Global Warming Is Warming [Greg Laden's Blog]

The latest data from NASA GISS has come out, showing a surprise result for the month of March.

Hat tip to Jeff Masters of Wunderground for sending this info. He’ll probably be blogging on it soon.

The surprise is that March, while expected to be warm due to human caused greenhouse gas pollution, turned out to be very warm globally. This is a surprise because the Earth supposedly just experienced a minor cooling La Niña event that ended in January. March 2017, it turns out, is the fourth warmest month since 1880 expressed as an anomaly from a 1951-1980 baseline (that’s a bit tricky, more on that below).

Here’s the current list of warmest months:

February 2016, 1.32°C
March 2016, 1.28°C
January 2016, 1.13°C
March 2017, 1.12°C
February 2017, 1.10°C
December 2015, 1.10°C

The key thing to notice here is all those years being very very recent.

The ranking of months is on a month by month basis. In other words, Feb 2016 is not necessarily the warmest month of all the months over 120 years. Rather, it is the warmest of all the Februaries over this period of time. This may seem like a strange way to do it, but it actually makes sense. Even though these are global values and thus integrate northern and southern seasons, there is a potential for intra-annual variation in global temperatures, for a number of reasons (including the uneven distribution of land and ocean between the northern and southern hemispheres). For this and other even more esoteric reasons having to do with how to track anomalies, we compare months to months (Januaries to Januaries, Februaries to Februaries, etc.).