Massive Monsoons Sweep Across Northern Hemisphere: Increased Rainfall Not Caused by Global Warming

There's been a lot of talk about climate change affecting rainfall patterns. Yet it may be natural fluctuations that could have the most impact in some regions. Natural swings in the climate may have significant intensified the Northern Hemisphere monsoon rainfall, according to a new study.

Monsoons are seasonal changes in the direction of the prevailing winds of a region. This causes wet and dry seasons throughout most of the tropics, though they're most associated with the Indian Oceans. The summer monsoon, in particular, is associated with extremely heavy rainfall. It can flood areas and cause massive damage. In fact, residents in Mumbai, India are used to the streets flooding with about two feet of water almost every summer. In addition, mudslides caused by strong monsoons can bury villages and destroy crops.

Monsoon rainfall in the Northern Hemispherer impacts about 60 percent of the World population in Southeast Asia, West Africa and North America. With global warming on the rise, predicting the impacts of this phenomenon on monsoon rainfall is crucial for both infrastructure planning and economic development.

In this particular study, researchers examined climate data in order to determine what happened in the Northern Hemisphere during the last three decades. Previously, researchers predicted that the summer monsoon circulation should weaken under the effects of global warming, leaving the area with less rainfall. Since global-mean surface-air temperature rose by about .72 degrees F during this time, researchers expected to see a corresponding decrease in rainfall.

Yet the research proved otherwise. The scientists found that over the past 30 years, the summer monsoon circulation has substantially intensified. In fact, they found that there was a 9.5 percent increase in summer monsoon rainfall in the Northern Hemisphere.

So why did this happen if overall temperatures rose? The researchers noted that a cooling in the eastern Pacific began in 1998. This cooling was a result of the long-term swings in ocean surface temperatures and is often more commonly referred to as La Nina. In addition, they found that another natural climate swing known as the Atlantic Multidecadal Oscillation also helped contribute to the increase in monsoon rainfall.

This study shows that there's a lot more happening with Earth's climate than just global warming. In addition, it reveals that future climate models need to take these factors into account.

"These natural swings in the climate system must be understood in order to make realistic predictions on monsoon rainfall and of other climate features in the coming decades," said Bin Wang, one of the researchers, in a press release. "We must be able to determine the relative contributions of greenhouse-gas emissions and of long-term natural swings to future climate change."

The findings are published in the Proceedings of the National Academy of Sciences.