Drought increases CO2 concentration in the air

Drought increases CO2 concentration in the air
Land ecosystems are important for the absorption of anthropogenic CO2 emissions. Credit: ETH Zurich

ETH researchers have shown that during drier years, the concentration of carbon dioxide in the atmosphere rises faster because stressed ecosystems absorb less carbon. This global effect is so strong that it must be integrated in the next generation of climate models.

Land ecosystems absorb on average 30 percent of anthropogenic CO2 emissions, thereby tempering the increase of CO2 concentration in the atmosphere. But plants need water to grow. When a drought occurs and soils dry out, plants reduce photosynthesis and respiration in order to conserve water and preserve tissues. As a consequence, they are no longer able to capture from the surrounding air. While this effect can be easily observed in the lab, measuring its impact on the whole planet has proved quite difficult. One of the greatest challenges has been to measure where and how often droughts occur globally. In a new study, Vincent Humphrey, climate researcher in the lab of Sonia Seneviratne, Professor for Land-Climate Dynamics at ETH Zurich, used innovative satellite technology to measure the global sensitivity of ecosystems to water stress. The study was carried out in collaboration with the Laboratoire des Sciences du Climat et de l'Environnement (France) and the University of Exeter (United Kingdom).

Using satellites to measure droughts

Plants are usually able to access water deep in the soil through their roots. However, conventional satellites only see what happens at the surface and cannot measure how much water is available underground. In the last few years, a new type of satellite mission has been used to measure extremely small changes in the Earth's . It was found that some small perturbations of the gravity field are caused by changes in . When there is a major drought in a given region, there is less water mass and gravity is consequently slightly weaker over that region. Such variations are so small that they are imperceptible to humans. But by measuring them with satellites, scientists are able to estimate large-scale changes in water storage to an accuracy of about four centimetres everywhere on the planet.

Using these new satellite observations of storage, Vincent Humphrey and his colleagues were able to measure the overall impact of droughts on photosynthesis and ecosystem respiration. They compared year-to-year changes in total over all continents against global measurements of CO2 increase in the atmosphere. They found that during the driest years, such as 2015, natural ecosystems removed about 30 percent percent less carbon from the atmosphere than during a normal year. As a result, the concentration of CO2 in the atmosphere increased faster in 2015 compared to normal years. At the other end of the scale, during the wettest year on record in 2011, CO2 concentrations increased at a much slower rate due to healthy vegetation. These results help us understand why atmospheric CO2 growth can vary a lot from one year to the other, even though CO2 emissions from human activities are comparatively stable.

Drought increases CO2 concentration in the air
The map shows anomalies in water storage estimated from perturbations of the Earth's gravity field. The year 2015 was particularly dry on average, with intense droughts over South America, South Africa and Eastern Europe. Credit: Visualizations: ETH Zurich/Vincent Humphrey; data: NASA-GSFC

Crucial for monitoring emissions

During the last century, the concentration of CO2 in the atmosphere has been steadily increasing because of human activities. "Now that most countries around the world have agreed they should limit CO2 emissions, we are facing the challenge of monitoring human CO2 emissions to a level of accuracy higher than ever before," says Vincent Humphrey. In order to precisely evaluate the impact of climate policies, researchers must first develop vegetation models that can quantify and predict the perturbations introduced each year by . "Thanks to our new results, we can now prove that the effects of droughts are stronger than has so far been estimated by vegetation models," says Sonia Seneviratne. Ultimately, these observations will be integrated into the next generation of models. They should improve the ability to track CO2 emissions and verify that they meet the targets set in international climate agreements.


Explore further

How plants use carbon affects their response to climate change

More information: Vincent Humphrey et al, Sensitivity of atmospheric CO2 growth rate to observed changes in terrestrial water storage, Nature (2018). DOI: 10.1038/s41586-018-0424-4
Journal information: Nature

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Aug 30, 2018
So what? I can't believe the funding these climate change researchers get for stuff like this.

Aug 30, 2018
So what? I can't believe the funding these climate change researchers get for stuff like this.

really? You know how much they get paid for such important research to find out what's going on? No, you don't.
It would make more sense if you complained about the big profits greedy oil companies make, that would dwarf the scientist's wages, at our expense.

Aug 30, 2018
They get paid, these articles are a joke. We ask oil companies to produce all that fuel, you nit wit.

Aug 30, 2018
Lions Tigers and Bears! Oh my!

Aug 30, 2018
A joke?

I am the one laughing, . at you who keep on buying their pollution-puffing stuff. I get my house and horsepower from the sun now.

Aug 30, 2018
Science and grandpa and copy/paste, Oh my!

Aug 31, 2018
CO2 has nothing to do with temperature, the data is clear. It may have effects on other things, like increased vegetation leading to increased oxygen levels. Doesn't sound catastrophic to me. But I guess it's stupid to infer increased vegetation with increased CO2, because it doesn't fit your childish few of knowing-it-all.

Sep 02, 2018
We have no idea what a 30% increase in CO2 will do, beyond more vegetation.Thankfully, temperature didn't follow the rise of CO2, like the Gore movie proposed with no snow by 2015.

Sep 02, 2018
google... "Due to the rise in CO2 ... Earth's plants and trees have sprouted enough new leaves since the early 1980s to cover twice the area of mainland United States, according to new research."

Sep 02, 2018
Lions Tigers and Bears! Oh my!


This gets more profound every time I read it. It really tackles the complexity of the climate system and the current warming dataset.

CO2 has nothing to do with temperature, the data is clear.


Dear Lord. I mean, be a denier all you want. But if you come on here and deny basic physics you look like a dimwit. CO2 has an impact on the temperature - that's the basis of the greenhouse effect that makes life on Earth possible. If greenhouses gases didn't result in warming, we would not exist. This is like saying "gravity has nothing to do with the Earth's orbit, the data is clear" and getting annoyed when you get laughed at.

Increasing CO2 MUST result in an increase in temperatures. It's not physically possible for it not to. This is BASIC physics.

Sep 03, 2018

Increasing CO2 MUST result in an increase in temperatures. It's not physically possible for it not to. This is BASIC physics....HAWW...HEE....HAWW...HEEE

The Chicken Little Jackass brays yet again.
This jackass brays about knowing the physics of CO2, yet he boasts about all the, wasteful, CO2 spewing jaunts he goes on.
Keep braying at the heretics Jackass, you'll save the world.

Sep 03, 2018
Increasing CO2 MUST result in an increase in temperatures. It's not physically possible for it not to. This is BASIC physics.

And the basics aren't even particularly difficult physics.

Sep 03, 2018
Increasing CO2 MUST result in an increase in temperatures. It's not physically possible for it not to. This is BASIC physics.

And the basics aren't even particularly difficult physics.


Even I can grasp this and if I can these idiots can too

Sep 04, 2018
"Increasing CO2 MUST result in an increase in temperatures"

30% CO2 rise has hardly moved temperature, you dope.

Sep 04, 2018
The history of CO2 and temperature going back hundreds of millions of years show no correlation
what so ever.

You just read BS articles and call others idiots, you moron.

Sep 04, 2018
Looking a graphs the past 400,000 years; the CO2 levels are a function of temperature, not the other way around.

Our weird 30% rise in CO2 the past 50 years still has unknown consequences, but temperature rise is hardly one of them. If temp rose appreciably, we would be in big trouble, but it didn't.

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