Severe Weather Is Increasing in the US because of Climate Change

 Watching the collection of network news programs, one is struck by the rate at which severe weather events or threats of severe weather are presented.  Almost daily, there are weather maps with various bright colors indicating potential flooding, tornadoes, blizzards, and such.  Is this a change in reporting strategy, or is climate change really causing dramatic changes in weather patterns?  When global warming first became a news topic, it seemed that noticeable changes might be expected on a century timeframe.  Now it appears that change is coming much more rapidly.  Is the rate of change down to the decade scale, or is it even quicker than that? 

A quick survey of easily available data provides some insight.  Since carbon dioxide (CO2) is the main driver for warming, one should realize that for all the talk of carbon reduction there is little indication that the rise in atmospheric CO2 concentration has been altered.  It continues to rise at an increasing rate.  Consider data from the Environmental Protection Agency (EPA).

This chart accounts for other greenhouse gases by converting their various effects into CO2 equivalences.

This presents a more precise picture and suggests greenhouse gases continue to increase but perhaps at a slightly slower rate.

The effect of global warming is to produce air and water possessing more energy.  Warmer air can hold more moisture and warmer oceans can produce that additional moisture.  With more energy and moisture available one would expect more extreme weather events.  The EPA provides a short summary of several observable weather features over time.

“U.S. and Global Temperature.Average temperatures have risen across the contiguous 48 states since 1901, with an increased rate of warming over the past 30 years. Eight of the top 10 warmest years on record have occurred since 1998. Average global temperatures show a similar trend, and all of the top 10 warmest years on record worldwide have occurred since 2005. Within the United States, temperatures in parts of the North, the West, and Alaska have increased the most. “

“Seasonal Temperature.  As the Earth warms overall, average temperatures increase throughout the year, but the increases may be larger in certain seasons than in others. Since 1896, average winter temperatures across the contiguous 48 states have increased by nearly 3°F. Spring temperatures have increased by about 2°F, while summer and fall temperatures have increased by 1.4°F. “ 

“High and Low Temperatures.Many extreme temperature conditions are becoming more common. Since the 1970s, unusually hot summer days (highs) have become more common over the last few decades in the United States. Unusually hot summer nights (lows) have become more common at an even faster rate. This trend indicates less “cooling off” at night. Although the United States has experienced many winters with unusually low temperatures, unusually cold winter temperatures have become less common—particularly very cold nights (lows). Record-setting daily high temperatures have become more common than record lows.”

“Heat Waves.   Heat waves are occurring more than they used to in major cities across the United States. Heat waves are occurring three times more often than they did in the 1960s—about six per year compared with two per year. The average heat wave season is 47 days longer, and individual heat waves are lasting longer and becoming more intense. “

The following chart illustrates the significant decade-by-decade changes observed in heat wave data. 

“U.S. and Global Precipitation.  Total annual precipitation has increased over land areas in the United States and worldwide. Since 1901, precipitation has increased at an average rate of 0.1 inches per decade over land areas worldwide. However, shifting weather patterns have caused certain areas, such as the Southwest, to experience less precipitation than usual.”

“Heavy Precipitation.  In recent years, a higher percentage of precipitation in the United States has come in the form of intense single-day events. The prevalence of extreme single-day precipitation events remained fairly steady between 1910 and the 1980s but has risen substantially since then. Nationwide, nine of the top 10 years for extreme one-day precipitation events have occurred since 1996. The occurrence of abnormally high annual precipitation totals (as defined by the National Oceanic and Atmospheric Administration) has also increased.”

“Tropical Cyclone Activity.  Tropical storm activity in the Atlantic Ocean, the Caribbean, and the Gulf of Mexico has increased during the past 20 years. Storm intensity, a measure of strength, duration, and frequency, is closely related to variations in sea surface temperature in the tropical Atlantic and has risen noticeably during that time. However, changes in observation methods over time make it difficult to know for sure whether a longer-term increase in storm activity has occurred. Records collected since the late 1800s suggest that the actual number of hurricanes per year has not increased.”

“River Flooding.  Increases and decreases in the frequency and magnitude of river flood events vary by region. Floods have generally become larger across parts of the Northeast and Midwest and smaller in the West, southern Appalachia, and northern Michigan. Large floods have become more frequent across the Northeast, Pacific Northwest, and parts of the northern Great Plains, and less frequent in the Southwest and the Rockies.”

“Drought.  Average drought conditions across the nation have varied over time. The 1930s and 1950s saw the most widespread droughts, while the last 50 years have generally been wetter than average.  Specific trends vary by region, as the West has generally experienced more drought while the Midwest and Northeast have become wetter. A more detailed index developed recently shows that over the period from 2000 through 2020, roughly 20 to 70 percent of the U.S. land area experienced conditions that were at least abnormally dry at any given time. However, this index has not been in use for long enough to compare with historical drought patterns.”

One of the weather features most observable and most newsworthy is the incidence of tornadoes.  It was not covered by the EPA report, but this source provided annual incidence data over the period 1950-2020.  The number of tornadoes observed is low in the early years, gradually increasing until about 1990.  Over that period from 1950 to 1990, the annual average of observed tornadoes was 710.  Over the period 1990-2020, the annual average was 1229.  The incidence rate was higher and rather flat suggesting that the differences may be due to more precise detection and recording methods rather than an actual increase in rate.  Another source provided a more interesting way to look at tornado data as it relates to climate change.

“Annual tornado activity from 1955 to 2013.  The black squares represent the number of days per year with a tornado classified as a E(F1) or greater, and the black line and circles represents the decade’s average number of tornado days.  The red triangles represent the number of days per year that had more than 30 tornadoes classified as (E)F1 or greater, while the red line and circles represent the decade’s average number of tornado outbreaks.”

The number of days when a tornado was observed began falling after about 1975.  This may indicate that the number of storms that are generated and propagate across the nation has decreased as well.  What has changed is the number of incidences when a storm condition can generate 30 or more tornadoes in a single day.  Perhaps there is some sort of threshold of energy and/or moisture content that more easily generates tornadoes.  The annual tornado incidence data could be interpreted as an increase in these multiple tornado events as the world became warmer.

There is another way to look at weather severity.  “Follow the money” is usually productive advice.  This source provides tabulations of costs of severe weather events over the period 1980-2020.  The annual cost (in billions of dollars) from severe weather incidents, averaged over a decade, increased from 18.4 in the 1980s, to 28.48 in the 1990s, to 53.98 in the 2000s, to 84.5 in the 2010s.  Those costs are growing at a greater than inflation rate, suggesting that climate change is providing more destructive and costly events.  It is even more ominous to tally the maximum damage cost of any year within a decade.  That quantity increases from 45 in the 1980s to 65 in the 1990s, to 235 in the 2000s, to 330 in the 2010s.

Yes, it appears that climate change is increasing weather severity, and the severities are increasing from decade to decade.  The data is not able to indicate definitively that the rate of change is accelerating, but it would not be surprising if it was. 

Climate change is no longer an issue that can be put off to the next generation.  It is happening now and it is getting worse.

You can learn a little about a lot of things or you can learn a lot about a very few things. Guess which is the most fun.