The oceans absorbed more CO₂ in the 2000s

Monitoring climate change means (among other things) tracking annual changes in global greenhouse gas emissions and corresponding increases in atmospheric CO₂ concentration. This can be confusing, however, as there is no perfect year-to-year correlation between the two.

Our CO₂ emissions are released into the atmosphere, but the atmosphere interacts with other parts of the Earth's carbon cycle, which result in a₂ outside. In the short term, the two sinks that matter most are oceans and terrestrial ecosystems. CO₂ dissolves in seawater to maintain a balance with air, and photosynthetic organisms on land and in the oceans absorb CO₂. Ocean currents or weather conditions on the land that affect plant growth will change the amount of CO₂ to be out of the atmosphere.

Terrestrial ecosystems were generally thought to be the main source of this variability. But a team of researchers led by Tim DeVries from the University of California, Santa Barbara and Corinne Le Quéré at the University of East Anglia decided to investigate the role that the oceans play.

A confusing image

Changes in continental and oceanic wells result in significant variability in the amount of CO₂ increases every year. Although emissions from humans have increased relatively steadily, one year can see the concentration increase by 2.5 parts per million, while the following year it increases by 1.7 parts per million. .

This is particularly difficult because both key numbers can be used to control each other. Estimating emissions from each country each year can be tricky. Atmospheric concentration is therefore, in a way, the ultimate proof that the estimates are accurate. But watching the change in focus can not tell you exactly which shows have been recorded this year.

<img alt = "The annual increase in atmospheric CO₂ varies a bit in time. It also gradually increased 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”/>

Each year, a group of researchers publishes updated estimates of the activity of all parts of the carbon cycle, thus doing the math that helps to show how the CO caused by humans₂ the shows are part of the big picture. This task is based on measurements and estimates of the national accounts of emissions, but also on model simulations of the oceans and terrestrial ecosystems. These help to show how the weather and ocean circulation of the year should affect their uptake of CO₂.

Of course, no model is a perfect representation of reality, so it's worth checking out these numbers.

In this study, the researchers compared the models with two other methods of monitoring the terrestrial and oceanic carbon cycle. We take measurements of carbon in the ocean, as well as factors like the depletion of the ozone layer, like CFCs, and we use an independent model to determine the amount of these gases that must enter the ocean over time in order to match all the data. . Another method uses available CO measurements₂ in the air just above the surface of the sea and in the water just below to determine the amount of ocean absorbed.

A model comparison

Some interesting things come up when comparing the results of each of these methods over the last three decades. General trends align fairly well. However, the decade-to-decade change is smaller in the models typically used for annual carbon cycle updates. The other two approaches show greater fluctuations in the amount of CO₂ go to the ocean during the 1990s and 2000s.

Terrestrial ecosystems evolved in the same directions, but the oceans had a greater influence than we had generally perceived, which means that a little less came from the land.

<img alt = "From the CO₂ humans emit by burning fossil fuels or clearing forests, some go into oceanic and terrestrial ecosystems (blue line), the rest remaining 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_decadal_d -2.png 2x”/>

In the 1990s, some interesting events occurred. The major eruption of Mount Pinatubo in 1991 affected the climate of the world for a few years. The land and the ocean have absorbed a little more CO.₂ Meanwhile. But the 1990s also saw mainly El Niño conditions in the Pacific (including an incredibly strong El Niño in 1998), which reduced the amount of carbon that poured into ocean and terrestrial ecosystems.

The different methods have shown that oceans are responsible for about 10% of this variation, the majority of which is due to changes on land.

In the 2000s, by contrast, the carbon uptake of the atmosphere climbed over the years dominated by La Niña conditions in the Pacific. And here, the methods estimate the contribution of the ocean to about 40%.

In both cases, the models used for annual updates had the role of the ocean at half (or less). The annual studies have almost balanced the accounts, but there is still a slight discrepancy between the totals of each part of the carbon cycle and the changes measured in the atmosphere. If the absorption patterns of ocean and terrestrial ecosystems do not vary sufficiently, they probably contribute to this imbalance.

For now, this study can help climatologists understand atmospheric CO₂ Numbers. But beyond that, a better scientific understanding of how the carbon cycle responds to climate variability can help improve all types of model projections in the future. More measurements around the world would certainly make things easier.

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