I suppose I may as well take this opportunity to respond to that paper you posted, and also to make a couple of minor corrections to that long post that I typed in a hurried frenzy.
I don’t know what you feel that paper contributes to this discussion. It simply opines that climate models slightly underestimate overall cloud cover outside the Arctic and some overestimate high altitude cloud cover. Even assuming the authors are right, the most that it would mean is an argument for slightly lower climate sensitivity, which itself is a very complicated and much-studied topic with a vast abundance of data. There have been other papers, generally of a denialist bent, trying to argue for lower climate sensitivity, and they’ve been mostly discredited.
In any case, it doesn’t in any way refute anything I wrote about cloud cover feedbacks. I stand by all of it, though for the sake of accuracy I should make a minor correction. I should have said that the latest IPCC assessments of the balance between positive and negative cloud feedbacks are that cloud cover constitutes a net small positive feedback, not negative, contributing approximately +0.6 W/m2 to warming. I was thinking about the IPCC radiative forcings chart where cloud-aerosol interactions are assessed as a small net negative, but that is a forcing, not a feedback, caused by the effects of man-made aerosols on the microphysical properties of clouds (like the Twomey effect). Coincidentally, the magnitude of this forcing is just slightly less than that of the estimated positive cloud feedback, though there’s a lot of uncertainty around both.
Just by way of another small clarification, land use changes like deforestation, while indeed a small net negative effect, are obviously a forcing, not a feedback. Land use changes are of course an independent first-order effect and not a climate feedback. I hate it when I type faster than my brain is capable of making words.
Some land use changes are totally man-made and climate-independent, as when farmland adjacent to existing suburbs is paved over to make more suburbs.
Other land use changes are semi-feedback. As when, due to climate change, farmland becomes marginal for its current use and is either re-cropped or is preferentially converted to more suburbia. Depending on which new crop or which non-ag land use, that may be net positive or negative on feedback. But it is in response to changed microclimate and is therefore a flavor of feedback.
Finally, we have natural land use changes driven entirely by climate, as when forest gives way over time to grassland or grassland gives way over time to semi-arid as the rainfall & temperature patterns shift. Change in the opposite direction is also possible. Those are pure feedbacks, not forcings.
Looping back to my first example, as coastal cities or those with freshwater supply challenges become less habitable or uninhabitable, new cities will have to be built elsewhere to contain the population. If e.g. Miami decamps en masse back to e.g. inland New Jersey & New York states, the land use changes there will be totally man-made, but are a feedback response to the developing problems down in FL.
I admit I may not be using either “forcing” or “feedback” in the precise manner IPCC does. And I welcome any corrections anyone may have.
But I suspect that as actual change gets going at a pace and scale that causes material human adaptations, the difference between the two as applied to land use changes will be increasingly hard to tell apart.
I have no argument with your various prognostications, but the concept of “land use changes” is really a straightforward matter of definition. It refers to purely human-driven land use changes of which deforestation and increases in cropland area are major elements. These are negative forcings for a number of separate reasons; forests are generally darker than croplands, so deforestation increases albedo and contributes to cooling due to more IR leaving the surface; croplands more readily accumulate snow cover in winter and retain it longer, again increasing albedo; and deforestation reduces CO2 uptake.
But human-driven land use changes that may be encouraged by climate change factors are not feedbacks, although one might well want to consider microclimate trends when projecting such changes. Climate feedbacks have a specific definition as being physically coupled to some underlying climate phenomenon. A good example of an important feedback, for instance, is the increase in tropospheric water vapor as a direct physical result of rising temperatures, which magnifies the effect of GHG forcing.
Your other point about some land surface changes that are directly driven by climate change being feedbacks is absolutely right, but these are not called land use changes. They’re simply called albedo feedbacks, and there are many examples – desertification, droughts, forest fires, etc. By far the most important example is the reduction of polar ice cover, both over land and over ocean, since both open water and land surfaces are much darker than ice. It’s one of the major reasons for accelerated Arctic warming. These are pure feedbacks, but not “land use changes” in the lexicon of the IPCC or anyone else that I know of.
