The world’s forests do a lot of work to counteract carbon emissions, breathing in that CO2 so trees can grow. Many climate change models have assumed that trees will continue to do so at a pretty consistent rate, which will help offset humanity’s carbon footprint. Unfortunately, researchers have discovered a problem in that thinking: trees don’t immediately recover from droughts.
The thinking had been that, once a drought passed, trees would be right back to converting CO2 and water into additional mass. However, researchers based out of the University of Utah have looked at almost 75 years worth of tree ring data from 1,300 forest locations around the world, and they’ve discovered that trees take anywhere from 2 to 4 years to return to their normal growth rates following a drought.
That’s bad news for climate change, because while those trees aren’t growing they aren’t taking I as much CO2, which means our climate change models need to be modified, and in general, the new numbers won’t be as reassuring. There are droughts along the West Coast of the United States right now, such as in Washington state, which are worse than normal, and as the century passes, we should expect more frequent and severe droughts, especially in semi-arid areas.
How much does this set us back? Well, over a century, these increased droughts will reduce CO2 intake by forests by around 1.6 metric gigatons, which is about one quarter of expected U.S. emissions over that time. The U.S. does produce a lot of CO2, but we’re not responsible for all of it, and a lot of those projections assume that we’re going to get better about CO2 emissions in the future.
The droughts, of course, are either caused or worsened by human activity. Droughts are not infrequent in the western United States, but higher temperatures make them worse, so they last longer, and trees take even longer to start growing again.