Intenser, wetter, windier storms in a warming world

 From  Inside Climate News

The federal government counts 52 tropical cyclones since 1980 that, with the cost adjusted for inflation, have caused, on average, $20 billion in damages in the United States. There were a record seven so-called “billion dollar” cyclones just last year.

With climate change helping produce a global horror film of extreme weather disasters this summer, and the peak Atlantic hurricane and Western fire seasons just arriving, a new landmark United Nations climate report by the Intergovernmental Panel On Climate Change offers the most thorough evaluation of the physical science associated with global warming so far, including the climate science of tropical cyclones.

Made public Monday, the IPCC report was written by 234 scientists from 66 countries and approved by 195 member governments of the IPCC.

To meteorologists, tropical cyclones are rotating, organized systems of clouds and thunderstorms that originate over tropical or subtropical waters. In the North Atlantic, central North Pacific and eastern North Pacific they are called hurricanes once wind speeds reach 74 miles per hour. Major hurricanes, categories 3 to 5, pack wind speeds of 111 miles per hour to more than 157 miles per hour, and cause damage that ranges from devastating to catastrophic.

The IPCC authors did not do original research for their report. Rather, they assessed the state of knowledge and the confidence in it based on previously published scientific reports.

Hugh Willoughby, a professor at Florida International University in the Department of Earth and Environment who has been studying hurricanes for decades, said the IPCC report’s assessment of hurricanes reveals an unsurprising picture of evolving science.

“It is consistent with what we have thought for 40 years,” said Willoughby, who flew more than 400 missions into hurricanes as a meteorologist with the federal government and led the National Oceanic and Atmospheric Administration’s Hurricane Research Center from 1995 to 2002. “What is new is more and more (hurricane) events that fit the pattern, and that is what you would expect.” 

To determine six, key takeaways about tropical cyclones and climate change from the IPCC report, Inside Climate News interviewed Willoughby and two academic researchers whose work was cited by the report’s authors: Colin Zarzycki, an assistant professor of meteorology and climate dynamics at Pennsylvania State University and Phil Klotzbach, a hurricane expert and research scientist at Colorado State University’s Department of Atmospheric Science.

• More Major Tropical Cyclones. It is likely, the report found, that the percentage of major tropical cyclones—those reaching categories 3 to 5—increased over the last four decades. Scientists are confident in saying that there will be more frequent storms in the highest intensity categories of 4 and 5.
• Wetter, Windier Tropical Storms. Warmer air holds more moisture, and human-driven climate change is making tropical cyclones wetter. The authors found that, generally, storms with extreme daily precipitation are projected to intensify by about 7 percent for each 1 degree Celsius of global temperature warming. The authors also expressed high confidence in projections that peak wind speeds in the most intense tropical cyclones—categories 4 and 5—will increase with increasing global warming.

• Tropical Storms are Shifting North. In the North Pacific, tropical cyclones are reaching their maximum intensity farther north than before, potentially exposing areas that have no experience with tropical cyclones to a risk of dealing with them in the future. The report said this is partly explained by changes in global-scale tropical atmospheric circulation. 
• More Explosive Tropical Cyclones. With warmer sea-surface temperatures, the frequency of storms that rapidly intensify has increased.
• Slower [Moving] Tropical Cyclones that Can Do More Damage. When slower moving cyclones make landfall, they can drop more rain, cause more wind damage and sustain a larger storm surge simply because they hang around longer. The IPCC authors cited research in 2019 that provided evidence that translation speed for Atlantic storms decreased 17 percent from 1900 to 2017. In addition, what scientists call “meanders” and “stalls” in tropical cyclone paths have become increasingly common, along with the slower speeds.

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Hurricane Harvey struck the Texas coast in August 2017. Credit: NOAA

Slightest heat magnifies hurricane risk

 From Climate News Network

Any climate change at all will mean a hurricane risk for the storm-prone Caribbean, even if global average temperatures are contained to a rise of no more than 1.5°C by 2100. But a rise of 2°C could be disastrous: the hurricane hazard could grow fivefold.

