Why looking for global warming in the oceans is a good idea
— gavin @ 23 February 2005 - (
)
A lot of press and commentary came out this week concerning a presentation and press release
from Tim Barnett and Scripps colleagues presenting at the AAAS meeting (The Independent,
John Fleck ,(and again) David Appell…etc). Why did this get so much attention given that there
is no actual paper yet?
Basically, it is because it is a really good idea. The background is this: whenever forcings
change, there is a delay in the climate response because of the large thermal inertia of the oceans
– it‘s takes a long time to warm them up or cool them down. While they are changing, there will
be a ‗radiation imbalance‘ at the top of the atmosphere. In the case of an increase in greenhouse
gases (which cause a warming), that implies that the planet will be absorbing more solar
radiation than it emits as longwave radiation. This imbalance will persist until the planet regains
it‘s ‗normal‘ quasi-equilibrium. (The planet is never in perfect equilibrium of course, there are
small fluctuations in the annual mean that occur in the absence of any forcings, but these
fluctuations are small compared to the current anthropogenic forcings and the implied net
imbalance).
This imbalance is really an important quantity – estimates of how much warming is in the
‗pipeline‘, the size of the aerosol cooling effect etc. all depend on knowing what this number is.
However, it is very difficult to measure from space. Getting an accurate global average of all the
long wave energy coming out, along with a correctly calibrated estimate of all the solar radiation
coming in and estimating the difference between them to the necessary accuracy (fractions of a
W/m2) is currently beyond our technical capabilities.
So then, how do we estimate it? All of that energy has to be going somewhere, and it is easy to
show that neither the land surface nor the glaciers can be storing this energy. Therefore it is
going into warming the oceans and indeed historical analysis of ocean temperatures by Levitus
and colleagues in 2000, and updated recently in GRL does show warming that is consistent with
the radiative imbalance suggested by climate models (around 0.5 W/m2 from 1955 to 1995 and
possibly as high as 0.7 W/m2 over the last decade, Hansen et al (2002)).
The advantage of the ocean heat content changes for detecting climate changes is that there is
less noise than in the surface temperature record due to the weather that affects the atmospheric
measurements, but that has much less impact below the ocean mixed layer. The disadvantage is
that comprehensive ocean measurements do not go back very far.
Previous work by Barnett‘s group showed that coupled models when forced with greenhouse
gases did give ocean heat content changes similar to that shown in the data. But questions
remained concerning the degree of decadal variability, the length of the record and the balance in
the models between aerosol forcing and climate sensitivity (which can‘t really be disentangled
using this measure). (A recent report from the National Academies discusses this in more detail).
With the latest round of modelling results now having been performed and archived for the IPCC
4th Assessment Report, the time is appropriate to revisit the question with more up-to-date
models and observations.
When this is done, will it really provide the ‗final proof‘ of man-made global warming? As I
indicated above, the preliminary work by Levitus, Barnett, Hansen and others has already
demonstrated that this is a good approach. Thus it is more a question of refining the details,
rather than suddenly ‗proving‘ global warming. If the latest round of models compare better to
the data than they did before (as claimed at the AAAS), and if the result is robust to some of the
remaining uncertainties (in aerosol forcing, ocean model components etc.), then it will certainly
add to the ‗balance of evidence‘ that man-made global warming is already here.
Comments (pop-up) (30)
30 Responses to “Why looking for global warming in the oceans is a good idea”
1. 1
Rich Rando says:
23 February 2005 at 4:12 PM
One week previous to the Barnett press release Scripps issued a press release describing
research by Koppers and Staudigel on undersea volcanic activity.
It is my understanding that many oceanographers believe that volcanic activity, including
phenomena such as deep-sea thermal vents, can affect ocean currents. Additionally, if a
single above-sea volcanic eruption can effect global temperatures, is it not reasonable to
assume that the thermal energy released below the sea does so also? How much is known
about such effects, if any? Is Barnett‘s seeming certainty perhaps a bit premature?
Thanks.
2. 2
DrMaggie says:
23 February 2005 at 5:45 PM
For those of us without direct access to the AGU‘s publications, a free-access version of
the 2005 Geophysical review Letters paper by Levitus et al. is available here… (Link via
the publications page of the NODC Ocean Climate Laboratory, which is full of links to
interesting stuff.)
While on the topic of the oceans‘ response to warming, I would very much like to see a
RealClimate posting on the effects on sea levels of GW. If I understand correctly, thermal
expansion is an important factor, not just the melting of ice caps. (Just to remind Stefan
of his response to my previous request a while back ;-)…)
3. 3
Bruce Frykman says:
23 February 2005 at 7:01 PM
Regarding global warming shouldnt science be ―looking for it‖ anywhere they can find
it?
4. 4
dave says:
23 February 2005 at 8:23 PM
Great! I mentioned talking about the warming of the oceans and Levitus, et. al. in
comment #19 in this post and now you‘re covering it. I was unaware of this new
information, which is quite welcome.
A correction: your link for ―Levitus and colleagues in 2000″ actually points to the
abstract for another paper by Levitus et. al. Anthropogenic Warming of Earth’s Climate
System in Science 2001 292: 267-270. You can find this paper here. The 2000 paper
Warming of the World Ocean can be found here Science 2000 287: 2225-2229.
Good topic! Thanks.
