A new study published in the journal Nature has found that the world’s forests, as well as other habitats that store carbon in plants and soils, are losing their ability to absorb carbon due to increasingly unstable conditions caused by human activities.
According to the experts, the short-term impacts of rising temperatures, deforestation, and farming on a variety of vulnerable landscapes will make it increasingly difficult and less likely for terrestrial carbon stores to recover in the longer term. This phenomenon will reduce the overall carbon storage capacity of the land and thus undermine efforts to curb the rising levels of atmospheric greenhouse gases.
“We found that large regions of the world are vulnerable to sudden and dramatic changes to their landscape, because the ability of their ecosystems to absorb carbon starts to destabilize,” said study co-author Patrick McGuire, a climate scientist at the University of Reading in the UK.
“For example, forest fires in California are more likely because of extremely dry and hot conditions caused by a hotter atmosphere. More fires means that forest turns to scrubland, sometimes permanently. This reduces the land’s overall ability to suck carbon out of the atmosphere as it did before. This creates a vicious cycle as areas such as these become more vulnerable to the effects of climate change in the future.”
The scientists discovered that, from 1981 to 2018, many ecosystems around the globe moved from a phase of high productivity, when plants were able to absorb more carbon, to one of low productivity, in which plants partially lost their capacity to absorb it. The scale of such fluctuations creates a greater risk of destabilization, possibly leading to abrupt landscape changes as ecosystems cannot adapt to climate change, deforestation, or biodiversity loss.
The study found that the regions most at risk usually have less forest cover and more cropland, are warmer, and have experienced higher rises in temperature, and a larger number of extreme weather events, such as heatwaves or cold snaps. These areas include the Mediterranean Basin, Southeast Asia, and the west coasts of North and Central America. According to the researchers, these vulnerable regions have developed a “memory” – which they describe as a “temporal autocorrelation” – meaning that years when carbon uptake was lower are more likely to be followed by years when it diminishes even further.
However, in some areas – such as the tropical forests of the Amazon and parts of central and northern Europe – the carbon absorption capacity has in fact increased. Nevertheless, the scientists warn that regions such as the Amazon will likely face other climate threats, such as shifts in regular patterns of rainfall. These global variations will make it more challenging to predict the impact of schemes to absorb carbon, such as planting more trees.
“Ecosystems on land currently absorb almost one-third of the carbon emissions created by humans. If they start to absorb less carbon, the earth’s natural ability to curb climate change diminishes. This means we may need to cut man-made carbon emissions even faster than we had previously thought,” McGuire concluded.
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