The Met Office yesterday confirmed that the warm record of 2016 was mainly driven by a very strong El Nino.
Guest essay by Dr David Whitehouse, GWPF Science Editor
Not that you would have heard this fact in the news. But Peter Stott, Acting Director of the Met Office Hadley Centre, said in no uncertain terms that, “a particularly strong El Nino event contributed about 0.2°C to the annual average for 2016.”
By removing this temporary El Nino contribution from the Met Office’s 2016 data, it becomes obvious that global average temperatures would be essentially identical to where they were in 2014 (see fig 1). Since the El Nino warming is fading and global temperatures are dropping rapidly, they are close to being back to where they were before the latest El Nino started.
There are two ways to look at the just released global temperature of 2016 and press releases from NASA, NOAA and the Met Office work hard to reflect only one of them.
The emphasis is on long-term warming with the press releases stressing that we are living in the warmest decade of the past 150 years (since instrumental records began) concluding that global warming is continuing unabated. This is one way of seeing the data, but it is not the main lesson which comes out of studying what 2016 adds to the picture of recent warmth.
2016 was clearly among the warmest of years, but what distinguishes it from the previous years in this century? Everyone agrees it is the strong El Nino. But how strong was its influence?
The NASA GISS dataset has the global temperature of 2016 at 0.99 +/- 0.1°C compared to 0.87 +/- 0.1°C for 2015, a difference of 0.12°C. However, NASA’s Gavin Schmidt said that their estimate of the boost to global temperatures given by the El Nino in 2016 was 0.12°C, that is the difference between 2015 and 2016.
The press release from the Met Office says that 2016 is one of the warmest two years on record and that according to the HadCRUT4 dataset it was 0.77+/- 0.1°C above what it calls the long-term average, which is actually calculated between 1961-1990. 2015 was 0.76+/- 0.1°C making 2016 and 2015 statistically indistinguishable from one another.
However, Peter Stott, Acting Director of the Met Office Hadley Centre said, “A particularly strong El Nino event contributed about 0.2°C to the annual average for 2016.” This means that without the El Nino 2016 would have had a global temperature of about 0.57+/- 0.1°C which is the same as 2014 and within the errors of 2010 (0.56) and 2005 (0.54). It would also have been in the 95% confidence range of 2013, 2010, 2009, 2007, 2006, 2005, 2003 and 2002. In other words, using the Met Office’s 0.2°C El Nino (ENSO) correction 2016 has not been a record warm year but statistically in the same region as the previous 15 years. Gavin Schmidt of NASA disagrees, saying on Twitter, “Oh my. What tosh. In ENSO corrected data-sets 2016 is still record warm.”
According to NOAA 2016 was 0.07°F warmer than 2015, which is 0.04°C. Considering the error in the annual temperature is +/- 0.1°C this makes 2016 statistically indistinguishable from 2015, making any claim of a record using NOAA data specious.
Fig 1 shows the HadCRUT4 data for the so-called “hiatus” period. The recent El Nino years of 2015-16 are prominent. Also on the graph is the 2016 temperature without the El Nino contribution, as calculated by the Met Office. 2015 – a year with an equally strong El Nino effect – is cautiously interpolated – although the 2016 El Nino estimate is the main datapoint, (NASA Giss says that the correction for 2016 is 0.12°C and 0.05°C for 2015. The Met Office has a figure almost twice as much for 2016 which represents a significant difference of opinion between the Met Office and NASA). However, even with just the 2016 El Nino compensation the data shows that the pause hasn’t gone away. It has simply been interrupted by two very strong El Nino years. Note that there were moderate El Ninos in 2002-3 and 2009-10. Compensating for those El Ninos as well as the one in 1998 would make very little difference to the graph, and certainly would not invalidate the pause in the data. In fact it would make the temperature flatter.
Time will tell how far global temperatures will drop in the next couple of years. But there is a good chance that the pause will be re-established once the El Nino warmth tails off.
The Berkeley Earth team also confirmed that the 2015/2016 El Niño was responsible for a record year – read here