The Earth’s thermostat – response to large cooling events
The Earth needs an active control on climate to keep it from going runaway icehouse, and to keep the planet habitable long-term.
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Despite significant climate change over time, and associated mass extinctions, the climate has never changed so dramatically to cause all life to go extinct. This requires active operating processes mitigating and stabilising the climate. The most common theory is that there is a “thermostat” operating via a temperature control on weathering, which in turn removes atmospheric CO2. However, despite being generally assumed to function to some degree (and used in long-term climate models), until now there has been no evidence of the thermostat actually operating in the geological past.
We analysed lithium isotope ratios, which inform on weathering, through a major climate cooling period and glaciation xxx million years ago. Known as the Hirnantian, at the end of the Ordovician, it represents the second largest mass extinction in Earth history, due to the big change in climate.
We found that lithium isotope ratios increase during this cooling event, implying decreasing weathering, and hence decreased CO2 drawdown. This is exactly what would be expected if the thermostat operated to stabilise climate: decreased temperatures resulting in decreased CO2 removal, allowing the greenhouse gas to build up in the atmosphere again, and warm the climate back to its original state.
Combined with our discovered weathering response during warming events, this study provides the final bit of proof of the existence and operation of the weathering thermostat that controls and mitigates long-term climate.
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Universities: UCL, Birkbeck
Principal Researcher: Philip Pogge von Strandmann
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