September 2017 smashed multiple climate records, alarming scientists and further negating a favorite talking point of climate science deniers.

First and foremost, last month was the hottest September ever recorded in the four decades of satellite data analyzed by the University of Alabama at Huntsville (UAH).

Equally amazing, “of the 20 warmest monthly global average temperatures in the satellite record, only September 2017 was not during an El Niño,” reports Dr. John Christy, director of UAH’s Earth System Science Center — and an infamous climate science misinformer.

Global records for hottest month or year typically occur when the underlying human-caused global warming trend gets a temporary boost from an El Niño’s enhanced warming in the tropical Pacific. So when temperature records are set in the absence of an El Niño, it is another sign that the underlying human-caused global warming trend is stronger than ever.


In fact, the last time the record for the hottest September was set in a year without an El Nino was 2013 — and that record was a stunning 0.58°F (0.32°C) lower.

It’s especially remarkable to see these records in the UAH satellite data. Christy, along with his UAH colleague Roy Spencer, famously screwed up the satellite temperature measurements of the troposphere for decades (see chart below). Indeed they consistently underestimated global warming:

CHANGES IN UAH LOWER ATMOSPHERE TEMPERATURE TREND ESTIMATES, GROWING CONSISTENTLY WARMER OVER TIME AS COOL BIASES AND ERRORS ARE REMOVED. CREATED BY JOHN ABRAHAM.

This more than decade-long series of miscalculations helped create one of the most enduring myths among climate science deniers: that the satellite data didn’t show the global warming that the surface temperature data did.

Even now, one of the favorite (false) talking points of Sen. Ted Cruz (R-TX) and his fellow climate science deniers is that “satellites find no warming since 1998,” which replaced the “there’s been no warming since 1998” talking point after that one fell apart when 2014 became the hottest year on record — and again when 2015 blew away the 2014 record. And then again when 2016 topped 2015.

“The signal of global warming has become so dominant that even the deniers’ own favorite cherry-picked datasets clearly now show it,” climatologist Michael Mann told ThinkProgress. For those who live in the world of real scientific analysis, rather that conservative talking points, satellite data, ground-based weather stations, sea-based buoys, and even weather balloons all reveal a steady long-term warming trend.


Mann added, “even the questionable UAH satellite record, which has historically underestimated the rate of global warming as a result of serial mathematical errors, can no longer obscure the anomalous warming of the planet.”

On top of record warmth, “September 2017 has become the most active month on record for Atlantic hurricanes,” as the Weather Channel has reported. This is as measured by the Accumulated Cyclone Energy (ACE) index, “calculated by adding each tropical storm or hurricane’s wind speed through its life cycle.”

Storms like Harvey, and especially Irma and Maria, weren’t just epically powerful, they were long-lasting — which is just what you would expect on a warming planet, where the warm water needed to sustain a major hurricane extends over larger and larger regions.