Originally published on Forbes.com on July 14, 2021

Figure 1. Number of events (bars, left axis) and total cost (lines, right axis) of billion-dollar weather disasters in the US between 1980 and 2020 (adjusted for CPI). Source: NOAA.

Western US and Canada are going through a rough period of heat waves. This past week, Death Valley reached 130F and broke the previous day-record of 129F in 1913. Las Vegas shot up to 117F and tied the all-time high set in 1942. Drought conditions are rated from extreme to exceptional in much of California, Nevada, and Arizona.

The debate about extreme weather/climate events and whether they can be attributed to global warming is alive and well. This debate is in focus for the fossil fuel industry, because fossil fuels are the cause of 75% of global greenhouse (GHG) emissions, which most scientists believe are driving global warming. The oil and gas industry are contributing at least 40% of global GHG emissions.

Oil and gas companies based in Europe are reinvesting in renewable energies in a direct approach to reduce their oil and gas production.

But in the US, companies are more cautious, preferring to make indirect changes such as greening their operations, reducing methane leaks in wells and pipelines, and supporting carbon capture and storage (CCS).

To settle the debate, focusing on a single extreme weather event won’t do it. Yes, there may be an effect of global warming in the latest extreme weather event, but it’s hard to tease it out from other weather patterns, such as El Ninos.

The proper way is to look for worsening trends in data over a lengthy period, such as the past 50 years, when global warming temperature has risen at least 0.5°C. This is the subject of this article.

Physical effects of climate change.

Physical data on global warming is incontrovertible. These are measured results or consequences of the extra heat energy that the earth is getting:

• Arctic sea ice is melting as seen on satellite photos in summer.
• Glaciers are retreating except for a few that have increased due to extra snow.
• Sea level is rising at 2-3 mm per year at present, as measured by satellite.
• Corals are bleaching and intervals between bleaching are narrowing, such as the Great Barrier Reef.

Humanitarian effects of climate change.

These are climate effects related to human suffering or loss of life. Gregory Wrightstone in his book called Inconvenient Facts, argues that global droughts, wildfires, tropical storms and hurricanes, when plotted over the past 50 years or so, do not show worsening trends and do not support climate change due to global warming.

NOAA has released data on extreme weather events in the US for the years 1980 – 2020. In this 40-year period, the global temperature has gone up a little over 0.5°C (NOAA’s own data), compared with over 1.1°C since the industrial revolution began in 1850.

Figure 1 shows there were a total of 291 disasters costing more than $1 billion. The total cost almost reached $2 trillion, compared with the annual US budget revenue of $3.4 trillion for 2020.

The upward bending trend is compelling that weather disasters are worsening. No turnover of the curve can be seen. But let’s dissect the data of Figure 1.

First – droughts and wildfires. The number of droughts and wildfires in each year have not increased (Figure 2), but both are occurring more frequently (meaning in more years). Droughts occur in the west and south of US, while wildfires are concentrated in the west.

The climate change connection? Higher temperatures over deserts implies lower rainfall, longer summers, and more heat waves and droughts. One study showed an average temperature that was higher by just 1 degree was the cause of greater wildfire damage over the Northern Rockies.

Figure 2. Number and cost of billion-dollar droughts and wildfires in the US in the past 40 years. Source: NOAA.

While the total number of wildfires dropped by 25% between 1991 and 2020, the total burned area increased by almost 4 times and reflects the increasing frequency of Figure 2. Three of the largest burned areas were in 2015, 2017, and 2020. The burned area is a better indicator of wildfire disaster.

Second – severe storms, which are mostly tornadoes, hail and storm damage. Figure 1 makes it clear that the number and cost of severe storms has worsened since 1980. This is the strongest trend of all weather events in the figure.

Third – flooding. Billion-dollar flooding events tend to occur close to the Gulf of Mexico or large rivers, where heavy rainstorms, 10 – 20 inches, depend on a warm source of moisture. A closer look at Figure 1 makes it clear that the number and cost of flooding in the US has worsened since 1980, but the trend is weaker than severe storms in Figure 1. 

A three-day flood occurred in southeast Louisiana in August 2016, with over 30 inches of rain falling in some places. The climate change connection? More water vapor in the air instigates extremely heavy rainfall. In one study, climate models predicted 10% more rainfall and a 40% greater chance of such flooding (meaning a return period reduced from 50 to 30 years).

Figure 3. Tropical cyclones are coastal hurricanes along the south and east coasts of the US. Source: NOAA.

