Global Warming Continues to Accelerate
March 25, 2013
A new study of ocean warming has just been published in Geophysical Research Letters by Balmaseda, Trenberth, and Källén (2013). There are several important conclusions which can be drawn from this paper.
- Completely contrary to the popular contrarian myth, global warming has accelerated, with more overall global warming in the past 15 years than the prior 15 years. This is because about 90% of overall global warming goes into heating the oceans, and the oceans have been warming dramatically.
- As suspected, much of the ‘missing heat’ Kevin Trenberth previously talked abouthas been found in the deep oceans. Consistent with the results of Nuccitelli et al. (2012), this study finds that 30% of the ocean warming over the past decade has occurred in the deeper oceans below 700 meters, which they note is unprecedented over at least the past half century.
- Some recent studies have concluded based on the slowed global surface warming over the past decade that the sensitivity of the climate to the increased greenhouse effect is somewhat lower than the IPCC best estimate. Those studies are fundamentally flawed because they do not account for the warming of the deep oceans.
- The slowed surface air warming over the past decade has lulled many people into a false and unwarranted sense of security.
The main results of the study are illustrated in its Figure 1.
Figure 1: Ocean Heat Content from 0 to 300 meters (grey), 700 m (blue), and total depth (violet) from ORAS4, as represented by its 5 ensemble members. The time series show monthly anomalies smoothed with a 12-month running mean, with respect to the 1958–1965 base period. Hatching extends over the range of the ensemble members and hence the spread gives a measure of the uncertainty as represented by ORAS4 (which does not cover all sources of uncertainty). The vertical colored bars indicate a two year interval following the volcanic eruptions with a 6 month lead (owing to the 12-month running mean), and the 1997–98 El Niño event again with 6 months on either side. On lower right, the linear slope for a set of global heating rates (W/m2) is given.
The Data
In this paper, the authors used ocean heat content data from the European Centre for Medium-Range Weather Forecasts’ Ocean Reanalysis System 4 (ORAS4). A ‘reanalysis’ is a climate or weather model simulation of the past that incorporates data from historical observations. In the case of ORAS4, this includes ocean temperature measurements from bathythermographs and the Argo buoys, and other types of data like sea level andsurface temperatures. The ORAS4 data span from 1958 to the present, and have a high 1°x1° horizontal resolution, as well as 42 vertical layers. As the authors describe the data set,
“ORAS4 has been produced by combining, every 10 days, the output of an ocean model forced by atmospheric reanalysis fluxes and quality controlled ocean observations.”
Accelerated Global Warming
As illustrated in Figure 1 above, the study divides ocean warming into three layers for comparison – the uppermost 300 meters (grey), 700 meters (blue), and the full ocean depth (violet). After each of the Mt. Agung, Chichón, and Pinatubo volcanic eruptions (which cause short-term cooling by blocking sunlight), a distinct ocean cooling event is observed in the data. Additionally, after the very strong El Niño event of 1998, a cooling of the upper 300 and 700 meters of oceans is visible as a result of heat being transfered from the surface ocean to the atmosphere.
One of the clearest features in Figure 1 is the rapid warming of the oceans over the past decade. As we have previously discussed, the warming of the shallower oceans has slowed since around 2003, which certain climate contrarians have cherrypicked to try and argue that global warming has slowed. However, more heat accumulated in the deeper oceans below 700 meters during this period. The authors describe the ocean warming since 1999 as,
“the most sustained warming trend in this record of OHC. Indeed, recent warming rates of the waters below 700m appear to be unprecedented.”
Their results in this respect are very similar the main conclusion of Nuccitelli et al. (2012), in which we noted that recently, warming of the oceans below 700 meters accounts for about 30% of overall ocean and global warming. Likewise, this new study concludes,
“In the last decade, about 30% of the warming has occurred below 700 m, contributing significantly to an acceleration of the warming trend.”
The warming of the oceans below 700 meters has also been identified by Levitus et al. (2012) and Von Schuckmann & Le Traon (2011), for example.
