Publications by James E. Hansen pubs.giss.nasa.gov, his latest book is: Storms of My Grandchildren: The Truth About the Coming Climate Catastrophe and Our Last Chance to Save Humanity. Amazon.com
Runaway climate change
Runaway climate change describes a scenario in which the climate system passes a threshold or tipping point, after which internal positive feedback effects cause the climate to continue changing, even absent further external forcings. The runaway climate change continues until it is overpowered by negative feedback effects which cause the climate system to restabilise at a new state. The phrase “runaway climate change” is used to describe a theory in which positive feedbacks result in rapid climate change. Some astronomers use the similar expression runaway greenhouse effect to describe a situation where the climate deviates catastrophically and permanently from the original state – as happened on Venus.
Clathrate gun hypothesis
Clathrate gun hypothesis is the popular name given to the hypothesis that rises in sea temperatures (and/or falls in sea level) can trigger the sudden release of methane from methane clathrate compounds buried in seabeds and permafrost which, because the methane itself is a powerful greenhouse gas, leads to further temperature rise and further methane clathrate destabilization – in effect initiating a runaway process (positive feedback loop) as irreversible, once started, as the firing of a gun.
In its original form, the hypothesis proposed that the “clathrate gun” could cause abrupt runaway warming in a timescale less than a human lifetime, and might be responsible for warming events in and at the end of the last ice age. This is now thought unlikely.
However, there is stronger evidence that runaway methane clathrate breakdown may have caused drastic alteration of the ocean environment and the atmosphere of earth on a number of occasions in the past, over timescales of tens of thousands of years; most notably in connection with the Permian extinction event, when 96% of all marine species became extinct 251 million years ago.