again.
Ice in Greenland is obviously melting. But over the next century, it'll spill 1,000 times less water into the ocean than occurred 8,000 years ago. It will have a negligible effect on the Gulf Stream.
In his movie An Inconvenient Truth, Gore claimed that scientists were discovering that the current is "surprisingly fragile". However, the IPCC scientists write in their 2007 report: "None of the current models simulates an abrupt reduction or shut-down" of the Gulf Stream.
But what sort of nightmare would ensue if Gore were right? Siberia-like conditions in Europe? Actually, no. Europe would need to plunge by almost 13C to get that cold. Halting the Gulf Stream wouldn't achieve anything near that.
Gore and others have bought into a popular myth: that the Gulf Stream is the reason that western European winters are so much warmer than those of eastern North America. It is true the Gulf Stream provides a few degrees of extra heat to Europe, but it actually warms the west side of the North Atlantic almost as much. It's not the reason Europe is warmer than the US in winter; warm winds are. Let's hear from the IPCC again: "Catastrophic scenarios about the beginning of an ice ageÂ… are mere speculations, and no climate model has produced such an outcome. In fact, the processes leading to an ice age are sufficiently well understood and completely different from those discussed here, that we can confidently exclude this scenario."
Gore's claims have received a lot of notice. Hopefully, the careful work of the IPCC will also receive the attention that it deserves.
• Bjorn Lomborg is the author of Cool It: The Sceptical Environmentalist's Guide to Global Warming (Cyan-Marshall Cavendish).