Some ‘Missing Heat’ Found
Kevin Trenberth past comments about ‘missing heat’ drew considerable attention. The phrase refers to the fact that the heat accumulation on Earth since about 2004 (e.g. from warming oceans, air, and land, and melting ice) that instruments were able to measure could not account for the amount of global heat accumulation we expected to see, based on the energy imbalance caused by the increased greenhouse effect, as measured by satellites at the top of the Earth’s atmosphere.
These new estimates of deeper ocean heat content go a long way towards resolving that ‘missing heat’ mystery. There is still some discrepancy remaining, which could be due to errors in the satellite measurements, the ocean heat content measurements, or both. But the discrepancy is now significantly smaller, and will be addressed in further detail in a follow-up paper by these scientists.
So what’s causing this transfer of heat to the deeper ocean layers? The authors suggest that it is a result of changes in winds related to the negative phase of the Pacific Decadal Oscillation and more frequent La Niña events.
Good News for Climate Sensitivity? Probably Not
Recently there have been some studies and comments by a few climate scientists that based on the slowed global surface warming over the past decade, estimates of the Earth’s overall equilibrium climate sensitivity may be a bit too high. However, as we previously discussed, these studies and comments tend to neglect the warming of the deep oceans below 700 meters.
Does the warming of the deep ocean support these arguments for lower equilibrium climate sensitivity? Probably not, as Trenberth explained (via personal communication),
“it contributes to the overall warming of the deep ocean that has to occur for the system to equilibrate. It speeds that process up. It means less short term warming at the surface but at the expense of a greater earlier long-term warming, and faster sea level rise.”
So the slowed warming at the surface is only temporary, and consistent with the ‘hiatus decades’ described by Meehl et al. (2011). The global warming end result will be the same, but the pattern of surface warming over time may be different than we expect.
The real problem is that in the meantime, we have allowed the temporarily slowed surface warming to lull us into a false sense of security, with many people wrongly believing global warming has paused when in reality it has accelerated.
Global Warming Wake Up Call
Perhaps the most important result of this paper is the confirmation that while many people wrongly believe global warming has stalled over the past 10–15 years, in reality that period is “the most sustained warming trend” in the past half century. Global warming has not paused, it has accelerated.
The paper is also a significant step in resolving the ‘missing heat’ issue, and is a good illustration why arguments for somewhat lower climate sensitivity are fundamentally flawed if they fail to account for the warming of the oceans below 700 meters.
Most importantly, everybody (climate scientists and contrarians included) must learn to stop equating surface and shallow ocean warming with global warming. In fact, as Roger Pielke Sr. has pointed out, “ocean heat content change [is] the most appropriate metric to diagnose global warming.” While he has focused on the shallow oceans, actually we need to measure global warming by accounting for all changes in global heat content, including the deeper oceans. Otherwise we can easily fool ourselves into underestimating the danger of the climate problem we face.
Climate Denial Crock of the Week 
March 25, 2013 at 1:44 pm
Will surface temps be removed from the climate discourse at last?
March 25, 2013 at 2:32 pm
Well we live at the surface, so it still matters!
But as far as judging the pace of change is concerned, it would be a good thing if people recognised that the oceans are the biggest part of the climate system. Apart from anything else, there’s thermal inertia to think about.
March 25, 2013 at 2:39 pm
if Trenberth is right next ipcc report will have to be radically different
March 25, 2013 at 3:23 pm
Sadly, Maurizio, we already know it won’t be. This is because government reviewers will make sure it is not too alarming. They will do this, primarily, by continuing to ensure all positive feedback mechanisms now observed are excluded from consideration.
http://thinkprogress.org/climate/2013/01/31/1524981/why-climate-scientists-have-consistently-underestimated-key-global-warming-impacts/
March 25, 2013 at 4:17 pm
Because surface temperatures have not been rising? Is that your argument during a period when, according to NASA:
“With the exception of 1998, the nine warmest years in the [world-wide] 132-year record all have occurred since 2000.”
?
March 25, 2013 at 4:39 pm
Roger – if “about 90% of overall global warming goes into heating the oceans” what is the point of measuring anything else?