[Response: Thanks. I've corrected the links - gavin]
5. 5
Gary says:
23 February 2005 at 9:03 PM
I am new to all this so bear with me. Surely with all the attention to global warming by so
many people, there does not need to be any more proof that global warming is taking
place. I agree that we should be watching what the planet is doing and the need for
research to be ongoing, but surely we should be acting on what we now have as evidence
on global warming. The fact is that the oceans are getting warmer. This could take some
time to work out by how much and by what causes. Time is something you should not
play with due to the fact before you know it, it‘s to late to doing anything about it.
6. 6
Dano says:
23 February 2005 at 9:25 PM
Gary is indeed new to all this if he hasn‘t spent time at the several IndyFunded sites that
disseminate cherry-picked information stating the opposite of what you say. Welcome,
Gary. Welcome to RC.
Best,
D
7. 7
Peter J. Wetzel says:
23 February 2005 at 10:15 PM
It really doesn‘t seem reasonable to attribute ocean imbalances selectively to a particular
prominent forcing (GHG‘s) when ―comprehensive ocean measurements do not go back
very far‖.
Given the short length of the trustworthy oceanic observational record, particularly in the
deep ocean, the ocean response to multi-decadal and longer natural forcings is virtually
unknown. And any potential longer-time-scale internal oceanic oscillations are virtually
unobserved. Are ocean models so robustly based on first principles that they can be
trusted without validation against sound observations over the time scales of interest? Are
the observations of initial and boundary forcings of ocean models adequate to provide
good simulations? Given that the answer to this for atmospheric models is a resounding
―NO‖ (particularly because of sub-grid scale processes which need to be effectively pre-
ordained through parameterizations), and given that oceanic circulations have much
longer adjustment time scales, yet also have much more intense small scale (gyre)
circulations than the atmosphere, my instinct is that we are not even close to being able to
trust ocean models without long term validation data. There is so little understanding
about how the ocean parses its response to forcings by 1) suppressing (local convective
scale) deep water formation where excessive warming patterns are changed, 2) enhancing
(local convective scale) deep water formation where the changed excessive warming
patterns are co-located with increased evaporation and increased salinity, and 3) shifting
favored deep water formation locations as a result of a) shifted patterns of enhanced
warming, b) shifted patterns of enhanced salinity and c) shifted patterns of circulation
which transport these enhanced ocean features to critically altered destinations.
Why are any changes in (imbalances of) deep water formation so critical? Because deep
water formation is a clear positive feedback mechanism. Most deep water formation (in
today‘s climate) occurs where fairly saline water is chilled to near freezing. Thus cold
water is selectively sequestered into a slow, deep millenial scale circulation, leaving more
surface area to be dominated by warm, stable surface water. And in turn this warm
surface water is left in greater control of the shorter time-scale climate which we have
been able to observe during the instrumental period.
Before jumping to conclusions, there needs to be much better justification of the basic
assumption that we just happen to be sitting at a time when GHG forcing is larger than all
other potential long term (longer than the observational record) oceanic imbalances.
[Response: One thing to remember is that our expectation (admittedly based on models)
is that the planaetary radiation imbalance has only been greater than about 0.5 W/m2 on a
sustatined basis since the late 70s (i.e. Fig 14c in Hansen et al (2004)) though with a
notable dip due to Pinatubo in the early 1990s. Thus, the ocean records do go back far
enough to determine the magnitude of this. Our estimates of the changes in forcings over
that period are reasonable, and allow us to say pretty much unequivocally that the biggest
change over that period has been due to GHGs. It is therefore not jumping to conclusions
to make an attribution.
With respect to your comments about ocean models, you are completely correct. They
haven't reached the point of development when we are sure that they are doing everything
right for the right reasons, and so my instinct is to be very cautious in interpreting ocean
model results that rely on shifts in the location of deep water production etc. However,
the physics of the change of heat storage is much more related to how heat anomalies
diffuse through the thermocline in the bulk of the oceans (not at the poles). You get very
similar results using slab oceans (no changes in transports etc.), and similar results using
very different conceptual models - in this sense it is a robust result. We aren't talking
about deep water here - most of the action is in the top 700m i.e. below the mixed layer,
but not in the really slow deep circulations. Features related to the decadal variability,
particularly in the Pacific, are probably tied to the interactions of ENSO variability and
the sub-tropical gyres, and are clearly more difficult to model. They therefore remain a
challenge to explain.- gavin ]
8. 8
dave says:
23 February 2005 at 10:27 PM
Re: Barnett‘s paper, decadal variability?
Here‘s the full Barnett et. al. paper Detection of Anthropogenic Climate Change in the
World‘s Oceans.
I am interested in the statement
But questions remained concerning the degree of decadal variability, the length of
the record and the balance in the models between aerosol forcing and climate
sensitivity (which can‘t really be disentangled using this measure).
The length of the record is about 45 years. Decadal variability? In the world ocean heat
content in the surface/mid layers? Here‘s a quote (from Fleck quoting Warming of the
world ocean, 1955-2003 – abstract linked in as ―recently in GRL‖ in the post).
However, the large decrease in ocean heat content starting around 1980 suggests
that internal variability of the Earth system significantly affects Earth‘s heat
balance on decadal time-scales.
Aside from model uncertainty questions, which are understandable, what natural process
could possibly cause significant temperature variability in the ocean system, which has
such a huge inertia, on timescales as small as a decade? What am I missing here? It seems
quite incredible.
