Pause? Slowdown? Whence? Wither?

The Pause has been in the news again. There is a new paper in Nature Climate Change (pdf here) by Fyfe et al, with numerous notable authors, saying that there really was a slowdown, but not a stop, in global warming. This is partly in response to a paper last year from Karl et al, basically saying it was an artefact of ship/buoy bias, and disappeared after appropriate adjustment. There is an extensive summary in Scientific American here, and good coverage by Sou here. Also Tamino

I'm with Gavin, as quoted in SciAm. I think it's a pointless argument. Yes, warming was a bit slower for a few years. Unless someone can show some statistical significance of something, I don't see why it should even have a name.

However, that seems to be a minority view. I write a lot about temperature anomaly series and their trends, and I argue a lot about Pause matters, so I should say something. What I want to do is to show how the Trend Viewer can be used to show how pauses originate, and to give an idea how unusual is the one under discussion.

Here is a typical plot which I used in discussion at WUWT. It shows the history of the NOAA index since 1960. I suggest that you open up the Viewer here. The active features make it much easier to follow what is going on. The values of trend for all possible subintervals of 1960-2016 are shown on a triangle, plotted in color with x-axis the end time of the interval, and y-axis the start. I actually don't show trends of less than a year; short trends are along the hypotenuse, and the axis there is where a trend of zeo length would be. Length of trend goes with distance from the hypotenuse, and is marked with white lines. Here is that plot:



You'll find description in the text of the viewer page, and links to earlier posts. But I'd urge you to use the interactivity to help figure it out. There is an associated time series plot:



You'll see a red and blue dot, indicating the ends of a trend line for a chosen interval - here Jan 2001 to Dec 2013. Below the graph is a block of information about the chosen interval:



You can choose the interval in different ways - with the colored bars or nudgers on the time series plot (see page for details) or by clicking on the triangle. The dots will move and the text will change. The text info is a good way to work out the triangle. Just click for response.The rest of the space has buttons that you can click to choose different datasets, time intervals, or style. With style, instead of just trend you can have trend colored where significant (different from 0 at 95%), or you can choose to plot a CI or a t-value (see page info).

The plot uses rainbow shading for colors, except for brown at zero, and grey at 1.7°C/Century, chosen as a representative AGW value. If you look along the hypotenuse, there are sharply alternating reds and blues, with some labelled events. These correspond to peaks and dips, which are actually located where red and blue met. On the left of a peak, short trends are positive (red), and afterward, blue. For a dip, it's the opposite. Peaks are usually ENSO related, dips usually ENSO or volcano.

Where there is a peak, the red tends to propagate downward. That is where you hold the end point on the peak, but extend the start backward. Trends tend to be positive, but less when longer. And the blue propagates right, as the start is held on the peak, but the end moves forward. Dips behave oppositely.

You'll see the recent Pause region marked. It's a greenish/yellow area, with trends generally positive but closer to zero than surroundings. And you can see why. Blues on the diagonal are extending cross cool bars, with a deficit of reds above which could extend balancing warm downward. Somewhere between the blue and green you'll see a sketchy brown line. On the blue side of that, trends are zero. Sometimes there are brown-edged islands.

So you can look around for other pauses or slowdowns. You should look for cool colors a long way from the hypotenuse. That distance is a measure of the trend duration. And, depending on what impresses you, you can look for a long slowdown or a shorter actual hiatus. But you should also check either the CI's in the text info or show the plot with significance mask to see whether your pause actually stacks up.

If you do this, you will see that the recent pause is larger than most in that triangle. There are cool colors bottom left, the fringe of the Big Pause from about 1950-1970. You can see this better if you switch to the time range starting 1901.

So you can see where the current Pause came from, and why it is ending. The current El Nino makes a red blob at the top, and that extends down. The green area is being closed off. Remember, the right edge is the current month. Some say that after the El Nino the Pause will return. I think that is fairly unlikely. You'll see that cool regions tend to form islands. For a long time the 1997/8 El Nino has anchored the Pause. I think this El Nino will now be the anchor for whatever slowdowns we have in the future.