Well this becomes more entertaining by the moment. Those who staked so much on the "Amazongate" story, only to see it turn round and bite them, are now digging a hole so deep that they will soon be able to witness a possible climate change scenario at first hand, as they emerge, shovels in hand, in the middle of the Great Victoria Desert.

Here's the story so far. In January the rightwing blogger Richard North claimed that the Intergovernmental Panel on Climate Change had "grossly exaggerated the effects of global warming on the Amazon rain forest". In 2007 the Panel had claimed that "up to 40% of the Amazonian forests could react drastically to even a slight reduction in precipitation". Reduced rainfall could rapidly destroy the forests, which would be replaced with ecosystems "such as tropical savannahs."

North asserted that this "seems to be a complete fabrication", though see this update too. His story was picked up by hundreds of other climate change deniers, some of whom went so far as to claim that it destroyed global warming theory. It was also run by the Sunday Times, which headlined its report "UN climate panel shamed by bogus rainforest claim".

Two weeks ago the Sunday Times published a complete retraction. That, you might think, would be the end of the matter. How wrong you would be. Far from accepting that they had made a mistake, the promoters of this story now seem determined to compound it. On Sunday our old friend Christopher Booker asserted that "an exhaustive trawl through all the scientific literature on this subject by my colleague Dr Richard North (who was responsible for uncovering "Amazongate" in the first place), has been unable to find a single study which confirms the specific claim made by the IPCC's 2007 report … all observed evidence indicates that the forest is much more resilient to climate fluctuations than the alarmists would have us believe."

There is no doubt that the IPCC made a mistake. Sourcing its information on the Amazon to a report by the green group WWF rather than the substantial peer-reviewed literature on the subject, was a bizarre and silly thing to do. It is also an issue of such mind-numbing triviality, in view of the fact that the IPCC's 2007 reports extend to several thousand pages and contain tens of thousands of references, that I feel I should apologise for taking up more of your time in pursuing it. But the climate change deniers have made such a big deal of it that it cannot be ignored.

It is also true that nowhere in the peer-reviewed literature is there a specific statement that "up to 40% of the Amazonian forests could react drastically to even a slight reduction in precipitation". This figure was taken from the WWF report and it shouldn't have been.

But far from "grossly exaggerating" the state of the science in 2007, as North claimed, the IPCC – because it referenced the WWF report, not the peer-reviewed literature – grossly understated it. The two foremost peer-reviewed papers on the subject at the time of the 2007 report were both published in Theoretical and Applied Climatology. The references are below. They are cited throughout the literature on Amazon dieback.

What do they tell us? That the projection in the IPCC's report falls far, far short of the predicted impacts on the Amazon.

The first paper, by Cox et al, predicts a drop in broadleaf tree cover from approximately 80% of the Amazon region in 2000 to around 28% in 2100 (Figure 6). That is bad enough, involving far more than 40% of the rainforest. But the forest, it says, will not be largely replaced by savannah: "When the forest fraction begins to drop (from about 2040 onwards) C4 grasses initially expand to occupy some of the vacant lands. However, the relentless warming and drying make conditions unfavourable even for this plant functional type, and the Amazon box ends as predominantly baresoil (area fraction >0.5) by 2100."

In other words, the lushest region on earth is projected by this paper to be mostly replaced by desert as a result of global warming (and the consequent reduction in rainfall) this century. I hope I don't have to explain the consequences for biodiversity, the people of the Amazon or climate feedbacks, as the carbon the trees and soil contain is oxidised and released to the atmosphere.

So what does the second paper say? Betts et al go even further. In their model runs: "By the end of the 21st Century, the mean broadleaf tree coverage of Amazonia has reduced from over 80% to less than 10%."

They are slightly more sanguine about the savannah/desert balance. "In approximately half of this area, the trees have been replaced by C4 grass leading to a savanna-like landscape. Elsewhere, even grasses cannot be supported and the conditions become essentially desert-like."

