I'll have the next update for 2016 soon, but with Roy Spencer announcing that UAH rose slightly in November, it seems highly likely that all datasets will make 2016 the warmest year on record. The joke has always been that in a few years time this will lead to 2016 being declared the start of a new pause.
Except we didn't have to wait that long. In the last few days there's been a flurry of nonsensical articles pointing to the rapid decline of temperatures following on the peak of the recent El Niño, as evidence for the end of global warming, or the start of a new ice age, or whatever.
Tamino has some great articles detailing the sorry history:
- How Stupid Does David Rose Think You Are?
- Ross Clark Turns Crybaby in the U.K. Spectator
- A Sordid Tale of Climate Denial
Here's my own take. This started with an article in a Mail on Sunday article by David Rose, with the catchy headline Stunning new data indicates El Nino drove record highs in global temperatures suggesting rise may not be down to man-made emissions . The headline claims in the article are:
Global average temperatures over land have plummeted by more than 1C since the middle of this year – their biggest and steepest fall on record.
The news comes amid mounting evidence that the recent run of world record high temperatures is about to end.
The fall, revealed by Nasa satellite measurements of the lower atmosphere, has been caused by the end of El Nino – the warming of surface waters in a vast area of the Pacific west of Central America.
The second two points are obvious and irrelevant. Of course the run of record breaking weather will end, it would be terrifying if it didn't. And you don't need NASA to tell you that the end of an El Niño causes a fall in temperatures.
Tellingly, Rose never quotes a source for the data he's using, but it's clearly the RSS v3.3 TLT land data.
But using that source his claim that temperatures have plummeted by more than 1C since the middle of this year
is not correct -
they've dropped about 0.5 ° C since the middle of the year - you have to go back to March to make the case for a drop of 1 °C.
Rose claims that this is the biggest and steepest fall on record
, but doesn't back this up with any figures.
Nor does he really explain what significance he attaches to this fall.
If the fall is simply the fall from a very high peak, it means nothing and is expected.
If he's suggesting that this trend is meaningful and will continue he's almost certainly going to be wrong.
(In fact as I write November's RSS figures have been published and show land temperatures rose by over 0.2 ° C.)
But he's wrong to claim that this is the sharpest fall on record (assuming he means over any 8 month period). The trend from March to October was -127.6 ° C / century, which alone should tell you how meaningless an 8 month trend is. But this is only the 6th sharpest 8 month fall. By contrast the 8 months from August 2015 to March this year saw an upward trend of 156.3 ° C / century. This was the steepest 8 month rise in RSS TLT land temperature history.
I suspect that what Rose actually did was take the difference between the temperatures for March and October. That does give you the claimed biggest difference, but it's a terrible way to calculate the steepness of the fall. It ignores all the months between the start and finish, and in this case gives far to much prominence to that single cool final month.
But the main question is why did he only refer to land temperatures, rather than global temperatures? It's difficult to avoid the suspicion that it's purely cherry-picking. Here's a graph showing the last 2 years of RSS 3.3 TLT data for both land and global temperatures.
It's obvious from the graph that the peak of El Niño was much higher over land, and there was one very big drop in October over land, compared with a much smaller one globally.
Rose's justification for only looking at land values is:
The satellite measurements over land respond quickly to El Nino and La Nina. Temperatures over the sea are also falling, but not as fast, because the sea retains heat for longer.
This gives the impression that sea values will catch up with the land values, but this is not really true. It isn't that the land responds more quickly than the sea, it's that the land responds more strongly. To illustrate the problem, here's a comparison of the entire data set for RSS using a 12 month rolling average.
A few things seem obvious from this graph:
- There's no evidence that the globe responds slower to El Niño or La Niña events. The peaks and troughs are happening at the same time.
- Land values always show higher peaks during El Niños, and bigger drops during La Niñas
- The difference between the two values in 2016 was the biggest on record.
- The global peak in 2016 was higher than the super El Niño peak in 1998, but the land only peak in 2016 was much higher than the one in 1998.
- In part this can be explained by the fact that land only temperatures are increasing faster than global temperatures.
To put figures on that last point - the global trend given by RSS 3.3 over the entire satellite era is 1.36 ° C / century. But for land only the trend is 1.79 ° C / century.
Which raises one obvious question - do those trying to deny the existence of global warming really want to emphasize the land only data?
Post Script
It should also be mentioned that all the above is using the old 3.3 version of RSS. The newer version 4 (TTT, land) only shows a 0.54 ° C drop between March and October, whilst November 2016 sets the record for warmest November.
No comments:
Post a Comment