Home » Climate Change » Climate Predictions for St. Louis: Dangerously Hot

Climate Predictions for St. Louis: Dangerously Hot


Only in recent years have advances in climate modeling made it possible for climate scientists to start modeling climate on a regional or local level. Previously, projections could only be made for large areas, such as the United States or all of North America. Two studies have now modeled climate projections for St. Louis, and a third has modeled them for Columbia. When I discussed local climate change in my posts on the National Climate Assessment (see here), I was interpreting color gradations off of maps covering larger areas. These studies focus directly on areas in Missouri.

In the next couple of posts I’m going to report on 3 of these studies. Before I start, however, I want to note that each study uses a different method, and makes different assumptions about how people will respond to climate change. The result is that while each study provides information about how the climate will change in Missouri, their results are not directly comparable. Further, please note that all climate change projections contain some uncertainty, and with projections for local areas, that uncertainty is magnified.

Hayhoe, VanDorn, Naik, and Wuebbles (2009) studied climate change in the Midwest, including St. Louis. The effects of climate change are expected to be sensitive to how humans respond to climate change. If we curtail our emissions, they are expected to be less. If emissions remain high, they are expected to be greater. The Hayhoe group studied emissions using a low emissions scenario (B2) and a high emissions scenario (A1fi). The B2 scenario is a commonly used low emissions scenario, while the A1fi scenario is the highest emissions scenario available.

Table 1 shows the projected change in the annual average temperature (°F) for 3 time periods under the low and high emissions scenarios.

Temp Change Table

(Click on tables or charts for larger view.)

The projections in Table 1 are for the Midwest as a whole. They show that the increase is expected to grow as time passes, that the differences between the emissions scenarios increase over time, and that the increase in temperature is projected to be larger during the summer than the winter. Even under the low emissions scenario, the average annual temperature is projected to increase 5.0°F by the end of the century, and it is expected to increase by a whopping 10°F under the high emission scenario.

The Hayhoe group was interested in looking at more than just change in average annual temperature, however. The way in which climate change is most likely to directly impact Missouri is through a change in extremely hot days. In urban areas, extremely hot days can be killers. In 2003, an extended heat wave in Europe killed an estimated 70,000 people, and in Chicago, a heatwave in 1995 killed 500 people in just 4 days. What, the Hayhoe group wondered, was in store for the Midwest?

They looked at 9 Midwestern cities, including St. Louis. They found that currently St. Louis experiences 36 days over 90°F each year, and 2 days over 100°. But under the high emissions scenario, they projected that by the end of the century St. Louis would experience 105 days over 90° and 43 over 100°. I constructed charts to illustrate the change. They show the days occurring consecutively, centered on the end of July. Figure 1 shows the current situation, Figure 2 shows Hayhoe et al’s projection.

Hot Day Calendar Past

Figure 1: Current days over 90°F (orange) and over 100°F (red), 2070-2099. Data source: Hayhoe et al 2009.

Hot Day Calendar Future

Figure 2: Projected days over 90°F (orange) and 100°F (red), 2070-2099. Data source: Hayhoe et al 2009.









Under the Hayhoe projection, days over 90° begin June 10, and continue through September 22. That’s more than 3 months. Days over 100° begin July 11 and continue through August 22. That’s almost a month-and-a-half. Can you imagine 43 days with temperatures over 100°?

Figure 3: High temperature at Midway Airport, Chicago, Summer 1995. Data: Weather Underground

Figure 3: High temperature at Midway Airport, Chicago, Summer 1995. Data: Weather Underground

For comparison sake, Figure 3 shows the high temperature at Midway Airport in Chicago during the summer of 1995, the year of their heat wave. There were only 28 days where the high was above 90°, and only 2 days when the high was above 100°.

The Hayhoe group projected that climate change would bring Missouri no more than a slight increase in precipitation. They projected, however, that there would be a 22% reduction in summer precipitation, when it is most needed, and an increase during the remainder of the year. Further, they projected that more precipitation would occur during heavy precipitation events (more than 2 inches per day), with longer, hotter dry periods between. There have been two recent examples of heavy precipitation events: in late December, up to 8 inches of rain fell over 2-1/2 days in Missouri. In March, up to 20 inches of rain fell over 4 days in Louisiana. Both resulted in severe record flooding.

There are many ways in which climate change might bring indirect effects to Missouri. Hot, humid summers might cause a decrease in air quality, leading to an increase in asthma and other respiratory diseases. Hotter summers and warmer, wetter winters might lead to an increase in disease vectors, such as ticks and mosquitoes. Warmer temperatures may threaten water quality during parts of the year, etc. The list could go on.

The Hayhoe et al projections are the most dire of the 3 I will review, perhaps because they used the A1fi Scenario, the highest emission scenario. In the next post, I will report on climate projections for the St. Louis Region by local researcher John Posey.


Hayhoe, K, J VanDorn, V. Naik, and D. Wuebbles. 2009. “Climate Change in the Midwest: Projections of Future Temperature and Precipitation.” Technical Report on Midwest Climate Impacts for the Union of Concerned Scientists. Downloaded from http://www.ucsusa.org/global_warming/science_and_impacts/impacts/climate-change-midwest.html#.VvK-OD-UmfA.

Weather Underground. 2016. Chicago, IL. Data downloaded 3/8/16 from https://www.wunderground.com/us/il/chicago.


  1. Judy Pass says:

    Truly frightening. I’m reading your post on my IPad. Is that why I can’t see Figures 1, 2, & 3?

    Judy Judyhpass@gmail.com Sent from my iPad


    • mogreenstats says:

      Sorry about that. The post accidentally “went live” before I had finished writing it. The completed version should have gone live Thursday morning.

  2. Katharine Hayhoe says:

    Unless Posey uses a downscaling method that resolves the tails of the daily distribution of temperature AND downscales to a weather station, his extremes will be lower because of spatial averaging. Differences in temperature variables also depend on the scenario used, which is highER and lowER in our case, not high and low (implying that the future will fall between those bounds). Have to be super-careful with these comparisons, there is a high risk of apples to oranges if not.

    • mogreenstats says:

      Thank you for the clarifications, I’m glad to have it. Would you agree with the overall conclusion of the post, that the differences between your temperature projections and Posey’s were generally consistent with the different scenarios used?

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