The potential that global warming has to dry up water resources in the American West and the food supplies of 1 billion people in the poorest regions of Africa and Asia are the focus of two studies released today.
One of the studies published in the journal Science found that nearly 60% of the changes in river flow, snow pack and winter temperatures in the West over the past 50 years are due to warming caused by human activities, such as the burning of fossil fuels like coal, oil and natural gas.
"We're headed for a potential disaster because of the lack of snowpack," says lead author Tim Barnett, a marine research physicist at Scripps Institution of Oceanography at the University of California, San Diego. "In California, we don't have enough reservoirs, so we rely heavily on the Sierra snowpack for our water."
Already, the changes of the past five decades have meant less snow pack and more rain in the mountains, rivers that run dry by summer, and overall drier summers in the region.
Barnett says the climate models used in the study were conservative, using only the low end of the temperature changes predicted due to global warming.
And although the West has gone through natural wet and dry cycles in the past, the current water flow trends differ significantly in length and in strength from natural variations in the past, the researchers concluded.
The findings may draw skeptics in light of this winter's phenomenal snow bonanza in the West. For those who say that this season's snowfall is evidence that global warming isn't occurring, Barnett says, "That's only looking at weather; we are looking at climate. You have to look at long-term changes as a rule."
"Our results are not good news for those living in the western USA," he says, and notes that the changes might make "modifications to the water infrastructure of the western U.S. a virtual necessity."
In Africa and Asia, global warming's likely effect on agriculture is even more ominous, as detailed in a separate study led by David Lobell, a senior research scholar at Stanford University, also in California. Lobell and his colleagues found that many of the world's poorest regions could face severe crop losses in the next 20 years because of climate change.
In the study, the researchers focused on 12 areas where most of the world's 1 billion malnourished people reside, including much of Asia, sub-Saharan Africa, the Caribbean and Central and South America.
The researchers found that crops in southern parts of Africa and Asia appear to be the most vulnerable to a warmer world: "In Africa, corn, sorghum and wheat will likely be most affected, while in Asia, the crops are wheat, rice, corn, canola, millet," says Lobell.
Temperature and rain are the key factors that affect crops. The study authors analyzed 20 climate models and concluded that by 2030, the average temperature in most areas could rise 1.8 degrees Fahrenheit, while precipitation in some places — including South Asia, South Africa, Central America and Brazil — could decrease.
"The majority of the world's 1 billion poor depend on agriculture for their livelihoods," Lobell says. "Unfortunately, agriculture is also the human enterprise most vulnerable to changes in climate. Understanding where these climate threats will be greatest, for what crops and on what time scales, will be central to our efforts at fighting hunger and poverty over the coming decades."