Isn't that reassuring? It is worth noting that both these papers are referenced elsewhere in the IPCC's 2007 report.

They are not alone. One of the runs in a 1999 paper by White, Cannell and Friend, also published in a peer-reviewed journal (see below) shows almost the entire Amazon basin as desert by the 2080s (Figure 2b(ii)).

Compare these projections to Booker's claim that "all observed evidence indicates that the forest is much more resilient to climate fluctuations than the alarmists would have us believe."

So now the promoters of the Amazongate story have three options. They can persist in claiming that the IPCC was wrong, but this time on the grounds that it underestimated the likely response of the Amazon to climate change. But that would create more problems for them than it solved. They could fall back on their age-old defence and claim that it's all irrelevant, because the scientists' projections for how the Amazon might respond to climate change are based on models. But that would oblige them to suggest a better means of predicting future events. Tealeaves? Entrails? Crystal balls? Or they could quietly slink away before this doomed crusade causes them any more embarrassment, and find something more useful to do.

Booker ends his piece by maintaining that on "the only occasion" on which I had attempted to expose the misinformation he peddles, I got it wrong and had to apologise to my readers. Yes, I did get one of my claims wrong and I said so as soon as I discovered it. This is where Christopher and I differ: I admit my mistakes, he does not.

But I'm fascinated by his assertion that this was "the only occasion" on which I pulled him up. Either he has a very short memory or a very selective one. To prompt some glimmer of recognition, here are some of the other occasions on which I have pointed out his mistakes:

In 2007 I showed that Booker and North had used cherry-picking to support their claim that speed cameras had impeded the decline of deaths on the roads. They had ignored the latest evidence (which flatly contradicted their claims), misquoted a House of Commons report and changed the date of an article of mine, which had the effect of making their narrative more convincing.

In 2008, I showed how Booker had misquoted scientific papers, engaged in cherry-picking and relied on the word of a man convicted under the Trade Descriptions Act for making false claims about his qualifications to support his contention that white asbestos cement "poses no measurable risk to health".

I also drew attention to my favourite Bookerism: his observation, in February 2008, that "Arctic ice isn't vanishing after all." The "warmists", he pointed out, had made much of the fact that in September 2007 northern hemisphere sea ice cover had shrunk to the lowest level ever recorded. But now it had bounced back, proving how wrong they were. To reinforce this point, he helpfully published a graph, showing that the ice had indeed expanded between September and January. I pointed out that the Sunday Telegraph continued to employ a man who cannot tell the difference between summer and winter.

In 2009, I detailed six howling mistakes about climate change in just one of his columns. Last month I lambasted him for falsely claiming that under EU rules you'll be able to bury dead pets only after "pressure cooking them at 130 degrees centigrade for half an hour".

I don't mean to spend my life correcting Booker's mistakes, but the volume of misinformation he has published is mindblowing, and someone has to call him to account. Other journalists, perhaps wisely, don't bother.

All this is good knockabout stuff. But we're in danger of forgetting that it concerns a deadly serious matter: a change in the climatic conditions which have made human civilisation and the current human population possible, and, specifically, the degradation of the most wonderful and beautiful of the world's ecosystems into desert and scrubby grassland. It is hard to overstate the irresponsibility of those who misrepresent the science in order to persuade people that no action needs to be taken.

References:

PM Cox et al, 2004. Amazonian forest dieback under climate-carbon cycle projections for the 21st century. Theoretical and Applied Climatology, 78, 137–156. DOI 10.1007/s00704-004-0049-4

RA Betts et al, 2004. The role of ecosystem-atmosphere interactions in simulated Amazonian precipitation decrease and forest dieback under global climate warming. Theoretical and Applied Climatology, 78, 157–175. DOI 10.1007/s00704-004-0050-y

A White, MGR Cannell, AD Friend, 1999. Climate change impacts on ecosystems and the terrestrial carbon sink: a new assessment. Global Environmental Change, 9, S21-S30.

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