Linking Large-scale Weather Events and Climate Change

Between August 11th and 14th, over 25 inches of rain fell on southeastern Louisiana, killing 6 people and leaving 20,000 more stranded and without homes.

The Lower Mississippi River Forecast called it a one in 1,000 years rain, resulting from a slow moving pressure cell. It was the worst disaster since Hurricane Sandy, according to CNN. one in 1,000 years deluge of rain flooded large parts of Louisiana, as a result of a slow-moving pressure cell. It was the worst disaster since Hurricane Sandy, according to CNN.

In fact, this year has seen a surge in extreme weather events all around the world according to NOAA. According to James White, Director of the Institute of Arctic and Alpine Research at the University of Colorado, they all have one thing in common: climate change.

"Every storm out there has the fingerprint of climate change on it,” said White. “There’s just more energy out there” , this energy augments pre-existing storm cells, like adding a tailwind to an already accelerating car.

White explained that scientists have observed an increase in large rainfall events, especially those that rank in the top 20% of precipitation. As the climate continues to change and the oceans warm, we’re likely to see even more big rain events like the one in Louisiana, he predicted, and they are likely to become even more severe.

It is impossible for scientists to attribute a single extreme weather event to one specific cause like climate change.It can also be difficult to suss out all of the complex convergence of events that contribute to specific flood events.

Was this  major flood enhanced by oceanic and atmospheric temperatures made warmer by climate change?

White and other scientists say that this is increasingly the case.

As the climate warms, more water evaporates from the oceans into the atmosphere. At the same time, warmer air is able to carry even more water vapor: For every 1 degree C increase, the atmosphere can carry 7 percent more moisture.

As the Earth has warmed some 4-7 degrees celsius in the past 5,000 years, thanks to increases in heat-trapping carbon dioxide, more moisture has been available in the atmosphere to fuel storms. The result: a greater potential for intense precipitation like the 2-day downpour experienced in Baton Rouge last month.

“We have observed an increase in the top twenty percent of rainfalls,” said White, alluding to the increase in large rain events experienced in the last ten years, and it seems there’s more to come.

“There’s going to be more big rains,” said White. “It’s the inevitable result of a warmer planet”.  

Scientists project that heavy rainfall events are likely to increase worldwide, but particularly across the Midwest and Northeast United States.

These large rain events can be expensive. Though the cost of these events is driven by multiple factors (such as an increase in property value and  amount of property owned in affected areas), we are spending increasing amounts of money to mitigate the damage caused by increased precipitation. In Louisiana alone, there have been more than 40 weather events resulting in a billion or more dollars worth of damage in the past 30 years.

In 2012 alone, there 32 such events in the U.S., making it the 2nd costliest year on record, according to the EPA. These more frequent events are only part of the equation, the US has also developed a habit of implementing costly infrastructure in the path of the storm. Projects such as bridges, levees, and dams that have been known to fail under extreme stress, adding to the economic impact of such events.

Thanks to the work of World Weather Attribution, there are new models and methodologies for analyzing and predicting how much of a role climate change may play in such events. Though there were many complicating factors in WWA’s study, such as weather over the Gulf Coast, the WWA believes that the Louisiana floods are indeed consistent with the types of events they would expect to occur in a warmer climate.

These types of large scale rain events are likely to continue to occur with increasing frequency, White said. And he pointed out that even with increased awareness of climate change, these large patterns take centuries, if not thousands of years to reverse.

White's advice?

“Until one generation is willing to forego short term gains for the long term benefit of its children, we won’t be able to address climate change