Heat Records Falling Around the World in 2018

The first five months of 2018 were the fourth warmest in global records going back to 1880, according to NOAA.  Along the way, a number of extreme heat events have occurred already this year.  In recent weeks across the Northern Hemisphere, these records have included an impressive number of all-time highs (an all-time high is the warmest temperature reported on any date at a given location).

Setting an all-time high is no small accomplishment, especially for locations that have long periods of record (PORs). All-time highs are especially noteworthy when you consider that, on average, the planet is warming more during winter than during summer, and more at night than during the day.  Urban heat islands are no doubt contributing somewhat to the heat records achieved in large urban areas, but the extreme heat of 2018 has also played out in remote rural areas without any urban heat islands.

As of July 13, the U.S. Records summary page maintained by NOAA showed that 18 U.S. locations had set or tied all-time highs so far this year, as opposed to 10 locations that set or tied all-time lows.  There is an even sharper contrast between the number of all-time warm daily lows (40) and all-time cool daily highs (5), which has been a common pattern in recent years.
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The increasing frequency and intensity of heat waves is among the most obvious and well-documented effects of climate change.  For the globe, The 2013 Intergovernmental Panel on Climate Change (IPCC) report noted that “a large amount of evidence continues to support the conclusion that most global land areas analyzed have experienced significant warming of both maximum and minimum temperature extremes since about 1950” and concluded that “it is . . . very likely that human influence has contributed to observed global scale changes in the frequency and intensity of daily temperature extremes since the mid-20th century, and likely that human influence has more than doubled the probability of occurrence of heat waves in some locations.”

Stanford University climate scientist Noah Diffenbaugh published a 2017 study showing how a relatively small shift in the global average surface temperature of just 1°C (1.8°F) in the past century has dramatically increased the odds of extreme heat events.  In the case of the July 2018 California heat wave, Michael Wehner of Lawrence Berkeley National Laboratory, who is working to conduct extreme event attribution studies in advance of an event, said in an interview with axios.com, "[i]n probabilistic terms, climate change increased the chances of the heat wave by about 20 to 50 times," adding that there is at least a 99% likelihood that human-induced climate change "increased the severity of this heat wave."

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