It should be noted that the IPCC definition of climate forcing due to land use changes is particularly specific and deals only with albedo changes, because that’s the only effect that can be broken out as a unique forcing. Forests have other effects, most importantly acting as carbon sinks that take up CO2 and help to mitigate warming. But in assessing climate forcings, that effect is rolled up in the net CO2 forcing. In that respect deforestation should be considered a “bad thing” in the fight against climate change.
I linked to this article to address your statement:
This article is interesting, once you get past the crocodiles. It’s from a reliable source. Stratocumulus clouds (we call them low clouds in western Oregon) have a significant effect on weather because they increase the local albedo (they reflect sunlight), and they’re very difficult to predict even with modern weather forecast models. This article talks about significant improvements in how the more modern climate models deal with stratocumulus clouds with respect to increased CO2. It’s not good news.
Also interesting is that this article contradicts the paper you originally cited, which appears to claim (from my quick reading of it) that all climate models underestimate the extent of low cloud formation, and that some models overestimate the extent of high cloud formation. Since low clouds (as you correctly state, and as the second article correctly states) are generally associated with negative feedback due to albedo effect, and high clouds are generally associated with positive feedback due to the dominance of absorption and re-emission of outgoing IR, that first paper appears to be implying that we’re underestimating the negative cloud feedbacks, whereas the NASA article implies the opposite due to reductions in low cloud formation. But they may well be talking about different timeframes.
But these sorts of contradictions aren’t really surprising. The IPCC assesses the whole topic of cloud formation as having a “low level of scientific understanding”. So more research is definitely needed. The scary thing about clouds is that, though the best current judgment is that their net effect on climate is small, that small magnitude is the result of a balance of two competing effects that are each independently very large. A significant decrease in low cloud formation would definitely be a grim prospect. But this is far from being established. The consensus continues to support a small absolute magnitude of cloud feedback, at least if you regard the IPCC Fifth Assessment as the most authoritative view on the matter to date.
I don’t think these papers are talking about the same aspects of cloud modeling. The first paper mostly focused on how accurately climate models simulated vertical cloud formation, i.e. convective clouds. And it’s 8 years old. This paper pointed out areas that climate models could improve in. The second paper is more recent, and mostly focuses on low clouds. As far as I can see, these two papers don’t contradict one another.
For example, a decrease in stratocumulus clouds over mid-latitude oceans may increase marine algae growth, increasing O2 production and consuming CO2. But a decrease in stratocumulus cloud penetration onto continents may desiccate land plants and lead to wild fires and increases in CO2. So it gets complicated. See link: https://nph.onlinelibrary.wiley.com/doi/full/10.1111/nph.15283
Fair enough, but ISTM that this sentence in the conclusions has a pretty plain meaning:
Results show that all models underestimate the total cloud cover (51% to 62%) against observations (64%) at all latitudes, except in the Arctic. Low- and mid-level altitude clouds are underestimated by all the models (except in the Arctic), while high altitude cloud cover is overestimated by some models.
I would also add that while I have a good deal of respect for the work being done by the climate groups at NASA, that one article describing a paper by one guy strikes me as not just speculative but way over the top. This, for example:
… stratocumulus clouds thinned at a fairly steady pace as CO2 concentration increased—until the concentration reached roughly triple today’s level. At that point, the clouds broke up. And without their cooling effect, global temperature jumped by 8°C (about 14°F) … If we continue releasing greenhouse gases at our current rate, he added, we could reach that point again somewhere around the beginning of the next century.
8°C (14°F) temperature rise due to a tripling of CO2 “somewhere around the beginning of the next century”? Remember that the stated goal of the Paris climate agreement is to limit temperature rise to less than 2°C and to “pursue means” to keep it to no more than 1.5°C. Now it’s true that we’re very likely to miss those targets, but the track that we’re on is projected to more likely lead to something like a 3°C increase by the end of this century. And that would be fairly catastrophic. But 8°C by around the beginning of the next century? If that happens, we are well and truly doomed. I mean really, climate change is indeed an existential problem, but stuff like this is at best highly speculative hyperbole and undermines sound arguments.
