James Hansen

We know the IPCC scientists have been under pressure from certain governments to water down their findings, and we also know that the IPCC reports can be out of date before release - due to the rigors of the peer review process, and the especially active research efforts of late that don't have time to be included - but some scientists, including James Hansen, the highly respected Head for NASA's Goddard Space Flight Centre, are now criticising the IPCC for a serious underestimation of the potential runaway effects of climate change:

The Earth today stands in imminent peril

...and nothing short of a planetary rescue will save it from the environmental cataclysm of dangerous climate change. Those are not the words of eco-warriors but the considered opinion of a group of eminent scientists writing in a peer-reviewed scientific journal.

Six scientists from some of the leading scientific institutions in the United States have issued what amounts to an unambiguous warning to the world: civilisation itself is threatened by global warming.

They also implicitly criticise the UN's Intergovernmental Panel on Climate Change (IPCC) for underestimating the scale of sea-level rises this century as a result of melting glaciers and polar ice sheets.

Instead of sea levels rising by about 40 centimetres, as the IPCC predicts in one of its computer forecasts, the true rise might be as great as several metres by 2100. That is why, they say, planet Earth today is in "imminent peril".

In a densely referenced scientific paper... some of the world's leading climate researchers describe in detail why they believe that humanity can no longer afford to ignore the "gravest threat" of climate change.- Independent

From the document itself:

West Antarctica seems to be moving into a mode of significant mass loss.... Gravity data yielded mass loss of approximately 150 km3 yr in 2002–2005.... A warming ocean has eroded ice shelves by more than 5 m yr over the past decade.... Satellite QuickSCAT radiometer observations..., initiated in 1999, reveal an increasing area of summer melt on West Antarctica and an increasing melt season over the period of record. Attention has focused on Greenland, but the most recent gravity data indicate comparable mass loss from West Antarctica. We find it implausible that BAU [Business As Usual] scenarios, with climate forcing and global warming exceeding those of the Pliocene, would permit a West Antarctic ice sheet of present size to survive even for a century.

Our concern that BAU GHG scenarios would cause large sea-level rise this century... differs from estimates of IPCC (2001, 2007), which foresees little or no contribution to twenty-first century sea-level rise from Greenland and Antarctica. However, the IPCC analyses and projections do not well account for the nonlinear physics of wet ice sheet disintegration, ice streams and eroding ice shelves, nor are they consistent with the palaeoclimate evidence we have presented for the absence of discernable lag between ice sheet forcing and sea-level rise.

The best chance for averting ice sheet disintegration seems to be intense simultaneous efforts to reduce both CO2 emissions and non-CO2 climate forcings. As mentioned above, there are multiple benefits from such actions. However, even with such actions, it is probable that the dangerous level of atmospheric GHGs will be passed, at least temporarily. - Climate Change & Trace Gases p. 26 (PDF)

This is the latest in a raft of recent studies that indicate the IPCC's worst case scenarios could potentially be a walk in the park compared to reality. If so, Al Gore's oft-quoted statement that political inaction is a "moral issue" becomes increasingly relevant.

In an email to The Independent, Dr Hansen said: "In my opinion, among our papers this one probably does the best job of making clear that the Earth is getting perilously close to climate changes that could run out of our control."

... Dr Hansen said we have about 10 years to put into effect the draconian measures needed to curb CO2 emissions quickly enough to avert a dangerous rise in global temperature. Otherwise, the extra heat could trigger the rapid melting of polar ice sheets, made far worse by the "albedo flip" - when the sunlight reflected by white ice is suddenly absorbed as ice melts to become the dark surface of open water. - Independent