08 Apr 2013: Analysis

Probing the Reasons Behind
The Changing Pace of Warming

A consensus is emerging among scientists that the rate of global warming has slowed over the last decade. While they are still examining why, many researchers believe this phenomenon is linked to the heat being absorbed by the world’s oceans.

by fred pearce

Whatever happened to global warming? Right now, that question is a good way of starting a heated argument. Some say it is steaming ahead. But others say it has stalled, gone into reverse, or never happened at all — and they don’t all run oil companies or vote Republican.

So what is going on?

First, talk of global cooling is palpable nonsense. This claim relies on the fact that no year has yet been hotter than 1998, an exceptional year with a huge planet-warming El Nino in the Pacific Ocean. Naysayers pretend that 1998 was typical, when it was anything but, and that temperatures have been declining since, which is statistical sleight of hand.

Meanwhile consider this. According to the National Oceanic and Atmospheric Administration (NOAA), all 12 years of the new century rank among the 14 warmest since worldwide record-keeping began in 1880. The second-warmest year on record, after 1998, was 2010. This is not evidence of cooling.

But there is a growing consensus among temperature watchers that the pace of warming in the atmosphere, which began in earnest in the 1970s
NASA’s James Hansen says the rate of warming ‘seems to be less this decade than it has been during the prior quarter century.’
and seemed to accelerate in the 1990s, has slackened, or stalled, or paused, or whatever word you choose. It may turn out to be a short blip; but it is real. “Although the first decade of the 21st century was the warmest on record, warming has not been as rapid since 2000,” says Pete Stott, head of climate monitoring and attribution at the UK’s Met Office, one of the leading keepers of the global temperature. He calls it a “hiatus” in warming.

In a blog last week, James Hansen, the retiring head of NASA’s Goddard Institute for Space Studies (GISS), agreed that “the rate of global warming seems to be less this decade than it has been during the prior quarter century”

Something is going on. With heat-trapping greenhouse gases accumulating in the atmosphere ever faster, we might expect accelerated warming. So it needs explaining.

There are a number of theories. Hansen suggested that extra emissions of particles in Asian smogs could be shading the Earth and camouflaging the greenhouse effect. In a February post on RealClimate, his Goddard Institute colleague Gavin Schmidt instead pointed to fewer warming El Ninos and more cooling La Ninas. He suggested that adjusting for their influence produced an unbroken pattern of warming.

Schmidt’s analysis certainly hints at a role for the oceans in all this. And most researchers on the case argue that, one way or another, the most likely explanation for the heating hiatus is that a greater proportion of the greenhouse warming has been diverted from the atmosphere into heating the oceans. A new study from Kevin Trenberth of the National Center for Atmospheric Research in Boulder, Colorado, published online in Geophysical Research Letters, found that ocean warming has been accelerating over the last 15 years.

Richard Allan of the University of Reading in England says simply: “Warming over the last decade has been hidden below the ocean surface.” If you take the oceans into account, he says, “global warming has actually not slowed down.”

This should not come as a surprise, notes Chris Rapley of University College London. The oceans are the planet’s main heat sinks. More than 90 percent of the extra heat trapped in the atmosphere by greenhouse gases ends up there. But, while climate models are good at calculating atmospheric processes, they are poorer at plumbing the ocean-atmosphere
‘Warming over the last decade has been hidden below the ocean surface,’ says a climate scientist.
interactions that determine how fast and how regularly this happens.

That makes those interactions a big source of uncertainty about atmospheric global warming, especially over the short term. If oceans grab a bit more heat one year, they can shut down that year’s warming. Equally, if they release a bit more they can accelerate atmospheric warming. This matters. “The way the ocean distributes the extra energy trapped by rising greenhouse gases is critical... [to] global surface temperatures,” says Allan. For forecasters trying to figure out the next decade or so, oceans could screw it all up.

