The best context for understanding decadal temperature changes comes from the world’s sea surface temperatures (SST), for several reasons:

• The ocean covers 71% of the globe and drives average temperatures;
• SSTs have a constant water content, (unlike air temperatures), so give a better reading of heat content variations;
• A major El Nino was the dominant climate feature in recent years.

HadSST is generally regarded as the best of the global SST data sets, and so the temperature story here comes from that source, the latest version being HadSST3.  More on what distinguishes HadSST3 from other SST products at the end.

The Current Context

The chart below shows SST monthly anomalies as reported in HadSST3 starting in 2015 through November 2019.
A global cooling pattern is seen clearly in the Tropics since its peak in 2016, joined by NH and SH cycling downward since 2016.  In 2019 all regions had been converging to reach nearly the same value in April.

Then  NH rose exceptionally by almost 0.5C in the over four summer months, in August exceeding previous summer peaks in NH since 2015.  Now in the last 3 months that warm NH pulse has reversed sharply.  Meanwhile the SH and Tropics bumped upward, but despite that the global anomaly changed little due to strong NH cooling.

Note that higher temps in 2015 and 2016 were first of all due to a sharp rise in Tropical SST, beginning in March 2015, peaking in January 2016, and steadily declining back below its beginning level. Secondly, the Northern Hemisphere added three bumps on the shoulders of Tropical warming, with peaks in August of each year.  A fourth NH bump was lower and peaked in September 2018.  As noted above, a fifth peak in August 2019 exceeded the four previous upward bumps in NH.

And as before, note that the global release of heat was not dramatic, due to the Southern Hemisphere offsetting the Northern one.  The major difference between now and 2015-2016 is the absence of Tropical warming driving the SSTs.

The annual SSTs for the last five years are as follows:

Annual SSTs	Global	NH	SH	Tropics
2014	0.477	0.617	0.335	0.451
2015	0.592	0.737	0.425	0.717
2016	0.613	0.746	0.486	0.708
2017	0.505	0.650	0.385	0.424
2018	0.480	0.620	0.362	0.369

2018 annual average SSTs across the regions are close to 2014, slightly higher in SH and much lower in the Tropics.  The SST rise from the global ocean was remarkable, peaking in 2016, higher than 2011 by 0.32C.

A longer view of SSTs

The graph below  is noisy, but the density is needed to see the seasonal patterns in the oceanic fluctuations.  Previous posts focused on the rise and fall of the last El Nino starting in 2015.  This post adds a longer view, encompassing the significant 1998 El Nino and since.  The color schemes are retained for Global, Tropics, NH and SH anomalies.  Despite the longer time frame, I have kept the monthly data (rather than yearly averages) because of interesting shifts between January and July.

1995 is a reasonable (ENSO neutral) starting point prior to the first El Nino.  The sharp Tropical rise peaking in 1998 is dominant in the record, starting Jan. ’97 to pull up SSTs uniformly before returning to the same level Jan. ’99.  For the next 2 years, the Tropics stayed down, and the world’s oceans held steady around 0.2C above 1961 to 1990 average.

Then comes a steady rise over two years to a lesser peak Jan. 2003, but again uniformly pulling all oceans up around 0.4C.  Something changes at this point, with more hemispheric divergence than before. Over the 4 years until Jan 2007, the Tropics go through ups and downs, NH a series of ups and SH mostly downs.  As a result the Global average fluctuates around that same 0.4C, which also turns out to be the average for the entire record since 1995.

2007 stands out with a sharp drop in temperatures so that Jan.08 matches the low in Jan. ’99, but starting from a lower high. The oceans all decline as well, until temps build peaking in 2010.

Now again a different pattern appears.  The Tropics cool sharply to Jan 11, then rise steadily for 4 years to Jan 15, at which point the most recent major El Nino takes off.  But this time in contrast to ’97-’99, the Northern Hemisphere produces peaks every summer pulling up the Global average.  In fact, these NH peaks appear every July starting in 2003, growing stronger to produce 3 massive highs in 2014, 15 and 16.  NH July 2017 was only slightly lower, and a fifth NH peak still lower in Sept. 2018.

