Arguments
Levitus et al. Find Global Warming Continues to Heat the Oceans
Posted on 25 April 2012 by dana1981
Levitus et al. had previously published updated ocean heat content (OHC) data on the National Oceanic Data Center (NODC) website, labeled as "Levitus et al. in preparation" (Figure 1).
Figure 1: Global OHC for the upper 2000 meters of oceans (NODC)
Levitus et al. (2012) is now in press, discussing the OHC data published by NODC. Figure 2 below (from Levitus et al.) presents the data in a similar fashion to Figure 1 above, but breaks out the data to show the OHC contribution from the 700 to 2000 meter ocean layer.
Figure 2: Time series for the World Ocean of ocean heat content (1022 J) for the 0-2000m (red) and 700-2000m (black) layers based on running pentadal (five-year) analyses. Reference period is 1955-2006. Each pentadal estimate is plotted at the midpoint of the 5-year period. The vertical bars represent +/- 2 times the standard error of the mean (S.E.) about the pentadal estimate for the 0-2000m estimates and the grey-shaded area represent +/- 2*S.E. about the pentadal estimate for the 700-2000m estimates. The blue bar chart at the bottom represents the percentage of one-degree squares (globally) that have at least four pentadal one-degree square anomaly values used in their computation at 700m depth. Blue line is the same as for the bar chart but for 2000m depth. From Levitus et al. (2012)
Data and Main Findings
Levitus et al. use OHC measurements from ARGO floats corrected for systematic errors, as well as data from expendable bathythermographs (XBT) and mechanical bathythermographs (MBT), with the necessary corrections applied. A bathythermograph is an instrument which has a temperature sensor and is thrown overboard from ships to record pressure and temperature changes as it drops through the water. These were the main instruments used to measure OHC before the ARGO float network was deployed starting about a decade ago to provide more accurate and consistent data.
The authors discuss some of their key results:
"The World Ocean accounts for approximately 93% of the warming of the earth system that has occurred since 1955. The 700-2000m ocean layer accounted for approximately one-third of the warming of the 0-2000m layer of the World Ocean. The thermosteric component of sea level trend was 0.54 ±.05 mm yr-1 for the 0-2000m layer and 0.41 ±.04 mm yr-1 for the 0-700m layer of the World Ocean for 1955-2010."
Significant Ocean Heating Below 700 Meters
This harkens back to some of the discussions between Skeptical Science and Roger Pielke Sr., who rightly noted that we cannot adequately measure global warming by considering surface temperatures alone, as most of the global heating has accumulated in the oceans. However, we noted at the time that Dr. Pielke was only considering the heating of the upper 700 meter ocean layer, which is also an incomplete measure of global warming. Levitus et al. confirm this by noting that in the upper 2000 meters, approximately one-third of the total heating has occurred below 700 meters.
Dr. Pielke had argued based on the 700 meter OHC data that global warming had slowed. Levitus et al. note this leveling off in the upper 700 meters in recent years, but that this recent flattening is much less apparent in the 2000 meter data, meaning that more heat is being stored in the 700-2000 meter layer recently (Figure 2).
"One feature of our results is that the previous multidecadal increase in OHC700 that we have reported [Levitus et al., 2009] (updated estimates available online at www.nodc.noaa.gov) leveled off during the past several years. This leveling is not as pronounced in our OHC2000 estimates indicating that heat is being stored in the 700-2000m layer as we have shown here."
Consistent with Meehl's Hiatus Periods
Meehl et al. (2011) examined what climate models predict will happen during 'hiatus' decades in which surface temperatures plateau for short periods of time. They found that during these hiatus decades, less heat accumulates in the upper layers of the ocean, and more accumulates in the deeper layers (Figure 3).