[Response: As mentioned above, this appears to be related to variability in the central
Pacific, and is indeed larger than people may have initially anticipated. My guess is that
heat content changes related to ENSO events and their interaction with decadal variability
in the gyres are probably responsible, but I'm basically just handwaving here. If I find a
paper that addresses it more clearly, I'll let you know. - gavin]
9. 9
Grundt says:
23 February 2005 at 11:44 PM
Gavin, thank you very much for this excellent post. RealClimate is managed by serious
scientists.
Gavin: ―…The disadvantage is that comprehensive ocean measurements do not go back
very far. …‖ ―….But questions remained concerning the degree of decadal variability,
the length of the record and the balance in the models between aerosol forcing and
climate sensitivity (which can‘t really be disentangled using this measure). …..‖
―…..When this is done, will it really provide the ‗final proof‘ of man-made global
warming? As I indicated above, the preliminary work by Levitus, Barnett, Hansen and
others has already demonstrated that this is a good approach. Thus it is more a question
of refining the details, rather than suddenly ‗proving‘ global warming….‖
Wetzel: ―… the ocean response to multi-decadal and longer natural forcings is virtually
unknown. …‖ ―…my instinct is that we are not even close to being able to trust ocean
models without long term validation data…‖
Dave: ―…what natural process could possibly cause significant temperature variability in
the ocean system, which has such a huge inertia, on timescales as small as a decade?
What am I missing here? It seems quite incredible…‖
What are we missing?… It is scaring
10. 10
Bolo says:
24 February 2005 at 2:06 AM
‗Surely with all the attention to global warming by so many people, there does not need
to be any more proof that global warming is taking place.‘
–Gary
I wish this were true, but I live in the US and know that it is not. I‘ve met many people
who think global warming is junk science and even more that just don‘t seem to care at
all.
Its quite amazing, actually. Virtually every developed or developing country takes it
seriously, yet we seem to have our hands over our ears shouting ‗No, its too costly to
worry about it! It probably doesn‘t exist anyways. La la la la… I can‘t hear you.‘
Ok, I exaggerate somewhat. But that‘s the prevailing attitude throughout much of the
country and in most areas of government. I hope its changing, but I just don‘t know.
11. 11
ted says:
24 February 2005 at 5:36 AM
Is there a good primer or recent reference on modeling ocean response to changes in
surface insolation?
In particular it seems important to look at changes in deep water or intermediate water
formation (rates and temperature) — for example: will anthropogenic warming increase
the rate of Mediterranean Intermediate Water formation or change the temperature of the
resulting water mass? Will it change the rate of saline outflow from the Red Sea? It
seems like a lot of these processes won‘t reach equilibrium for thousands of years.
12. 12
Tom Huntington says:
24 February 2005 at 9:55 AM
There is at least one other robust indicator of planetary warming that has not been
discussed in this posting – warming of the continents. For those interested in other
indicies of continental heat gain the paper by Beltrami and others
http://envscilab.stfx.ca/2001GL014310final.pdf would be a useful resource. In
comparison with heat gain by the oceans, these other terms are substantially smaller, but
they illustrate how widespread the observed warming is.
13. 13
Jeffrey Davis says:
24 February 2005 at 3:32 PM
Without dipping too much into the politics, the White House officially acknowledges
global warming and anthropogenic sources. The ―I can‘t hear you‖ response is from the
popular media.
14. 14
Joseph O'Sullivan says:
24 February 2005 at 7:56 PM
The George Bush record on climate change policy:
September 2000 George Bush made a campaign promise to require power plants to
reduce CO2 emissions. March 2001 after election the President George Bush in a letter to
republican senators stated that no reduction of CO2 would be required. When asked about
the change, the White House replied that the President never intended to regulate CO2
emissions and the campaign promise was put in a speech by a speech writer without the
presidents knowledge.
As widely reported in the media in June 2003, the White House suppressed references to
climate change in an EPA report. Dropped from the report were references to a 2001
National Research Council report‘s conclusions that greenhouse gases were the only
likely explanation for the global warming. The President had commissioned and praised
the report earlier. Also omitted was a 1999 study documenting an increase in global
temperature, but the EPA report included a study partially paid for by the American
Petroleum Institute that refuted global temperature increase.
In August 2004 the administration sent a letter to congress stating that human-released
greenhouse gases were the only likely explanation for the global warming that occurred
over the past thirty years. When questioned about the why he changed the climate change
position George Bush replied, ―Ah we did? I don‘t think so.‖
The conservative Heritage Foundation asked ―why the about face?‖
The change in policy is only cosmetic. This is again another rhetoric technique. You
make a small change to change your public image, but the change is only a surface
change. You make yourself look good by seemingly embracing a position or policy that
you disagree with but it is only a token effort, and you really don‘t accept the position or
policy. The goal is to calm down or stop your opponents by making them think they have
won, without actually giving in to them.
The President has a negative public image in environmental policy. By apparently
accepting climate change science he is trying to improve his image as an environmental
president. But there is no substantive change in the climate change policy. The
environmentalist community uses the word ―greenwashing‖ to describe such a tactic.
Look at the current climate change materials on the EPA website. The main theme is that
there is climate change but there is so much uncertainty about the science. Conservative
think tanks take a very similar position.
For example, on the EPA site:
―Figuring out to WHAT EXTENT the human-induced accumulation of greenhouse gases
since pre-industrial times is responsible for the global warming trend IS NOT EASY.
This is Because OF OTHER FACTORS, both NATURAL and human, affect our planet‘s
temperature. SCIENTIFIC UNDERSTANDING of these OTHER FACTORS â��
MOST NOTABLY NATURAL climatic variations, changes in the sun‘s energy, and the
cooling effects of pollutant aerosols â�� REMAINS INCOMPLETE.‖
The language used emphasizes uncertainty.
