Do Hurricanes Feel The Effects Of Climate Change?

Do Hurricanes Feel The Effects Of Climate Change?
Satellite image on Sept. 7, 2017 shows three hurricanes: Irma in the center just north of the island of Hispaniola, Katia on the left in the Gulf of Mexico and Jose in the Atlantic Ocean on the right.

Hurricane Harvey, with its historical amount of rainfall over Texas, followed by a string of Hurricanes Irma, Jose and Katia in the North Atlantic basin in 2017, has triggered longstanding questions about any linkage between hurricanes and climate.

Can we really blame these recent hurricanes on climate changes? Or are they simply a coincidence of nature happening once every few decades, similar to the triple of Hurricanes Beulah, Chloe and Doria back in 1967?

Answering these questions lies at the heart of the current hurricane climate research that atmospheric scientists are trying to understand. There are signs that climate change can influence hurricanes in several different ways. However, these signals are inconclusive due to our inadequate understanding of how hurricanes interact with the environment.

Link to ocean temperature

Much as a flu virus morphs in different environments and becomes more infectious in cold winter temperatures, hurricanes depend on the ambient environment for their existence and motion. To what extent the surrounding environment affects hurricane development is indeed among the most extensively studied topics in hurricane research.

Evidence of the environment’s role on hurricane development has been noted since the early 1950s, yet a major milestone was achieved by Kerry Emanuel at MIT in his studies of hurricane dynamics in the late 1980s.

His idea was to consider hurricanes as heat engines that can extract heat from the ocean surface and exhaust it at the upper troposphere. In this way, Emanuel was able to obtain a mathematical expression showing how the maximum potential intensity a hurricane can attain in a given environment depends on sea surface temperature and temperature near the top of the atmospheric troposphere around 14 kilometers, or 8.8 miles, above the sea. A warmer sea surface temperature would result in a higher intensity, according to Emanuel’s formulation.

The ‘fuel’ for hurricanes comes from the energy in the ocean’s heat.
The ‘fuel’ for hurricanes comes from the energy in the ocean’s heat.

In essence, Emanuel’s relationship between hurricane intensity and sea surface temperature dictates how strong a hurricane can be for a given environmental condition. Numerous studies have then confirmed the importance of sea surface temperature in controlling hurricane maximum intensity, and suggest an increase of 2-3 percent in hurricane strength per 1 Celsius degree increase in sea surface temperature under favorable conditions.

From this perspective, it is thus very tempting to assert that hurricane intensity variations must be connected to the global climate due to the vital role of ocean temperatures in hurricane development. Indeed, many studies of hurricane intensity climatology consider ocean temperature as a main proxy to detect the future trend in hurricane intensity change.

The common consensus among these studies is a conclusion that future hurricanes will tend to be stronger than those in the present-day climate, assuming that sea surface temperature will continue its current warming trend into the future.

Looking at extremes for clues

While we can expect an increase in hurricane intensity as a result of rising ocean temperatures, how to interpret this result to one specific hurricane turns out to be very different.

For an intuitive illustration of how difficult this can be, consider how climate change can affect aspects of our weather, such as the daily variation of temperature.

For instance, a future air temperature warming of 0.5 degrees in the next 10 years would be mostly masked out by any daily temperature variation, which is in the range of 10 degrees between day and night. In this sense, it would be hasty to jump to a conclusion that the high intensity of Hurricane Harvey or Irma is caused by climate changes, simply because fluctuations in local weather conditions could contribute much more than climate change signals.

On top of the day-to-day intensity fluctuations due to local environmental conditions, hurricanes may also possess chaotic behaviors that cause their intensity to highly vary. A recent study showed internal variations of hurricane intensity could be as large as 10-18 miles per hour, which is larger than what would be induced by climate change.

On the other hand, one should not naively deny any claim that the extreme impacts of Hurricane Harvey or Irma are symptoms of climate changes.

08 29 hurricane harvey
Extreme events, such as the rain associated with Hurricane Harvey, provide an opportunity for researchers to study the effects of climate change because they are outside the day-to-day variability of weather.
AP Photo/David J. Philip

Some research has indicated that the change in global climate could lead to a shift of the jet stream behaviors over North America. Flooding related to Harvey was unusual in part because the storm stalled over Texas for much longer than any other hurricane. So while our current knowledge does not allow us to connect Harvey’s intensity to any specific changes in climate, the abnormality of the Harvey stalling for a long period over land could be a manifestation of the shift in global circulation in a warmer climate.

Likewise, the emergence of triple hurricanes in the Atlantic basin during September 2017 could be another potential signal of the more favorable conditions for hurricane formation from climate change.