Figure 3: Left: composite global linear trends for hiatus decades (red bars) and all other decades (green bars) for top of the atmosphere (TOA) net radiation (positive values denote net energy entering the system). Right: global ocean heat-content (HC) decadal trends (1023 J per decade) for the upper ocean (surface to 300 m) and two deeper ocean layers (300–750m and 750 m–bottom), with error bars defined as +/- one standard error x1.86 to be consistent with a 5% significance level from a one-sided Student t-test. From Meehl et al. (2011)
The Meehl model results are exactly what Levitus find is happening. We are in the midst of a hiatus decade where global surface warming has been dampened, the increase of the upper OHC has slowed, but more heat is going into the deeper ocean layers.
Putting Ocean Heating Into Perspective
The amount of global warming which has gone into the oceans over the past 55 years is quite impressive.
"The global linear trend of OHC2000 is 0.43x1022 J yr-1 for 1955-2010 which corresponds to a total increase in heat content of 24.0±1.9x1022 J"
This is an immense amount of energy being added to the oceans which Levitus et al. put into perspective (emphasis added):
"We have estimated an increase of 24x1022 J representing a volume mean warming of 0.09°C of the 0-2000m layer of the World Ocean. If this heat were instantly transferred to the lower 10 km of the global atmosphere it would result in a volume mean warming of this atmospheric layer by approximately 36°C (65°F)."
Levitus et al. note that of course this heat won't be instantly transferred to the atmosphere (fortunately!), and that this comparison is simply intended to illustrate the immense amount of energy being stored by the oceans.
This heating amounts to 136 trillion Joules per second (Watts), which as Glenn Tramblyn noted in a previous post, is the equivalent of more than two Hiroshima "Little Boy" atomic bomb detonations per second, every second over a 55-year period. And Levitus et al. note that this immense ocean heating has not slowed in recent years - more of it has simply gone into the deeper ocean layers.
Spoiler Alert
Coincidentally, a team led by several Skeptical Science contributors recently submitted a paper for review which uses this NODC OHC data from Levitus et al. and comes to many of the same conclusions regarding continued global warming. With any luck, the paper will be published in a few months and we'll have more to say on the subject at that time. In the meantime, Levitus et al. have once again reminded us that although the surface warming may have been dampened in recent years, global warming hasn't magically vanished, and that heat stored in the oceans will eventually come back to haunt us.
The amount of heat accumulating in (mostly) the 0-700m layer north of 70 degrees in the Atlantic over 50 yr. is on the order of 5e21 J
this is a trend of 1e20 J/yr
i note that melting 300GT/yr ice as indicated by PIOMASS is a heat sink of that order of magnitude.
sidd
Levitus et al. have once again reminded us that although the surface warming may have been dampened in recent years, (...)
Isn't this inconsistent with the results from Foster & Rahmstorf 2011 that found that the warming have continued without any slowdown?
Or the "surface warming" of what dana1981 is talking about is not the global surface temperature but just the sea surface temperature?
The skeptic refrain for some years has been 'It (the surface) hasn't warmed since X and the climate scientists don't know why' Well here is a big part of the answer. Thats one of the good things about science, many people, all chipping away at problems, often finds the answer
So queue change of opinion from skeptics in 3...2...1........ chirrup...
Three separate trend lines, one each for El Nino, neutral and La Nina years. Funnily enough, they all seem to have the same slope. The graph (pdf)
The page it's from
Steve L @8 - looks like the caption (which I copied from the paper) is incorrect. Good catch, I'll fix it in the post.
From Peru @4 - I should also note that ENSO - one of the factors considered by F&R - acts to transfer heat to the lower ocean layers, which is what Levitus are observing. So the two are not incompatible.
AR4 concludes a net global, anthropogenic forcing since 1750 of +1.6 [+0.6 to +2.4] W m–2.
So, Levitus find a decrease in forcing since 1955?
As a non-scientist, I often find the varying forcing amounts confusing myself.
What appears to be consistent is that, the shorter the time period under consideration, the smaller the forcing number.
I'm sure those fully in the know can explain better.