The highest summer NH peak came in 2019, only this time the Tropics and SH are offsetting rather adding to the warming. Since 2014 SH has played a moderating role, offsetting the NH warming pulses. (Note: these are high anomalies on top of the highest absolute temps in the NH.)

What to make of all this? The patterns suggest that in addition to El Ninos in the Pacific driving the Tropic SSTs, something else is going on in the NH.  The obvious culprit is the North Atlantic, since I have seen this sort of pulsing before.  After reading some papers by David Dilley, I confirmed his observation of Atlantic pulses into the Arctic every 8 to 10 years.

But the peaks coming nearly every summer in HadSST require a different picture.  Let’s look at August, the hottest month in the North Atlantic from the Kaplan dataset.
The AMO Index is from from Kaplan SST v2, the unaltered and not detrended dataset. By definition, the data are monthly average SSTs interpolated to a 5×5 grid over the North Atlantic basically 0 to 70N. The graph shows warming began after 1992 up to 1998, with a series of matching years since. Because the N. Atlantic has partnered with the Pacific ENSO recently, let’s take a closer look at some AMO years in the last 2 decades.
This graph shows monthly AMO temps for some important years. The Peak years were 1998, 2010 and 2016, with the latter emphasized as the most recent. The other years show lesser warming, with 2007 emphasized as the coolest in the last 20 years. Note the red 2018 line is at the bottom of all these tracks. The short black line shows that 2019 began slightly cooler, then tracked 2018, then rose to match previous summer pulses, before dropping the last three months to again match 2018 below other years.

Summary

The oceans are driving the warming this century.  SSTs took a step up with the 1998 El Nino and have stayed there with help from the North Atlantic, and more recently the Pacific northern “Blob.”  The ocean surfaces are releasing a lot of energy, warming the air, but eventually will have a cooling effect.  The decline after 1937 was rapid by comparison, so one wonders: How long can the oceans keep this up? If the pattern of recent years continues, NH SST anomalies may rise slightly in coming months, but once again, ENSO which has weakened will probably determine the outcome.

Footnote: Why Rely on HadSST3

HadSST3 is distinguished from other SST products because HadCRU (Hadley Climatic Research Unit) does not engage in SST interpolation, i.e. infilling estimated anomalies into grid cells lacking sufficient sampling in a given month. From reading the documentation and from queries to Met Office, this is their procedure.

HadSST3 imports data from gridcells containing ocean, excluding land cells. From past records, they have calculated daily and monthly average readings for each grid cell for the period 1961 to 1990. Those temperatures form the baseline from which anomalies are calculated.

In a given month, each gridcell with sufficient sampling is averaged for the month and then the baseline value for that cell and that month is subtracted, resulting in the monthly anomaly for that cell. All cells with monthly anomalies are averaged to produce global, hemispheric and tropical anomalies for the month, based on the cells in those locations. For example, Tropics averages include ocean grid cells lying between latitudes 20N and 20S.

Gridcells lacking sufficient sampling that month are left out of the averaging, and the uncertainty from such missing data is estimated. IMO that is more reasonable than inventing data to infill. And it seems that the Global Drifter Array displayed in the top image is providing more uniform coverage of the oceans than in the past.

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December 30, 2019 at 08:39PM

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December 30, 2019 at 08:21PM

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December 30, 2019 at 04:34PM

Some seem to believe that a EU emission decrease will have a huge effect on world emissions, as is shown in this curious tweet from a Belgian politician (my emphasis):

Without getting the EU climate neutral, you will not get the world below 2 degrees C. And if we do not achieve that, the costs and losses cannot be foreseen.

This is a bold statement and it doesn’t make much sense. Firstly, the EU emissions were in the order of 10-11% of world emissions in 2018 and secondly, developing countries like China and India have strongly rising emissions without engagements to lower them, so their emissions are very likely to further increase in the future, likely even after 2030. Africa will likely follow soon.

He rightfully got criticized for that in the reactions on the tweet. In this post, I want to go a step further and try to find out how EU emissions relate to global emissions and to what extent these are big enough to compensate for the increase from the developing regions.

