The Southern Ocean has recovered its ability to suck vast amounts of carbon dioxide from the atmosphere, overturning fears the natural “sink” had stalled with dire consequences for future climate change.
Acting like a giant lung, the Southern Ocean carbon sink accounts for about 40 per cent of the ocean uptake of anthropogenic carbon dioxide.
Climate scientists had feared the uptake of carbon dioxide by the Southern Ocean had slowed in what was feared to be a “feedback” response to human activity.
New research published today in the journal Science reveals that rather than stalling, the amount of CO2 being absorbed by the Southern Ocean was on the rise again.
It is thought that changes in weather — particularly wind patterns and temperature in the Pacific and Atlantic oceans — were responsible.
The findings have invigorated debate about how well scientists understand the natural variations in the earth’s climate.
Lead author Nicolas Gruber, from ETH Zurich, said the research did not address directly whether fluctuations in the sink strength were because of natural or human-induced variability.
“The starting hypothesis is that they are a result of natural variations,” Dr Gruber told The Australian.
Benny Peiser from the London-based Global Warming Policy Foundation said it was “not the first time that lengthier observations have led to the demise of a short-term climate scare”.
“The fact that researchers now acknowledge they cannot predict future trends indicates that they don’t fully understand the underlying physics and mechanisms,” Dr Peiser said.
Contributing author Dorothea Bakker, from the University of East Anglia, said the variation in the Southern Ocean carbon sink was larger than expected on the basis of the growth of atmospheric CO2 alone.
“The Southern Ocean behaves like a giant lung — breathing in and absorbing vast amounts of CO2 from the atmosphere, and releasing it later in the year,” Dr Bakker said.
“The seas around Antarctica absorb significantly more CO2 than they release. They basically help to slow down the growth of greenhouse gas in the atmosphere and lessen the rate of climate change.”
CSIRO Southern Ocean expert Steve Rintoul, who was not part of the research team, said the new analysis showed the strength of the Southern Ocean carbon sink varied with time more strongly than expected. “The weakening and strengthening of the Southern Ocean carbon sink reflects changes in ocean temperature and carbon dioxide driven by variations in the winds blowing on the ocean surface,” Dr Rintoul said.
He said the wind changes were caused by human activities such as greenhouse gases emissions and by natural variability. “The results show that overall, the Southern Ocean sink is keeping pace with the increase in atmospheric carbon dioxide. “This is in contrast to some earlier studies based on model experiments and atmospheric data that concluded the Southern Ocean carbon sink was weakening.”
GWPF science spokesman David Whitehouse said the recovery of the Southern Ocean carbon sink “could be yet another explanation for the surface temperature hiatus”.
He said the research was “another alarmist claim removed by science, showing that the ‘settled science’ isn’t settled at all.
“The fact is that the current models do not fit the observations, so there we have a vital part of future climate prediction shown to be not predictable,” Dr Whitehouse said.
“No one knows why the Southern Oceans are doing this, and no one can say what will happen next. It seems the Southern Ocean, along with a little bit of help from the sun, means that future climate projections, especially decadal ones, have become far more uncertain.
“The closer you look at widely held certainties, the more complex and less understood they become — that’s the science of a complicated earth.”
In a press release, University of East Anglia said while the research results may look to be good news for climate change, the effect could be temporary, and trends can’t be predicted reliably.