One of the first followers of this blog, eSell, asked in the post “You got to have faith (about the pause as seen by the KNMI) if I could give my opinion on an article he found on the Royal Society website called 10. Does the recent slowdown of warming mean that climate change is no longer happening?. Because I was planning to do a post on the pause anyway, I decided to upgrade that reply to a post. This post to be exact. Following are my opinions on this article as an interested member of the public.
First let me say that it is some change that climate scientists (other than the “3%” skeptic ones) start to acknowledge the existence of the pause. That was different just a couple years ago. The mainstream media still doesn’t even mention it, at least here in Belgium. Most members of the public are not even aware of it, they think temperatures are still going up rapidly.
It also caught my attention that the term global warming was not used once. Although they were speaking about rising global avearage temperatures, they insisted on using the term climate change. They probably want to avoid confusion talking about global warming in a period when there is no global warming for one and a half decade.
Back to the article. As often in climate communication, the statements that were made were basically correct, but very one-sided and it is more important what they didn’t say.
It is correct that a cooling trend of about a decade and a half is not that significant in the long term. As far as the sparse data can be trusted, there has been a warming trend since the measurements started in the 1850s. There were also cooling trends during 1880-1910 and 1950-1980. The climate system is more like a cycle and it will warm or cool, about every 30 years or so.
It is also true that the subsequent peaks were higher than the previous and while we have technically a standstill of temperatures it is still at a high level.
It is also true that air can hold much less heat than water, that oceans (3/4 of the earth surface) have a big influence on the climate and that during El Niño events heat is coming out of the ocean. The 1998 El Niño was a very big one that left a very strong spike in the global temperature record and was also a step change in the records.
It is true that the sun is less active.
It is true that volcanic activity can increase the amount of (reflective) aerosols and have an cooling effect on temperatures.
It is true that there has been heatwaves in 2003, 2012 and 2013.
They basically state that it is a combination of heat going in the oceans in stead of in the air (where it is being measured), combined with some small influences like the low sun acitvity and volcanoes.
I heard that argument before. Global warming is not noticeable anymore because the heat is going into the (deep) ocean in stead of in the air. In this article the explanation seemed to be centered around the El Niño-Southern Oscillation (ENSO), which is a naturally occurring phenomenon. It consists of a El Niño phase and a La Niña phase. During a La Niña event there is a heat uptake in the east-central tropical Pacific Ocean. The ocean surface will warm by the radiation of the sun. The trade winds will pile up the water at the Western side and hold that warm water below the surface. This means that a cool surface will be measured because the warm water is hidden below that cool surface. When those winds slow down, the piled up water sloshes back to the East and the warm water is coming back to the surface. A warm surface will be measured. This could give a spike in the global temperature records, like for example the 1998 El Niño event which even gave a step change bringing global temperatures to a higher level than before. It is now said that if a next strong El Niño events comes (some day it will come) temperatures could rise again. Et Voilà, global warming is back again.
The remark of the sun activity is a surprise to me. Indeed, solar activity is low, but in the past the sun has been neglected as a potential cause. It is the first time I see it being used as an argument for the pause by scientists who adhere to the anthropogenic warming theory. They think the influence is small though. The same with volcanoes. They think that it is a small effect. Yet, some think that the warming of the planet will cause more volcano eruptions in Northern latitudes because of melting ice which results in less pressure on the earth’s crust…
That is no real surprise. They can’t say ENSO, solar activity and volcanoes are a big influence, because they believe that the influence of (anthropogenic) CO2 is the main driver of the increased global temperatures. So those natural influences can’t be big, otherwise it would go against the theory. Yet they are big enough to counter the temperature rise expected from CO2.
Does this mean that they are right that natural variability is masking the anthropogenic warming? Could be, but not necessarily. The influence of the natural variation on the pause is only part of the equation. If one accepts that a low solar activity and La Niña events have enough oumph to substantially mask the increase, then we should also accept that earlier high solar activity and predominantly El Niño events have enough oumph to substantially attribute to the earlier rise. One can not separate them both. It is not only during this pause that these have an effect, they were also part of the rise.
They may be right that the pause may not invalidate the theory of anthropogenic warming, but it definitely makes it weaker. The anthropogenic warming theory says that CO2 is the main driver of temperature rise in our climate system. In that decade and a half we were responsible for about 30% of all human emitted CO2 in the atmosphere. Although we emitted unprecedented amounts of CO2 in the atmosphere, we saw a standstill of temperatures, yet according to the theory we would expect to find an increase. Not only from the emissions in that time frame of the pause, but also the long term forcing of the accumulation of the CO2 that was emitted from the 1950s until the late 1990s. The pause tells us that there is at least one, probably more, elements in the climate system that are as big as the forcing of all that CO2 is. Otherwise it could not hold back temperatures with an unprecedented load of CO2 in the atmosphere.
This natural variation has not been accounted for by climate models (which are based on the theory), so they never foreseen the pause and are running way too high. This is the comparison Dr. Roy Spencer made of 90 climate models and two observational datasets (one surface dataset in green and one satellite based in blue):
Only two model runs come in the neighborhood of the observations. All the rest is (way) above. Yet, these are the things we base our policies on.
They also don’t tell about other problems with the theory. The highest absolute temperatures were measured in the 1940s, before humans emissions started to rise strongly. Not only that, the slope of the rise in temperatures during the 1910-1940s is quite similar to that of the 1980s-2000s. So the assumed natural temperature rise has the same slope as the assumed anthropogenic temperature rise.
Which brings us to other possible cause(s) of the rise: what was the cause for the rise of the 1850s-1880s and later of the 1910s-1940s? This couldn’t have to do with human emissions. What we do know from history is that in the 1850s we came out a period called the Little Ice Age, which was a cold period of ± 500 year. A competing theory is that our current rise in temperatures is caused by the recovery of that cold period. If there was a cold period of about 500 years, why would a subsequent period of 160 year having gradual higher temperatures be that unusual?!
The graph they added (that was showing that there was really a trend upwards in the instrumental record) was probably to frame anthropogenic warming as a long time trend. Yet in the light of the a possible recovery of the Little Ice Age, this could well be a meaningless exercise.
The future will tell. One thing is sure, change will happen. Up or down. Temporary or a step change. We are now in a situation were we put unprecedented amounts of CO2 in the atmosphere. China and India are developing. Africa wants to join in too. Whether we want it or not, we are actually doing the “experiment” of seeing what happens when CO2 levels increase. The longer the pause lasts, the bigger the discrepancy between the theory and what we observe. And the worse it looks for the theory.