No Warming Since 1997–A Better Way To Show It
By Paul Homewood
While there has been an increasing realisation that global temperatures have flatlined for the last 10 to 15 years, there have been attempts to muddy the waters by claims of cherry picking start and end dates.
The UK Met Office did precisely this last year in response to David Rose’s article in the Mail on Sunday, saying:-
The linear trend from August 1997 (in the middle of an exceptionally strong El Nino) to August 2012 (coming at the tail end of a double-dip La Nina) is about 0.03°C/decade, amounting to a temperature increase of 0.05°C over that period, but equally we could calculate the linear trend from 1999, during the subsequent La Nina, and show a more substantial warming.
As we’ve stressed before, choosing a starting or end point on short-term scales can be very misleading.
At the time I dealt with the inaccuracy of their statement, (August 1997 was not “in the middle”, but “at the start” of the El Nino, and August 2012 was in the middle of another El Nino). Nevertheless, in principle, they were spot on. To take a linear trend from an El Nino year, such as 1998, will give a totally different result to a trend from a La Nina year such as 1999. The two Woodfortrees graphs below show this well, using 1998 and 1999 as start points.
http://www.woodfortrees.org/plot/hadcrut3vgl/from:1998/plot/hadcrut3vgl/from:1998/trend
To get around this problem, let’s look at the GISS Temperature Map, comparing the 2012 annual temperatures with a 1997-2011 baseline.
The top right hand corner shows “0.00”. This is the anomaly, or difference, between 2012 temperatures and the average of 1997-2011. In other words, global temperatures last year were unchanged from the average of the previous 15 years.
Ah, I hear you say! This could hide the fact that temperatures were still rising between 1997 and 2011 on average. But,
a) They were not.
b) If they were, 2012 would be colder than the previous few years, which it is not, and would be a concern if it was.
At a stroke, we have eliminated the problem of cherry picking start years. Whichever year we start with, is only one of, in this case, fifteen, and therefore has very little effect on the overall average.
But what about 2012? Is this an unrepresentative year to choose? Was it affected by La Nina, or other factors? The answer is emphatically no. While La Nina conditions affected the first two months, mild El Nino conditions took over until August. For the year as a whole, it is safe to say that ENSO conditions were effectively neutral. The Multivariate ENSO Index , or MEI, from NOAA, that I have copied below, shows this well.
MEI Index (last update: 8 April 2013)
| 2012 | 2013 | |
| DEC/JAN | -1.045 | +0.042 |
| JAN/FEB | -0.706 | -0.163 |
| FEB/MARCH | -0.417 | -0.171 |
| MARCH/APRIL | +0.059 | |
| APRIL/MAY | +0.706 | |
| MAY/JUNE | +0.903 | |
| JUNE/JULY | +1.139 | |
| JULY/AUG | +0.579 | |
| AUG/SEP | +0.271 | |
| SEP/OCT | +0.103 | |
| OCT/NOV | +0.166 | |
| NOV/DEC | +0.037 |
http://www.esrl.noaa.gov/psd/enso/mei/table.html
As an added check, we can look at the latest GISS anomaly numbers. Temperature anomalies, during the last three months of ENSO neutral conditions, are virtually the same as last year’s average.
| 2012 | 0.56C |
| 2013 | 0.57C |
http://data.giss.nasa.gov/gistemp/tabledata_v3/GLB.Ts+dSST.txt
Conclusion
Temperatures during 2012, and indeed so far this year, are exactly the same as the average of the last 16 years. This has nothing to do with the choice of start year, and there is nothing to suggest that current temperatures are being influenced by untypical ENSO or any other conditions.
It cannot be disputed – warming stopped 16 years ago.
NOT A LOT OF PEOPLE KNOW THAT 
In so many of these comparisons of trends, not just these above, no statistical significance is stated. So the question is asked, is there any real statistical difference between them all?
Things are looking up since Hansen left 😉
An interesting idea but does it clarify what the climate is doing or just highlighting the medium term changes in weather. IMO it’s the latter. Climate variations are by their nature a long term trend.
Have you been following the extreme April cold in the central US and much of Canada? Minot, North Dakota is averaging almost 17 degrees below normal for April. The average high has been 32 and average low 18. Those are normal January temperatures for Chicago, despite 3 months of rising sun angle. Also, there are still three feet of snow on the ground in the Duluth, Minnesota area and we are only 5 days from May.
Coldest spring ever in Norway….2013
Up until a few weeks back, here in England 50km north of London, it’s been about 10 degrees below average for a looooong time, around 3 during daytimes and down to -3 at nights. Leaves only just starting to grown on trees and bushes.
You may not know this but your link below the NASA figure links to a figure on the NASA site that has ‘0.01’ top right hand corner temperature anomaly, as opposed to the ‘0.00’ shown here. What gives?
It looks like GISS have been adjusting their historical numbers again!
They do it quite frequently, and it always seems to increase the warming trend. For instance