From DOE/LAWRENCE LIVERMORE NATIONAL LABORATORY
Clouds are impeding global warming… for now
Lawrence Livermore National Laboratory researchers have identified a mechanism that causes low clouds – and their influence on Earth’s energy balance – to respond differently to global warming depending on their spatial pattern.
The results imply that studies relying solely on recent observed trends are likely to underestimate how much Earth will warm due to increased carbon dioxide. The research appears in the Oct. 31 edition of the journal, Nature Geosciences.
The research focused on clouds, which influence Earth’s climate by reflecting incoming solar radiation and reducing outgoing thermal radiation. As the Earth’s surface warms, the net radiative effect of clouds also changes, contributing a feedback to the climate system. If these cloud changes enhance the radiative cooling of the Earth, they act as a negative, dampening feedback on warming. Otherwise, they act as a positive, amplifying feedback on warming. The amount of global warming due to increased carbon dioxide is critically dependent on the sign and magnitude of the cloud feedback, making it an area of intense research.
The researchers showed that the strength of the cloud feedback simulated by a climate model exhibits large fluctuations depending on the time period. Despite having a positive cloud feedback in response to long-term projected global warming, the model exhibits a strong negative cloud feedback over the last 30 years. At the heart of this difference are low-level clouds in the tropics, which strongly cool the planet by reflecting solar radiation to space.
“With a combination of climate model simulations and satellite observations, we found that the trend of low-level cloud cover over the last three decades differs substantially from that under long-term global warming” said Chen Zhou, lead author of the paper.
“The key difference is the spatial pattern of global warming”, said Mark Zelinka, LLNL climate scientists and co-author of the study. “Not every degree of global warming is created equal, in terms of its effect on low clouds.”
In response to increased carbon dioxide, climate models predict a nearly uniform warming of the planet that favors reductions in highly reflective low clouds and a positive feedback. In contrast, over the last 30 years, tropical surface temperatures have increased in regions where air ascends and decreased where air descends. “This particular pattern of warming is nearly optimal for enhancing low cloud coverage because it increases low-level atmospheric stability that keeps the lower atmosphere moist and cloudy”, said Stephen Klein, the third co-author.
“Most satellite data starts around 1980, so linear trends over the last three decades are often used to make inferences about long-term global warming and to estimate climate sensitivity,” said LLNL’s Chen Zhou, lead author of the study. “Our results indicate that cloud feedback and climate sensitivity calculated from recently observed trends may be underestimated, since the warming pattern during this period is so unique.”
Global temperature has gradually increased over the instrumental record due to increased greenhouse gas concentrations. But superimposed on this warming are large temperature fluctuations due to natural internal variability of the climate system, as well as influences from volcanic eruptions, aerosol pollution and solar variability. Whereas warming due to CO2 tends to be relatively spatially uniform, surface temperature trends due to internal climate variability and aerosol pollution are highly non-uniform, with trends on one side of an ocean basin often opposing those on the other. Trends computed over short time periods are often strongly influenced by factors other than CO2 and can be highly misleading indicators of what to expect under CO2-forced global warming.
The team emphasized that clouds are particularly sensitive to subtle differences in surface warming patterns, and researchers must carefully account for such pattern effects when making inferences about cloud feedback and climate sensitivity from observations over short time periods.
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The work was funded by the Regional and Global Climate Modeling Program of the Office of Science at the U. S. Department of Energy (DOE) under the project “Identifying Robust Cloud Feedbacks in Observations and Models.”
The paper: http://www.nature.com/ngeo/journal/vaop/ncurrent/full/ngeo2828.html
Impact of decadal cloud variations on the Earth’s energy budget
Chen Zhou, Mark D. Zelinka & Stephen A. Klein
Feedbacks of clouds on climate change strongly influence the magnitude of global warming1, 2, 3. Cloud feedbacks, in turn, depend on the spatial patterns of surface warming4, 5, 6, 7, 8, 9, which vary on decadal timescales. Therefore, the magnitude of the decadal cloud feedback could deviate from the long-term cloud feedback4. Here we present climate model simulations to show that the global mean cloud feedback in response to decadal temperature fluctuations varies dramatically due to time variations in the spatial pattern of sea surface temperature. We find that cloud anomalies associated with these patterns significantly modify the Earth’s energy budget. Specifically, the decadal cloud feedback between the 1980s and 2000s is substantially more negative than the long-term cloud feedback. This is a result of cooling in tropical regions where air descends, relative to warming in tropical ascent regions, which strengthens low-level atmospheric stability. Under these conditions, low-level cloud cover and its reflection of solar radiation increase, despite an increase in global mean surface temperature. These results suggest that sea surface temperature pattern-induced low cloud anomalies could have contributed to the period of reduced warming between 1998 and 2013, and offer a physical explanation of why climate sensitivities estimated from recently observed trends are probably biased low4.
This is essentially what was predicted by the late Dr. William Gray years ago. He also showed another negative feedback in high altitude water vapor. The net effect would be a small increase in precipitation and a small warming (CS = .2-.4 C).
https://stevengoddard.wordpress.com/2015/05/09/dr-bill-gray-explains-why-climate-models-dont-work/
Also keep in mind the changes in clouds we have seen are not proof of this negative feedback. There could be other causes which is what these pseudo-scientists are trying to claim. In that sense they are right. Don’t just accept this is feedback without more evidence. Doing that is just another version of the same mistake they are making.
I do wish warmists would read from the same playbook because when they don’t they really do confuse me.
Deniers claim: The world is not warming that fast
Warmists Rebuttal: Look at GISS jerks!
Deniers claim: The models overestimate warming
Warmists Rebuttal: No they don’t jerks!