The EPA continues:
―Nevertheless, the Intergovernmental Panel on Climate Change (IPCC) stated there was a
―discernible‖ human influence on climate; and that the observed warming trend is
―unlikely to be entirely natural in origin.‖ In the most recent Third Assessment Report
(2001), IPCC wrote ―There is new and stronger evidence that most of the warming
observed over the last 50 years is attributable to human activities‖
This section is trying to cast doubt on the IPCC report, one of the most comprehensive
climate change studies. The term ―nevertheless‖ is used to imply that the IPCC
conclusions are going beyond or contrary to what is scientifically known, and this section
uses quotation marks around ―discernible‖,
―unlikely to be entirely natural in origin‖ and ―There is new and stronger evidence that
most of the warming observed over the last 50 years is attributable to human activities‖ to
make key IPCC conclusions seem questionable.
The current White House climate change policy is continued research, but not any action.
Regardless of what the White House proclaims in public sound bites, it still questions the
basic climate science.
15. 15
Grundt says:
24 February 2005 at 8:58 PM
Re # 12: It is amazing, for me, to learn about the overwhelmingly high heat gain of
oceans compared to the other components.
This paper helps very much to understand how important is to think well before jumping
with any conclusion
Thank you!
16. 16
dave says:
24 February 2005 at 10:46 PM
Re: Warming in the Pipeline
From Hansen et. al. (2002)
It is also inferred that the planet is now out of radiation balance by 0.5 to 1 W/m2
and that additional global warming of about 0.5°C is already ―in the pipeline‖.
I have always been a bit baffled by the physical processes involved here. This is an
important subject which is not widely and clearly understood by non-scientists like me.
Yet it is a crucial finding and I believe that many people, including environmentalists and
policy advocates, do not understand its implications.
Is there some simple intuitive explanation of how this pipeline warming is estimated with
respect to an equilibrium climate sensitivity at a doubling of CO2 equivalent (thus
including methane, ozone, aerosols, CFCs…)? How and at what point do the oceans
come into heat balance? Don‘t the oceans have to absorb heat not only in the surface/mid
layers but right down to the bottom for radiative heat balance to occur? And isn‘t that a
process that takes hundreds to thousands of years?
If I‘ve asked a poorly formulated question and missed some basic assumptions, that‘s
OK. Still, the gist of what I‘m trying to find out remains. And I think others could benefit
from understanding this important result.
[Response: A big part of the response to any radiative forcing is what happens to sea
surface temperatures (since they control most of the feedbacks that are important in the
equilibirium response). The presence of the radiaitve imbalance at the top of the
atmosphere is an indication that the sea surface has not warmed up sufficiently to match
the forcing. This is because (as you note) deeper layers of the ocean are also heating up.
However, this is a slow process, and the sea surface will come close to equilibrium with
the forcing in around 30 to 50 years. It is because the deep ocean adjusts so slowly, that
the long term remaining imbalance will be small and barely noticeable in the surface
temperature data. Given an actual imbalance, you can estimate how much further the sea
surface will need to warm to remove it - this is the warming 'in the pipeline'. The number
comes from using the climate sensitivity (say 3+/-1 C) so if the imbalance is 0.7 W/m2,
you might expect ~0.5 C of additional warming eventually. Most of that however will
come within a few decades. - gavin]
17. 17
Tom Huntington says:
25 February 2005 at 3:57 PM
I have a question for the experts at RealClimate: From Levitus et al. 2005 GRL (cited in
the initial posting above) Figure 1 there appears to be a loss of about 4 X 10^22 J in
ocean heat content from about 1979 to 1987. Where did this vast amount of heat go?
Looking at Levitus et al. 2005 Figure 3, no other heat sink can account for such a large
flux. Did it go back out into space through the top of the atmosphere? If a significant
fraction of this heat lost from the ocean went into the atmosphere one might have
expected the surface air temperature to have increased faster during this period than
during the subsequent period of the 1990s when the ocean heat content gained >5 X
10^22 J, but this is not what was observed (see reference Figure 2.7c in the IPCC TAR
Working group I).
18. 18
Ferdinand Engelbeen says:
25 February 2005 at 6:29 PM
In addition to #17, there is a discrepancy between the modelled inflow of extra heat into
the oceans in the 1955-2000+ period and the TOA balance, which shows a large loss of
heat in the 1985-2000 period.
Based on ocean data and models, the extra inflow of heat was calculated to be between
0.2 W/m2 (Levitus) via 0.5 to 0.7 W/m2 (Hansen for the last decade).
But at the top of the atmosphere, there is an increasing loss of energy in the tropics of 3
W/m2 since 1985, according to Chen e.a. (see
http://pubs.giss.nasa.gov/docs/2002/2002_ChenCarlsonD.pdf )
As that is in the 30N-30S band, that represents 50% of the earth‘s surface, of which a
large part is ocean…
The loss of heat was due to increased Hadley cell circulation, resulting in decreased cloud
cover. The increase in insolation of 2 W/m2 from the cloud cover decrease was
accompanied by an extra outgoing 5 W/m2 heat flow…
How does that fit in the ocean models?