The unrealized warming has been fairly constant over the past ~50 years whereas the radiative forcing increases the further back in time you choose your initial point. So if you look at the unrealized warming starting at any date from 1950 to 2010, it will be a fairly constant number. But the radiative forcing from 1950 to 2010 is larger than the forcing from 1990 to 2010, for example.
Hopefully I got that right.
In this respect Levitus's finding seem to be confirmatory.
The other ramification is that this decline in forcing will mean that the predicted Equilibrium Climate Sensitivity temperature response in a few centuries time will not occur.
David Stockwell is discussing this point here:
http://landshape.org/enm/levitus-data-on-ocean-forcing-confirms-skeptics-falsifies-ipcc/
There are 2 issues here; the forcing and the heat accumulation as a proxy for the delayed temperature stabilising effect which is the equilibrium sensitivity.
In this respect is CO2 forcing mitigated by Stefan Boltzmann and Beers Law effects to such an extent that further increases in CO2 at a linear rate do not have further temperature increases, or at least only minimal ones.
The reason for this is that Stefan Boltzmann effects are non-linear: From 200K-250K radiated energy increases from 91-222 W/m^2 – an increase of 131 W/m^2.
From 300-350K radiated energy increases from 459-851 W/m^2 – an increase of 392 W/m^2.
This is a result of T^4.
Given this for CO2 forcing to continue to have a temperature effect must it increase at a greater than linear rate as well? And does this explain Levitus's finding of a reduced forcing for extra CO2?
CO2 is increasing faster than exponentially, according to Tamino's analysis, meaning that forcing is increasing faster than linearly.
Even linear forcing means the climate is in a constant state of catch-up - faster than linear forcing is not good news.
I still remain mystified as to why self describe "skeptics" think that simply citing a well known physical effect which is incorporated into all Global Circulation Models (GCMs) (as both the Planck feedback and Beer's Law) will show the predictions of those GCMs to be false, without any need of calculation on their behalf. It is as though they thought yelling "But E=mc^2" would disprove the special theory of relativity.
That the ocean continues to warm therefore proves that the Earth has not reached its equilibrium temperature for the current forcing. The rise in insolation from the purported "grand solar maximum" is so slight that the Earth passed the equilibrium response to that increase long ago, and hence the reduction of insolation since the 1980s does not result in continued warming due to thermal inertia, but instead partially compensates for the increasing anthropogenic forcing.
the rate at which the ocean warms tells you what the earth imbalance is, not the forcing.
You're confusing the two terms, they may look the same but they're not. The forcing gives you the imbalance produced by an agent (sun, GHG, etc.) while keeping the temperature constant and allowing no action by the feedbacks. The former tells you the actual energy imbalance while the system evolves.
For example, immagine to apply a instantaneous constant forcing. At time t=0 the imbalance equals the forcing. At later times the planet warms and the imbalance gets smaller untill it's zero when the new equilibrium is reached.
The 1.6 W/m2 from 1750 is the forcing and it would also be the imbalance if you magically prevented the planet to warm and the feedback to operate. But the planet has obviously warmed and the feedbacks operated; Levitus' imbalance tells you what is left to reach equilibrium. This is what someone call the warming in the pipeline.
For his next trick, I guess he'll prove that the height of Everest has been vastly overestimated by looking at measurements taken three-quarters of the way up. Brilliant!
Sure, equilibrium has not been reached for whatever is forcing ocean temperature in the top 2000m, but atmospheric temperatures appear to be reaching equilibrium. If atmospheric warming is driving the ocean warming then ocean temperatures should follow .
And what are you basing this assertion on, precisely?
Plenty of recent posts here at SkS showing the opposite.
As for the rest of your comment, I suggest "reading the OP..."
This is why the change in ocean surface layers in the tropical Pacific (the tilting of the thermocline) during El Nino/La Nina has such a dramatic effect on global surface temperatures. See SkS post: How increasing carbon dioxide heats the ocean.
The continued warming of the ocean, as Riccardo pointed out above, means there is more global warming 'in the pipeline'.