May 28, 2019

expert reaction to study looking at trends in ocean carbon sinks

Research published in PNAS found that the ocean carbon sink may be responsible for approximately 10-40% of the observed decadal variability of CO₂ buildup in the atmosphere over the last 20 years. 

Dr Phillip Williamson, Honorary Reader, University of East Anglia (UEA), said:

“Only around half of the carbon dioxide that we are adding to the atmosphere stays there, the rest is taken up by the ocean and by plants on land.  Since less CO2 dissolves in warmer water, ‘simple chemistry’ suggests that ocean uptake should be declining.  DeVries and colleagues found that other processes are also involved: between 2000-2010, measurements showed an unexpected increase in the rate of carbon removal by the ocean, following a decrease in the period 1990-2000.  The new study provides evidence that the recent increase was caused by changes in ocean circulation and biology; however, such effects are not yet well-represented in climate models.  Whilst future climate behaviour may therefore be more dynamic than indicated by current models, there is scope for model improvement – since we now have a better understanding of the interacting factors that are responsible for decadal-scale variability in the carbon cycle.”

Prof John Shepherd, Emeritus Professor in Earth System Science, University of Southampton, said:

“Not all of the CO2 that is emitted stays in the atmosphere, and the rate at which it accumulates depends on the magnitude of the natural carbon sinks, as well as on the level of CO2 emissions.  This work confirms that the size of both the land and ocean sinks varies somewhat from decade to decade.  This is not surprising, but understanding these variations is important in improving the ability of climate models to track and predict short term decadal ‘wiggles’ in climate change as well as the long-term trend.  The international team of researchers involved show that the variations of the natural sinks observed are rather larger than those of the models – so oceans could potentially absorb more, or less, carbon than some models had suggested.  This supports earlier suggestions that our current models are still a bit less responsive than the real world, and may not yet capture all of the climate change to be expected in the future.”

‘Decadal trends in the ocean carbon sink’ by Tim DeVries et al. was published in PNAS at 20:00 UK time on Monday 27 May 2019.

Declared interests

Dr Phillip Williamson: “Dr Phil Williamson is an Honorary Reader at the University of East Anglia, funded by UKRI/NERC.  He was not involved in the preparation of the PNAS paper.”

None others received.