No Evidence That Climate Change Causes Weather Extremes: (4) Tornadoes

Tornadoes are smaller and claim fewer lives than hurricanes. But the roaring twisters can be more terrifying because of their rapid formation and their ability to hurl objects such as cars, structural debris, animals and even people through the air. Nonetheless, the narrative that climate change is producing stronger and more deadly tornadoes is as fallacious as the nonexistent links between climate change and other weather extremes previously examined in this series.

Again, the UN’s IPCC (Intergovernmental Panel on Climate Change), whose assessment reports constitute the bible for the climate science community, has dismissed any connection between global warming and tornadoes. While the agency concedes that escalating temperatures and humidity may create atmospheric instability conducive to tornadoes, it also points out that other factors governing tornado formation, such as wind shear, diminish in a warming climate. In fact, declares the IPCC, the apparent increasing trend in tornadoes simply reflects their reporting by a larger number of people now living in remote areas.

A tornado is a rapidly rotating column of air, usually visible as a funnel cloud, that extends like a dagger from a parent thunderstorm to the ground. Demolishing homes and buildings in its often narrow path, it can travel many kilometers before dissipating. The most violent EF5 tornadoes attain wind speeds up to 480 km per hour (300 mph).

The U.S. endures by far the most tornadoes of any country, mostly in so-called Tornado Alley extending northward from central Texas through the Plains states. The annual incidence of all U.S. tornadoes from 1954 to 2017 is shown in the figure below. It’s obvious that no trend exists over a period that included both cooling and warming spells, with net global warming of approximately 1.1 degrees Celsius (2.0 degrees Fahrenheit) during that time.

But, as an illustration of how U.S. tornado activity can vary drastically from year to year, 13 successive days of tornado outbreaks in 2019 saw well over 400 tornadoes touch down in May, with June a close second – and this following seven quiet years ending in 2018, which was the quietest year in the entire record since 1954. The tornado surge, however, had nothing to do with climate change, but rather an unusually cold winter and spring in the West that, combined with heat from the Southeast and late rains, provided the ingredients for severe thunderstorms. 

The next figure depicts the number of strong (EF3 or greater) tornadoes observed in the U.S. each year during the same period from 1954 to 2017. Clearly, the trend is downward instead of upward; the average number of strong tornadoes annually from 1986 to 2017 was 40% less than from 1954 to 1985. Once more, global warming cannot have played a role. 

In the U.S., tornadoes cause about 80 deaths and more than 1,500 injuries per year. The deadliest episode of all time in a single day was the “tri-State” outbreak in 1925, which killed 747 people and resulted in the most damage from any tornado outbreak in U.S. history. The most ferocious tornado outbreak ever recorded, spawning a total of 30 EF4 or EF5 tornadoes, was in 1974.

Tornadoes also occur more rarely in other parts of the world such as South America and Europe. The earliest known tornado in history occurred in Ireland in 1054. The human toll from tornadoes in Bangladesh actually exceeds that in the U.S., at an estimated 179 deaths per year, partly due to the region’s high population density. It’s population growth and expansion outside urban areas that have caused the cost of property damage from tornadoes to mushroom in the last few decades, especially in the U.S.

Next: No Evidence That Climate Change Causes Weather Extremes: (5) Wildfires

No Evidence That Climate Change Causes Weather Extremes: (3) Hurricanes

This third post in our series on the spurious links between climate change and extreme weather examines the incidence of hurricanes – powerful tropical cyclones that all too dramatically demonstrate the fury nature is capable of unleashing.

Although the UN’s IPCC (Intergovernmental Panel on Climate Change) has noted an apparent increase in the strongest (Category 4 and 5) hurricanes in the Atlantic Ocean, there’s almost no evidence for any global trend in hurricane strength. And the IPCC has found “no significant observed trends” in the number of global hurricanes each year.

Hurricanes occur in the Atlantic and northeastern Pacific Oceans, especially in and around the Gulf of Mexico; their cousins, typhoons, occur in the northwestern Pacific. Hurricanes can be hundreds of miles in extent with wind speeds up to 240 km per hour (150 mph) or more, and often exact a heavy toll in human lives and personal property. The deadliest U.S. hurricane in recorded history struck Galveston, Texas in 1900, killing an estimated 8,000 to 12,000 people. In the Caribbean, the Great Hurricane of 1780 killed 27,500 and winds exceeded an estimated 320 km per hour (200 mph). The worst hurricanes and typhoons worldwide have each claimed hundreds of thousands of lives.

How often hurricanes have occurred globally since 1981 is depicted in the figure below.

You can see immediately that the annual number of hurricanes overall (upper graph) is dropping. But, while the number of major hurricanes of Category 2, 3, 4 or 5 strength (lower graph) seems to show a slight increase over this period, the trend has been ascribed to improvements in observational capabilities, rather than warming oceans that provide the fuel for tropical cyclones.

The lack of any trend in major global hurricanes is borne out by the number of Category 3, 4 or 5 global hurricanes that make landfall, illustrated in the next figure. 

It’s clear that the frequency of landfalling hurricanes of any strength (Categories 1 through 5) hasn’t changed in the nearly 50 years since 1970 – during a time when the globe warmed by approximately 0.6 degrees Celsius (1.1 degrees Fahrenheit). So the strongest hurricanes today aren’t any more extreme or devastating than those in the past. If anything, major landfalling hurricanes in the U.S. are tied to La Niña cycles in the Pacific Ocean, not to global warming.

