Study: Tipping point looms as climate change dries out Earth

In this 2018 file photo, Cape Town’s main water supply from the Theewaterskloof dam outside Grabouw, Cape Town. South Africa has declared that the drought afflicting Cape Town and other parts of the country is a national disaster. (Bram Janssen/AP photo via Courthouse News)

(CN) – Researchers have found Earth’s ability to trap greenhouse gas emissions is compromised by the increasing frequency and severity of droughts and heatwaves associated with climate change – meaning we’ll likely reach the tipping point sooner rather than later.

The study by Columbia University researchers and published Wednesday in Nature is the first of its kind to quantify the effects of the year-to-year variability in carbon uptake into the atmosphere. The researchers found wetter-than-average years are not enough to compensate for the release of carbon emitted by humans.

“Essentially, if there were no droughts and heat waves, if there were not going to be any long-term drying over the next century, then the continents would be able to store almost twice as much carbon as they do now,” said Pierre Gentine, the study lead and an engineer with the Earth Institute.

The authors set out to explore the relationship between land masses and their ability to store carbon and soil moisture and weather patterns, all of which combine to potentially trap some of what’s being emitted by humans at an increasingly alarming rate around the globe.

“Because soil moisture plays such a large role in the carbon cycle, in the ability of the land to uptake carbon, it’s essential that processes related to its representation in models become a top research priority,” Gentine said.

But even as scientists grapple to understand the terrestrial ability to sequester carbon, they acknowledge that only about 50 percent of the emissions are taken up by the land. The rest seeps into the atmosphere and the oceans, which explains coral bleaching and the acidification of the ocean.

“It is unclear, however, whether the land can continue to uptake anthropogenic emissions at the current rates,” Gentine said. “Should the land reach a maximum carbon uptake rate, global warming could accelerate, with important consequences for people and the environment.”

A tool used in assessing the interplay between the hydrologic cycle – variability of rain events – and the land’s ability to trap carbon is a unit of measure called net biome production, a complicated equation that measures the net amount of carbon that is lost or gained in a given region.

Gentine and study co-author Julia Green found the measurement was highly dependent on soil moisture content, which in turn was highly dependent on rainfall variability. This means the land will lose more of its ability to store carbon as droughts and heatwaves increase, as they are expected to in the coming decades due to human-caused climate change.

“If soil moisture continues to reduce NBP at the current rate, and the rate of carbon uptake by the land starts to decrease by the middle of this century – as we found in the models – we could potentially see a large increase in the concentration of atmospheric CO2 and a corresponding rise in the effects of global warming and climate change,” Green said.

Another effect of the loss in soil moisture is reduced vegetation, which also serves as an important carbon sink to store greenhouse gas emissions.

Scientists believe these studies will help modelers in their efforts to more precisely predict the effects of climate change, as global temperatures continue to rise and carbon emissions around the planet show no sign of abating.