The figures – each representing a rise above the long-term average for most of human history – are significant. In 2015 195 nations, including the US, signed up to the Paris Agreement – a promise to contain the rise in global heating to “well below 2°C” by the century’s end. The undeclared but widely-understood intention was a limit of 1.5°C.

In the last century, in response to a rise in carbon dioxide emissions from fossil fuel use, planetary average temperatures have already risen by 1°C, and the Atlantic states of the US and the islands of the Caribbean have been hit by a series of ever more devastating windstorms, as ocean temperatures warm and make hurricanes more probable.

And researchers warn that as global heating continues – with forecasts of a rise of more than 3°C by 2100 – more are on the way.

But the US is wealthy and resilient. British scientists report in the journal Environmental Research Letters that they decided to take a look at the probability of windstorm and heavy rainfall assault on the Caribbean, where half of the 44 million people of the archipelago live within 1.5kms of the coast, and where devastation can be so intense it could take six years to recover.

The poorer and more vulnerable you are, the greater your hurricane risk. Even a tiny heat rise can spell disaster.

Tropical cyclones have become more destructive

Two severe tropical cyclones over northern Australia. Analysis of satellite records from 1979 to 2017 has found a clear rise in the most destructive storms, in keeping with climate predictions about global heating. Photograph: Nasa Earth Observatory/EPA

From The Guardian:

Tropical cyclones have become more intense around the globe in the past four decades, with more destructive storms forming more often, according to a study that further confirms the theory that warming oceans would drive more dangerous cyclones.

Analysis of satellite records from 1979 to 2017 found a clear rise in the most destructive cyclones – also known as hurricanes or typhoons – that deliver sustained winds in excess of about 185km/h.

Experts told Guardian Australia the finding was in line with climate model predictions and the knowledge that increasing ocean temperatures gave tropical storms more energy.  Dr Hamish Ramsay, a senior research scientist at CSIRO who studies cyclones, said: “This study confirms what the climate models have been predicting for some time – that the proportion of the most intense storms will increase as the climate warms.”

While climate scientists have long predicted that global heating would deliver stronger cyclones, a trend that was statistically significant has been challenging to identify in part due to the natural swings in the world’s climate masking changes.

Published in the leading journal the Proceedings of the National Academy of Sciences, the study was carried out by scientists at the US government’s National Oceanic and Atmospheric Administration.

The scientists did not try to find a cause for the increase in more dangerous cyclones, but said the trends were consistent with understanding of physics and modelling, and the finding “increases confidence that [tropical cyclones] have become substantially stronger, and that there is a likely human fingerprint on this increase”.

The probability of a cyclone reaching wind speeds greater than 185km/h had risen by about 15% over the 39 years studied.

“[The study] suggests that the climate change signal in the data is potentially already emerging and this is something that climate scientists have been saying for some time,” Ramsay said. “We maybe at a point now where we are starting to evidence from observational data that supports what the models have been telling us.”

Ramsay said as well as increasing the wind speeds in cyclones, warming oceans would also likely see cyclones delivering more rainfall. There was still uncertainty as to whether the numbers of all categories of cyclones would rise or fall under climate change.

Previous research has found that when cyclones form, they are tending to move more slowly, while delivering more rain.

Dr Greg Holland, a senior scientist emeritus at the National Center for Atmospheric Research in Colorado, has studied cyclones for about 40 years.  The Melbourne-based scientist said while there were legitimate arguments over the finer details of trends and intensity in relation to tropical cyclones: “The work all points in the same direction – the proportion of the most intense cyclones is going up.”

He said: “There is nobody saying the trend will go the other way. The physics has been well set out for 30 or 40 years. If you get a warmer ocean then the intensities of cyclones goes up. That’s a 5% or 10% increase in maximum winds for every 1C of warming in the ocean. The world is warming and its because we have put more greenhouse gases into the atmosphere.

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