Large stretches of arid land have become greener since the 1980s due to rising concentrations of carbon dioxide, which fertilizes plant growth, a new study shows.

While this greening has long been noted in satellite imagery, its direct link to carbon dioxide (CO2) has been difficult to prove, explained study leader Randall Donohue, an environmental scientist at Australia’s Commonwealth Scientific and Industrial Research Organization.

“There are so many processes occurring simultaneously that affect plant behavior, it is very difficult to determine which process is responsible for any given change,” he told NBC News in an email. Teasing out a CO2 fertilization effect amongst the other processes “hasn’t been done before,” he added.