Many US heat records from 1930s, but average temps still rising | Fact check

Kate S. Petersen, USA TODAY
·4 min read

The claim: Post implies past July heat records show there is no contemporary climate change

A June 29 Facebook post (direct link, archive link) shows a map of the U.S. with purported July high-temperature records listed for each state. Most of the listed heat records were set before 1940.

"Wow, climate change was really bad ~100 years ago," reads the caption.

The post was shared more than 100 times in two weeks.

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Our rating: Missing context

The implied claim is wrong. Average U.S. and global temperatures are increasing due to climate change, according to long-term temperature records. The fact that past extreme weather events produced record-high temperatures does not mean that sustained warming isn't happening.

Average US temperatures continue to rise

Since 1940, average U.S. temperatures have risen around 1.8 degrees in July and more than 2 degrees when all months are considered, according to National Oceanic and Atmospheric Administration data. All states in the continental U.S. have warmed, as have Hawaii and Alaska.

Worldwide, average temperatures have risen around 1.8 degrees since 1940, and the rate of warming has increased significantly since 1982.

These findings have been corroborated by many climate research organizations, which report similar long-term warming trends. Researchers worldwide have also documented the consequences of this warming, which includes polar ice loss and sea level rise.

More: Can we count on renewable energy? Four ways wind, solar and water can power the US

The sustained warming trend in the U.S. is causing:

Modern global warming is caused by greenhouse gas emissions from human activity, according to NASA.

Weather can cause extreme temperatures, differs from climate

The map in the Facebook post is labeled as having been created by Chris Martz, who did not respond when USA TODAY asked about the source of the data.

However, many of the state temperature figures and dates in the map appear to correspond to NOAA data for record-high temperatures that were set in July. The data for some states is slightly off.

USA TODAY was unable to locate official July high-temperature record data for 17 states, but when all months are considered, more than half of state record temperatures were set in the 1930s or earlier.

However, a record-high temperature is set during an extreme weather event that cannot, by itself, be used to determine whether an area's climate is changing over time, Sean Birkel, the Maine state climatologist, previously told USA TODAY.

"Variability within the climate system can produce remarkable extremes associated with the happenstance of weather," he said. "A single record high or low temperature in one spot on the planet does not provide the context needed for understanding climate. Climate is measured from weather conditions – including temperature, precipitation, wind, etc. – that are averaged over many years or decades."

When the entire record is considered, temperatures are clearly increasing in the U.S. and worldwide.

Many U.S. high-temperature records were set during the 1930s, a time when droughts, heat waves and poor farming techniques contributed to extreme heat throughout the central U.S.

USA TODAY reached out to the Facebook user who shared the post for comment but did not immediately receive a response.

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This article originally appeared on USA TODAY: Old extreme heat records consistent with global warming | Fact check

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