October 1st, 2020 by Carolyn Fortuna
They’re called hurricanes in the Atlantic Ocean, typhoons in the western Pacific Ocean, or cyclones in the Indian Ocean, and they pose some of nature’s fiercest fury. The warmer the water temperatures, the more heat energy is available, and the higher the potential is for these devastating storms to develop. As humans continue to release planet-warming greenhouse gases, the likelihood of hurricane activity increases. Hurricane seasons are destined to damage greater numbers of homes, cause increased economic damage, and take more human lives than ever before.
It’s time for US leaders to wake up to the threat of the climate crisis to mitigate the strength and frequency of hurricanes for the good of people, planet, and livelihoods.
A Little Background About Hurricanes
Off the west coast of Africa, just north of the equator, a thunderstorm forms. It might be one more towering thunderstorm cloud, or it might grow into something quite different – a hurricane. Drawing enough energy from the warmth of the tropical ocean water, a circling thunderstorm often grows into a single tropical storm with winds blowing more than 39 miles per hour, or, if it grows even larger and winds swirl faster than 74 miles per hour, it is called a hurricane.
The Atlantic Ocean’s hurricane season peaks from mid-August to late October. Hurricanes are enormous heat engines that deliver energy on a staggering scale. They draw their heat from warm, moist ocean air and release it through condensation of water vapor in thunderstorms. Storm surges can accompany hurricanes as a dome of water comes ashore, with water level reaching as high as 33 feet if the confluence of storm and high tide happens at the same time.
The warming water of a hurricane is largely a result of climate change, the buildup of greenhouse gases in the atmosphere that has heated the oceans 0.41 degrees Celsius during the last 50 years. For decades, climate researchers using computer models have predicted that the warming ocean and atmosphere would likely increase the intensity of natural disasters like hurricanes.
While it’s been nearly impossible to predict future trends from a single hurricane season in the past, scientists can take historical and other data and run models to get a glimpse of what future hurricane seasons may look like. More recently, though, high-resolution datasets and more sophisticated models have allowed researchers to find the fingerprint of climate change in individual weather events.
Hurricane Seasons & Climate Change: The Studies Say It All
Timothy Hall, a senior research scientist at NASA’s Goddard Institute for Space Studies, believes society is not preparing itself for a more stormy future. “The awareness of the impact of climate change on hurricanes, human society, and infrastructure is really lagging where the science is,” he states.
A study by Kerry Emanuel and associates in the American Meteorological Society’s Journal of Climate shows an increase in both the frequency and severity of hurricanes and other ocean storms, “robust across the models downscaled, in response to increasing greenhouse gases.” There is a particularly strong increase off the coast of North America. The paper also indicates that rapid intensification — the sudden acceleration in a hurricane’s intensity — “increases rapidly with warming.”
Hurricanes can change communities unalterably, so stronger hurricanes pose particularly significant threats. “What society should be concerned about is the frequency of high-category hurricanes, categories 3, 4, and 5,” Emmanuel explains. Storms of these frequencies pose great uncertainty for coastal communities, because “adaptation to changes in infrequent events [like hurricanes] is notoriously flawed and unduly influenced by politics and special interests.”
According to NOAA, 85% of all damages from hurricanes come from category 3, 4, and 5 storms.
Emmanuel and team are not alone in their determination that anthropogenic climate change has directly affected warming oceans and resulting hurricane seasons. A study in Nature Communications states that there is “a detectable increase of Atlantic intensiﬁcation rates with a positive contribution from anthropogenic forcing and reveal a need for more reliable data before detecting a robust trend at the global scale.”
Sea surface temperatures (SSTs) at any given time, even at the global scale, are determined by a mix of human and natural factors. In order to separate these factors for an attribution study regarding Hurricane Harvey in 2017, a team of researchers sought to find an attributable human influence — if any — to the precipitation during hurricane seasons. Covariate‐based statistical models permitted the researchers to isolate the effect of anthropogenic warming on the probability of large storms under fixed El Niño/Southern Oscillation (ENSO) conditions. They also estimated the amount of excess precipitation attributable to global warming, addressing the change since 1950 in return value for the (fixed) contemporary probability estimate of the observed precipitation total.
The results? Significant changes in both the likelihood and magnitude of observed precipitation totals in the Houston, Texas, region from Hurricane Harvey were likely attributable to anthropogenic climate change.
Examining the hurricane record in the Atlantic basin from 1986 to 2015, a study found rapid intensification increased 4.4 mph per decade. The study’s authors attribute most of the gains to a shift into the warmer phase of the Atlantic Multidecadal Oscillation, which is a climate cycle that affects the sea surface temperature of the North Atlantic Ocean based on different modes on multidecadal timescales.
Compared with the strong hurricane years of 2005/2010, the ocean heat content during 2017 was larger across the tropics, with higher sea-surface temperature (SST) anomalies over the eastern Main Development Region (EMDR) and Caribbean Sea. Yet a study shows that dynamical/thermodynamical atmospheric conditions were less prominent than in 2005/2010 across the tropics. The results suggest that unusually warm SST in the EMDR, together with the long fetch of the resulting storms in the presence of record-breaking ocean heat content, may be key factors in driving the strong TC activity in 2017.
Sea level rise over the coming century will lead to higher storm surge levels on average for upcoming hurricane seasons. Precipitation rates will increase at the global scale, as will storm intensity.
The question of how hurricanes can change with future anthropogenic warming is an important issue, particularly owing to the large societal impacts from extended hurricane seasons. We must recognize that oil sheen on Louisiana shores, humanitarian crises, and chemical contamination due to hurricanes are not aberrant, isolated incidents.
It’s time for more people to join in the rallying cry to become a zero emissions world. That’s the hope to limit future the severe fervor of hurricane seasons. We also clearly need to continue to reduce uncertainties in climate model projections of hurricane-related environmental variables for downstream impact projections through additional funding for research. It will be money well spent.
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