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The Daily Mail (June 20, 2007) reports on a research article published in the Philosophical Transactions of the Royal Society A:

"A group of US scientists may have given the clearest warning yet that global warming is presenting an imminent threat to civilisation.

The six experts described the Earth as being in 'imminent peril' and warned that a UN panel on climate change grossly underestimated the scale of sea-level increases this century.

In an article published in the journal the 'Philosophical Transactions of the Royal Society A.', the group led by James Hansen, the director of NASA's Goddard Institute for Space Studies wrote:

'Recent greenhouse gas emissions place the Earth perilously close to dramatic climate change that could run out of control, with great dangers for humans and other creatures.'

The paper predicts that sea levels may rise by several metres by 2100, compared with a forecast from the UN Intergovernmental Panel on Climate Change published in February that predicts sea levels increasing between 18 and 59 centimetres.

The group has called for extensive efforts to reduce CO2 emissions and other greenhouse gases to help keep the climate within the range of the past one million years."

One of the authors of this research article is Liner David Lea.

Here is an excerpt from the article:
"The imminent peril is initiation of dynamical and thermodynamical processes on the West Antarctic and Greenland ice sheets that produce a situation out of humanity's control, such that devastating sea-level rise will inevitably occur. Climate forcing of this century under BAU would dwarf natural forcings of the past million years, indeed it would probably exceed climate forcing of the middle Pliocene, when the planet was not more than 2-3°C warmer and sea level 25+/-10m higher (Dowsett et al. 1994). The climate sensitivities we have inferred from palaeoclimate data ensure that a BAU GHG emission scenario would produce global warming of several degrees Celsius this century, with amplification at high latitudes.

Such warming would assuredly activate the albedo-flip trigger mechanism over large portions of these ice sheets. In combination with warming of the nearby ocean and atmosphere, the increased surface melt would bring into play multiple positive feedbacks leading to eventual nonlinear ice sheet disintegration, as discussed by Hansen (2005). It is difficult to predict time of collapse in such a nonlinear problem, but we find no evidence of millennial lags between forcing and ice sheet response in palaeoclimate data. An ice sheet response time of centuries seems probable, and we cannot rule out large changes on decadal time-scales once wide-scale surface melt is underway. With GHGs continuing to increase, the planetary energy imbalance provides ample energy to melt ice corresponding to several metres of sea level per century (Hansen et al. 2005b)."
You can view the full text of the article here:
Climate change and trace gases