This paper basically says that deniers were right that it wasn’t warming that fast and not as fast as the models…. or perhaps what they are saying is that it is warming fast, the models are right BUT the clouds will soon change and the warming will be even more pronounced and the models will have to be adjusted upwards.
So which is it? Are deniers right about current warming observations or are warmists wrong about the models and they are going to have to show more warming?
They were wrong for the right reasons.
Am I mistaken, or is the clear translation of their technical jargon that the reality doesn’t match the models?
Reality doesn’t match the models at present but reality can be changed when needed.
Interesting that some questions the believed cloud effect.
The only problem is, that the cloud cover by all means have to be corrolated to CO2 (warming), so as to call it a responce to CO2. Clouds have their own life and could just as well cause the temperature changes we observe. Even the temperature is not corrolated to CO2.
http://climate4you.com/images/HadCRUT4%20GlobalMonthlyTempSince1958%20AndCO2.gif
Finally, the Mosher said something I can generally agree with: “GCMs are just window dressing for policies decided on other grounds”. It is a memorable day. Global warming / Climate Change is just a cloak for the introduction of damaging policies that the elite want to force on us.
“Global temperature has gradually increased over the instrumental record due to increased greenhouse gas concentrations.”
One little problem here. The amount of temperature increase due to doubling CO2 is only about 0.3C where less than 0.2C has manifested so far. Any additional warming beyond this, if it exists, must have a cause unrelated to CO2. If excess warming is occurring, it would be better to identify other reasons for why it’s happening, rather than trying to explain how excessive GHG warming is still happening, even though we aren’t measuring enough of it.
C’mon! These intelligentsia MUST be climate scientists … coming to a conclusion like that!
It also looks like CYA .
“… we found that the trend of low-level cloud cover [observed] over the last three decades differs substantially from that [modeled] under long-term global warming…”
You mean that the misbehaving and unruly data is refusing to follow the lead of the models? With apologies to Berthold Brecht:
Stating that the data
Had forfeited the confidence of the scientists
And could win it back only
By redoubled efforts. Would it not be easier
In that case for the scientists
To dissolve the data
And choose another?
TGB
I write this more to explain it to myself than anything else, but I would also like help in understanding what I am misunderstanding about the Zhou paper.
SST = Sea Surface Temperature
EIS = Estimated Inversion Strength
LCC = Low Cloud Cover
“… changes in EIS are well explained (r =0.94) by a linear combination of the tropical mean SST and the difference between SST in tropical strong ascent regions and the tropical mean SST ( see Methods), with the latter explaining more decadal variance in EIS (Fig. 2d).”
“Physically, EIS increases with this SST difference because free-tropospheric temperatures throughout the tropics are controlled by the moist adiabat set by the SST in tropical ascent regions, whereas SSTs in tropical descent regions affect the temperature of boundary layer only locally. As a result, LCC variations over the twentieth century are primarily induced by the SST pattern instead of changes in tropical mean SST (Supplementary Text 1 and Supplementary Fig. 6).“
Me: So, out of all of that, what I take is the oceans do not warm uniformly across space, and so there are something like localized convection cells that occur because of the differential. Does that make sense? And, that this non-uniform warming (what they call the “SST pattern”) causes the EIS to increase (basically, because warm air rises and cold air falls in to take its place).
“The above mechanism explains the abnormal decadal net feedback during the satellite era (1979-present), when surface warming is most pronounced over tropical ascent regions where deep convection occurs, with cooling over tropical descent regions, particularly in the Eastern Pacific where low clouds are common (Supplementary Fig. 7).”
Me: Ummm…I’m pretty sure the ascent is caused by the fact that it is warmer; not vice versa.
“The pronounced warming in the tropical ascent regions causes the tropical troposphere to warm and, in the absence of equivalent warming in descent regions, causes the tropical EIS to increase significantly (Fig. 2d), contributing positively to the LCC trend. Meanwhile, the SST-induced LCC reduction over the broader tropical oceans is not strong enough to compensate the EIS-induced LCC increase (Fig. 2c).”
Me: So, as I understand it, they say:
1) If the EIS goes up, or
2) If the SST goes down,
3) Then, there is more LCC
So, the EIS is high (during the time period studied), creating more LCC, but the SST is going up, which should reduce LLC; and, ultimately, the effect of the EIS overwhelms the effect of the SST (for the time period studied).
Their conclusion is that the LCC is affected more by the “pattern” of SST (i.e., it is different in different places at any given time) than by the steady increase of SSTMean. Essentially, all of this amounts to saying that if the sea doesn’t warm perfectly evenly across space, then EIS will play a role in the amount of LCC. Personally, I think that’s a big, fat “duh,” but I am seriously concerned by the fact that these researchers seem to imagine that the uneven heating (or perhaps simply the magnitude of the differences in the late 20th century) is “abnormal” in some way.
Their evidence for the abnormality of this situation is in the supplementary materials. In Supplementary Figure 2 they compare the EIS anomalies from two datasets and their simulations. Their two simulations are very consistent with one dataset, but wildly inconsistent with the other. I haven’t had time to break it down further, or to examine the rest of the supplementary materials, but their first piece of evidence doesn’t even qualify as weak or suggestive due to the gross discrepancy between the two sets of actual data in my opinion.
I’m also concerned about the assumption that it is valid to compute a long-term average LCC. As the sea surface temperature rises, it is not obvious to me that this will result in more spatially uniform warming, which is what would be required to damp the strength of the EIS impact on LCC. Also, it seems to me that there is no reason to dismiss the possibility that there is a connection between systematically increasing SSTMean, and more extreme SST “patterns” as they call them, thus those darn clouds just might continue to unrelentingly impede global warming.
Thank you for listening.
Barbara