Northern Hemisphere Could Experience More Tropical Rainfall Due To Climate Change
April 3, 2013

Northern Hemisphere Could Experience More Tropical Rainfall Due To Climate Change

Brett Smith for - Your Universe Online

Rising global temperatures are expected to cause catastrophic change worldwide; however a team of UC Berkeley and University of Washington scientists has found that the Northern Hemisphere will see a greater shift in tropical rainfall patterns compared to the Earth´s southern half.

Based on climate data and simulations, the climatologists found that rising temperatures will cause significant shifts in rainfall patterns around the Amazon, sub-Saharan Africa or East Asia, according to the team´s report in the Journal of Climate.

“A key finding is a tendency to shift tropical rainfall northward, which could mean increases in monsoon weather systems in Asia or shifts of the wet season from south to north in Africa and South America,” said lead author Andrew R. Friedman, from UC Berkeley.

While previous studies have shown that the average global temperature is increasing, the Earth is not warming uniformly. Because the Northern Hemisphere contains more land mass, it warms faster than the ocean-dominated south.

“Tropical rainfall likes the warmer hemisphere,” said co-author John Chiang, from the Berkeley Atmospheric Sciences Center. “As a result, tropical rainfall cares a lot about the temperature difference between the two hemispheres.”

The rising temperatures are expected to affect weather patterns that typically occur in latitudinal bands around the Earth. According to the researchers, a warmer Northern Hemisphere causes atmospheric overturning to grow weaker in the north and stronger in the south, shifting rain bands northward.

“It really is these borderline regions that will be most affected, which, not coincidentally, are some of the most vulnerable places: areas like the Sahel where rainfall is variable from year to year and the people tend to be dependent on subsistence agriculture,” co-author Dargan M. W. Frierson , from the University of Washington, said in a statement. “We are making major climate changes to the planet and to expect that rainfall patterns would stay the same is very naïve.”

To reach their conclusions, the team used over 100 years of climate data. By comparing the annual average temperatures in both hemispheres, along with rainfall during the 20th century, the researchers noticed that sudden changes in the temperature differential coincided with rainfall disturbances in the equatorial tropics.

The biggest weather pattern change in the study was approximately one-half degree Fahrenheit that occurred in the late 1960s. This event coincided with a 30-year drought in sub-Saharan African that caused famines and increased desertification across North Africa. The temperature change also corresponded to a decrease in the monsoon activity across East Asia and India.

“If what we see in the last century is true, even small changes in the temperature difference between the Northern and Southern hemispheres could cause measureable changes in tropical rainfall,” Chiang said.

The Berkeley scientist said that the climate change conversation too often looks at the big picture and not the finer details that could be affected by global warming.

“Global mean temperature is great for detecting climate change, but it is not terribly useful if you want to know what is happening to rainfall over California, for example,” Chiang said. “We think this simple index, inter-hemispheric temperature, is very relevant on a hemispheric and perhaps regional level. It provides a different perspective on climate change and also highlights the effect of aerosols on weather patterns.”