The key to understanding how and how the ability of the oceans to absorb CO2 will vary is alkalinity. A study published in Geophysical Research Letters models future changes in the most unfavourable emissive scenario
In 2300 carbon absorption in the oceans will be half of today
(sustainabilityenvironment.com) – The oceans cover 70% of the Earth’s surface and play a crucial role in absorbing CO2 from the atmosphere, storing it for hundreds of years. But this ability varies as the planet’s climate system changes. And in a warmer climate, the ability to absorb and retain carbon in the oceans is likely to decrease.
Not just that. The amount of CO2 that the world’s oceans can absorb could peak in 2100, and then begin a steady decline as the global temperature rises. In 2300, the masses of salt water on the Planet would be able to store carbon in the oceans at half the rate today. Although this situation is compatible only with the worst-case scenario of global warming among those identified by the IPCC, with the global thermometer surpassing the quota +4°C by the end of the century.
Alkalinity and tipping point for carbon in the oceans
This is supported by a study published in Geophysical Research Letters that uses predictive models to estimate the behavior of the oceans and their future role as carbon sinks. And it identifies alkalinity as the most important factor to consider. The decline, in fact, would happen because of the appearance of a surface layer of water with low alkalinity that hinders the ability of the oceans to absorb CO2.
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The process described in the study is triggered by extreme climate change, which increases rainfall and slows down ocean currents. The surface of the oceans is thus covered by a warm layer of fresh water that does not mix easily with the cooler, alkaline waters below. Saturating with CO2 over time, this surface layer has a lower alkalinity and therefore a lower capacity to absorb CO2.
An important element, is the attention to alkalinity, because, according to the simulations conducted by the researchers, it is thanks to the alkalinity that you can find a tipping point for the oceans as efficient carbon wells, that is a point exceeded which the dynamics is jammed and the decline happens to accelerated and irreversible in human times.
“Whether it is this or the collapse of the ice sheets, in our future there is potentially a series of connected crises that we must avoid at all costs”, comments Pedro DiNezio, co-author of the study. Today the oceans absorb about 30% of the carbon dioxide released every year into the atmosphere by natural and anthropogenic causes.