[Response: And yet it warms! Two things can be going on here, firstly, the loss in the
tropics may be more than compensated for in the rest of the world (which is consistent
with the extensive Southern Ocean warming observed by Gille (2002) ), and secondly,
the data from the tropics may be less complete or accurate than claimed, although I am
not aware of any specific reasons why that might be. I would therefore go with my first
answer. - gavin]
19. 19
dave says:
25 February 2005 at 11:15 PM
Re: Latest Levitus et.al.
Finally, a link for the full Levitus et. al. (2005) paper Warming of the world ocean, 1955
– 2003, which I had not been able to read at AGU (agu.org).
A noteworthy quote:
For the Atlantic, Pacific, and Indian Oceans the increases of heat content (linear
trends) are respectively 7.7, 3.3, and 3.5 x 1022 J. As with our previous work, it is
the Atlantic Ocean that contributes most to the increase in heat content.
Also, if you look at Table T2 in this paper, you will see that ocean sea surface heat
storage 0-700m from 1955-2003 (in W/m2) is always higher at northern latitudes than the
corresponding southern latitudes in every case, even with the extensive Southern Ocean
warming as noted by Gavin responding to #18.
20. 20
Stephen Berg says:
26 February 2005 at 9:16 PM
Here‘s a little something I wrote up on a train from Paris to London on a vacation (I have
a B.Sc. in physical geography, so I am not an expert to the extent of Drs. Mann, Bradley,
etc.):
Skeptics often cite volcanism as a cause for climate change and Greenhouse Gas (GHG)
increases. It is a cause or a trigger for ―catastrophic‖ changes over a short term period.
However, it leads primarily to the onset of ice ages or cool periods rather than a warmer
period (due to volcanic ash that blocks out the sun). Since volcanism in long-term periods
(i.e. decadal and century timespans) is relatively constant, one would expect GHG
fluctuations to be minimal. In other words, fluctuations in global GHG concentrations are
not dependent (generally) on volcanic events.
Another aspect of climate change which is often cited (and is dealt with in this portion of
RealClimate) is the temperature of the oceans. As the atmosphere warms, the ocean must
as well, since there is a coupling effect between the two ecosystems.
Skeptics say that submarine volcanism explains the current warming of the oceans.
However, this is completely untrue, since over decadal or century-long periods, such
volcanism (caused by sea floor spreading and undersea earthquakes) remains fairly
constant, since the rate of sea floor spreading (or tectonic activity) remains fairly
constant. This, in an unchanged situation (i.e. with no other variables present, such as
atmospheric temperature fluctuation) would result in a relatively constant mean ocean
temperature.
Now, since there are variables present (GHG concentration, atmospheric temperature
changes, etc.), the ocean temperature cannot remain constant if it seeks to find
equilibrium (like all things in nature). Therefore, this argument by the skeptics is
inaccurate and leads to the confusion of the general public (due to the disinformation
done in the media today).
21. 21
Ferdinand Engelbeen says:
27 February 2005 at 5:03 PM
While the distribution of heat over the oceans is a complicated matter, due to radiative
in/output (modulated by cloud cover), ocean and air currents, some more discrepancies
arise.
Greenhouse gases are rather well mixed over both hemispheres, but Levitus 2005 points
to differences in aerosols between the NH and the SH. The influence of aerosols is mostly
in the NH, were a significant lower warming (than over the SH) should be visible. But
that is not the case, it is the opposite which happens. That is even more striking for the
Indian Ocean, where the northern part is heavily loaded with aerosols, causing 13 +/- 2
W/m2 less insolation, compared to the southern part. But both parts are warming at near
equal speed.
[Response: You are confusing heat content gain with surface air temperature rise. They
are in fact opposing phenomena. SAT in zones of deep ocean mixed layers is expected to
warm more slowly than average, precisely because the energy is warming the deeper
ocean layers instead of the surface. While aerosols do play a part in hemispheric
differences, the biggest difference in the SAT trends is because of the greater expanse of
ocean in the SH. ]
Moreover, if we compare the 9-13 year sun cycle with the global sea surface
temperatures (SST), the variation is app. 0.2-0.3 K within a cycle (see the bottom graph
at NASA). That a variation of only 0.1% (app. 1.3 W/m2 TOA) in direct sunlight may
give such a large variation at the ocean‘s surface is probably a question of modulation of
cloud cover. How that translates into real W/m2 variation at the sea surface is something
the physicist may calculate… See further the discussion about sun cycle – cloud cover
within the comments at http://www.realclimate.org/index.php?p=42
[Response: A student activity worksheet? I have no idea where those numbers come
from or what they are based upon. The best evidence (so far) is that there is about a 0.1K
cycle in surface tempertures associated with sunspot cycles, and that is only detectable
once all volcanic and ENSO-related activity is substracted out (White et al, 1997).]
