According to measurements by NASA’s GISS global temperature monitoring service, April of 2017 was warmer than all past Aprils in the climate record with the single exception of 2016.

The month came in at 0.88 degrees Celsius above NASA’s 20th Century baseline and fully 1.1 degrees Celsius above 1880s averages. This measure was just 0.01 C warmer than now third warmest 2010 and 0.18 C shy of last year’s record. All of the top ten hottest Aprils on record have occurred since 1998 and six of the top ten hottest Aprils have occurred since 2010.

(During April of 2017, and with only a few moderate exceptions, most of the world experienced above normal to considerably above normal surface temperatures. Image source: NASA GISS.)

The first four months of 2017 now average around 1.21 degrees Celsius warmer than 1880s ranges. This number is about tied with 2016’s overall record warmth which was spurred by a combined strong El Nino and the incredible buildup of greenhouse gasses in the Earth’s atmosphere that we have seen for over more than a century. It is also a warming that is now strong enough to start bringing on serious geophysical changes to the Earth System. The longer readings remain so warm or continue to increase, the more likely it is that instances of global harm in the form of glacial melt, sea level rise, ocean health decline, severe storms and other extreme weather will worsen or emerge.

This year, ENSO neutral conditions trending toward the cooler side of average during the first quarter should have helped to moderate global temperatures somewhat. As is, though a slight cooling vs the first quarter of 2016 is somewhat evident, the broader, more general counter-trend cooling that we would expect following a strong El Nino is practically non-apparent.

(A mildly warm Kelvin Wave forming in the Equatorial Pacific brings with it the chance of a weak El Nino by summer of 2017. This warming of such a broad region of surface waters may combine with atmospheric CO2 and CO2e in the range of 405 and 493 ppm respectively to keep global temperatures near record highs of around 1.2 C above 1880s averages during 2017. Image source: NOAA EL Nino.)

Very strong Northern Hemisphere polar warming during the winter months appears to be a primary driver pushing overall global temperatures higher during recent months. Meanwhile, southern hemisphere polar amplification is becoming more and more apparent over time.

In April, the trend of Northern Hemisphere polar amplification/warming was readily apparent in the NASA measure despite a seasonal relative cooling. Under global warming related heat forcing, we would expect to see the highest temperature departures during late fall through winter. And as 2016 transitioned into 2017, this kind of warming was amazingly evident.

(Only the very far north and the very far south saw below average temperatures in NASA’s zonal measure. Meanwhile, temperatures in the lower Arctic were particularly warm. Image source: NASA GISS.)

Anomalies during April in the higher latitudes did cool somewhat to 2 to 2.6 C above average in the key 65 to 75 N Latitude zone. Highest departures continued to be very considerable for April — ranging from 4 C to as much as 7.5 C above average over Northeastern Siberian, the East Siberian Arctic Shelf, the Bering Sea and parts of Northwest Alaska. Meanwhile, temperatures over the Central Arctic dipped to slightly below average as polar amplification in the southern hemisphere appeared to take a break before warming again in March.

Globally, according to GFS model reanalysis data, temperatures appeared to cool through the end of April. However, by early May another warm-up was underway and, if the GFS measure is any guide, it appears that May will likely be about as warm as April overall. This track would tend to make May of 2017 the 1rst to 4th warmest on record if the trends analysis bears out.

Links:

NASA GISS

NOAA EL Nino

Global and Regional Climate Anomalies