Some bits of the puzzle have been known for a while. For instance, during El Nino years, warm water spreads out across the equatorial Pacific and the ocean releases heat into the air, warming the air measurably. That is what happened in 1998.

But while El Ninos come and go within a year or so, there are other cycles in heat distribution and circulation of the oceans that operate over decades. They include the Pacific Decadal Oscillation and the Atlantic Multidecadal Oscillation (AMO), both of which have been implicated in climate fluctuations in the 20th century. So have these or other ocean cycles been accelerating the uptake of heat by the oceans?

Virginie Guemas of the Catalan Institute of Climate Sciences in Barcelona, believes so. In a paper published in Nature Climate Change this week, she claims to provide the first “robust” evidence linking ocean uptake of heat directly to what she calls the recent “temperature plateau” in the atmosphere.

By plugging detailed measurements of recent atmospheric and sea temperatures into EC-Earth, a European model of interactions between atmosphere, oceans, ice and land surfaces, Guemas found that about 40 percent of the take-up was in the tropical Pacific, and another 40 percent in the tropical and North Atlantic.

She told me that it seems likely the changing thermohaline ocean circulation, which starts in the North Atlantic, plus the cycles of El Nino and perhaps the AMO, may play a prominent role. She thinks her model could have predicted the recent slowdown of atmospheric warming ahead of time.

That would be a breakthrough, but nobody has done it yet. Meanwhile, the climate modellers are skating on thin ice when they make predictions that play out over the timescales of a decade or so on which ocean cycles seem to operate. These forecasters can claim that, all things considered, they
Some scientists privately admit they were caught by surprise by the slackening pace of warming.
have done pretty well. But the forecasts remain hostages to fortune.

If anything, the recent pause shows the model forecasts in a good light. Myles Allen, a climate modeller at Oxford University in England, reported in Nature Geoscience last month on an audit of one of his own forecasts, which he made in 1999. He had predicted a warming of a quarter-degree Celsius between the decade that ended in 1996 and the decade that ended in 2012. He found that, in the real world, temperatures got too warm too soon during the 1990s; but the slackening pace since had brought the forecast right back on track.

That shows the forecast is performing well so far, but Allen admitted it might not stay that way. If temperatures flat-line out to 2016, his model’s prediction for that year will look no better than a forecast based on a series of random fluctuations.

Some in the mainstream climate community privately admit that they were caught out by the slackening pace of warming in the past decade or so. Back in the 1990s, some suggested — or at least went along with — the idea that all the warming then was a result of greenhouse gases. They were slow to admit that other factors might also be at work, and later failed to acknowledge the slowdown in warming. As Allen pointed out earlier this year: “A lot of people were claiming in the run-up to the Copenhagen 2009 [climate] conference that warming was accelerating. What has happened since then has demonstrated that it is foolish to extrapolate short-term climate trends.”

Not surprisingly they have been taken to task for this hubris. Roger Pielke Jr., an environmental studies professor at the University of Colorado at Boulder, who enjoys baiting the mainstream, told me last month: ”It is good to see climate scientists catching up with the bloggers. They should ask why it took so long to acknowledge what has been apparent to most observers for some time.”

But modellers are now responding more actively to the new real-world temperature data. For instance, the Met Office’s Stott reported last month that global temperatures were following the “lower ranges” of most model forecasts, and that higher projections were now “inconsistent” with the temperature record.

And last December, the Met Office downgraded its best guess for temperatures in the five years to 2017 from 0.54 degrees C higher than the
One researcher says the heat recently absorbed by the oceans might be released back to the atmosphere soon.
average for the late-20th century average to 0.43 degrees higher. It said the new forecast was the first output of its latest climate model, HadGEM3, which incorporates new assessments of natural cycles.

But the problem is that these cycles are not well integrated into most climate models. Natural cycles could switch back to warming us again at any time, admits Stott. But he has no clear idea when.

The stakes for the climate forecasting community are high. It may be unfair, but the brutal truth is that if the climatologists get their forecasts for the coming decade badly wrong, then a great many in the public will simply not believe what they have to say about 2050 or 2100 – even though those forecasts may well be more reliable.