While there is no recent increase in solar activity, the average activity still is (much)
higher now than in the beginning of the 20th century. According to different solar
reconstructions, the average increase in solar activity since the Maunder minimum may
have been three times the variation within one cycle…
[Response: ... or as little as one times the solar max/min variation. It is the quantification
of 'much higher' that is at issue here. Estimates of the magnitude long term solar changes
remain mostly speculative (Foukal et al, 2004). ]
That solar activity is largely underestimated was a topic at the SORCE meeting last
October:
―Widespread empirical evidence from the extensive Earth climate datasets suggests the
presence of an 11-year solar signal of order 0.1K in surface, atmospheric, and ocean
temperatures. But general circulation models (GCMs) underestimate this response by as
much as a factor of five.‖
[Response: Find a proper reference for the quotation about the GCM results - as far as I
can tell none of the presentations at that meeting made that claim. ]
Thus that greenhouse gases and aerosols are the only/dominant factors in recent ocean
temperature increases seems to be a little premature…
[Response: No-one is claiming that GHG + aerosols are the only mechanism, the claim is
that they are the dominant forcings. Well mixed GHG are exerting a forcing of around
2.4W/m2 more than during the pre-industrial. At the largest supportable value for long
term solar (0.3%), it has only contributed 0.6W/m2 since the Maunder Minimum. It
would need to be 8 times that to even equal GHGs. Plus, over the last 25 years, there has
been no siginficant change in solar. The ocean heat content analysis by Barnett (and in
other groups) show that the changes are most consistent with the GHGs becoming
increasingly dominant over this time. - gavin]
22. 22
Ferdinand Engelbeen says:
28 February 2005 at 9:09 PM
Sorry, I was comparing heat content (not SST, neither SAT) of different parts of the
oceans down to 300 m depth (where most of the variation is visible), based on the data of
Levitus e.a. which can be downloaded from the NOAA web site. If you plot the NH data
against the SH data, the heat content of both is varying more or less simultaneous (with
larger amplitude in the SH) and the trend is near equal. That means that the NH parts of
all oceans, which have a smaller volume, are heating faster than the SH parts. As the
area/volume ratio for the NH parts of the oceans is practically the same as for the SH, the
surface heating (W/m2) must be larger in the NH parts, within the constraints of heat
exchange via ocean and air currents (and partly by the difference in warming area in the
tropics vs. the cooling areas in the higher latitudes)…
While the general heat increase due to GHGs is app. 2.4 W/m2 since the industrial
revolution, the global reduction (direct and indirect) by sulfate aerosols is estimated to be
over 1 W/m2 (see Hansen. As most of this is over the NH (be it mostly over land), this
should have a discernable influence on the difference of heat inflow between NH and SH
parts of the oceans, the other way out than observed…
I suppose that the NASA doesn‘t give students any wrong data. But while the graph was
only for SST (sea surface temperature, something different of SAT – surface air
temperature, even at sea), the influence of the solar cycle and volcanic episodes (El
Chicon and Pinatubo) is visible globally in the oceans until a depth of 300 m in the
Levitus data. The global amplitude (down to 300 m) is between 1E+22 and 3E+22 J,
compared to ~4E+22 J for the increase in heat content in the period 1955-2003 [note:
there seems to be a discrepancy in units between the story of Levitus and the data]. The
ENSO and other recurrent phenomenon shouldn‘t have much influence on the ocean‘s
global heat balance. The variation in heat of average 2E+22 J in only one decade for the
upper 300 m needs a lot of heat inflow variation at the surface…
About solar, there is certainly an underestimate, depending on the model, of at least a
factor 2. See the ―optimal coefficient‖ experiments of Physicsweb
While the exact mechanism for the influence of the solar cycle on cloud cover still is not
known, the influence nevertheless is observed, see Kristjánsson. A change of 2% in cloud
cover over a sun cycle, good for a change of 3 W/m2 in the tropics (see Chen e.a. and
cooler (0.5 K) and dryer climate in Boston to give one known example…
Thus the ―only 0.6 W/m2″ in insolation since the Maunder Minimum, in reality may have
been fortified to a difference of several W/m2… While there is no change in solar
strength in the past 25 years, the level still is high and the oceans still may not be in
equilibrium with the heat inflow…
And models don‘t reflect SST/outgoing IR/cloud cover variations over the last decades,
even not over the 60N-60S latitude band (leaving not much area to be checked…). See
Allan & Slingo 2002
23. 23
Eli Rabett says:
1 March 2005 at 4:21 PM
Without imputing motives to someone I have observed to be earnest, post 22 is
practically the optimal throw the spaghetti against the wall missive. It is almost
impossible to untangle, has many unidentified assumptions, some of which are at best
questionable but stated as accepted, and finds the trees but ignores the forest. Answering
it completely would require a long deconstruction during which the back and forth would
include repeated, but you didn‘t answer point 54 (well yes we did, back in our 36th post).
One can only start, perhaps with the first paragraph. My question would be what is the
characteristic mixings time for surface waters between, say the south and north
Atlantic/Pacific.
24. 24
Peter Hearnden says:
2 March 2005 at 10:02 AM
Posts #22 and #23 seem to me to sum up a lot of the honest scientific contrarianism
responses and the better replys.
Profuse obscure detail, that takes ages to for those who fully understand the details to
work through (and longer, if at all, for those like me who don‘t), is presented and,
somehow ‗O.J. Simpson is not guilty‘ because we all get lost in debate about it and can‘t
see the wood for the trees?
Nope, climate isn‘t a technicality? If current ideas are wrong it will be obvious? You
don‘t need to be Einstein to know e=mc2, broadly, works, nor do you need to be Isacc
Newton to know the accelleration due to the gravity of Earth is, broadly, 9.81m/s/2 (OK,
in a vacuum).
No, only if the broad measures change will my thinking (mid prediction warming)
change. Getting lost in detail ,x, y, z, let alone ‗he said‘ ‗you said‘ ‗they say‘ ‗you‘re
dishonest‘ ‗no you‘re dishonest‘ ‘stop ad homming‘ ‗no you stop ad homming‘ are just
distractions (which, sadly, I‘ve fallen for several times).
So, contrarians, where are the obvious problems with the consensus view? The huge
errors, the huge faults?
