May 15, 2023 - Energy & Environment

Tropical Cyclone Mocha's intensification fits climate-driven pattern

A local resident looks from a window in Myanmar as Tropical Cyclone Mocha hits.

A man looks from a window in Myanmar's Rakhine state during Tropical Cyclone Mocha on May 14. Photo: Sai Aung Main/AFP via Getty Images

Tropical Cyclone Mocha, which struck Myanmar and Bangladesh as a high-end Category 4 storm on Sunday, is a catastrophic example of a rapidly strengthening storm — one that leaps multiple intensity categories.

Why it matters: Rapid intensification, along with higher rainfall rates, are key ways that climate change is influencing nature's strongest storms.

  • Studies show such storms are becoming increasingly common and the magnitude of the rapid intensification is rising.

Threat level: Aid organizations are scrambling to respond to Cyclone Mocha, which came ashore just north of Sittwe, Myanmar, packing maximum sustained winds of 155 mph, making it a high-end Category 4 storm.

  • At its peak intensity about 8 hours before landfall, it had maximum sustained winds of 175 mph, putting it tied for first place on the list of the most intense tropical cyclones on record for the North Indian Ocean Basin, per meteorologist Jeff Masters.
  • As its winds ebb, it has since been dumping copious amounts of rain across inland areas of Bangladesh and Myanmar, while spreading moisture into southwestern China.

Zoom in: Cyclone Mocha went through at least two major bursts of rapid intensification, with sustained winds climbing by about 90 mph in 48 hours.

  • When examining its strengthening over a shorter period, when the storm's winds climbed by 60 mph, Cyclone Mocha ranks among about the top 1% of the Bay of Bengal's rapidly intensifying storms, according to meteorologist Kieran Bhatia.
  • Conditions were ideal for rapid intensification, with light winds aloft and warm ocean waters from the surface to deeper depths.

Context: In recent years, some astonishing feats of rapid intensification have occurred.

The big picture: The oceans are absorbing the vast majority of extra heat going into the climate system from burning fossil fuels, and ocean waters are warming as a result.

  • So, too, are air temperatures. Physics' Clausius-Clapeyron relationship holds that for every 1°C (1.8°F) of temperature increase, there is about a 7% increase in the water-holding capacity of the atmosphere.
  • The world has warmed by about 1.2°C (2.16°F) since the preindustrial era, though some areas are warming far faster than others.

Between the lines: Sea surface temperatures where the storm rapidly intensified in the central Bay of Bengal were about 2°C (3.6°F) above average for this time of year, providing even more moisture for the storm to tap into.

  • Multiple studies in recent years have pointed to climate change as a key suspect behind shifts in the frequency and magnitude of rapidly intensifying storms.
  • For example, a 2020 study published in the Proceedings of the National Academy of Sciences found that tropical cyclones are now more likely to reach higher categories across much of the globe.
  • In addition, a 2019 paper in the journal Nature Communications found a trend in Atlantic hurricanes toward more rapid intensifiers during the 1982-2009 period. Computer modeling showed this was unlikely due to natural climate fluctuations alone.
  • Another paper, published last year, found that "extreme rapid intensification events," with sustained winds that increased by at least 57 mph in 24-hours, have become more common worldwide.
  • And yet another, more regional paper, published in 2021, found that stronger storms will pose a far greater risk to low-lying Bangladesh in coming decades.

What they're saying: "If you increase the available energy that a cyclone can convert into wind, you increase the likelihood of more rapid intensification events that result in more category 4 and 5 storms," said Jim Kossin, a meteorologist at The Climate Service, a private company.

  • "Climate change is increasing this available energy."

Yes, but: Karthik Balaguru, a climate scientist at Pacific Northwest National Laboratory, urged caution about attributing Cyclone Mocha's intensification to climate change directly, but said the storm's behavior is consistent with research findings.

  • It will take a detailed climate attribution study of this individual storm to identify the roles that climate change played, Balaguru told Axios in an email.
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