Record February heat in the US is consistent with global warming trend

Temperatures for most of the eastern half of the US in February 2017 have been unseasonably warm, with record highs in the 50s, 60s and even 70s. Dozens of record highs, and all time highs for the month of February, fell between February 16 and 22 in the Plains, Midwest, Great Lakes and East. From February 1 through 28, the US broke 5,452 daily high maximum and 4,686 daily high minimum temperature records, compared to 213 daily low maximum and 84 daily low minimum records.[1] This means there were 34 heat records broken for every one cold record.

Falcon Dam, Texas reported a high temperature of 107°F on February 23, 2017.[2] If verified, this would be the highest temperature ever recorded in the US during February.

Chicago set new daily temperature records on four consecutive days from February 17 through 20, with temperatures reaching 67°F, 70°F, 69°F, and 70°F respectively.

The February 18 temperature reading of 70°F was only the fourth time Chicago reached 70°F in February in records dating back to 1871, and it soon hit 70°F for a fifth time on February 20.[3][4] 

Record or near-record warmth has also been recorded in other towns in the Midwest, including Milwaukee, Madison, Green Bay, Omaha, Minneapolis, and Detroit.[3] After setting several daily record highs between Friday and Tuesday, Milwaukee (71°F), Madison (68°F), and Green Bay (65°F) established all-time February record highs on Wednesday afternoon, February 22.[4]

Daily temperature records were also set in the Northeast. New York City experienced high temperatures in the 60s on February 19, with several locations setting daily records. (JFK airport set a record at 68°F as did LaGuardia airport at 66°F. Central Park was 65°F, 1°F shy of its daily record.)

On February 24, many northeastern cities—including Boston, Buffalo and Cincinnati—achieved all-time record February warmth with temperature in the 70s.[5]

To see comprehensive lists of temperature records set in February 2017, see these two by Jason Samenow in the Washington Post[4][5], and Linda Lam's piece at The Weather Channel.[7]

Extreme heat events, such as the February heat waves in the US, are the kind of weather events that increase the most as the climate warms. The more extreme the heat wave, the more likely it is due to the change in the climate. And global warming has led to a dramatic surge in the frequency of the most extreme heat events.

As climate change advances, spring is arriving much sooner

The timing of leaf-out, migration, flowering and other seasonal phenomena in many species is closely tied to local weather conditions and broad climatic patterns.[8] In 2017, spring blooms and foliage are running 3 weeks earlier than normal across much of the southern and central United States due to warm weather.[8]

Snow and ice levels were also at near historic lows due to warm weather on February 21, 2017.[4] Snow covered 16.5 percent of the Lower 48 states, the second lowest amount since the National Oceanic and Atmospheric Administration began keeping records in 2004.[4] Only 2016's 16.1 percent, on this date, was lower.

Observed long-term trends towards shorter, milder winters and earlier spring thaws are altering the timing of critical spring events such as bud burst (the emergence of new leaves on a plant at the beginning of each growing season) and emergence from overwintering (the process by which some organisms pass through or wait out the winter season).[9]

In North America as a whole, the length of time in a calendar year when temperatures are consistently warm enough for agricultural activity lengthened by 6 days between 1982 and 2011.[10]

Global warming increases the frequency of record heat

A small shift in climate leads to a dramatic increase in the frequency of temperatures at the high end. The very most extreme events are the events most affected by climate change. As the average global temperature rises and the climate shifts, hot temperatures that were extreme under the old climate are closer to the middle of the new temperature range. Under the earth's climate system events closer to the midpoint of the climate range occur much more frequently than events closer to the extremes, as shown in the graphic on the right. The shifting bell curve also leads to the occurrence of never-before-seen extremes in high temperatures.[11][12][13]

...it is the rarest and the most extreme events - and thereby the ones with typically the highest socio-economic impacts - for which the largest fraction is due to human-induced greenhouse gas emissions.[14]

Due to global warming, the most extreme heat events now impact a global area 10 times greater than in the period 1951-1980.[11]

The impact on moderate heat waves is also dramatic, with a seventy-five percent share of moderate heat events now attributed to climate change.[14]

Many urban areas across the globe have witnessed a significant increase in the number of heat waves, with the largest number of heat waves occurring in the most recent decade studied, 2003-2012.[15]

Heat waves have generally become more frequent across the US in recent decades, with western regions setting records for numbers of these events in the 2000s. Recent multi-month extreme heat events in the US are unprecedented since the start of reliable instrumental records in 1895. There has also been a dramatic increase in nighttime temperatures in the US, reducing the number of critically important relief windows during heat waves.[9]