Forecasters badly need a way to forecast the ocean fluctuations, and it could just be that Guemas’s new study will help them do that. She claims that her findings open the way to the future delivery of “operational decadal climate predictions.” For now she is cautious about making firm predictions, but told me she believes that “the heat that has been absorbed recently by the ocean might very well be released back to the atmosphere soon. This would be the scenario of highest probability. It would mean an increased rate of [atmospheric] warming in the next decade.”

It would indeed. If natural cycles start pushing towards strong warming, they will add to the continued inexorable upward push from rising concentrations of heat-trapping greenhouse gases. In that case, we would see climate change returning to the rapid pace of the 1990s. Whatever happened to global warming? The odds may be that by 2020 it will have come roaring back.

POSTED ON 08 Apr 2013 IN Climate Policy & Politics 


"Warming" isn't the only environmental concern that exists. We should strive to be a sustainable society, and even if global warming isn't happening very rapidly, or even at all, it isn't a reason to ignore all conservation efforts. We may survive the next few centuries, but if we don't make serious effort to become more environmentally conscious, out society will inevitably implode.

Posted by Joseph Ferguson on 08 Apr 2013

So, in other words, the science is not settled ... just as we deniers suspected all along.

Posted by Mark J on 08 Apr 2013

No, the "deniers" have been saying that it's all an invented liberal hoax meaning to destroy capitalism.

Posted by David M. on 08 Apr 2013

"He had predicted a warming of a quarter-degree Celsius between the decade that ended in 1996 and the decade that ended in 2012. He found that, in the real world, temperatures got too warm too soon during the 1990s but the slackening pace since had brought the forecast right back on track."

That's just pure luck. His models are wrong no matter what twist you put on it. Climate modellers just don't have a clue and only can explain what went wrong afterwards, just like economists.

"Method Wrong + Answer Correct = Bad Science"

Posted by Hoi Polloi on 08 Apr 2013

Lately, I have been reading headlines with "should", "could", and "may" in them. It is, as if the science community is trying to find something they can throw at us, that will stick to the wall. I don't think some of the outcome from this Alarmist panic was bad. Conservation is a good thing. But next time lets actually have some organized debate with out the condescending propaganda we have had over the last 20 years.

Posted by Ronald Clark on 08 Apr 2013

I'm wondering how these findings fit with this new study:

On a separate note, it's extremely frustrating how every attempt to discuss the complexities of science is met with a "Yippee" from skeptics/deniers. There's no "should," "could," or "may" to climate change. Of 13,950 peer reviewed climate science articles between 1991 and 2012 only 24 reject climate change. When 99.8 percent of doctors tell you have cancer you don't waste your time looking for the 1 in 100 person who thinks the MRI machine may have failed.

Just as a human temperature only a few degrees above normal signals a serious illness, a global average warming of a few degrees (much higher in certain regions) signals serious problems for our planet. OUR planet. There's no yippee when anyone dies of heatstroke, loses a crop to drought and goes bankrupt, or loses a home to a flood and can't rebuild. No one is immune.

Posted by Anna Brittain on 08 Apr 2013

I do not understand why there is so much discussion about air temperature. Who cares ? Global warming is not about temperature but warming.

Water and ice can have nearly the same temperature, but everybody knows that it can take a month of sunny days to completely melt ice on a Canada or Swedish beach. What can you tell with your thermometer about the history of warming in such a case ? Nothing.

In the earth system the heat capacity of ocean is the only thing that count. Air is epsilon, nul, non significant, uninteresting. If we have some wind from the north it gets cold, if we have wind from the south it gets warm. What does it mean ? Nothing at all. Just that there is wind.

The heat variation of the ocean is online with prediction and that is what is telling us thatg lobal warming is there. This huge quantity of warmth is in store, real and will count in the future.

