Get Used to the American West in Flames: What Living With the 'New Normal' Will Mean
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June temperatures produced 2,284 new daily highs nationwide and tied 998 existing records. In most places, the shoe-melting heat translated into drought, and the Department of Agriculture set a record of its own recently by declaring 1,297 dried-out counties in 29 states to be “natural disaster areas.” June also closed out the warmest first half of a year and the warmest 12-month period since U.S. record keeping began in 1895. At present, 56% of the continental U.S. is experiencing drought, a figure briefly exceeded only in the 1950s.
Higher temperatures have a big impact on plants, be they a forest of trees or fields of corn and wheat. More heat means intensified evaporation and so greater water stress. In New Mexico, researchers compared the drought of the early 2000s with that of the 1950s. They found that the 1950s drought was longer and drier, but that the more recent drought caused the death of many more trees, millions of acres of them. The reason for this virulence: it was 1ºC to 1.5ºC hotter.
The researchers avoided the issue of causality by not claiming that climate change caused the higher temperatures, but in effect stating: “If climate change is occurring, these are the impacts we would expect to see.” With this in mind, they christened the dry spell of the early 2000s a “global-change-type drought” -- not a phrase that sings but one that lingers forebodingly in the mind.
No such equivocation attends a Goddard Institute for Space Studies appraisal of the heat wave that assaulted Texas, Oklahoma, and northeastern Mexico last summer. Their report represents a sea change in high-level climate studies in that they boldly assert a causal link between specific weather events and global warming. The Texas heat wave, like a similar one in Russia the previous year, was so hot that its probability of occurring under “normal” conditions (defined as those prevailing from 1951 to 1980) was approximately 0.13%. It wasn’t a 100-year heat wave or even a 500-year one; it was so colossally improbable that only changes in the underlying climate could explain it.
The decline of heat-afflicted forests is not unique to the United States. Global research suggests that in ecosystems around the world, big old trees -- the giants of tropical jungles, of temperate rainforests, of systems arid and wet, hot and cold -- are dying off.
More generally, when forest ecologists compare notes across continents and biomes, they find accelerating tree mortality from Zimbabwe to Alaska, Australia to Spain. The most common cause appears to be heat stress arising from climate change, along with its sidekick, drought, which often results when evaporation gets a boost.
Fire is only one cause of forest death. Heat alone can also do in a stand of trees. According to the Texas Forest Service, between 2% and 10% of all the trees in Texas, perhaps half-a-billion or so, died in last year’s heat wave, primarily from heat and desiccation. Whether you know it or not, those are staggering figures.
Insects, too, stand ready to play an ever-greater role in this onrushing disaster. Warm temperatures lengthen the growing season, and with extra weeks to reproduce, a population of bark beetles may spawn additional generations over the course of a hot summer, boosting the number of their kin that that make it to winter. Then, if the winter is warm, more larvae survive to spring, releasing ever-larger swarms to reproduce again. For as long as winters remain mild, summers long, and trees vulnerable, the beetles’ numbers will continue to grow, ultimately overwhelming the defenses of even healthy trees.