Climate science, from Bali to Copenhagen

By Richard BLACK

One of the main reasons why governments decided two years ago to drawup a new global agreement on climate change was a major report published just before that year's UN climate summit in Bali.Its top-line conclusions produced a collective and decisive politicalmove in favour of a global agreement bigger and bolder than anything seen before in the environmental field.

This was the Fourth Assessment Report (AR4) from the IntergovernmentalPanel on Climate Change (IPCC) - the distillation of research into climate past and present, melting ice, atmospheric changes, dates ofbird migrations and harvests, projections of future social andeconomic development, in fact any field that could throw light on how the climate was changing and how it might change over the next century, and what implications that carried for humankind and the natural world.

Now, as delegations wend their way to Copenhagen for the summit that was supposed to finalise that new global agreement, one question delegates might be asking is: what have scientists discovered since the AR4 that might influence decisions?

Overall I would say that all the new elements that were publishedsince have only confirmed or emphasised what the IPCC wrote in itsreport," says Jean-Pascal van Ypersele, the organisation'svice-chairman, who is otherwise employed at the Catholic University of Louvain in Belgium."Actually, the state of climate knowledge has been remarkably stableover the last 20 years.

Of course it's much more sophisticated, wehave numbers when we only had qualifications in broad terms; butoverall what we know today was already quite well known 20 years ago.

"Hot issue Spend enough time in the company of what you might term "mainstream"climate scientists, and you realise just how much frustration there is over the notion - widely promulgated in some circles since the AR4 -that temperatures are not rising anymore.

Their frustration stems from three main arguments:

• Of the two widely-used global temperature records, only one - the UKHadCRUT3 record - shows an apparent plateau from 1998 to 2008, whereasthe other - the US GISTEMP record - indicates that temperatures haverisen since then.

• It is self-evident that natural cycles of cooling and warming will sometimes add to the steady warming influence of elevated greenhousegas levels and sometimes obscure it - and that is what is happening now.

• 1998 was an abnormally warm year because of the strong El Ninoeffect, whereas 2008 was cooled by the opposite phenomenon - La Nina -so choosing this period is "cherry-picking".

Mike Lockwood, a physicist from the UK's Reading University whose work has helped quantify the relative influences of various factors ontemperatures, is especially vehement about the third of these points.

"Why pick a date other than it suits your argument?" he says."If I take 1997 or 1999 as the starting point, temperatures rise; so what right have you got to take 1998? That's bad science - a really specious argument."

-BBC