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Don Paul: Human activity is driving costly, and deadly, weather years

The year 2018 was a costly one for extreme weather events, though not nearly as costly as the previous year.

A point well taken: There will be no more low-cost weather years. Burgeoning populations in vulnerable locations, along with ongoing mean global warming and its impacts, make “easy” years all but impossible.

In terms of pure dollar costs, 2018 U.S. losses were down to around $50 billion from $306 billion in the costliest year ever, 2017. A Vox article and NOAA statistics point to these lower costs, but they must be kept in perspective. For example, the now-accepted fatality count of 2,975 from Hurricane Maria in Puerto Rico is tied to a 2017 storm, as are most of its costs. However, some of these fatalities occurred in 2018, and some of those costs were incurred in 2018 with the agonizingly slow infrastructure repairs there. Disasters can overlap years, even if costs and fatalities are statistically assigned to a particular year.

This year, we still lost hundreds of lives, tens of thousands homes, and thousands of livelihoods to extreme weather, most of which has at least some link to our mean warming climate. (I say “mean warming” because the global average temperature is rising, but not all regions of the globe are warming — at least at any one time.) Here are the main 2018 events.

The impact of a warming climate on Hurricane Florence seems clearer, based on peer-reviewed evidence gathered by professor Jennifer Davis, at the Rutgers Climate Institute. Florence arrived with weaker winds than forecast at landfall. However, most of Florence’s devastation came due to a well-forecast stalling inland, predicated upon weakened upper-level steering winds linked to arctic warming. That warming is producing more frequent blocking patterns in the upper atmosphere because it weakens the jet stream, and these blocks lead to stalled or near-stalled weather systems.

The most recent costly and deadly disasters tied to this climate-linked tendency were Florence and the wettest storm ever, Harvey.

The link of Hurricane Michael’s sudden and explosive intensification to climate is less certain. Eastern Gulf hot water temperatures and a lack of disruptive wind shear allowed Michael to intensify far beyond earlier intensity forecasts. The above-average Gulf sea temperatures may be tied to climate, but they have also occurred from time to time before accelerated warming.

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In general, however, sea surface temperatures as well as deeper ocean temperatures are definitely warming in the mean, at least partly because the oceans absorb much of the extra heat from the atmosphere.

As we all know, wildfires in the west were horrific in 2018, and the warming climate in concert with the previous five-year drought undoubtedly played a role in the ferocity of the flames. It must be remembered, though, that other factors played a role.

Active fire suppression of smaller fires leaves more fuel on the ground for future fires. People spark some of these fires, usually inadvertently. Even a California utility apparently bears some responsibility for one of the worst fires. Nature can even play a cruel trick even when a long drought ends. Following winter rains and snows, vegetation in California flourishes in the spring. California summers are always dry, and that vegetation always dries out in the low humidity air, leading to more late summer and autumn wildfires. That particular phenomenon cannot be tied directly to climate change, but hotter air temperatures that are so connected lower dew points/humidities below the already dry seasonal averages. Fire ignition grows more likely.

One as-yet poorly tracked side effect of these fires is the more frequent critical air pollution that accompanies them, especially in basin regions such as Los Angeles, where pollutants can be trapped beneath temperature inversion layers. Numbers on exacerbated asthma attacks and effects on other lung disease from this past year are not yet available.

Heat-related deaths average 600 per year in the United States, according to the Centers for Disease Control and Prevention. That number will continue to slowly increase in a nonlinear fashion with a warming climate, and some years will be much worse than others. For example, a 2003 heat wave in mostly non-air-conditioned Europe killed 70,000. Those kinds of horrific numbers are very unlikely here in the foreseeable future.

More flooding rains unrelated to tropical cyclones are occurring with greater frequency, as accurately predicted in 1980s climate models. More heating leads to more evaporation and more water vapor available for precipitation. For every 1 degree Celsius increase in atmospheric temperature, the air can hold an additional 7 percent more water vapor. As an example of what this kind of increased atmospheric vapor load can produce, consider flooding in a portion of Maryland not far from Baltimore that came from 8 inches of rain in two hours. It was the second time in two years that such flooding had occurred in the same region. The fourth National Climate Assessment released this past autumn notes U.S. annual rainfall has increased by 5 percent since 1990, despite lengthy regional droughts in arid regions.

Then, too, there is the amount of massive flooding and the mudslides that occur after heavy rain in places like wildfire-stricken California after hundreds of hills are denuded of vegetation.

Some good weather news: Since records began in 1950, this was the first year in which there were no “violent” (EF-4 or EF-5) tornadoes. And 2018 was also the least deadly on record since 1875, with only 10 fatalities. Tornado frequency on an annual basis is decidedly nonlinear and inconsistent. Ties to tornado frequency and intensity from a warming climate are poorly understood. It was as recently as April 2011 when tornadoes in Alabama killed hundreds, and just two months later the EF-5 tornado in Joplin, Mo., killed 158.

We still have vast populations and structures lying in harm’s way from increasing extreme weather events and flooding. Some events will have direct links to our mean warming climate, and some will have weaker or even no demonstrable links. But there can be no question the warming climate itself is linked to human activity.

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