The growth in the amount of CO2 in the Earth’s atmosphere has been slowed by the increased ability of plants to soak up the gas. A new study says vegetation has helped offset a large fraction of human related carbon emissions between 2002 and 2014. Plants have become more absorbent, because of extra CO2 in the atmosphere.
The slowdown, though, can’t keep pace with the overall scale of emissions. Over the past 50 years, the amount of CO2 absorbed by the Earth’s oceans, plants and vegetation has doubled and these carbon sinks now account for about 45% of the gas emitted each year because of human activities.
Researchers now report that since the start of the 21st century there has been a significant change in the amount of carbon dioxide taken up by the plants and trees. The new analysis suggests that between 2002 and 2014 the amount of human caused CO2 remaining in the atmosphere declined by around 20%.
Reports earlier this year indicated that there has been an increase in the number of trees and plants growing on the Earth, the so-called greening of the planet. But the authors of this new study believe that this isn’t the main cause of the slowdown in the rise of CO2.
"There have been reports of the greening of the land surface but what we found was that was of secondary importance to the direct effect of CO2 fertilisation on the plants that are already there," lead author Dr Trevor Keenan told BBC News.
"We have a huge amount of vegetation on the Earth and that was being fertilised by CO2 and taking in more CO2 as a result."
Another important element in the story is the impact of a hiatus in global temperature increases on the behaviour of plants. Between 1998 and 2012 temperatures went up by less than in previous decades. This has impacted the respiration of vegetation.
"The soils and ecosystem are respiring so as temperatures increase they respire more, releasing more CO2 into the atmosphere," said Dr Keenan.
"In the past decade or so there hasn’t been much of an increase in global temperatures, so that meant there wasn’t much of an increase in respiration and carbon release so that was fundamentally different in the past decade or so compared to previous periods."