Home » Climate Change » The First Half of 2018 Was Hot, but Not Record-Breaking

The First Half of 2018 Was Hot, but Not Record-Breaking


Figure 1. Source: National Oceanographic and Atmospheric Administration, 2018.

The first half of the year was hot across the USA, but not record-breaking. So says data published by the National Oceanographic and Atmospheric Administration, on their Climate-At-A-Glance data portal.

Figure 1 shows the average temperature across the 48 contiguous states for the months January – June. Nationwide, the first half of 2018 was the 13th hottest on record. There is a lot of variation from year-to-year, but the data show 4 distinct periods: at the beginning of the 20th Century, the average temperature was lower. During the 1930s-1950s, it was higher. From the 1960 to about 1980, it was cooler again, but not as cool as at the turn of the century. Then, beginning about 1980, the temperature began an upward trend. This upward trend is larger than any other trend in the record, due to global warming.

For larger view, click on figure.

Figure 2. Source: National Oceanographic and Atmospheric Administration, 2018.

Figure 2 shows the average temperature in Missouri for the months January – June. The first half of 2018 was the 93rd hottest on record across Missouri (out of 124 years). If you look more closely, the data reveal that May and June have been extremely hot, but the average across the period is lowered by the fact that we had an extraordinarily cool April – the 2nd coolest on record.







Figure 3. Data source: Hayhoe et al., 2003; Weather Underground, 2018.

Since the end of April, it has been hot; we’ve had a long stretch of days with the temperature above 90. In Missouri, May – June were the hottest on record. If climate change projections are correct, however, it’s nothing compared to what’s coming by the end of the century. Climate modelers have projected that under the high emissions scenario (which we continue to follow), by the end of the century the average number of days each summer when the high temperature reached above 90°F will triple, from 36 to 105. There will be 43 days above 100, the predict. (See here.) To try to figure out what that meant, I put a 105-day stretch on a calendar, and discovered that it would stretch from mid-June through the final weeks of September. I’ve reproduced that calendar as Figure 3. Dates projected to be above 90 are in orange, dates projected to be above 100 are in red. For comparison, I’ve marked on it the days in 2018 when the temperature was actually above 90°F in yellow, and dates when the temperature topped out below 90 in white. Dates in black had not yet occurred when the graphic was created (7/15/18).

You can see that we have a long way to go to equal what is predicted for us by the end of the century.

In terms of precipitation, the first half of 2018 was very close to average across Missouri (Figure 4). Across the Contiguous USA, it was just a touch above average (Figure 5). However, the averages do not tell the full story. After suffering a severe multi-year drought, the American West experienced a wet winter in 2017, but dry conditions returned in 2018. More on this in the next post, but Figure 6 shows that a drought centered on the Four Corners Area has once again gripped much of the West.

Figure 4. Source: National Oceanographic and Atmospheric Administration, 2018.

Figure 5. Source: National Oceanographic and Atmospheric Administration, 2018.









Figure 6. Source: Riganti, 2018.

All-in-all, for the first half of the year, the temperature and precipitation pattern for Missouri and the Contiguous USA were consistent with climate change predictions contained in the reports of the Intergovernmental Panel on Climate Change and the U.S. Global Change Research Program. Not every year will be a record year, they predict, but the trend will be towards warmer temperatures. Changes in precipitation will vary by region. For Missouri the reports predict no change or a slight increase in the average annual amount of precipitation.

Extremely hot days are associated with a number of undesirable effects, including increased deaths from heat exhaustion, increased respiratory illness, and reduced productivity. For a fuller discussion, see here.


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.

National Oceanographic and Atmospheric Administration. 2018. Climate-at-a-Glance. Data downloaded 2018-07-19 from https://www.ncdc.noaa.gov/cag/national/time-series.

Riganti, Curtis. 2018. U.S. Drought Monitor, July 17, 2018. National Drought Mitigation Center. Downloaded 7/19/2018 from http://droughtmonitor.unl.edu.

Weather Underground. St. Louis Downtown, IL >> History >> Monthly. Downloaded 2018-07-19 from https://www.wunderground.com/history/monthly/us/il/cahokia/KCPS/date/2018-7?cm_ven=localwx_history.

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