Despite the tidal wave of environmental criticism directed at coal plants, a new study shows how emissions from coal and other fossil fuels have a huge benefit: they are greening the world’s most arid regions.

Indiana University researchers reviewed dozens of studies on the global greening phenomenon that’s been occurring over the last few decades and concluded it’s a result of increasing concentrations of CO2 in the atmosphere.

The study found a “consistent and statistically significant increase in the availability of soil water (11%) was observed under elevated CO2 treatments in both drylands and non-drylands, with a statistically stronger response over drylands (17% vs. 9%).”

For years, satellite images have shown vegetation expanding into the Earth’s drylands, including areas of the Mediterranean, Sahel, Middle East, China, Mongolia and South America. Indiana researchers considered other factors, such as increased rainfall and land use changes, but found CO2 is the only viable reason for the increased greenness.

“We know from satellite observations that vegetation is greener than it was in the past,” Lixin Wang, the study’s lead author and Indiana University Earth sciences professor, said in a statement. “We now understand why that’s occurring, but we don’t necessarily know if that’s a good thing or not.”

Wang’s findings mark another study linking a greening Earth to increasing carbon dioxide levels — which scientists say is being caused by increased use of fossil fuels, including coal, oil and natural gas.

While the U.S. Environmental Protection Agency legally defines CO2 as a pollutant, the greenhouse gas is essentially plant food because it’s essential for plant growth. Increasing CO2 levels drive what is called “CO2 fertilization.” The extra CO2 is basically a substitute for water, meaning plants in water-scarce regions need less water to thrive.

Scientists have also found increased CO2 allows plants to use water more efficiently. Wang’s study found “elevated carbon dioxide significantly enhanced soil water levels in drylands more so than it did in non-drylands,” according to the study’s press release.

“Importantly, the observed response lends weight to the hypothesis that any additional soil water in the root zone is then available to facilitate vegetation growth and greening under enhanced carbon dioxide,” Wang said.

Wang isn’t the first researcher to note the greening benefits of CO2. Famed physicist Freeman Dyson has been touting the benefits of increased CO2 concentrations for years.

“I like carbon dioxide, it’s very good for plants. We know sort of the non-climate effects of carbon dioxide are good — they’re very strong,” the Princeton physicist told IEEE Spectrum in an interview last year. “It’s good for the vegetation, it’s good for the natural vegetation as well as for the farms.”

“Essentially carbon dioxide is vital for food production, it’s vital for wildlife,” Dyson said. “Carbon dioxide is a substitute for water, so if you have less carbon dioxide plants need more water to survive, so it produces deserts.”

While many scientists have acknowledged the benefits of rising CO2, some have argued the benefits of increased vegetation could eventually be overshadowed by temperature rises.

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