[Response: We broadly endorse this view, and will not allow the kinds of discussion here
that often swamp unmoderated message boards. Please stick to the issues raised in
particular posts, and try and pick one issue at a time - only confusion is served by
bringing in twenty unrelated issues whose only link is that they use the word 'radiation'. gavin]
25. 25
Ferdinand Engelbeen says:
2 March 2005 at 3:52 PM
I realize that I have combined too many points in one comment (by my search to find the
answers). But if someone can give an answer to the only one question which matters:
why the relative large variability over the global oceans? That such a large amount of
heat can escape or can be added in such short time intervals, are either increase or
decrease of ice volume or heat input from space / escape to space.
For the upper 300 m, where the variation is most visible, there are peaks in heat content
of the global oceans around 1962 (but the data before 1961 are highly variable), 1979,
1990 (small) and 2002.
While GHGs/aerosols may be the dominant factor in the average increase, they are
emitted in rather continuous increasing amounts for GHGs and increasing + constant
(after 1975) amounts for sulfate aerosols.
In comparison: the sunspot maxima where in 1957 (large), 1969 (small), 1980,
1989/1991 (double peak) and 2000/2002 (double peak).
The large volcanic eruptions in the past half century (reaching the stratosphere) were
Agung (1963), El Chichon (1982) and the Pinatubo (1992). Smaller one‘s were
Fernandina (1968 ) and Fuego (1974). See Hofmann e.a.
A fingerprinting study of the ocean data, compared to GHG/aerosols, ice volumes, solar
variance and volcanic influences may give some more insight…
26. 26
Ferdinand Engelbeen says:
2 March 2005 at 5:32 PM
In response to #23,
There seems to be little exchange in surface waters between the NH and SH (as good as
is the case for air currents), see the main sea currents. The world wide deep water
exchange (the ―conveyor belt‖) has an overturn of app. 1500 years…
27. 27
David Pierce says:
8 March 2005 at 7:43 PM
I‘ve been intrigued to see how the issue of decadal variability has played out in regards to
our 2001 paper (Barnett, Pierce, and Schnur 2001, Science v. 292, p. 270; ). Some people
looked at parts of that work (for example, the lower right panel of Figure 1) and point out
how the climate model oceans show a smooth and pretty much unbroken increase in heat
content over the historical period. As we all know, the real world doesn‘t show a smooth
and unbroken increase in heat, so the model is obviously crazy, right?
Um, no. What we do (by ―we‖ I mean the people who ran the model — Warren
Washington‘s group at NCAR) is run the climate model repeatedly; in this case, it was
run five times. Each repetition has somewhat different starting conditions, so the details
of exactly how it evolves is different in each of those five ―ensemble members‖. The
differences between these ensemble members represent the unpredictable parts of daily
weather variability that we can‘t forecast more than a couple weeks in advance. But when
you average all the ensemble members together, you average out the unpredictable short
timescale variability, and are left with the slow, predictable part that is consistent across
*all* the ensemble members. In this case, it comes from human factors — greenhouse
gases and sulfate aerosols released into the atmosphere by cars, smokestacks, and so on.
So my point is that yes, the actual climate model runs we used *do* show a lot of decadal
and higher frequency decadal variability. But, we went to some effort to remove the
unpredictable part of that variability. The remainder is the predictable part, which is the
smooth, unbroken increase in temperature over the years. Since it takes some effort to get
at this predictable part of the signal, and yet that‘s been one of the notably misunderstood
parts of our work, it does give one the feeling that in the science of climate change, no
good deed goes unpunished. In any event, we will show the unpredictable part in the
upcoming work (i.e., the paper that is the origin of the press conference that this topic is
about), so people can see it and directly compare for themselves.
As a side note, this is related to a common misperception I frequently see in the ―letters to
the editor‖ column of our local paper. Every time there is a snowstorm somewhere,
somebody writes in asserting that this disproves predictions of a warming climate.
Actually, the future evolution of temperature, both regionally and globally, will have the
complex ups and downs on yearly to decadal time periods that it has always had. But,
taken over many decades (say, 30-60 years) the overall trend will, on average, be towards
generally increasing temperatures.
28. 28
Ferdinand Engelbeen says:
9 March 2005 at 11:58 AM
In response to #27, some questions remain:
The increase of ocean heat content in Barnett, Pierce and Schnur 2001 is only compared
to GHGs and aerosols, all other human and natural influences excluded. But there are
offsets between GHGs/aerosol combinations and solar activity (especially as derived by
Hoyt and Schatten), which may have been underestimated (see Stott e.a. 2003)
If one simply should compare only the influence of solar (by H&S or even LBB) with the
increase in heat content of the oceans, one can get a similar conclusion: that solar is the
main driving force in ocean heat content. Which also explains much of the observed large
variations. One only needs to increase the direct insolation variance with a factor 3-5 (e.g.
by observed variations in cloud cover, see also my comment #18)…
Secondly, and even more important, the increase in observed heat content (based on
NOAA data) is near equal for the NH and the SH (see: World oceans), while the
area‘s/volumes are different. If one corrects for area (NH 43%, SH 57%), the upper 700
m NH parts of all oceans are heating over 40% faster than the SH parts (see World
oceans corrected).