There is one good measure for the skeptics: the ice in the northern hemisphere.

Posted by kervennic on 08 Apr 2013

"There is one good measure for the skeptics: the ice in the northern hemisphere. "

Don't forget the ice in the southern hemisphere too. Remember just last year when the Antarctic ice sheet had melted to record lows due to global warming. This year the Antarctic ice sheet is growing again and it's also due to global warming. That's also a good measure for the skeptics, global warming does it all. Wahoo!

Posted by klem on 09 Apr 2013

The world's ocean are showing a similar behavior as the air i.e. that warming has [slowed, abated, paused, etc.].


As others have stated, there are those (on both extremes) who use the latest research to claim victory for their side. The end is still a long way off. We still do not know how much warming will occur due to added concentrations of atmospheric CO2.

One thing that we are starting to understand is that nature has a much greater influence than estimated previously, and our climate models need to be refined to accommodate this. Even Hanson has admitted (see above) that global warming has (apparently) lessened in the past decade. This is a surprise to many scientists, who expected continued acceleration. Neither the air nor the oceans have heated as expected. The reason is still conjecture, and may be until we gather enough data to explain it.

I still chuckle at those above who think that a majority opinion is how science works. The search for the truth is what matters, even if that truth contradicts everything we think we know.

Posted by Daniel on 10 Apr 2013

I do not know. It refers to a nature article that is behind a pay wall, but which has the following title "Robust warming of the upper ocean..."

Posted by kervennic on 11 Apr 2013

A lot of studies and prediction have been undertaken but scientists should come to a consensus the possible methods to reduce global warming and the effect of global warming on crop production. An interdisciplinary research team needs to be built up to address this vital issue.

Posted by Dr. Ratikanta Maiti on 11 Apr 2013

Answer me this: why are the oceans suddenly absorbing heat now, and not before?

Posted by jimbrock on 11 Apr 2013

Ok, i see that the answer is just falling in the news. There is a new Geophys. Letters (Balmaseda et al.) that shows that the missing heat has just been buried in the deep ocean and that it is ready to burp out in the next El Nino.



So i guess the uncertainty is not about the pace of warming and heat but how it will affect local temperature in the future.

Ocean still provide food for many people and is a key element to rain patterns that feed the rest, let alone temperature influence.

Posted by kervennic on 11 Apr 2013

We predicted the slowing of global warming in 2008. See the article in Nature by Keenlyside et al.

Posted by Mojib Latif on 11 Apr 2013

"Of 13,950 peer reviewed climate science articles between 1991 and 2012 only 24 reject climate change. When 99.8 percent of doctors tell you have cancer you don't waste your time looking for the 1 in 100 person who thinks the MRI machine may have failed."

Doctors have a proven track record on diagnosing cancer. (Though unfortunately they don't have a proven track record on curing it.)

Climate scientists don't have a proven track record. On anything. At all. So it would be rather prudent to check out whether they know what they are talking about.

Secondly, there obviously aren't 13,926 "peer reviewed climate science articles between 1991 and 2012" that demonstrate the truth of AGW. Most articles that mention AGW take it as a given.

Posted by James Evans on 11 Apr 2013

On sustainability, check out what Kansas is doing.

Basic physics says that warmth moves towards cold. The oceans are plenty cold, no wonder the oceans are warming. Oh, that's right that theory has doubters and so it can't be trusted...duh!

Posted by Harry Applin on 11 Apr 2013

It just can't be accident that every scientist who claims there is CAGW* is in the pocket of government, and that government stands to make huge gains from public gullibility and belief in CAGW.

(* Catastrophic AGW)

Posted by Tomcat on 15 Apr 2013

To me, the scary thing is that if the heating of the oceans is penetrating down to 700 meters, the massive offshore methane hydrate deosirs along the continental shelves may become unstable. Any insight on that from the experts.

