A sub-alpine forest in Colorado. Forests in the southwestern US are expected to be among the hardest-hit, according to the projections resulting from the study. Sydne Record

Forests can slow the warming of our planet by absorbing around 25% of the emissions of carbon dioxide (a greenhouse gas), but only if the forests are healthy. And, according to a new study published today in the journal Ecology Letters, North American forests might not be healthy enough to help in the near future.

When temperatures get too high and stay high year after year, whole forests in North America could be devastated, the researchers said. Heat or drought weakens trees, making them more susceptible to fire, disease, and insects, thereby preventing healthy growth, and diminishing their absorption rate of carbon dioxide.

“There is a critical and potentially detrimental feedback loop going on here,” Noah Charney, study author and researcher at the University of Arizona, said in a press release.

In fact, forests could actually turn into a source of CO2 in the atmosphere — maybe as soon as 2050 — because the trees could die faster than they could absorb carbon dioxide. If they die, they would release trapped carbon, adding to the vicious cycle and helping accelerating climate change.

The newly published study combined widely-used climate projection models, tapped 1,457 sample sites across the continent, and utilized the North American historic tree-ring records from 1900 to 1950 to arrive at their results.

Projected change in forest growth rates for the second half of this century. With the exception of coastal areas, growth rates are projected to go down throughout the North American continent. Noah Charney

By 2075, trees in the north and southwest (including the Rocky Mountains, Canada, and Alaska) could grow as much as 75% slower than normal.

The study challenged previous research, which had suggested that trees in colder areas could grow larger with warming temperatures and absorb more CO2.

The researchers say their work adds to the evidence that carbon emissions need to be monitored in order to have any impact on limiting the effects of a continually warming world.