Home / Science / The oceans absorbed extra CO₂ in the 2000s

The oceans absorbed extra CO₂ in the 2000s

Plankton swirls in the Gulf of Aden between Yemen and Somalia.
Enlarge / Plankton swirls in the Gulf of Aden between Yemen and Somalia.

The monitoring of climate change means (among other things) the monitoring of annual changes in global emissions of greenhouse gases and the corresponding increases in atmospheric CO.two concentration. However, this can be confusing because there is no perfect correlation from one year to the other between the two.

Our COtwo Emissions are released into the atmosphere, but the atmosphere interacts with other parts of the Earth's carbon cycle, which attract some COtwo outside. In the short term, the two most important sinks are oceans and terrestrial ecosystems. COtwo dissolves in seawater to maintain a balance with the air, and photosynthetic organisms on land and in the oceans take COtwo. Changing ocean currents or climate on the earth that affects the growth of plants will alter the amount of COtwo being taken out of the atmosphere.

In general, it is thought that terrestrial ecosystems were the dominant source of this variability. But a team of researchers led by Tim DeVries at the University of California, Santa Barbara and Corinne Le Quéré at the University of East Anglia decided to investigate the role played by the oceans.

A confused image

Changes in terrestrial and oceanic sinks lead to a large variability in the amount of COtwo increases every year. Although the emissions caused by humans have increased quite well, a year can see that the concentration increases 2.5 parts per million, while the next increases 1.7 parts per million.

This is especially challenging because the two key numbers can be used to verify each other. Estimating each country's emissions each year can be complicated, so atmospheric concentration is, in some ways, the ultimate "pudding test" that we have these correct estimates. But just observing the change in concentration can not tell you exactly what emissions occurred that year.

<img alt = "The annual increase in atmospheric COtwo It varies a little over time. It has also been gradually increasing as global emissions increased. "Src =" https://cdn.arstechnica.net/wp-content/uploads/2019/05/co2_data_mlo_anngr-640×474.png "width =" 640 "height =" 474 "srcset =" https: //cdn.arstechnica .net / wp-content / uploads / 2019/05 / co2_data_mlo_anngr.png 2x”/>
Enlarge / The annual increase in atmospheric CO.two It varies a little over time. It has also been increasing gradually as global emissions increased.

Each year, a group of researchers publishes updated estimates of the activity of all the different parts of the carbon cycle, making calculations that help show how CO caused by humanstwo The emissions fit into the big picture. That task is based on measurements and estimates of national emissions accounting, but is also based on model simulations of oceans and ecosystems on earth. These help show how the year's weather and ocean circulation patterns should be affecting their adoption of COtwo.

Of course, no model is a perfect representation of reality, so it's worth reviewing those numbers.

In this study, the researchers compared the models with two other methods to track the carbon cycle of the earth and the ocean. One takes measurements of carbon in the ocean, as well as things like CFCs that cause ozone depletion, and uses an independent model to determine the amount of these gases that must be moved to the ocean over time in a way that matches with all the data. . Another method uses the available CO measurestwo in the air, just above the surface of the sea, and in the water, just below it, to find out how much the ocean is taking.

A comparison of models

Some interesting things come up when you compare the results of each of these methods in the last three decades. The general trends align pretty well. However, the variation from one decade to the next is less in the models that are normally used for the annual updates of the carbon cycle. The other two approaches show larger changes in the amount of COtwo Enter the ocean during the 90s and 2000s.

The terrestrial ecosystems had oscillations in the same directions, but the oceans contributed a greater influence than we had generally noticed, which means that a little less came from the earth.

<img alt = "From COtwo humans emit by burning fossil fuels or clearing forests, some enter the oceans and terrestrial ecosystems (blue line) while the rest remain in the atmosphere (yellow line). "src =" https://cdn.arstechnica.net/ wp- content / uploads / 2019/05 / carbon_sink_ocean_decadal_trends-2-640×447.png "width =" 640 "height =" 447 "srcset =" https://cdn.arstechnica.net/wp-content/uploads/2019/05 / carbon_sink_ocean_decadaltrad -2.png 2x”/>
Enlarge / From the COtwo Humans emit by burning fossil fuels or clearing forests, some enter the oceans and terrestrial ecosystems (blue line) while the rest remain in the atmosphere (yellow line).

In the 1990s, a couple of interesting things happened. The great eruption of Mount Pinatubo in 1991 affected the climate of the whole world for a couple of years and, therefore, the earth and the ocean absorbed a bit of extra CO.two during that time But in the 1990s El Niño conditions were also observed in the Pacific (including an incredibly strong El Niño in 1998), which reduced the amount of carbon flowing to the oceans and terrestrial ecosystems.

The different methods showed that the oceans were responsible for about 10 percent of that variation, and that most of them came from changes in the earth.

In the 2000s, on the other hand, carbon sequestration in the atmosphere increased in years dominated by La Niña conditions in the Pacific. And here, the methods put the contribution of the ocean at around 40 percent.

In both cases, the models used for the annual updates had the role of the ocean in half of that (or less). Annual studies approach the balance of books, but there is always a slight mismatch between the totals of each part of the carbon cycle and the change measured in the atmosphere. If the models for the capture of oceanic and terrestrial ecosystems are not sufficiently varied, they are probably contributing to this imbalance.

For now, this study can help the curious climate make sense of atmospheric CO.two numbers. But beyond that, a better scientific understanding of how the carbon cycle responds to climate variability can help improve all kinds of model projections in the future. Certainly, more than certain measures that are made around the world would make it easier.

PNAS, 2019. DOI: 10.1073 / pnas.1900371116 (About DOI).

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