By Bill Sullivan
Photo: Bill Sullivan
A pair of research teams operating independently has come to the same conclusion: The Southwest portion of the United States, which has experienced rapid population growth, may become even more arid as global temperatures continue to rise.
That prediction is based on a study of seasonal rainfall variations between 56,000 and 11,000 years ago as recorded in cave stalagmites. Geoscientist Stephen Burns of the University of Massachusetts, Amherst, and colleagues at the University of New Mexico published their findings in Nature Geoscience, which also featured a second study that offered similar results.
According to Burns, data from his group’s study supports modern evidence that the polar jet stream shifts to the north in response to climate warming. When the polar jet stream retreats, winter precipitation in the Southwest decreases.
“Likewise, in periods when the Northern hemisphere’s climate is cooler, the polar jet stream sinks southward and winter rains increase in the desert Southwest, probably in response to advancing glaciers in Northern latitudes,” Burns says.
Only a few research teams have used isotope analysis from calcite sampled from ancient speleothems to analyze long-term patterns, but the new method is believed to be more precise than previous studies of lake bed sediment records. Any doubts about reproducibility were eliminated when another team (without prearrangement) reported similar conclusions in the same journal from tests run in a different cave.
“Results from our two groups reproduce each other incredibly well, which is a quite exciting and satisfying validation of the overall method,” Burns said.
