The Climate in Emergency

A weekly blog on science, news, and ideas related to climate change

Cyclone Pam

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Last week was a strange week for weather in the South Pacific. Not only were four tropical cyclones active all at the same, but one of those four was Cyclone Pam, a monster storm equivalent to a Category 5 hurricane that more or less flattened the island nation of Vanuatu. Of course, climate change is involved.

To be clear, Pam was the same kind of storm that is called a hurricane or a typhoon in other parts of the world. By a rather confusing accepted convention, the words for these storms vary depending on both how strong they are and where they are on the planet. “Tropical cyclone” is the collective term.

Vanuatu is among those several archipelagos that curve around Australia between Southeast Asia and New Zealand. In material terms it is very poor, and its average life expectancy, adult literacy rate, and availability of doctors are all lower than what people in the “developed” world are used to. That being said, it is a democracy, its life expectancy is quite good compared to economically similar nations, and the people did extremely well in terms of both environmental sustainability and quality of life–at least until last Saturday.

Only 20 people are confirmed dead so far, but some of the more remote islands have not been contacted yet. The nation had good disaster planning and successfully evacuated a lot of people. More dramatically, tens of thousands of people are homeless, their crops completely destroyed. Those people will be dependent on food aid for months. Many currently have no access to fresh water and some people are drinking salt water instead–a practice that will kill them if fresh water supplies don’t arrive soon. The aftermath of the storm could kill more people than the storm did, and the disaster could change the political and economic outlook of the country for a long time, depending on how the reconstruction process goes.

Vanuatu also threatened New Zealand (remember, in the Southern Hemisphere tropical cyclones track south), triggering storm warnings and possible evacuations, but the storm seems to have been a complete non-issue in New Zealand. There’s little to no information available online and my Kiwi friend is happily posting pictures of her dogs on Facebook, just like normal.

The other three storms in the same basin are, individually, unremarkable–the only thing is there are so many of them.

How Unusual Is This?

Most of my readers are American, and we do not get news about the South Pacific very often. Most of us probably didn’t know Vanuatu existed until this week. So, to put this newsworthy weather in context:

Cyclone Pam was probably not a record-breaking storm, but it was among the most powerful known to history, with estimated top sustained winds of 165 mph and gusts up to 200 mph. Its central pressure could have been as low as 879 millibars, which would put it behind just two Atlantic hurricanes. Unfortunately, no one flies aerial reconnaissance into Pacific storms, so there is no way to know for sure exactly what Pam’s numbers were.  Vanuatu itself rarely gets hit by cyclones because it is a very small place (total land area is just larger than the state of Connecticut, divided among many islands) in a very large ocean.

But we also don’t have very good historical records for the area’s weather. In fact, there’s really only about thirty years of tropical cyclone data for Vanuatu–how Pam relates to historical trends is therefore very hard to say.

Four active storms in the same basin is unusual, though hardly unprecedented. It has happened at least twice before in the Atlantic, and is probably more common than our records suggest because storms that never made landfall were easy to miss until modern times. Two storms at once in the same basin is actually quite common. Essentially, how “friendly” a given ocean basin is to tropical cyclone formation varies and a very storm-friendly ocean forms a lot of storms. Interestingly, the same large atmospheric pattern that caused the four storms last week is also causing cooler temperatures in the United States this week. Whether this particular pattern is anything other than chance seems unclear.

What Does Cyclone Pam Have to Do with Climate Change?

In general, climate change is a trend and part of that trend is probably more powerful tropical cyclones. Whether storm behavior is actually changing is hard to say, because we have too little historical information. At least some studies have shown definite increases. We do know that storm surges are getting worse because of rising sea level, and that storm surges are usually the deadliest part of the storm.

Specifically, the ocean surface around Vanuatu was a few degrees warmer than normal at the time Pam moved through it, thus feeding more energy and moisture into the storm. That warmth was partially due to global warming and partially due to a weak El Niño–and nobody knows what the relationship between global warming and El Niño is. It is possible they interact. Very large storms often have sea surface temperature anomalies underneath them, which is ominous in a world of rising temperatures.

But sea surface temperature alone does not dictate the power of a tropical cyclone. Instead, the upper limit of potential storm power in any one place and time is based on the difference between sea surface temperature and the troposphere as a whole. The troposphere is the part of the atmosphere where weather happens. Above it is the stratosphere an there is a distinct boundary, called the tropopause, between the two. The thing is that while the sea is definitely warming, the troposphere is warming, too. If both warm at the same rate, the upward boundary on storm power will not change (although other aspects of storm behavior could).

As it happens, the difference between sea and sky is increasing in the South Pacific, enough to have raised the potential storm intensity for that region by about 5 mph per decade. That is a lot–it adds up to an increase of almost 20 mph since I was born. Presumably, not all storms reach their potential, but increasing potential suggests increased storm intensity over time. Climate models so far predict only a much smaller rise in storm severity potential for the future, which could mean that something other than the greenhouse effect is causing much of the shift–or it could mean the models are overly optimistic.

Basically, what we’re looking at is a real possibility that tropical cyclones in the South Pacific and the Indian Ocean have gotten more severe in recent decades, though it’s hard to say how much more severe because we don’t have enough data–and the probability that such storms are going to get more severe going forward. The only real question is how much worse are they going to get?

The Take-away

I have written before about tropical cyclones as a human rights issue, since the poor and otherwise disenfranchised bear a disproportionate burden from disaster. I have also written before about how wind speed per se is not a good indicator of what climate change is doing to these storms, since global warming is unquestionably increasing storm-related flooding whether wind speed changes or not–and flooding causes much more death and damage than wind.

But there is another point I had not encountered until recently, and it is a very good point.

Tropical cyclones are rare. While a few dozen might form in any given storm basin per year, the oceans are big places. It’s rare for a big storm to make a direct strike on the same place twice in a generation–Vanuatu, for example, has not been hit this bad before. That means that development patterns, building codes, public willingness to take evacuation orders seriously–cultural storm preparedness generally–is based largely on legend and rumor.

My area illustrates the point nicely; I live on the Atlantic side of the Eastern Shore of Maryland. We were hit by both Irene and Sandy, but neither did significant damage here. We’ve also weathered some severe nor’easters, but those are not hurricanes–the Ash Wednesday Storm of 1962 was hurricane-like in its destructiveness, but even that was 53 years ago. A lot of people (me included) have been born since then. I just asked my husband when the last disastrous hurricane hit us and he wasn’t sure. He guessed the 1950’s or 60’s. If a monster storm hits here next year, a lot of people could well ignore evacuation orders (because we survived Irene and Sandy, after all) and a lot of new waterfront housing will wash away–as will a lot of older buildings and farmlands made newly vulnerable by sea level rise and by the loss of coastal wetlands to development. Disasters are things that happen to other people, we will think, not to us.

And what cultural memory we do have of hurricanes is almost sixty years out of date.

Storm rarity means that society takes a long time to adapt to the new normal, needing perhaps two or three big storms to really get the message–and that could take 75 years. By that time, of course, there will be a new new normal, unless we as a society stop warping the atmosphere. That’s really what we’re looking at. If we do not stop pumping greenhouse gasses into the sky, climate will change faster than we can adapt to it and it will keep changing faster than we can adapt until anthropogenic climate change stops–or until we stop.



Author: Caroline Ailanthus

I am a creative science writer. That is, most of my writing is creative rather than technical, but my topic is usually science. I enjoy explaining things and exploring ideas. I have one published novel and another on the way. I have a master's degree in Conservation Biology and I work full-time as a writer.

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