A paper just published in Science Magazine helps explain variation we see in the long term Carbon-pollution caused upward trend Earth’s surface temperatures. The research also, and rather ominously, suggests that a recent slowdown in that trend is likely to reverse direction in the near future, causing the Earth’s surface temperature to rise dramatically.
The graph shown above represents the ongoing warming of the Earth’s surface owing to the increased atmospheric concentration of human generated greenhouse gas pollution, mainly CO2. But, have a look at the following graph of changes in concentration of CO2 in the Earth’s Atmosphere:
As you can see, the increase in CO2 is very steady, while the changes in Earth’s surface temperature is very squiggly. Why? In particular, the Earth’s surface temperatures seem to undergo a series of rapid increases or decreases, and now and then, seem to squiggle up and down along a slowly ascending plateau, as has been happening recently. Climate science deniers have taken this recent slowing in the increase of temperature as a signal that the link between CO2 concentrations and global surface temperatures is a hoax. But real climate scientists focus instead on actually explaining, rather than making up stories about, this variation.
There are several different factors that may cause the shorter term squiggles that we see superimposed on the longer term warming trend. The sun’s energy varies over decades, and this contributes a small amount to the variation. Aerosols (dust), either from human activities or volcanic activity, can produce a cooling effect, and this effect varies across time. If you look at the graph of temperatures, you’ll see a strong downward trend associated with the vast eruption of Mount Pinatubo in 1991, for example. A third source of variation in the upward march of the Earth’s temperature is not really a source of cooling or heating at all, but rather, a shift in where the heat goes. The graph on the top of this post is of “surface temperature,” which is a combination of land-based thermometers at roughly head-height, located at weather stations around the world, and sea surface temperatures. But well over 90% of the heat added to the Earth’s system by the human-caused greenhouse effect actually ends up in the ocean. A small percentage of variation in how much heat goes into, or comes out of, the ocean can cause a large variation in the “surface temperature.” You can think of the surface temperature measurements as a relatively small tail attached to a rather large dog, where the dog is the ocean and the tail is the land based thermometers and the sea surface. (I’ve developed this analogy here.)
That the behavior of the ocean is important can be understood by noting that while surface temperature increase has slowed in recent years, the temperature in the top couple of kilometers of the world’s oceans has continued to increase apace. You can also look at the relationship between the squiggle of the surface temperature curve and El Niño and La Niña events. The former are periods of time when the Pacific ocean is sending heat out into the atmosphere, and the latter are periods of time when the Pacific is sucking more heat in. The following graphic from Skeptical Science illustrates this nicely.
“ENSO” refers to the El Niño-La Niña cycling. The top line, in red, represents the change over time in surface temperature just during El Niño periods, while the blue line, along the bottom, represents change over time in surface temperature just using La Niña years. As you can see, many of the ups and downs in the long term surface temperature trend seem to represent ENSO variation.
Now, to the recently published study. The paper is “Atlantic and Pacific multidecadal oscillations and Northern Hemisphere temperatures” by Byron Steinmann, Michael Mann, and Sonya Miller, and is published in tomorrow’s Science. (Yes, I have a time machine.) From the abstract:
The recent slowdown in global warming has brought into question the reliability of climate model projections of future temperature change and has led to a vigorous debate over whether this slowdown is the result of naturally occurring, internal variability or forcing external to Earth’s climate system. To address these issues, we applied a semi-empirical approach that combines climate observations and model simulations to estimate Atlantic- and Pacific-based internal multidecadal variability (termed “AMO” and “PMO,” respectively). Using this method, the AMO and PMO are found to explain a large proportion of internal variability in Northern Hemisphere mean temperatures. Competition between a modest positive peak in the AMO and a substantially negative-trending PMO are seen to produce a slowdown or “false pause” in warming of the past decade.
The research (also reviewed here by Chris Mooney) combines observational data (temperature records and the indices for the AMO and PMO) with sophisticated modeling techniques to parse out the contributions of the Pacific and Atlantic oceans, the big dogs of climate change (the Pacific being the much bigger dogs) on surface temperature variability. Essentially, they are trying to determine how much of the squiggling, specially the recent slowing down of temperature increase, is accounted for by “internal variability” as opposed to “forcings.” The former includes the interactions of the surface and the ocean. “Forced” variation is, according to Michael Mann, means “… governed by drivers, be they human (increased greenhouse gas concentrations, sulphate pollutants) or natural (volcanoes, solar output changes). The internal variability is what’s left, it is the purely natural oscillations in the system that have no particular cause, just as weather variations on daily timescales have no particular cause, they just happen.”