Data for the North Atlantic basin, which has the best quality data available in the world, do, however, show heightened hurricane activity over the last 20 years. The figure below illustrates the frequency of all North Atlantic hurricanes (top graph) and major hurricanes (bottom graph) for the much longer period from 1851 to 2018.

What the data reveals is that the annual number of major North Atlantic hurricanes during the 1950s and 1960s was at least comparable to that during the last two decades when, as can be seen, the number took a sudden upward hike from the 1970s, 1980s and 1990s. But, because the earth was cooling in the 1950s and 1960s, the present enhanced hurricane activity in the North Atlantic is highly unlikely to result from global warming.

Even though it appears from the figure that major North Atlantic hurricanes were less frequent before about 1940, the lower numbers simply reflect the relative lack of observations in early years of the record. Aircraft reconnaissance flights to gather data on hurricanes didn’t begin until 1944, while satellite coverage dates from only 1966. While the data shown in the figure above has been adjusted to compensate for these deficiencies, it’s probable that the number of major North Atlantic hurricanes before 1944 is still undercounted.

The true picture is much more complicated, and any explanation of changing hurricane behavior needs to account as well for other factors, such as the now more rapid intensification of these violent storms and their slower tracking than before, both of which result in heavier rain following landfall.

The short duration of the observational record, and the even shorter record from the satellite era, makes it impossible to assess whether recent hurricane activity is unusual for the present interglacial period. Paleogeological studies of sediments in North Atlantic coastal waters suggest that the current boosted hurricane activity is not at all unusual, with several periods of frequent intense hurricane strikes having occurred thousands of years ago.

Next: No Evidence That Climate Change Causes Weather Extremes: (4) Tornadoes

No Evidence That Climate Change Causes Weather Extremes: (2) Floods

Widespread flooding and devastating tornadoes in the U.S. Midwest this May only served to amplify the strident voices of those who claim that climate change has intensified the occurrence of major floods, droughts, hurricanes, heat waves and wildfires. Like-minded voices in other countries have also fallen into the same trap of linking weather extremes to global warming.  

Apart from the IPCC (Intergovernmental Panel on Climate Change)’s dismissal of such hysterical beliefs, an increasing number of research studies are helping to dispel the notion that a warmer world is necessarily accompanied by more severe weather.

A 2017 Australian study of global flood risk concluded very little evidence exists that worldwide flooding is becoming more prevalent. Despite average rainfall getting heavier as the planet warms, the study authors point out that excessive precipitation is not the only cause of flooding. What is less obvious is that alterations to the catchment area – such as land-use changes, deforestation and the building of dams – also play a major role. 

Yet the study found that the biggest influence on flood trends is not more intense precipitation, changes in forest cover or the presence of dams, but the size of the catchment area. Previous studies had emphasized small catchment areas, as these were thought less likely to have been extensively modified. However, the new study discovered that, while smaller catchments do show a trend in flood risk that’s increasing over time, larger catchments exhibit a decreasing trend.

Globally, larger catchments dominate, so the trend in flood risk is actually decreasing rather than increasing in most parts of the globe, if there’s any trend at all. This is illustrated in the figure below, the data coming from 1,907 different locations over the 40 years from 1966 to 2005. Additional data from other locations and for a longer (93-year) period show the same global trend.

But while the overall trend is decreasing, the local trend in regions where smaller catchments are more common, such as Europe, eastern North America and southern Africa, is toward more flooding. The study authors suggest that the lower flood trend in larger catchment areas is due to the expanding presence of agriculture and urbanization.

Another 2017 study, this time restricted to North America and Europe, found “no compelling evidence for consistent changes over time” in the occurrence of major floods from 1930 to 2010. Like the first study described above, this research included both small and large catchment areas. But the only catchments studied were those with minimal alterations and less than 10% urbanization, so as to focus on any trends driven by climate change.

The second figure below shows the likelihood of a 100-year flood occurring in North America or Europe in any given year, during two slightly different periods toward the end of the 20th century. A 100-year flood is a massive flood that occurs on average only once a century, and has a 1 in 100 or 1% chance of occurring or being exceeded in any given year – although the actual interval between 100-year floods is often less than 100 years.

You can see that for both periods studied, the probability of a 100-year flood in North America or Europe hovers around the 1% (0.01) level or below, implying that 100-year floods were no more or less likely to occur during those intervals than at any time. The straight lines drawn through the data points are meaningless. Similar results were obtained for 50-year floods. 

Although the international study authors concluded that major floods in the Northern Hemisphere between 1931 and 2010 weren’t caused by global warming and were no more likely than expected from chance alone, they did find that floods were influenced by the climate. The strongest influence is the naturally occurring Atlantic Multidecadal Oscillation, an ocean cycle that causes heavier than normal rainfall in Europe and lighter rainfall in North America during its positive phase – leading to an increase in major European floods and a decrease in North American ones.

The illusion that major floods are becoming more common is due in part to the world’s growing population and the appeal, in the more developed countries at least, of living near water. This has led to people building their dream homes in harm’s way on river or coastal floodplains, where rainfall-swollen rivers or storm surges result in intermittent flooding and subsequent devastation. It’s changing human wants rather than climate change that are responsible for disastrous floods.

Next: No Evidence That Climate Change Causes Weather Extremes: (3) Hurricanes