Posted by Roger Faulkner on 23 Apr 2013

The only thing that has been settled on global warming is that it is not clearly understood or predictable by anybody thus far. Conservatives that refuse to admit greenhouse gasses even exist or bear watching are no worse than liberals that scream from the mountaintops (or poles) world demise based on bad science.

So far as the new theory on changing from "global warming" to "atmospheric warming" and "ocean warming" - it readily says in this article that is all hypothesis with no real data to back it up. I might suggest since it goes to great length to explain el nino and el nina as responsible for difficulty in predictions and it is proven science they occur based on warmer and cooler ocean currents that claiming the ocean got warmer while the air did not is very questionable.

So far as warmest 12 years since 1880 records - also by far more sampling stations in different
places and sadly a lot of the "scientists" that are doing that sampling are biased to the point I do not trust the results- they report a result they want that justifies their grant.

We can all agree on renewable energy and recycling benefit everybody. Lets shift a few 100 million dollars and countless man hours of very smart people from trying to prove or disprove
global warming into renewable energy and recycling which will definitely bear fruit and not just spur debate.

Posted by Reuben Dickison on 24 Apr 2013

It simple...We cannot predict the climate, just whether phenomena. The climate is chaotic...

Posted by Windguru on 24 Apr 2013

CO2 is not a primary climate driver. The fixation with CO2 is silly and distracting. The only reason that it occurred is that it fits a political meme and it found fertile root amongst the scientifically illiterate and superstitious. There is an excellent precis on what and what does not constitute valid science in:


Like him or hate him, Monckton's intellectual discipline and grasp of science far exceeds the reach of many who consider themselves experts. This includes James Hansen.

Posted by Shoshin on 02 May 2013


The easiest way to show you how important CO2 is as a Green House Gas (GHG) is to compare the surface temperature of Mercury which doesn't have an atmosphere and is the closest planet to the sun to that of Venus the second planet from the sun which is about twice as far from the sun as Mercury, BUT has a dense atmosphere mostly of CO2.


Which planet is hottest, Venus or Mercury?

"The surface temperature of Mercury is completely regulated by its closeness to the Sun and is about 430 C ( 806 F) at local Noon. Because of the Greenhouse Effect on Venus, the surface temperature is regulated by the trapped infrared energy which cannot escape back into space to balance what it receives from the Sun as is the case for Mercury. This means that the surface temperature of Venus is far hotter than on Mercury, in the neighborhood of 472 C ( 882 F). So, even though it is twice as far from the Sun and received 1/4 as much sunlight, it is hotter than Mercury!"

On Earth, CO2 has the same GHG effect in our atmosphere. Fortunately our atmosphere doesn't have as much CO2 as Venus! Water vapor actually contributes the largest GHG effect to the atmosphere, but the comparatively small amount of CO2 is critically important.

CO2 has increased by about 37 percent in the atmosphere since the beginning of the Industrial Age when CO2 was about 290ppmv. CO2 just reached 400ppmv last week. 400 parts per million volume may seem insignificant, but it is not. Ozone in the atmosphere which is critically important to protecting life on land from ultraviolet rays is measured in parts per trillion volume!

Carbon dioxide is a critical primary GHG.

Posted by balanceact on 16 May 2013

The polar ice caps are an enormous heat sink, because it requires a lot of heat to turn ice into water without increasing its temperature. This is known as the "heat of fusion" of water. Thus instead of seeing continuing dramatic global temperature increases, we are seeing dramatic reductions in the polar ice cover. As the amount of ice remaining decreases, we can anticipate that atmospheric and oceanic temperatures will continue to rise.

Posted by Jeff White on 17 Aug 2013


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Fred Pearce is a freelance author and journalist based in the UK. He serves as environmental consultant for New Scientist magazine and is the author of numerous books, including the newly released The Land Grabbers: The New Fight over Who Owns the Earth. In previous articles for Yale Environment 360, Pearce has written about a positive development that emerged from last year’s Rio+20 summit and explored the question of whether environmentalists are increasingly taking anti-science positions.



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