By KELLY LEVIN
With Hurricane Florence making landfall in the Carolinas, Super Typhoon Mangkhut headed for the Philippines, and Hurricanes Harvey, Irma and Maria fresh in our minds, many are asking what role climate change is playing in these disasters.
Scientists have known for years that global warming can exacerbate storms. But our understanding of the connection between hurricanes and climate change has evolved significantly in just the past year.
Here’s what the cutting-edge science shows:
Warming Can Lead to Slower-Moving Hurricanes
If storms hover above an area of land for long periods of time, they continue to dump rain, amplifying the risk of flooding. Very recent research has established a connection between warmer temperatures and the slowing of hurricane movement. A recent study in Nature found that from 1949 to 2016, the speed of tropical cyclones declined by 10 percent globally; North Atlantic tropical cyclones slowed down 20 percent over land areas during the same period. This slowing is part of the reason Hurricane Harvey caused so much damage when it stalled over Texas last year and is of significant concern as Florence comes ashore.
Storms Are Moving Poleward
Scientists suspect that human-caused warming can help explain why the latitude of where tropical cyclones reach their peak intensity has moved 53 and 62 kilometers poleward per decade in the Northern and Southern hemispheres, respectively, away from the tropics. While there has yet to be any signal of migration of storm intensity in the Atlantic, this migration is occurring in other ocean basins, especially the Pacific and South Indian Oceans. Regions that are further away from the equator could see an increased risk of intense storms. On the other hand, those communities closer to the equator, which rely upon tropical cyclone rainfall as freshwater, could see threats to their water supplies.
None of the statements above suggest that climate change causes hurricanes. However, it’s becoming more and more clear that a warming climate leads to more devastating hurricanes.
There have also been tremendous advancements regarding the attribution of specific extreme events being enhanced by climate change. According to Nature, there have been more than 170 scientific studies on attribution of extreme events and climate change published between 2004 and mid-2018. For example:
- One study found that the unusually active 2014 hurricane season in the Hawaiian islands was substantially more likely due to human-induced warming.
- In the Western North Pacific, scientists have found that the extreme energy of 2015 cyclone activity was largely caused by sea surface warming in the Pacific Ocean, with human-induced warming increasing the odds that the event occurred.
- Recent research found that with Hurricane Harvey, accumulated rainfall in the Houston, Texas area increased by an estimated 38 percent due to climate change-induced factors, including an increase in available moisture.
- Prior to Hurricane Harvey, ocean heat content was the highest on record in the Gulf of Mexico and globally. When Hurricane Harvey came, that ocean heat was lost through evaporative cooling, which was then transferred to the atmosphere as moisture and, in turn, record-breaking heavy rainfall. Researchers say that Harvey could not have been accompanied by so much rain without the influence of human-induced warming.
- In just the last several days, a group of researchers assessed the role of human-induced warming in Hurricane Florence, notably releasing their findings before the storm hit. Scientists estimated that the projected rainfall would be 50 percent heavier due to warming.
Building on Prior Research
This latest cutting-edge science builds on years of previous research on the connection between hurricanes and manmade warming. According to the 2014 U.S. National Climate Assessment, the intensity, frequency and duration of hurricanes in the North Atlantic, as well as the frequency of the strongest hurricanes, has increased since the early 1980s. And it’s projected to worsen—models suggest that with 2 degrees C (3.6 degrees F) of global temperature increase, average rainfall rates are projected to increase 10-15 percent within 100 kilometers of a storm.
While we may not see an overall higher frequency of storms over the long term, climate change can make them more devastating, with higher rainfall rates, more intensity, and higher storm surges driven by sea level rise. When climate impacts are combined with increased vulnerability as populations and the built environment grow and creep closer to the coast, this can spell disaster.
While the science will continue to evolve, we can’t ignore what we already know. We know that we can both reduce the risks associated with climate change by cutting global emissions to safe levels, and by making smart investments to ensure communities and infrastructure are more resilient.
The science has spoken. Now it’s time to act.
Editor’s note: This article originally appeared on the World Resources Institute‘s blog: https://www.wri.org/blog/2018/09/recent-scientific-advancements-show-new-connections-between-climate-change-and
Kelly Levin is a senior associate with WRI’s major emerging economies objective. She leads WRI’s Measurement and Performance Tracking Project, which builds capacity in developing countries to create and enhance systems that track emissions reductions associated with low-carbon development goals. She closely follows the negotiations under the UN Framework Convention on Climate Change, and analyzes related emissions reduction targets and actions. Kelly has conducted an annual review of climate change science for WRI since 2005. She was also the Research Director and lead author of the 2010-2011 World Resources Report, which was dedicated to climate change adaptation, and specifically to how governments can improve decision making in a changing climate.
Kelly pursued her doctoral work at Yale’s School of Forestry and Environmental Studies, where her research focused on adaptation policies to contend with climate impacts to biodiversity. During her PhD studies, she was also a writer for the International Institute for Sustainable Development (IISD) Reporting Services, covering biodiversity and climate change meetings, including the UN climate change negotiations. Kelly has also worked as a climate policy/technical analyst at NESCAUM (Northeast States for Coordinated Air Use Management), where she devoted her time to developing a regional greenhouse gas registry in the Northeast and assisting states in the development of the Regional Greenhouse Gas Initiative (RGGI).