Likewise, if the heat is being stored mostly below 700m, it is being stored mostly below 700m, i.e. it is not heating anything else.
March 25, 2013 at 8:13 pm
What is it about
““With the exception of 1998, the nine warmest years in the [world-wide] 132-year record all have occurred since 2000.””
that you don’t understand?!?
Here is a hint: It means the world IS heating.
Try to keep THAT thought in your head for more than a microsecond?
March 25, 2013 at 8:33 pm
Roger – you seem unable to understand the meaning of “must learn to stop equating”. Who knows why.
March 26, 2013 at 4:42 am
WTF are you talking about?
I know it is not the fact that the surface temperature record continues to rise and that is worth keeping track of for more than a microsecond.
Or are you pointing to something shiny again?
March 25, 2013 at 1:49 pm
In a world that is becoming increasingly scary, this latest information is frightening to the extreme.
March 25, 2013 at 2:22 pm
@Paul Handover : And keeps getting ever more so and yet so few people (outside the experts who know what they’re talking about eg. Jim Hansen, Mike Mann & well, Peter Sinclair) seem to actually realsie how deep a hole we’re digging ourselves into. The lack of understanding and appreciation of the situation, that we keep walking off this cliff is horrific. 😦
March 25, 2013 at 3:36 pm
Yes, very much so. But it’s even more challenging. In the sense that our lives are so inextricably caught up in all the ‘habits’ of modern life.
Take the example of the life that my wife and I live. Despite us being incredibly aware of the need for a sustainable life-style, here we are with two cars, a tractor, petrol-powered chain saws, chippers, water pumps and on and on.
We try to make changes by buying all our electricity from renewable sources, planting vegetables, trying to reduce food miles as much as we can, heating the house with a wood fire, not using air-conditioning, blah, blah, …
Yet, it’s all so trivial when the bigger picture is examined. Not seeing any way out of the mess is what scares me. Not seeing any concerted effort by any significant government or international organisation to make it clear that global chaos is right around the corner.
Sorry, don’t mean to be so dark-minded; not my usual outlook on life.
March 25, 2013 at 2:24 pm
Only a fool or a man making money off the land cannot see the death of our planet. We must be careful. The plants that create cures for many sicknesses are being destroyed in the tropics of South America. Each day another plant or animal is lost forever. Thank you for your thoughts. People want to believe we are okay. Look at Greenland?
March 25, 2013 at 2:27 pm
First, the heat will not affect in any way the warming over the next even hundreds of years,
Real Climate: “Neither is this heat going to come back out from the deep ocean any time soon (the notion that this heat is the warming that is ‘in the pipeline’ is erroneous [ http://www.realclimate.org/index.php/archives/2011/10/global-warming-and-ocean-heat-content/%5D.)”
… but it shows how powerful and underestimates negative feedback are, slowing down the warming (is why: “… this latest information is frightening to the extreme”!?)
Budyko (1998): “On balance, it is very difficult to conclude with higher accuracy whether the projected global warming would be globally beneficial to human society or not.”
Secondly, for those skeptics who consider, like me, that now dominates (determines warming) natural conjunction of natural 3 cycles: 6000, and the bi-, and millennium; global warming will end about 2250 AD years …
March 25, 2013 at 4:10 pm
Your statement is not warranted by your reference, which says that the deep-ocean heat does have an effect on upper ocean interactions with the atmosphere. Nice try.
Nonsense. Positive feedbacks dwarf negative feedbacks. The point of the Real Climate article was that deep ocean temperature changes confirm the overall energy imbalance caused by greenhouse gases.
Source please? This can not be found via Google or Google scholar
Another “skeptic” who doesn’t understand the greenhouse effect and the atmospheric lifespan of CO2. Sigh.
March 25, 2013 at 7:12 pm
is there any other kind?
March 25, 2013 at 3:43 pm
If we now know that it is warmer ocean water that is causing most of the increased melting of glaciers that are on the edges of Greenland and Antarctica, won’t this warming of the deep water be accelerating the disintegration of those glaciers?