Fourth – hurricanes along the US coast. The number and cost of hurricane disasters has worsened since 1980, but this is only a weak trend (Figure 3). These are the most costly disasters, partly because their damage can extend far inland via huge amounts of rainfall and flooding.

The graph shows that 2017 has a huge spike of costs in 2017 while 2020 has a big spike in number of billion-dollar events. When combined, the black line of the figure (5-year averaged costs) shows a pretty big hump in the last five years, although its only slightly bigger than the earlier hump around 2007.

As reported by NOAA, “The U.S. experienced [in 2020] a record-breaking number of named tropical cyclones (30), eclipsing the record of 28 set in 2005, the year of Hurricane Katrina. Of these 30 storms, a record 12 made landfall in the United States. And 7 of the 12 became billion-dollar disasters—also a new record.”

Separating out effects of climate change.

According to NOAA, the data can be biased by population increase and growth of towns and cities and crop insurance coverage in areas that are vulnerable such as the Gulf Coast of Florida.

The billion-dollar disasters have been normalized for CPI over time, but not for changes in exposure due to (1) population growth, (2) demographic shifts, and (3) rising value of property at risk. Whether these factors can explain all of the trend of increasing disasters of Figure 1 will require more study.

The total number of billion-dollar disasters increased by 8 times between 1980 and 2020 (Figure 1.) Meanwhile the number of US houses increased by a factor of 1.6 in this time. This doesn’t bridge the gap but insurance losses for houses, buildings and agriculture would need further study. 

The last five years is a statistical anomaly in the 40-year period of 1980-2020 (Figure 4). The top six disaster years, in terms of number of extreme events, include 2016-2020 plus one outlier: 2011. The relatively sudden increase of disasters in the years 2016-2020 is a statistical argument against an explanation in terms of more gradual population bias and growth of towns and cities and insurance coverages.

Figure 4. 2020 has more extreme events than any other year since 1980.   Source: NOAA.

The year 2021 seems to be heading in the same direction. Normally-cool Canada was embraced by a heat wave dome at the end of June. One town, Lytton in BC, recorded a temperature that was 4C higher than the previous all-time high for the whole of Canada. A research team was quoted as saying it was a 1-in-a-1,000 year event, and that the heat wave was virtually impossible without climate change. Sadly, the town of Lytton burned down during the heat wave.

But, to be fair, statistical anomalies in disasters have occurred before. Much larger anomalies in heat waves took place in the “dustbowl” years in the 1930s – for almost 10 years when the heat wave index averaged 0.6 compared to the 5 years of 2015-2020 when it was 0.1.

Although there is a small trend of heat wave index increasing from 1960 to the present, the overall plot from 1895 to 2020 is definitely not a gradually worsening condition that could be blamed on global warming.  

The year 2021 seems to be heading in the same direction. Normally-cool Canada was embraced by a heat wave dome at the end of June. One town, Lytton in BC, recorded a temperature that was 4C higher than the previous all-time high for the whole of Canada. A research team was quoted as saying it was a 1-in-a-1,000 year event, and that the heat wave was virtually impossible without climate change. Sadly, the town of Lytton burned down during the heat wave.

But, to be fair, statistical anomalies in disasters have occurred before. Much larger anomalies in heat waves took place in the “dustbowl” years in the 1930s – for almost 10 years when the heat wave index averaged 0.6 compared to the 5 years of 2015-2020 when it was 0.1.

Although there is a small trend of heat wave index increasing from 1960 to the present, the overall plot from 1895 to 2020 is definitely not a gradually worsening condition that could be blamed on global warming.  

Role of global warming.

It is possible that half a degree C of temperature change can influence certain billion-dollar weather disasters in the US. A 1C rise can cause wildfire areas to expand, and can magnify flooding because water vapor holds more water. Also, along the southeast coastline, warmer ocean temperature is known to intensify hurricanes.

The billion-dollar disasters that dominate the US since 2015, with 2020 the grandfather of all years, appears to statistically support this case (2020 is also when earth reached its highest temperature since the year 1600.)

The research team that looked at the recent Canada heat wave said the extreme temperature at Lytton  (4C above the all-time high for Canada) lay so far outside the historical range that it should never have occurred. Past data reveals a gradual increase in heat extremes, perhaps by 1C at most, because the climate is very stable — but Lytton has challenged that view.

It begins to look like population bias is only a part of the increase of billion-dollar disasters. This means the other part is due to global warming. Although more work is needed to sort this out, it is clear that the cost to the US of such disasters is enormous and it is accelerating. It would be good for the fossil energy industry to address this acceleration and deal with it before it gets much worse – and it is getting worse.