Quite a bit of attention was paid to the fact that in the global temperature data from NASA, and from NOAA, the year 2014 turned out to be the hottest on record. Even more attention ensued because so far this year has also been rather toasty world-wide, so much so that by February we set new record highs for average temperature over a 12-month period (sometimes called 12-month running means). Simply put, March 2014 through February 2015 was the hottest 12-month period on record in both NASA and NOAA data. Then when the numbers arrived for March of this year, it turns out we topped even that record; April 2014 through March 2015 became the new hottest 12-month period on record, for both NASA and NOAA data; here’s the NASA version (click the graph for a larger, clearer view):
Let’s put a red dot with an “x” through it on each month we set a new record for hottest 12-month period yet (click the graph for a larger, clearer view):
Many of the dots are crowded together; here’s a close-up of data since 1970 (click the graph for a larger, clearer view):
This made me curious to find, not just the times when we first reached a new high temperature world-wide, but the times when we last saw a low temperature world-wide. In case you too are curious, here’s the graph:
I do feel compelled to mention that all this talk of hottest this and coldest that means little. What really counts is the trend. Here are two estimates of the actual trend, one by a lowess smooth, another using a piecewise-linear fit:
Clearly the two trend estimates are in very good agreement. As for which is closer to the truth … that’s an open question which will remain open. But I will say that these smooths represent just about all we can really say we know about the trend. It might have shown more complex changes, but then again it might not. All we can say with confidence (in the statistical sense) is what is shown on that graph.
For the curiosity of the curiouser, we can put the two together: