Earth’s oceans help to slow global warming by absorbing carbon from our atmosphere – but fully observing this crucial process in the upper ocean and lower atmosphere is difficult, as measurements are taken not where it occurs, the sea surface, but several meters below. New research uses data from ESA, NASA, and NOAA satellites to rectify this, and finds that far more carbon is absorbed by the oceans than previously thought.
Much of the carbon dioxide emitted by human activity does not stay in the atmosphere but is taken up by oceans and land vegetation – so-called “carbon sinks.”
There are ongoing efforts to collect and compile in situ measurements of the ocean sink in the form of the Surface Ocean CO2 Atlas, or SOCAT, which contains over 28 million international observations of our oceans and coastal seas from 1957 to 2020. By delving into SOCAT’s vast database, scientists can identify how much carbon is being sucked out of the atmosphere and stored by our seas.
“However, there’s a catch: the measurements are not made right at the ocean surface where they are needed, but from a few meters down,” explains Andrew Watson of the University of Exeter, UK, lead author of the new study. Although the difference may be mere meters, the sea surface temperature changes with depth – and so, too, does its associated ability to absorb carbon from the atmosphere.
“Previous studies have ignored the small temperature differences between the surface of the ocean and the sampling depth, but we know that this has a significant impact on how carbon is held by the oceans in terms of salinity, solubility, stability, and so on,” adds Andrew. “But satellites can measure the temperature more or less exactly at the ocean surface – and when we do this, we find it makes a big difference.”
By applying satellite corrections to SOCAT data from 1992 to 2018 to account for temperature differences between the surface and at a few meters’ depth, the researchers find a substantially higher ocean uptake of carbon dioxide than previously thought. They were able to do this thanks to data from a suite of satellites such as ESA’s Envisat, NOAA’s AVHRR, EUMETSAT’s MetOp series, and the Copernicus Sentinel-3 mission, firstly as part of the OceanFlux research project (part of ESA’s Science for Society program) and then continued within two EU-funded projects.
The corrected figures reveal that the net flux of carbon into the oceans is underestimated by up to 0.9 Gigatonnes of carbon per year – a significant amount that, at times, doubles uncorrected values.
“These results are consistent with independent estimates of the size of the oceanic carbon sink – those based on global ocean surveys by research ships,” adds co-author Jamie Shutler, also of the University of Exeter. “Now that these two separate estimates of the size of the carbon dioxide ocean sink agree pretty well, we can view and use their results with greater confidence, and trust that they are most likely giving us an accurate picture of what is going on.”
Andrew and Jamie were both part of a Europe-wide research team – including researchers from Heriot-Watt University and UHI, Scotland – that previously used SOCAT data to estimate how carbon flows into and out of our oceans with unprecedented accuracy. They found that, in 2010 alone, three Gigatonnes of carbon were drawn into the ocean: about a third of the emissions caused by human activity. This finding contrasted with previous estimates of a quarter, leading Andrew, Jamie, and colleagues to conclude – as in this study – that the oceans’ role in capturing atmospheric carbon is being underestimated.
While this may bring positive benefits in terms of reducing atmospheric warming due to climate change, as more carbon dioxide is being removed from the air, the oceans are impacted by the carbon they absorb. They become more acidic, which threatens the health of marine ecosystems and makes it increasingly difficult for ocean life to survive.
“The importance of our oceans in both regulating climate and supporting biodiversity cannot be overstated,” adds ESA’s Craig Donlon. “Across all of ESA’s Earth observation activities, our aim is to fully account for the role of our oceans in terms of the carbon cycle. This key result, together with others built on the dedication and excellent collaboration of the ESA OceanFlux team, gives us a solid basis for that, and will help us to more accurately characterize and better understand our planet’s changing climate.”
The paper, published in Nature Communications, is entitled: “Revised estimates of ocean-atmosphere CO2 flux are consistent with ocean carbon inventory.”
For more on this climate science news story, read Oops! The World’s Oceans Soak Up Far More Carbon Than Most Scientific Models Suggest.
Reference: “Revised estimates of ocean-atmosphere CO2 flux are consistent with ocean carbon inventory” by Andrew J. Watson, Ute Schuster, Jamie D. Shutler, Thomas Holding, Ian G. C. Ashton, Peter Landschützer, David K. Woolf and Lonneke Goddijn-Murphy, 4 September 2020, Nature Communications.
DOI: 10.1038/s41467-020-18203-3
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8 Comments
nods head saying very good. carry on then.
The higher amount of CO2 consumed does not change the way high number of 410 ppm of CO2 in Earth’s atmosphere today. Years ago it was determined that 350 ppm was a safe number. We have shot way past this.
This fact is more salient when it comes to climate change, and much more frightening when it comes to the acidification of our oceans.
What do you mean by a “safe” number? It has been very much higher in the past and it didn’t stop evolution nor even kill things like sharks, horseshoe crabs, or lingula. Mass extinctions have happened, which some researchers have attempted to assign to high levels of CO2, but they lack convincing arguments because of the species that didn’t become extinct!
“Acidification” is a bogeyman that has no basis other than to convince science illiterates that something terrible is happening to the oceans. It is estimated that the pelagic zone surface has seen a pH decrease from 8.2 to 8.1 in the last century, based on a questionable model for the 8.2 value. The oceans are alkaline, probably always have been (even with much higher CO2 in the atmosphere), and almost certainly always will be, because they are strongly buffered. I’m reminded of the oft heard phrase, “Polly wants a cracker!”
Seems like significantly increased levels of CO2 in the ocean would decrease the freezing point and diminish the ice shelf in the polar regions. Diminished ice shelf would reduce the amount of solar energy reflected and cause an overall increase in energy absorbed. In which case the imminent need is to either artificially deflect more solar energy or offset by collecting that energy and transfer it to another form than thermal.
Interesting article.
Have you ever put a can of soda in the freezer to cool it quickly, and then forgotten about it? It WILL freeze, and at a temperature not much different from pure water. The salt in solution in sea water has a much greater effect!
Cue the environuts trying to distort this good news into bad news so they can keep clinging to their climate change religion.
An article that generates confusing comments to all people of science. The only ones who aren’t confused are politicians whose opinions are determined by the party they serve.
But this goes against everything I was taught to believe without question. This must be propaganda and it must be silenced immediately! Please learn to think for yourself and ask questions… lots of questions! Great article