Study finds climate sensitivity to carbon forcing has been underestimated – ‘Significantly larger values are attained during warm phases’Posted by Jim at Wednesday, November 16, 2016
By Ian Johnston
11 November 2016
(Independent) – It is a vision of a future so apocalyptic that it is hard to even imagine.
But, if leading scientists writing in one of the most respected academic journals are right, planet Earth could be on course for global warming of more than seven degrees Celsius within a lifetime.
And that, according to one of the world’s most renowned climatologists, could be “game over” – particularly given the imminent presence of climate change denier Donald Trump in the White House. […]
New research by an international team of experts who looked into how the Earth’s climate has reacted over nearly 800,000 years warns this could be a major under-estimate.
Because, they believe, the climate is more sensitive to greenhouse gases when it is warmer.
In a paper in the journal Science Advances, they said the actual range could be between 4.78C to 7.36C by 2100, based on one set of calculations.
Some have dismissed the idea that the world would continue to burn fossil fuels despite obvious global warming, but emissions are still increasing despite a 1C rise in average thermometer readings since the 1880s. [more]
ABSTRACT: Global mean surface temperatures are rising in response to anthropogenic greenhouse gas emissions. The magnitude of this warming at equilibrium for a given radiative forcing—referred to as specific equilibrium climate sensitivity (S)—is still subject to uncertainties. We estimate global mean temperature variations and S using a 784,000-year-long field reconstruction of sea surface temperatures and a transient paleoclimate model simulation. Our results reveal that S is strongly dependent on the climate background state, with significantly larger values attained during warm phases. Using the Representative Concentration Pathway 8.5 for future greenhouse radiative forcing, we find that the range of paleo-based estimates of Earth’s future warming by 2100 CE overlaps with the upper range of climate simulations conducted as part of the Coupled Model Intercomparison Project Phase 5 (CMIP5). Furthermore, we find that within the 21st century, global mean temperatures will very likely exceed maximum levels reconstructed for the last 784,000 years. On the basis of temperature data from eight glacial cycles, our results provide an independent validation of the magnitude of current CMIP5 warming projections.