Summary: The degree of global warming during the next few years might have large political effects, as the public policy debate appears to be at a critical point in its 29th year (from Hansen’s Senate testimony). Will the pause resume, or will we get rapid warming? Close examination of the monthly data will give us clues about this important question.
How can we see the short-term temperature trend?
There is no one true way to show trends in global temperature. Here are three different perspectives; all give roughly similar results. First, let’s look at a graph by NOAA of the global average surface temperature (their excellent interactive website shows data since the reliable instrument era began in 1880). The time period selected depends on what we are looking for. The following graph shows January’s. It minimizes the overall warming trend, which is concentrated in the months of May, June, & July. Click to enlarge.
The warming since 1950 — the period in which over half of the warming comes from anthropogenic causes — occurred almost entirely in two steps: 1981-83 (near the 1979-83 El Niño period) and 1998-99 (near the 1997-98 El Niño). Since then climate scientists have shown that the two century-long temperature rise has “paused” (aka the “hiatus”). There are various theories about the cause. Then came the spike of the 2015-2016 El Niño. The peak to peak rise, 1998 to 2016, was only 0.4°F.
What happens next? The El Niño might have been just a spike, after which temperatures will fall back to the 1998-2014 average — and the “pause” continues. If temperatures don’t fall back to their previous levels, then we begin a new watch. Will the 2015-16 El Niño start another stair step, with temperatures flat at a new high level? Or will temperatures begin a steady rise? The one month anomalies provide an easy if rough way to see which of these three scenarios unfolds, each having different political implications. Unfortunately, climate models cannot yet make reliable predictions for five to ten years horizons