One of the findings of this paper, important in climate research but perhaps a bit esoteric, is that the Pacific and Atlantic have mostly independent effects as sources of internal variation. This is not really new, but confirmed by this work. More exactly, treating them as independent provided good results.
But the most important finding is summarized in the following figure, taken from Figure 3 and also reproduced in a writeup by author Mann at Real Climate:
This shows the AMO, PMO, and the derived (combining the two) NMO values over time. Assume that the highest and lowest values are close to the maximum and minimum that these measures normally reach. Note that there is something of a periodicity in these values. That there would be makes sense. These values represent the way in which the oceans interact with the air, and we know that although there is not perfect periodicity (regularity) in that relationship, historically, every year the ocean is in a phase of removing heat from the atmosphere there is an increased chance of a reversal in that relationship. Now, step back from the contentious issue of climate change for a moment, and imagine that these are values of a blue chip stock you are thinking of investing in. Remember the cardinal rule of getting rich on the stock market: Buy low, sell high! Now, decide if you want to put your hard earned money ito the AMO or the PMO. Clearly, the PMO is at a minimum. Buy now because it is going to go up soon!
Remembering that the PMO was found to be a much bigger source of internal variability than the AMO, and that it is a major player in determining surface temperatures, this can only mean one thing. Things are going to heat up soon. Study author Michael Mann told me, “The PMO appears to be very close to a turning point, based on the historical pattern. So we don’t expect it to continue to plunge downward. We expect a turning point soon.” In his summary of the work in Real Climate, Mann notes that “the most worrying implication of our study [is] that the “false pause” may simply have been a cause for false complacency, when it comes to averting dangerous climate change”
We just had the warmest calendar year on record. Last month, January 2015, was probably the second warmest January on record. Using a 12 month moving average (like in the graph at the top of this post), the last 12 months were the warmest 12 months on record. I hear rumors that February, the month we are in, is relatively warm. We have been seeing signs of the Pacific belching out more heat lately, with El Niño threatening. This could all be a very short term trend, as we expect to happen frequently with the general upward march of surface temperatures owing to greenhouse gas pollution. But this latest paper indicates that it might not be; it could be the beginning of a longer upward trend. Whatever effects of surface warming you might be concerned with — increased storms, drought, more rapid melting of glacial ice, killer heat waves — expect more over the next decade than we have over the last decade. And we had quite a bit of that over the last decade.
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If I look at the graph of NMO, (which obviously has the high frequency content filtered out), it looks like the derivative is currently strongly negative (near peak negatine derivative). Looking leftwards on the graph it looks like the minimum is reached roughly fifteen years after such a steep descent. So that would imply that the minimum is still a ways off. Of course even if thats the case, it took a strongly negative NMO trend to counteract the increasing forcing, so even a decelerating downward NMO trend will not be strong enough to keep temps flat. Then 15-25 years from now, if the NMO is strongly climbing, will be when the big heatup is seen.
Yes, but the PMO is the primary contributor.
Global warming heating up?
I hope so.
LOL
The lack of updated forcings used in the model simulations clearly affect the results. The best available explanation is still a combination of increased volcanism, observational coverage bias, and some deep heat storage via natural variability in the pacific.
Paul S commenting on realclimate provides a link to monthly PDO values:
http://research.jisao.washington.edu/pdo/PDO.latest
You can see that in the past year the PDO has gone from strongly negative to strongly positive. So it looks like my slowturnaround is not likely.
I believe once the El Nino kicks in which it inevitably will soon there will be a rapid forcing and what I now call the Shakova scenario will unfold with gigatons of methane being released.
Google Natalia Shakova for more.
Robert, I should probably have included something about coverage bias in my writeup, but there are so many things to consider. For the record, Cowtan and Way have a temperature reconstruction that seeks to adjust for biases in coverage of the instrumental record. The idea is that relatively large less-covered areas are not average, but actually, biased warm, so only by estimating surface temperatures there and including that in the temperature curve can you have a more accurate curve. Interested readers should look at these two sources for more:
http://onlinelibrary.wiley.com/doi/10.1002/qj.2297/abstract
http://www.skepticalscience.com/cowtan_way_surface_temperature_data_update.html
Omega Centauri: Maybe, or maybe it will fluctuate back and forth for a while. But still, for the medium term, I’d buy stock in the PDO.
Kevin, well, that is one hypothesis. I’m skeptical of the “Shakova scenario.” That is not to say Methane being released in the Arctic (mainly from permafrost areas) isn’t important, but the whole “methane gun” hypothesis is highly questionable.
But, according to some who promote it you would be right. If there is an abrupt uptick in surface temperatures esp. in the Arctic, and the methane gun does not go off, then maybe it will have to be reconsidered or revised by those supporting it.
