Environment

Plants to thank for recent plateau in rise of atmospheric CO2

A new study has found that in response to increasing rates of human-induced CO2 in the atmosphere, the Earth's vegetation has increased the rate at which it absorbs carbon
A new study has found that in response to increasing rates of human-induced CO2 in the atmosphere, the Earth's vegetation has increased the rate at which it absorbs carbon
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This graph shows the steady CO2 growth rate over the second half of the 20th century, and an unexpected plateau from 2002 onwards
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This graph shows the steady CO2 growth rate over the second half of the 20th century, and an unexpected plateau from 2002 onwards
A new study has found that in response to increasing rates of human-induced CO2 in the atmosphere, the Earth's vegetation has increased the rate at which it absorbs carbon
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A new study has found that in response to increasing rates of human-induced CO2 in the atmosphere, the Earth's vegetation has increased the rate at which it absorbs carbon

We might have to treat our humble house plants to an extra helping of sunlight this week. As human-induced CO2 emissions continue to increase, a new study suggests that the Earth's vegetation has upped its game to help offset that growth. After a 40-year upward trend, the rate at which atmospheric CO2 levels increased hit a plateau between 2002 and 2014, thanks largely to plants plucking more CO2 out of the air than they have previously.

In 1959, the rate of growth of carbon dioxide levels in the atmosphere sat at about 0.75 parts per million (ppm) per year, and over the second half of the 20th century, that figure increased rapidly, up to 1.86 ppm per year in 2002. But in the years since then, the rate of growth has flatlined, despite the fact that human activity continues to pump out more and more CO2. That's not to say the amount of CO2 in the atmosphere isn't still going up – it is – but the rate of increase has slowed, remaining steady on about 1.9 ppm each year since 2002.

Not only that, but the amount of anthropogenic CO2 that stays in the air has dropped by around 20 percent. So where is it all going? New research, headed up by the Department of Energy's Lawrence Berkeley National Laboratory, analyzed data from the Global Carbon Project and ran computer models to determine what changes may be occurring in Earth's carbon cycle.

This graph shows the steady CO2 growth rate over the second half of the 20th century, and an unexpected plateau from 2002 onwards
This graph shows the steady CO2 growth rate over the second half of the 20th century, and an unexpected plateau from 2002 onwards

"We believed one of the planet's main carbon sinks had unexpectedly strengthened," says Trevor Keenan, a corresponding author of the paper. "The question was: which one?"

Oceans are considered a carbon sink, but computer models indicate their rate of absorption remains fairly stable. Instead, the team looked to vegetation, which can fluctuate year-to-year in terms of carbon uptake, and tested 10 "global dynamic vegetation models," which simulate different combinations of atmospheric CO2 levels, temperature, soil moisture, and other factors, to see how that carbon cycle might change over time.

From those models, it appears that over the decades these ecosystems have effectively doubled the rate of CO2 they absorb. In the 1950s, the Earth's vegetation absorbed between 1 and 2 petagrams (1 trillion to 2 trillion kg, or 2.2 to 4.4 trillion lb) of CO2 each year, but in the 21st century that number had risen to between 2 and 4 petagrams annually.

Interestingly, the models suggest that the increase in CO2 levels is itself responsible for the improved absorption performance of the planet's plants. With more CO2 in the air, the plants are better able to photosynthesize, meaning they grow better and further increase their rate of photosynthesis. That boom was helped along by the fact that plant respiration, a process which sees them take in oxygen and "exhale" CO2, didn't increase at the same rate.

"These changes decreased the amount of anthropogenic CO2 that stays in the atmosphere, and thus slowed the accumulation of atmospheric CO2," says Keenan. "This highlights the need to identify and protect ecosystems where the carbon sink is growing rapidly."

But as encouraging as these figures may appear, the news isn't quite as rosy as it may seem at a glance.

"Unfortunately, this increase is nowhere near enough to stop climate change," says Keenan. "We've shown the increase in terrestrial carbon uptake is happening, and with a plausible explanation why. But we don't know exactly where the carbon sink is increasing the most, how long this increase will last, or what it means for the future of Earth's climate."

The research was published in the journal Nature Communications.

Source: Berkeley Lab

16 comments
Jeff J Carlson
Your headline makes it seem like a fact when in fact this is a unproven theory ... none of this was based on observations but on running models ... all of which ignore the oceans ...
StevenR01
It sounds like the increase has stopped but that is not the case. The rate of INCREASE has not INCREASED. It is still increasing at an insane rate but that rate is not increasing. Not really a good thing.
Grainpaw
It couldn't hurt to do major reforestation projects, along with the other efforts to curb CO2.
Pablo
This was predicted years ago but got lost in the noise... Plants respond to changes in the environment like any other organisms would. Insufficient food, water or shelter, or contamination due to overpopulation negatively impact any living organism from amoeba right up to us. An increase in food supply, for instance, will support a population growth pattern until one of the above requirements is used up. Plants need CO2, water and sunlight, as long as sufficient supplies of the latter are available, an increase in CO2 will cause plant life to flourish, thereby absorbing it.
Ken Brody
The ultimate reliance on unverified computer models is a symptom of a dying pseudoscience. Real science is based on observation and measurement, both of which contradict the models. CO2 reached thermal saturation a decade ago. The effect of particulates, water vapor, cloud formation and the solar wind are ignored or incomplete in those models. All we seem to get is dire warnings that need more tax money.
Douglas Bennett Rogers
See "Land Use and Climate Change", Physics Today, Nov. This shows the very large role of arid lands agriculture.
habakak
And all of this while apparently we are destroying natural habitats and forest the world over!!! So. There are LESS natural forests and plants. And they absorb MORE CO2!! But models are always wrong because they never capture all the inputs.
Rann Xeroxx
The science of AGW will go down in history as the political agenda that set the trust in scientific method back for decades. All these stores about ice sheets, ocean rise, etc delegitimize the science behind it as they commented to be caused by AGW. There simply is no actual scientific proof that human released CO2 is the driving force behind modern climate. CO2 is a GH gas, it simply is not a very strong one and what humans have added is a percent of a percent of the air. Water vapor it the over all driver in that it is the most abundant and most dynamic. In fact a lot of climate models require a strong positive feedback with water vapor and CO2 and that feedback simply does not occur. The Sun has more to do with water vapor and its indirect with decreasing solar wind allowing more cosmic rays in that cause cloud formation. My point being is that I can see this study with CO2 absorption being correct. But this study is not about AGW, why mention it, let the study stand on its own.
PeterOsborne
This effect has been known since the 1850's, but the world wide greening has not been noted until this century. Fewer stoma in the leaves, less water lost during photosynthesis, more growth, more yield, faster tree growth up to maturity, over all, more CO2 is a win win proposition with no negative effects noted within geological time.
JohnOh
Human induced CO2 is a farce. IPCC neglect Henry's Law and the biosphere. They have tried to fudge the data, starting with Bolin's "buffer", going on to multiply the well-known CO2 atmospheric lifetime by a factor of 10 or so, then to partition off our emissions from the natural CO2 when needed to get the right isotope figures, and to mix it all up when otherwise needed. http://www.greenworldtrust.org.uk/Science/Scientific/CO2-flux.htm
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