And if the Arctic ice melts any faster, we will see ice free Arctic summers in the next couple of years… The question then becomes how quickly that ice-free time increases?
Another major issue is the change in productivity of the ocean life. When does fishing “go away”, for all intents and purposes?
Neil
March 25, 2013 at 4:01 pm
Neil, on your last question, global warming and ocean acidification are significant drivers in the ocean, but perhaps an even more pressing concern regarding fish stocks is the current methods of fishing – mainly, trawling. Another significant stress on fish population is industrial and agricultural runoff, creating vast ‘dead zones’ around tributaries and well into the surrounding ocean.
There are countless articles and studies warning about probable complete ocean fishery collapse by 2050. The world isn’t listening. It’s another threat to business-as-usual, or short-term profits.
March 25, 2013 at 4:20 pm
Hi Jim,
Yes, overfishing is probably the main problem up until now; but with plankton dropping significantly, and generally warming oceans, the downward trend will probably spiral down fishing as food source more quickly than 2050.
Heck – the jellyfish blooms have already had a huge effect on fishing. Many people around the work depend on the ocean for their protein.
We cannot forget the huge effects of plastic entering the food chain, either. Our plastic refuse and artificial clothing fibers have permeated the ocean. We can only hope that some bacteria evolves to be able to eat plastic… Otherwise, it will clog up the planet.
Disposable plastic = oxymoron.
Neil
March 25, 2013 at 4:43 pm
Yep. All this boils down to subsidizing the present by stealing from the future. It’s what we’re doing with AGW, pollution, overfishing, all of it. It’s even what we do with debt. It’s even what we do with our monetary systems.
But raising these issues poses a quandary for those who believe in the current system. True reaction against them REQUIRES a loss in the short-term – if not for society as a whole, then for particular businesses in specific. It’s why denial is so strong, and why you see a reaction to blog postings like this one.
Whatever. The bill is coming due, sooner or later.
March 25, 2013 at 7:39 pm
mmmm, jellyfish
March 25, 2013 at 10:00 pm
Thanks for that Peter. If I ever suffer from dry eye I shall be sure to use jellyfish snot.
March 25, 2013 at 4:36 pm
[…] Perhaps the most important result of this paper is the confirmation that while many people wrongly believe global warming has stalled over the past 10–15 years, in reality that period is “the most sustained warming trend” in the past half century. Global warming has not paused, it has accelerated. The paper is also a significant step in resolving the ‘missing heat’ issue, and is a good illustration why arguments for somewhat lower climate sensitivity are fundamentally flawed if they fail to account for the warming of the oceans below 700 meters. Most importantly, everybody (climate scientists and contrarians included) must learn to stop equating surface and shallow ocean warming with global warming. In fact, as Roger Pielke Sr. has pointed out, “ocean heat content change [is] the most appropriate metric to diagnose global warming.” While he has focused on the shallow oceans, actually we need to measure global warming by accounting for all changes in global heat content, including the deeper oceans. Otherwise we can easily fool ourselves into underestimating the danger of the climate problem we face. […]
March 25, 2013 at 5:00 pm
[…] Skeptical Science: A new study of ocean warming has just been published in Geophysical Research Letters by Balmaseda, Trenberth, and Källén (2013). There are several important conclusions which ca… […]
March 25, 2013 at 8:41 pm
What will happen when oceans warm further? => methane hydrate
March 26, 2013 at 2:28 am
Out here in the wild, wild West we talk of the “clathrate gun”:
http://en.wikipedia.org/wiki/Clathrate_gun_hypothesis
Have you heard of the Storegga Slide? Pretty dramatic stuff:
http://www.bbc.co.uk/news/magazine-12244964
When the Earth burps, watch out! 🙂
March 26, 2013 at 1:00 am
What this suggests to me is that we are due – overdue – for a huge El Nino event.
The rapid accumulation of energy over the last decade or so will be released into the atmosphere eventually, probably sooner rather than later. And when it does, it will make 1998 look like a mild year.