How Does Drought Impact CO2 Levels?

A new study from researchers at the ETH Zurich university in Switzerland have found that the amount of carbon dioxide (CO2) in our atmosphere increases during periods of excessive dryness caused by drought. This is because plants tend to conserve water and tissue by breathing less when the climate is drier and hotter, meaning that they absorb less carbon from the environment.

Indeed, the results of the study show that water scarcity caused by droughts has such a large impact on the ability of plants to absorb carbon that the phenomenon must be factored in to future projections of climatic behaviour, and indicate that state-of-the-art air quality monitoring networks should not be the sole point of call when it comes to quantifying carbon in the air.

Unsung heroes

According to the research undertaken by the ETH Zurich scientists, around 39.2 gigatons of carbon are pumped into the air from anthropogenic sources every year. Just under half of that amount (17.3 gigatons) remain in the atmosphere, exacerbating climate change, while 8.7 gigatons are absorbed by our seas and oceans. Approximately 11.2 gigatons - around 30% - of those original 39.2 are absorbed by land ecosystems, such as trees and plants.

However, when a drought happens, the soil becomes drier, there is less moisture in the air and plants are forced to conserve water to survive. To do this, they tone down their photosynthesis and breathe in less carbon, meaning there is more of it present in the atmosphere. This, in turn, will contribute to global warming, exacerbating a vicious cycle of extreme temperatures.

A new method of drought monitoring

Because of the fact that plants generally rely on water sources buried deep below the surface of the Earth, it has been historically difficult to monitor how much water they can access. However, a new type of satellite imagery has been developed in recent years to keep track of tiny fluctuations of gravitational pull. It has been discovered that a decreased amount of water stored below ground can have an imperceptible change on the strength of gravity in that region.

By using this satellite data in the new study, which has been published in the scientific journal Nature, the researchers are able to determine water storage amounts to within an accuracy of four centimetres. By mapping these projections against CO2 levels in the same region, the team were able to learn more about exactly how drought can impact carbon in the atmosphere.

A big impact

The results of the study showed that land ecosystems were capable of removing roughly 30% less carbon from the atmosphere in particularly dry years, such as the one experienced in 2015. Contrastingly, the healthy vegetation brought about by excessively wet years (such as 2011, the wettest year on record) contributed to a far slower growth rate of CO2 in the atmosphere.

Looking to the future, it has been projected that droughts are only likely to get hotter going forwards. With this in mind, it is imperative that future climate models incorporate the impact of droughts into their calculations, in order that we can obtain accurate projections of CO2 levels in the future.