American Southwest — subtropical part of the world, but one of those who saw the cycle of droughts — long and short — for thousands of years. Columbia University professor of Lamont-Doherty Observatory Richard Seager studied climate, and he believes that human-induced global warming has gradually led to the natural variability of the state where the constant drought may last for decades.
Seeger and his colleagues have studied the climate south-west, with a glance into the past ships plied the oceans in the 19th century, had data on sea surface temperature, and the data were used in a computer model of climate history. In addition to this, they used tree rings to look back until the Middle Ages.
"You start to see that there is a natural cycle of drought, big and small," — says Seeger. "But when you add the human impact in the form of rising greenhouse gas emissions, we can declare the American south-west region of persistent drought. There are signs that have to prove it. "
They found that in their climate models were periodic drought, as well as the drought in the south-west, which is about the Middle Ages lasted for hundreds of years.
This is not the first time that Seeger has sounded the alarm. In the 2007 report of Seeger and his colleagues showed that the south-west is the transition to a more arid climate, and then in December 2010, along with Gabriel Seeger Vekchi of NOAA (NOAA — National Oceanic and Atmospheric Administration — annotated. translator) revealed the cause of reduced rainfall in the winter. This decline is due to changes in the circulation of air and water masses, which in turn are associated with an increase in temperature.
Heating is not merely a transformation into a more arid climate, but as time goes on, tend to its increase.
Temperature increase seen in the region, reducing snowfall and causes early spring, which reduces the amount of water, forming a water system, which keeps most of the south-west: the region of the Great Plains to the Pacific Ocean and the boundaries between units. Oregon and southern Mexico.
The situation is aggravated by population growth, which has occurred in previous decades. This will lead to a complete depletion of water resources.
"I'm curious what all of this will make the south-west," — says Seeger.
Seeger also notes that natural fluctuations between wet and dry periods, mainly controls the circulation of El Niño and La Niña, the sea surface, the heating and cooling of the Pacific Ocean. "Anthropogenic impact is not as significant as compared to natural fluctuations," — says Seeger. "But you can observe this in the climate models. It works in all the sub-tropics. At the moment, human factor is weak, but in the coming decades it will become a serious problem. "
Such a drought in America only confirm izmeniniya future climate and how to warn of the consequences. Whatever it was, even the local population above described areas do not always know that dark chocolate is healthy chocolate. But in a very unhealthy way of life that they lead — it should be one of the fundamental knowledge to worry about your health.