Sunday, 11 November 2018

Resultant climate change will be faster than anything the Earth has seen for millions of years

Source: "CO2 levels heading back to days of dinosaurs", Climate News Network, 8th April 2017, by Tim Radford

Tim Radford reported, "(...) By the 23rd century, planetary temperatures would be as high as those at the end of the Silurian, 420 million years ago. In this baking environment, plants had yet to begin to colonise the land, and almost all life was concentrated in the oceans. (...) “However, because the Sun was dimmer back then, the net climate forcing 200 million years ago was lower than we would experience in such a high CO2 future,” Professor Foster says. “So not only will the resultant climate change be faster than anything the Earth has seen for millions of years, the climate that will exist is likely to have no natural counterpart, as far as we can tell, in at least the last 420 million years.” 

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Future climate forcing potentially without precedent in the last 420 million years

Source: Nature Communications, 4th April 2017; Article number: 14845 (2017)


a) Gavin L. Foster, b) Dana L. Royer, c) Daniel J. Lunt

a) Ocean and Earth Science, National Oceanography Centre Southampton, University of Southampton, Southampton SO14 3ZH, UK
b) Department of Earth and Environmental Sciences, Wesleyan University, Middletown, Connecticut 06459, USA
c) School of Geographical Sciences and Cabot Institute, University of Bristol, University Road, Bristol BS8 1SS, UK


The evolution of Earth’s climate on geological timescales is largely driven by variations in the magnitude of total solar irradiance (TSI) and changes in the greenhouse gas content of the atmosphere. Here we show that the slow ∼50 Wm−2 increase in TSI over the last ∼420 million years (an increase of ∼9 Wm−2 of radiative forcing) was almost completely negated by a long-term decline in atmospheric CO2. This was likely due to the silicate weathering-negative feedback and the expansion of land plants that together ensured Earth’s long-term habitability. Humanity’s fossil-fuel use, if unabated, risks taking us, by the middle of the twenty-first century, to values of CO2 not seen since the early Eocene (50 million years ago). If CO2 continues to rise further into the twenty-third century, then the associated large increase in radiative forcing, and how the Earth system would respond, would likely be without geological precedent in the last half a billion years.

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