From the climatological perspective, it is the frequency and magnitude of these abnormal extremes, such as the prolonged period over land of Hurricane Harvey or the extreme intensity of Hurricane Irma, that are often of utmost interest to researchers. This is because these extremes are signals of climate changes that can be distinguished from day-to-day variations.

Limits of our understanding

Along with direct impacts of climate on hurricane intensity, another conceivable influence of climate on hurricanes is the shift of the hurricane track pattern in the future climate.

In principle, a change in global air circulation patterns could influence the steering flows that guide hurricane movement, much like a leaf carried away by a river. As such, variations in global circulations associated with climate change could introduce another degree of variability to hurricane impacts that we have to take into account.

A recent climatological study led by James Kossin at University of Wisconsin suggested a poleward shift of the hurricane maximum intensity location in a warming climate. But unlike the connection between hurricane intensity and the ambient environment, the linkage between global circulation change and hurricane movement is much harder to quantify at present.

While research on hurricanes gives us a good sense of how hurricanes would change in a warmer climate, measuring this change and, in particular, tying a unique feature of one specific hurricane to climate change are beyond the current level of confidence.

In reality, there are several other factors that could strongly interfere with hurricane development, such as the change of atmospheric temperature with height. These factors directly affect the interaction of hurricanes with the surrounding environment. However, these are very difficult to quantify in the context of climate change due to the different time scales between hurricane development – measured on the order of days and weeks – and climate change, which occurs over decades.

The ConversationFrom a scientist’s perspective, the lack of understanding of climate impacts on hurricanes is disappointing, if not irritating. On the other hand, these uncertainties continue to motivate us to search for any possible link between hurricanes – including their intensity, frequency, time of formation and location – and climate. Better understanding of hurricane-climate relation is needed, as ultimately that knowledge can help serve society.

Chanh Kieu, Assistant Professor of Atmospheric Science, Indiana University

This article was originally published on The Conversation. Read the original article.

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Product Description: After major hurricanes Harvey and Irma made landfall in the United States in 2017, and as Hurricane Florence approaches the Carolinas in 2018, there have been renewed calls to do something about global warming. The popular perception that landfalling hurricanes in the U.S. are becoming more frequent or more severe, however, is shown to be incorrect. The 30 costliest hurricanes in U.S. history have indeed become more expensive in recent decades, but it is demonstrated that as damages have increased, hurricane intensity has not. The cause of increasing damages is increasing population and infrastructure in hurricane-prone areas. History has demonstrated that major hurricanes, sometimes arriving in pairs, have been part of Atlantic and Gulf coastal life for centuries. Even lake bottom sediments in Texas and Florida reveal more catastrophic hurricane landfalls 1,000 to 2,000 years ago than have happened more recently. Over the last 150 years, the number of major hurricanes hitting Texas has been the same when Gulf of Mexico water temperatures were below normal as when they were above normal. Harvey's record-setting rainfall totals were due to its slow movement, which cannot be traced to global warming (August 2017 was quite cool over most of the U.S.), combined with substantial land subsidence preventing rivers from draining more rapidly to the ocean. Major hurricane strikes in Florida since 1900 have, if anything, become somewhat less frequent and less severe. What has changed in Florida, again, is coastal development. The Miami - Fort Lauderdale metroplex now has a population of over 6 million, whereas a little over 100 years ago it was nearly zero. As a result, our vulnerability to major hurricane strikes has increased dramatically. Even with no change in hurricane activity, hurricane damages will continue to increase along with wealth and infrastructure in coastal areas. It is only a matter of time before our first trillion-dollar hurricane catastrophe occurs, and it will happen with our without carbon dioxide emissions from fossil fuel use.

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Product Description: This book provides research that shows tropical cyclones are more powerful than in the past with the most dramatic increases occurring over the North Atlantic and with the strongest hurricanes. Although such increases are correlated with warming oceans and are consistent with the thermodynamic theory of hurricane intensity, there remains doubt about the interpretation, integrity, and meaning of these results. Arising from the 5th International Summit on Hurricanes and Climate Change, this book contains new research on topics related to hurricanes and climate change. Bringing together international leading academics and researchers on various sides of the debate, the book discusses new research and expresses opinions about what is happening and what might happen in the future with regard to regional and global hurricane (tropical cyclone) activity.

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Product Description: A revealing look by someone who has loved the weather since his first memory--and has worked in the field for over 40 years--at what is really inside the man-made "climate change" agenda. The author shows through countless examples, the exploitation, politicization, and weaponization of weather and climate in an effort to promote an agenda that runs counter to the foundations this nation was built on.

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