How Long a Pause in Warming Does It Take to Question Global Warming?

From David Rose in The Daily Mail:

"Last week, halfway through yet another giant, 15,000 delegate UN climate jamboree, being held this time in the tropical splendour of Cancun in Mexico, the [British Meteorological] Office was at it again.

". . . Globally, it insisted, 2010 was still on course to be the warmest or second warmest year since current records began.

"But buried amid the details of those two Met Office statements 12 months apart lies a remarkable climbdown that has huge implications - not just for the Met Office, but for debate over climate change as a whole.

"Read carefully with other official data, they conceal a truth that for some, to paraphrase former US VicePresident Al Gore, is really inconvenient: for the past 15 years, global warming has stopped."
. . .
"Last week at Cancun, in an attempt to influence richer countries to agree to give £20billion immediately to poorer ones to offset the results of warming, the US-based International Food Policy Research Institute warned that global temperatures would be 6.5 degrees higher by 2100, leading to rocketing food prices and a decline in production.

"The maths isn't complicated. If the planet were going to be six degrees hotter by the century's end, it should be getting warmer by 0.6 degrees each decade; if two degrees, then by 0.2 degrees every ten years. Fortunately, it isn't.

"Actually, with the exception of 1998 - a 'blip' year when temperatures spiked because of a strong 'El Nino' effect (the cyclical warming of the southern Pacific that affects weather around the world) - the data on the Met Office's and CRU's own websites show that global temperatures have been flat, not for ten, but for the past 15 years."
. . .
"But though it was still successfully trying to influence media headlines during Cancun last week by saying that 2010 might yet end up as the warmest year, the small print reveals the Met Office climbdown. Last year it predicted that the 2010 average would be 14.58C. Last week, this had been reduced to 14.52C.

"That may not sound like much. But when one considers that by the Met Office's own account, the total rise in world temperatures since the 1850s has been less than 0.8 degrees, it is quite a big deal. Above all, it means the trend stays flat."
. . .
"But little by little, the supposedly settled scientific 'consensus' that the temperature rise is unprecedented, that it is set to continue to disastrous levels, and that it is all the fault of human beings, is starting to fray.

"Earlier this year, a paper by Michael Mann - for years a leading light in the IPCC, and the author of the infamous 'hockey stick graph' showing flat temperatures for 2,000 years until the recent dizzying increase - made an extraordinary admission: that, as his critics had always claimed, there had indeed been a 'medieval warm period' around 1000 AD, when the world may well have been hotter than it is now.

"Other research is beginning to show that cyclical changes in water vapour - a much more powerful greenhouse gas than carbon dioxide - may account for much of the 20th Century warming.

Even Phil Jones, the CRU director at the centre of last year's 'Climategate' leaked email scandal, was forced to admit in a littlenoticed BBC online interview that there has been 'no statistically significant warming' since 1995."
. . .
"The question now emerging for climate scientists and policymakers alike is very simple. Just how long does a pause have to be before the thesis that the world is getting hotter because of human activity starts to collapse?"
[emphasis added]