The effect is most noticeable in already arid climates. We're looking at you, Colorado Plateau and Desert Southwest:
Scientific models of the global carbon cycle – which are important for projecting climate change – don't account for this slow-down in growth. "The models assume there is no lag, so as soon as climate is better, so is growth," says Nate McDowell, who researches the physiology of tree death at Los Alamos National Lab in New Mexico. That means that models may overestimate the ability of ecosystems to store carbon – and underestimate the severity of future climate change.
If droughts do become more frequent and severe, (forest ecologist Bill Andregg) says, as climate models predict, "this suggests that more forests are going to spend more and more of their time recovering, and become less good at taking up carbon."Anderegg estimates that in Southwestern forests, the lag could amount to a 3 percent reduction in their carbon storage over a century. That may not sound like much, but when it comes to squirreling away the emissions we stubbornly keep spewing, we need all the help we can get.
And, of course, we know that the Southwest is headed for a period of long-term drought, as well as global warming. Given that aspens "fight" drought a lot, by opening their stoma, and that they're less resistant to the effects of doing this than are juniper, 40 years from now, a lot of Rocky Mountain hillsides are doing to be aspen-denuded.
And, otherwise, Andregg is right. It's working at the margins, but 3 percent is 3 percent.