Originally posted by shunyadragon
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Such estimates are the basis for the tentative inference, repeated now by a number of researchers actively involved in this very question, that 2015 would most likely have set a new record even without the El Nino effect.
There's a direct relevance to OP of this thread. The effect of El Nino on temperature tends to be somewhat delayed. This is the basis for my estimate of a high likelihood for 2016 setting another new record. What El Nino did, quite definitely, is push the last three months of 2015 to be substantially higher than the earlier months. The thing is... 2015 was on its way to a record even without this boost to the latter months. El Nino did help 2015 shatter the records by a large margin. But it isn't the whole story. The real reason we keep getting new hottest years, again and again and again, is because there's a consistent underlying increasing trend. That is, global warming. And in so far as we can estimate in quantified terms the contribution of El Nino; it looks like 2015 would have been a record in any case even without that boost. But WITH the boost; 2016 is going to get a big kick from El Nino as well. It will come down to how long this El Nino lasts. In 1998, it was 1997 that caught an El Nino effect in latter months and 1998 which caught an El Nino effect in earlier months. 1997 came within a whisker of setting a new record at the time (beaten only by 1995, using the GISTEMP dataset; others will show roughly similar patterns) 1998 blew it away. If the current El Nino lasts a reasonable time, it's likely that 2016 will beat out 2015.
Some references (papers which attempt to quantify the ENSO impact – all written well before this year) showing work that sets the theoretical basis for claims that 2015 would probably have been a record even without the ENSO boost.
- Thompson et al, A large discontinuity in the mid-twentieth century in observed global-mean surface temperature, Nature 453, 646-649 (29 May 2008) doi
- Foster et al, Global temperature evolution 1979–2010, in Environmental Research Letters, Volume 6, Number 4, Dec 2011, doi.
- Fawcett et al, On tropical cyclone activity in the Southern Hemisphere: Trends and the ENSO connection, Geophysical Research Letters, Volume 35, Issue 14, July 2008, doi
Some recent blog articles from (what I consider to be) reputable active working scientists in the field, specifically on the role of ENSO for the 2015 record.
- At open mind, by tamino (actually a statistician rather than pure scientist, but active publishing on climate related statistical analysis): el Niño and the 2015 Record-Breaking Heat.
- At realclimate, by Gavin Schmidt: 2015 temperatures. (Look at the update at the end of the blog post, which was added specifically to address this question of the ENSO contribution.)
Some data with my own comments. (Data from the most recent GISTEMP dataset.)
ElNinoYearsGISTEMP.JPG
This is month by month global temperature anomaly for 1997-1998, and for 2015. Vertical axis is a temperature anomaly in hundredths of a degree, measuring the rise above a baseline set 1951-1980. Horizontal axis is the month.
For 1997-1998 you can see the El Nino begin to kick in around about October 1997, with a big high in Feb 1998, and last through to about August 1998. In 2015 you have a substantial overall increase (which can be solidly attributed to 17 years warming) but the EL Nino effect kicks in for October 2015.
So – two points looking on the data.
- If we could ignore the impact of El Nino… then note that 2015 had to have average anomaly of 90 to set a new record over 2014. The first nine months already had an average of 92, even before the El Nino driven highs in the last three months. So yeah… the data gives a credible basis for thinking that we did not need the El Nino effect for 2015 to set a record.
- If we consider the El Nino impact… then indeed 2015 smashed the old records, with a help from those last three very high months. But El Nino usually lasts more than six months, so 2016 is probably going to get a bigger boost from the El Nino than 2015. So in real life, where El Nino does have a strong impact.. the data gives a credible basis for thinking 2016 is going to be another hot year and credibly likely to beat out 2015 if we get another six months of El Nino fuelled warmth.
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