Time to look at the data. I already had the BP Statistical Review of World Energy on my computer and it has a sheet detailing emission data.

My first plan was to take the big regions in the world and plot those, but there were some interesting countries that would drown in those bigger numbers. Therefor I separated the numbers of the US from North-America, Australia/New Zealand from Pacific Asia and of course the EU countries from Europe. However, not all EU countries were detailed in the BP data, only 27. The missing country is Malta. It is in the category “Other Europe” because it is so small, so that will not make much of a difference anyway.

I threw all that data in a spreadsheet and this is what Calc spitted out:

There are some interesting trends. As expected, only two regions lowered emissions: the EU and the US (in spite of being criticized for not subscribing to the Paris Agreement). Stable emissions are seen in Australia/New Zealand, “Other Asia” and “Other North-America”. All other countries/regions have rising emissions. Remember, this is three years after the planet was allegedly saved in Paris.

What if we now assume that the countries stay on the same course they were on in the last decade? I will draw a straight line with the same trend until 2030.

There is one obvious problem: China’s emissions went up very fast from the beginning of the 2000s, then stabilized and the last few years it started to increase again. I guess that the initial large increase will not continue, but I think emissions will keep rising, so I will project the same trend as after the bend.

This is how it looks like:

When I do a back-of-the-envelop calculation of the difference between the decreased and the increased emissions, then I get +222 million tonnes of carbon dioxide per year. This means that the decrease of emission of the EU and US will not even compensate for the increase of the rest, let alone limit global temperature increase to 2 °C. This is the result of not only for lowering EU emissions, but also the US emissions.

Yeah, would you say, but the EU is not necessarily going to lower its emissions at the same rate as in the previous decade. Its goals is zero emissions by 2050. Calculating a straight trend line until 2050 for the EU only gives this result (look at the dark green line):

That is a bit steeper downwards than we seen in the last decade, but again it obviously doesn’t compensate for the increase of the other countries that will have increasing emissions. There is still a surplus of 168 million tonnes of carbon dioxide per year. So, emissions will still increase globally, despite the intentions of the EU.

Going a step further: what is needed to limit global temperature increase to 2 °C? According to the IPCC SR15 summary for policymakers:

C.1. In model pathways with no or limited overshoot of 1.5°C, global net anthropogenic CO2 emissions decline by about 45% from 2010 levels by 2030 (40–60% interquartile range), reaching net zero around 2050 (2045–2055 interquartile range). For limiting global warming to below 2°C CO2 emissions are projected to decline by about 25% by 2030 in most pathways (10–30% interquartile range) and reach net zero around 2070 (2065–2080 interquartile range).

If I read that correctly, global emissions were projected to drop 25% from 2010 levels by 2030. Global emissions were 31,058 million tonnes carbon dioxide in 2010, 25% less means a maximum of 23,293 million tonnes by 2030.

If all countries/regions with increasing emissions will stabilize their emissions between 2020 and 2030, then total emissions still amounts to 32.000+ million tonnes. So, to get to 23,000+ tonnes, the countries with currently rising emissions will have to lower their emissions too. By how much? When I keep the 2050 EU deadline and decrease emissions of all other countries, then this is necessary to get at 23,000+ tonnes:

It seems that all countries will roughly have to do the same effort that the EU is wanting to implement. The chance that China and India decrease their emissions with more than 3% in the near future is likely a beautiful round number.

Another scenario: what if we let China and India emit and try to compensate for that by decreasing emissions in all other countries (including the EU) at the same rate? Then this is what we get:

Then a 7% decrease from 2020 until 2030 is needed for all other countries/regions. Also, the EU then needs to be “climate neutral” already by 2044 (instead of 2050 as intended) and the rest of the developing countries will have to refrain from developing.

This is just a quick-and-dirty calculation, but it indicates that the intention of the EU to lower its emissions will not have much effect globally, let alone influence the climate.

So unless he means something different with the statement “the world will not get below 2 °C without the EU getting climate neutral” than that the world will not get below 2 °C without the EU getting climate neutral, his statement is obviously strongly overestimating the effect of the EU on global emissions.

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December 30, 2019 at 02:49PM