Botkin has been publishing research on theoretical global warming, its potential ecological effects, and the implications for people and biodiversity since 1968.

In his testimony, he says he approached the subject as a scientist but laments that in recent years "the subject has been converted into a political and ideological debate".

He adds: "I have colleagues on both sides of the debate and believe we should work together as scientists instead of arguing divisively about preconceived, emotionally based 'positions'."

Botkin acknowledges the world has been going through a "warming period driven by a variety of influences", but says this is not unusual, and contrary to the characterisations by the IPCC and the White House National Climate Assessment, "these environmental changes are not apocalyptic nor irreversible".

He says: "My biggest concern is that both the reports present a number of speculative, and sometimes incomplete, conclusions embedded in language that gives them more scientific heft than they deserve."

Commenting on the warming period and the current plateau, where the earth's temperature has not changed for the past 17 years, he says: "The rate of change we are experiencing is also not unprecedented, and the 'mystery' of the warming 'plateau' simply indicates the inherent complexity of our global biosphere.

"Change is normal, life on earth is inherently risky; it always has been. The two reports, however, makes it seem that environmental change is apocalyptic and irreversible. It is not."

He draws attention to the weakness of the climate models. "The two reports assume and/or argue that the climate warming forecast by the global climate models is happening and will continue to happen and grow worse. Currently these predictions are way off the reality."

In other words, when the models are tested against real-world observations, they don't work. "This means that as theory they are fundamentally scientifically unproven."

He also has interesting observations on the weaknesses in the way the IPCC works.

"The fundamental IPCC and White House Climate Change Assessment approach has been to gather a huge number of scientists from a large number of disciplines, on the assumption that a kind of crowd approach to what can be agreed on is the same as true scientific advance."

The dangers of this "crowd-sourced approach", Botkin says, particularly where credentialled "experts" are involved, is that people are prone to "information cascade", in which error is compounded by group think, assumptions become unchallenged "fact" and observations play second fiddle to unchallenged models.

"The excellent scientists involved with the IPCC reports are no less prone to this than the excellent scientists who relied on Aristotelian models of a geocentric universe."

Botkin suggests that one way to improve the IPCC approach is to return to a reliance on science done by individuals and small groups with a common specific interest and focus and to move away from trying to make a complete, definitive model of every aspect of climate.

Also, he says to "get out of the blame game. None of the above suggestions can work as long as global warming remains a moral, political, ideologically dominated topic, with scientists pushed into, or at least viewed as, being either for or against a single point of view".