Sceptics' figures on global warming simply don't add up

Almost all climatologists expect warming to continue in the long term, but – because of natural fluctuations – they disagree about the immediate future, writes Geoffrey Lean.

By Geoffrey LeanPublished: 6:08PM BST 16 Oct 2009
Recent media reports suggested that global temperatures have not increased since 1998. Some sceptics say this proves that global warming has stopped, or reversed. I wish it were so. Alas, no such hopeful conclusion can be drawn.
Temperatures don't go steadily up or down, they naturally fluctuate around a trend: a cold week in April does not mean that winter will come in June. In any general trend, there will periods when they seem to go the other way.

Besides, it all depends on the dates picked: 1998 was anomalously hot because of an exceptionally strong El Nino, which always warms up the weather. Using it as a starting point produces a very different result than choosing the much cooler 1996, 1997, 1999 or 2000. On any long-term basis, temperatures have risen fast. The hopeful theory relies on Met Office temperature measurements. Nasa, which also takes readings, has the thermometer going up since 1998, with 2005 even warmer. The difference? The Met Office excludes the Arctic Ocean – the fastest-warming area on Earth.
Almost all climatologists expect warming to continue in the long term, but – because of natural fluctuations – they disagree about the immediate future. Part of the conclusion of one paper – "global surface temperatures may not increase over the next decade…" – is often cited by the sceptics. They rarely quote the rest of sentence "…as natural climate variations in the North Atlantic and tropical Pacific temporarily offset the projected anthropogenic warming".