Western North America suffered chronic drought from 2000 to 2004, causing forests to die, river basins to dry up. It was the strongest drought seen in 800 years. Sadly, it could also become the “new normal” in the coming decades; the “good old days”.
A group of ten researchers published their findings in the journal Nature Geoscience on Sunday, saying that such climatic extremes have increased as a result of global warming and that those we are currently experiencing will seem like better days in decades to come, with climate models and precipitation projections indicating that this period will actually be closer to the “wet end” of a drier hydorclimate during the last half of this century.
“Climatic extremes such as this will cause more large-scale droughts and forest mortality, and the ability of vegetation to sequester carbon is going to decline,” said Beverly Law, a co-author of the study, professor of global change biology and terrestrial systems science at Oregon State University.
“During this drought, carbon sequestration from this region was reduced by half,” Law said. “That’s a huge drop. And if global carbon emissions don’t come down, the future will be even worse.”
On top of the horrific damage the 2000-2004 drought had on the environment, its impact also cut carbon sequestration by more than half across a massive swath of Canada, the United States, and Mexico.
It’s not clear whether or not the current drought in the Midwest, now being called one of the worst since the Dust Bowl, is related to these same forces, Law said. This study did not address that, and there are some climate mechanisms in western North America that affect that region more than other parts of the country.
But we can be certain in the West of the country. Tree ring data shows that the last two periods with drought events of similar severity took place in the Middle Ages, from 977-981 and 1146-1151.
Ordinarily, Law said, the land sink in North America is able to sequester the equivalent of about 30 percent of the carbon emitted into the atmosphere by the use of fossil fuels in the same region. However, based on projected changes in precipitation and drought severity, scientists said that this carbon sink, at least in western North America, could disappear by the end of the century.
“Areas that are already dry in the West are expected to get drier,” Law said. “We expect more extremes. And it’s these extreme periods that can really cause ecosystem damage, lead to climate-induced mortality of forests, and may cause some areas to convert from forest into shrublands or grassland.”
The effects are driven by human-caused increases in temperature, with associated lower soil moisture and decreased runoff in all major water basins of the western U.S., researchers said in the study.
Although regional precipitations patterns are difficult to forecast, researchers in this report said that climate models are underestimating the extent and severity of drought, compared to actual observations. They say the situation will continue to worsen, and that 80 of the 95 years from 2006 to 2100 will have precipitation levels as low as, or lower than, this “turn of the century” drought from 2000-04.
“Towards the latter half of the 21st century the precipitation regime associated with the turn of the century drought will represent an outlier of extreme wetness,” the scientists wrote in this study.
These long-term trends are consistent with a 21st century “megadrought,” they said.