Wednesday, March 18, 2015

Cyclone Pam Trashed Vanuatu. Should We Blame Climate Change?

Adrian Banga surveys his home, destroyed by
Cyclone Pam in Port Vila, Vanuatu.
Photo by Dave Hunt/Associated Press  
After Cyclone Pam wrecked his Pacific island nation last weekend, Vanuati president Baldwin Lonsdale pointed an accusing finger at climate change for the disaster.

Was he right?

The answer probably is that Londsale was probably partly right.

Whis is usually the case when people discuss weather disasters.

This was a biggie, destroying or damaging most of the buildings on Vanuatu, killing at least 11 people and slamming the islands with winds of 165 mph, gusting to 200.

Some weather extremes can be tied pretty well to climate change. Other extremes are probably due to a variety of factors, and sometimes it's hard to tease out what, if any, effect climate change had.

Mashable this week had an analysis of whether Londsale was wrong or right.

Their conclusion: Global warming probably made things worse on Vanuatu, but other phenomenon also contributed to Cyclone Pam's power.

An excerpt from the Mashable article:

"Scientists say unusually mild sea surface temperatures and added atmospheric water vapor helped the storm intensify before slamming into Vanuatu. At the same time, rising sea levels likely made the storm more damaging than it would have been just a few decades ago."

The upshot was the unusually warm water temperature in the area, more than three degrees above normal, fueled the storm. Tropical systems tend to get stronger faster when water temperatures are above average.

One scientist Mashable quoted said part of the higher than average ocean temperatures in the area of Cyclone Pam is attributable to global warming - perhaps a third of the 3.6 degree warm temperature anomoly.

The rest of the warmth that fed Pam was probably part of a natural cycle and the El Nino cycle of warm Pacific Ocean waters.

Says Mashable, quoting Kevin Trenberth, a climate researcher at the Natinal Center for Atmospheric Research in Boulder, Colorado:

"The atmosphere all around there has 10 to 20 percent more moisture in it than a comparable storm in the 1970s would have had. The high sea surface temperature and the water vapor fueled the storm and undoubtedly increased its intensity and size, Trenberth said in an email conersation. "The winds were stronger, the storm surge is greater on higher sea levels."

Another influence on the storm was Madden-Julian, or MJO, a weather cycle that, as I noted in an earlier post, contributed to the intense winter this year in New England.

Again, Mashable:

"In certain instances, the MJO can encourage the air to rise, forming thunderstorms as well as tropical cyclones. Think of the MJO as a helping hand that likely aided the storm's rapid intensification."

It was a strong helping hand, too. As Dr. Jeff Masters at Weather Underground notes, this was the strongest MJO on record. Reliable measurements of the phenomenon date back to the 1970s.

On the sort of bright side, the strong MJO also gave a boost to the chances a pretty strong El Nino weather pattern could develop in the eastern Pacific. El Ninos tend to suppress, but not entirely eliminate hurricanes off and along the U.S. East Coast, so there's that. There might not be that many hurricanes to threaten the United States later this year, which would be a good thing.

In the grand scheme of things, global warming's effects on tropical cyclones is not totally clear, but early evidence seems to suggest there might be fewer of them in many parts of the world, but the ones that do get going will tend to be stronger than in the past.

There's a chance that might have been the case with Cyclone Pam, but of course we might never know for sure.

Of course, the most destructive part of any tropical cyclone is usually the storm surge. Air pressure is very low in these storms, so it doesn't press down on ocean water as much as areas that are getting normal air pressure, away from big storms.

When the tropical cyclone moves onto land, the ocean depth is greater at that point, so higher water rushes onto shore, propelled and made worse by strong winds and battering waves.

Global warming is also making ocean levels rise as ice caps melt. Plus ocean water, when it gets warmer, expands a little bit, also contributing to sea level rise.

If sea levels are higher than they used to be because of global warming, they have a higher starting point when the tropical cyclone arrives with its storm surge. So the flooding with the storm would be higher and deeper and more destructive than it would be without the underlying global warming.

Other scientists chimed in with their take on how climate change is affecting tropical cyclones and most think there's a link.

In a fairly technical report in,  atmospheric researcher Kevin Emanuel cited
Cyclone Pam, and Typhoon Haiyan which trashed parts of the Phillipines in 2013, as evidence that climate change might be making such storms worse.

"While Pam and Haiyan, as well as other recent tropical cyclone disasters, cannot be uniquely pinned on global warming, they have no doubt been influenced by natural and anthropogenic climate change and they do remind us of our continuing vulnerability to such storms."

Lonsdale, the president of Vanuatu, and other leaders of vulnerable, small Pacific island nations, certainly seem to have gotten that memo.

Those leaders are pointing to Vanuatu to drive home a need to create a globally funded insurance pool to help with the recovery from these mega-disasters, Reuters reported.

They'll make their case at climate change talks later this year.

Here's some drone footage of the destruction caused by Cyclone Pam:

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