This is completely opposite of what can be expected by models, as the cooling influence
of aerosols must be much higher in the NH than in the SH. And the melting of Arctic ice
in recent decades (less in Antarctica) adds to this discrepancy…
[Response: Instead of expecting what the models should do, one needs to actually look at
the models - which is what Barnett et al are doing. Remember too that reflecting aerosols
are not the only additional forcing - tropospheric ozone and black carbon are both more
prevelant in the NH, and are both warming factors. I would also question the point that
one 'only' needs to increase solar by a factor of 3-5 to get it to match. This is huge, and
there is no good evidence that it is that strong (for instance there should be a stronger
response to the 11 year cycle than observed). The fact that the known physics of
greenhouse gases (which are only uncertain to about 10%) do explain the trends, is then
much more likely than an additional (mysterious) solar effect, the evidence for which is
much more wishful thinking than actual facts. - gavin]
29. 29
Ferdinand Engelbeen says:
10 March 2005 at 5:02 PM
Gavin,
I liked to have a response of the Barnett team, but here are some remarks on your
response:
I haven‘t seen the new work of Barnett e.a., as it is not published (yet). But I am surprised
by your reaction. The (GCM) models don‘t reflect reality anywhere if the direct and
indirect cooling by (mostly) sulfate aerosols are not taken into account (see the IPCC
graph. That is the largest human induced cooling factor, some 1 W/m2 against the 2.4
W/m2 warming by GHGs since the start of the industrial revolution.
But most of the aerosols are emitted in the NH (see: IPCC graphs d)-h)). Thus the
radiation heat balance, according to the IPCC, in the NH must be far less positive than in
the SH (as example: a loss of 5 W/m2 TOA due to aerosols in the NH Indian Ocean). If
the models don‘t reflect such differences in radiation balance between the hemispheres,
then there is something wrong with the models…
But globally, the oceans are warming (much) faster in the NH than in the SH…
The solar cycle is visible in the upper 150 m of the oceans, with a variation in SST of
~0.1 K, from a TOA solar change of 0.5-1.5 W/m2. See White e.a.. From the same
source:
―Rind e.a. [1999]… …identified internal positive feedbacks that nearly doubled the
[note: modeled!] global average temperature response to solar forcing expected from the
Stefan Boltzmann radiation law‖.
That was due to increased global moisture content, decreased global average cloud cover
and decreased sea ice extent at high latitudes. Not (yet) a factor 3-5, but not a mystery
either.
The physics of GHG heating are known within rather strict limits, but the response of
climate on these physics, like evaporation, convection, the lapse rate discrepancy in the
tropics, and especially cloud cover are far from settled…
[Response: Why do you think aerosols are not included in the GCMs? They are in all the
simulations currently being analysed for the IPCC AR4, and one presumes that these are
the runs Barnett is working with. As I said before, other warming factors are also more
prevelant in the NH (specifically tropospheric O3 and black carbon - including its effect
on snow albedo). Our own (as yet unpublished - so you don't need to believe me)
simulations also show NH oceans warming at a slightly faster rate than the SH including
all of the forcings we have discussed.
With respect to solar you are confusing a forcing with the feedbacks. Feedbacks as
discussed by Rind are applicable to all forcings, not just solar, and the idea that climate
sensitivity is greater than S-B would suggest is well known. - gavin]
30. 30
Ferdinand Engelbeen says:
11 March 2005 at 11:38 AM
Gavin,
The GCM‘s I know of (and as described by the IPCC 2001) do include a large cooling
effect from aerosols. See Fig 2D in Crowley 2000
As most aerosols, especially sulfate aerosols, are emitted in the NH, the cooling effect
should be largest there. Which is contradicted by the observations.
Now you say that (current?) GCM‘s show a larger warming effect in the NH. As GHGs
are well mixed over the whole globe, that means that there is a net warming effect from
aerosols?
[Response: Crowley (2000) was not a GCM. Current GCMs (i.e. experiments that have
been done for the upcoming IPCC AR4) include many different forcings (up to 14
different things in our latest runs - see the link I gave previously). In particular, they
include tropopsheric O3, black carbon (a warming aerosol) and the indirect effect of
black carbon on snow albedo (again a warming effect). ]
Please explain the (difference between the) aerosol amounts/composition/effects
(especially for ocean heat content) over the NH and SH in the 2001 GCMs vs. current
GCMs for the calculations of the 1945-1975 period and the 1975-200x period.
[Response: Too much detail, you'll need to wait for the relevant publications to come out
(sorry!). ]
That all forcings have similar feedbacks can‘t be right. Solar has its largest influence in
the lower stratosphere (including changes in jet stream position), CO2 in the lower
troposphere. See KNMI: ―Solar forcing of climate change: evidence from the past‖.
Although the cosmic rays-cloud connection weakened in the past decade, the solar
luminosity-cloud connection still holds.
Short waves (visible light) are trapped in the upper 100 m of the oceans, leading to
warming of the whole layer. Long waves (infrared) light from the sun, GHGs, clouds, are
trapped at the surface of the oceans, directly leading to increased ―skin‖ temperature,
more water vapor (a very effective GHG), faster convection (with more loss of heat to
space in the tropics),… How each of them converts to real regional/global temperature
increases/decreases is another point of discussion…
[Response: You are strictly correct, but the feedbacks highlighted by Rind et al where
simply feedbacks from surface temperature changes, and therefore would be similar for
any process that changed surface temperatures. The details of the physics of different
forcings (i.e. ozone effects due to solar, snow albedo and cloud effects due to aerosols
etc.) do vary the feedbacks slightly differently though. - gavin]
[Source: http://www.realclimate.org/index.php/archives/2005/02/why-looking-for-globalwarming-in-the-oceans-is-a-good-idea/]