Mike Mann tried to clear up Robert Wray’s misunderstandings in his real climate post. Apparently it didn’t work.
“Shakova scenario will unfold with gigatons of methane being released.”
Kevin, ask Shakova why that never happened in the past (and I know that the absence of evidence is not quite the same as evidence of absence).
Hi Greg,
Our work was only a very small piece of the puzzle. When you consider the impacts of coverage bias with the detectable influence of volcanism and a greater predisposition towards negative PDO conditions and deep ocean storage you’re able to explain the discrepancy. Depending on the magnitude of the volcanic effect it could nearly explain it on its own.
As for the methane bomb hypothesis – I don’t think there are many working permafrost researchers who find it it compelling. It takes an awful lot of energy to thaw permafrost and in many areas it survived through the hypsithermal when conditions were much warmer in the Arctic without a methane release. This is very ice-rich permafrost as well meaning that it takes much more energy to thaw it.
Wow its complicated stuff and worrying. Who knows what we maybe unleashing on ourselves.
Robert, you can’t win that argument, I’m afraid. The Methane Bomb promoters are worried about methane on the sea floor in the Arctic Sea. I mentioned permafrost because that is where there is actual methane release happening. Most of the methane that bubbles off the crystals on the sea floor is is consumed/converted by microbes and ends up as biomass or CO2. But for some, the scarier the outcome of a scenario the more believable it is, for some reason.
see nuavo is a real idiot!
Like whats happening in Sao paolo?
no water 5 days a week.
Great article with some scary implications here which I must admit come as no surprise to me.
It has always made sense that when factors currently offsetting Global Overheating such as lower than usual solar activity, prolonged La Nina ENSO phases and aerosol pollution getting cleaned up some inevitably change, then Global Overheating will really kick in. I dread to think what the future holds in this regard.
Shared. Thanks for this, Greg Laden.
@11. Marco : I’m not sure about the “Shakova scenario ” exactly, what its details etc .. are; don’t really know enough to comment on precisely that.
However, what I gather of it and your comment there does remind me of a section in James Hansen’s ‘Storms of My Grandchildren’ (Bloomsbury, 2009) pages 161-165 dealing with the Paleocene-Eocene Thermal Maximum event (circa 55 million years ago) which was most likely caused by the sudden release of methane from hydrates (clathrates I think?) and caused a rash of minor extinctions. That scenario although still lots of uncertainties on it does worry me.
^ See :
http://en.wikipedia.org/wiki/Paleocene%E2%80%93Eocene_Thermal_Maximum#Methane_release
Plus :
http://en.wikipedia.org/wiki/Clathrate_gun_hypothesis
In addition to :
http://climatesight.org/tag/petm/
along with other sources.
The next ten years will be an interesting thing to observe.
^ Indeed. Plus to live through. “interesting trimes ” in the sense of the old Chinese curse.
But also so much to learn and see – just from Pluto, Ceres and Churyumov-Gerasimenko this year let alone onc ethe James Webb Space telescope flies.
I’ve found it kinda curious that the hottest years on record have been about every five years apart lately – 2005, 2010 now 2014. Probably (almost certainly) no significance to it (other than obvious Global Overheating trend) but still, *if* that trend continues – unlikely event -maybe 2018-9 then 2022-3 for next record breaking hottest years?
Also I will admit to a certain morbid curiousity on when Arctic sea ice finally reaches zero and then continues vanishing, what year (& month) will be the last we see under 400 pmm Co2 and who will be the last Denier standing?
But I wish these things weren’t happening as grimly fascinating in the horrible “car crash” type of way that they are.
Still we’re also seeing a lot of progress in many areas too despite those who keep dragging us backwards. What willbe thelats state of teh USA to accept equal marraige for all, whwillClinton becoemthe first Women prPOTUS and if not her then who and when, when will Australia finally become a Republc with an Aussie symbolic head as well de facto one? Will we see West Papua follow East Timor in breaking free of Indonesia’s “Javanese empire” , what new advances in science will there be and when and so much more.
Guess all generations live in interesting times but ours does seem particularly so. Hope we can make a positive difference to make our times memorable more for the right reasons than the wrong ones. (Although so much still beyond our control.)
Typo fix for clarity,- sorry (Please feel free to edit and then delete this accordingly Greg Laden!) That was meant to read :
What will be the last state of the USA to accept equal marriage for all, will Hilary Clinton become the first Women POTUS in 2016 and, if not her, then who and when, when will Australia finally become a Republic .. ?_
Yes, in a horrible “car crash” type of way – only you & I (and our families) are strapped in the passenger seats.
Mostly it has to do with ENSO: http://ggweather.com/enso/oni.htm
More warming?
And hamsters might fly.