Climate Change

January Deep Freeze after 2017 record losses in USA

Are Extreme Nat Cat Events the New Normal?

The new year in the United States has been ushered in by yet another series of extreme events – a pair of record-breaking Arctic air outbreaks that helped fuel crippling lake-effect snowfalls, such as those seen in Erie, Pennsylvania, as well as the development of a powerful coastal storm that brought snow to northern Florida, as well as blizzard conditions and coastal flooding to New England.

These events come on the heels of several record-setting extreme weather events across North America in 2017. Hurricane Harvey produced torrential rainfall of such magnitude that, based on long-term statistics, should only occur less than once in a thousand years. Two weeks later, Hurricane Irma’s Category 5 winds decimated the islands of the northeastern Caribbean then lashed Cuba and the Florida Keys before making a final landfall on the southwest coast of Florida. Less than a week later, Hurricane Maria would also pass through the Leeward Islands as a Cat 5 storm, bringing another round of devastation, this time including Puerto Rico where the electric infrastructure was almost completely crippled by Maria’s wind. Combined with damage from the year’s severe thunderstorm outbreaks and the California wildfires, 2017 was an extremely costly year.
The new year in the United States has been ushered in by yet another series of extreme events – a pair of record-breaking Arctic air outbreaks that helped fuel crippling lake-effect snowfalls. © picture alliance /
Damage from hurricanes, severe thunderstorm outbreaks and California wildfires made 2017 an extremely costly year

While most of the U.S. natural catastrophe activity in 2017 and so far in 2018 was within the historical range of natural variability, some aspects of these events are indicative of changes expected in a warmer climate. For example:


  • While the number of tropical cyclones is not expected to change in a warming climate, increased oceanic heat content may help storms become more intense – and remain intense for longer periods of time, assuming that atmospheric conditions are conducive to intensification. Thus, Hurricane Irma’s record length of time at Saffir-Simpson Cat 5 intensity may be illustrative of how future intense storms behave.
  • A warmer atmosphere can hold more moisture, leading to the potential for heavier rain rates and more severe flooding than observed in the past. Although the rapid growth of Houston and its suburbs over the past 50 years played a significant role in the severity of flooding during Harvey, torrential rain events are becoming more frequent as our climate warms.
  • Climate change is making California become drier and warmer. These factors not only extend the state’s wildfire season, they also cause the evaporation rate of water to increase as well. This means that extreme wildfire conditions will return to California after a rain event more quickly today than in the past.
  • Although rapid intensification of coastal low pressure systems, or “bomb cyclones,” are a fairly common occurrence in winter, our oceans can now provide more heat and moisture to these developing storms, potentially increasing rainfall and snowfall totals associated with them. Further, research investigating links between climate change and the northern hemisphere winter gives some indication that the Arctic polar vortex is more likely to become destabilized in a warmer world, potentially leading to more mid-latitude cold outbreaks.

It should be noted that the influence of human-caused climate change on the severity of each of the above events is highly uncertain. Since it is quite difficult to attribute all or part of an individual event’s severity to climate change, it is far more useful to view the influence of climate change on extreme events from a probabilistic perspective. For example, a rainfall event similar to the geographical size and severity of Hurricane Harvey in Texas might have an 1,000 year return period (0.1% annual probability of exceedance) in a stable climate, but might only be a 500-year return period (0.2% annual probability of exceedance) in a future, warmer climate, due to the fact that warmer air can hold more moisture. From this viewpoint, it is easier to understand how climate change may impact the frequency of extreme events and to make effective business decisions based on this information.

So are extreme events, like those seen in 2017 and so far this year, becoming the new normal? I’m not sure this is the correct question to ask. Instead, the question we should be asking is “Are extreme events like these becoming more likely to occur?” The answer to this question is (most likely) a yes.
Last year’s events and the early extreme weather in 2018 are a stark reminder of the incredibly important role that the insurance industry plays in helping people and communities rebuild in the wake of natural catastrophes. However, it’s important to recognize that we, as a society, don’t build our homes and businesses to withstand the weather extremes of today, let alone what we may experience in a warming world. Thus, it is more critical than ever to implement wise land use practices and strong building codes, like those in Florida, to help our communities to better endure both the extreme weather of today and the future. Doing would be a win-win situation for homeowners, communities, and the insurance industry alike.