Again, I think the main takeaway here is that cloud feedback overall is judged to be small according to the best modeling so far, but is subject to re-evaluation as the level of scientific understanding improves. This is likely the least well understood climate feedback.
Of course it’s “complicated”. But these sorts of arguments are among the standard talking points of denialist bullshit – the idea that things are so complicated that climate change may not be the problem we think it is because something something something “might” cause a miraculous reversal. But it always turns out that the mentioned phenomena are relatively minor factors in the larger scheme of forcings and feedbacks, if not entirely negligible.
To be clear, the carbon uptakes of vegetation including forests are important sources of climate mitigation. But while I don’t have the background to judge the scientific worth of that particular paper, in general the problem with these arguments has been that climate-induced changes to vegetation growth have not been shown to be major global influencers of climate. For example, one thing we sometimes hear from deniers is that CO2 enrichment is going to result in bigger, healthier crops that will suck ever more CO2 out of the air. The reality is that while CO2 fertilization is a thing, it’s likely to be limited and short-lived. Limited, because plant growth becomes quickly constrained by other factors like soil nutrients, and short-lived, because drastic changes in regional climates and the migration of pests and disease is likely to have overall negative impacts on crop harvests, especially in the poorer and most vulnerable countries.
But current CO2 is ~400ppm. Triple that is ~1200. AIUI, that’s pretty much what the “business as usual” = RCP8.5 assumptions would predict for the year 2100. And as I interpret the snip you snipped, the author suggests that a further 8C bump specifically due to the collapse of cloud cover would then occur on top of the rest of the already predicted temperature increases under RCP8.5.
Said another way, if the world sticks its head in the sand and keeps it there, RCP8.5 will happen and the author explains what he thinks will happen as a result.
Is RCP8.5 still a realistic possibility or has the world woken up enough to actually avert it? Darn good question I’m not qualified to answer. Further, will the world stay woken up enough as the costs mount and societies are under increasing strain and politics gets more fraught? Especially considering that “enough” gets to be a bigger and bigger lift as things get worse.
Again I don’t purport to have answers. But I don’t see the hyperbole you seem to in that paper. In effect he says “Under RCP 8.5, one of the official possibilities, we’re even more f***ed than most folks have noticed yet.”
Seems to me that’s a worthwhile warning, not Chicken Little exaggeration. Though I may have misread your (or his) intent here.
Weather systems aren’t really chaotic; the interactions between Earth’s surface an its atmosphere, on the scale of weather, follow the laws of physics and thermodynamics. The problem is getting enough data points and measurements, even with current satellite technology. Because of the temporal component, climate modeling runs into problems with feedback mechanisms, which currently aren’t well-enough understood. For all we know, climate models are underestimating the effects of increasing CO2.
A couple of comments about that. I don’t see what the paper has to do with the likelihood (or lack thereof) of the RCP 8.5 scenario, which incidentally carries an associated temperature increase of an estimated 2.6 to 4.8°C by 2100. My point is that the author is making hugely speculative claims that are not supported by evidence to date nor by consensus opinion. One might also note, in terms of that 8°C temperature rise, that a global temperature rise of less than that – an estimated 5 to 8°C over a period of 200,000 years – led to a major climate event called the Paleocene-Eocene Thermal Maximum that had profound effects on life on Earth some 55-60 million years ago. If we’re going to exceed that temperature increase in less than the next 100 years, we truly are irreversibly and completely fucked.
Another point is that it’s a mistake to consider RCP 8.5 to be a “business as usual” scenario, although it’s often been called that. It’s really a “doomsday scenario”, and assumes not only the absence of any and all mitigation policies, but wild increases in fossil fuel use, particularly coal. But we can already see that we’re on a different track: all major countries have signed on to the Paris climate agreement (at least in theory, on paper); electric cars are going mainstream, with GM committing to producing only electrics by 2035; coal use has been dropping, at least in the US, etc.
You may be interested in this article related to the unrealistic assumptions of RCP 8.5. To be fair, it’s an opinion piece that some have argued with, but it’s a well-grounded and very credible article:
The nature of chaotic systems has nothing to do with “following the laws of physics”; chaotic systems are perfectly deterministic. What defines them is that small changes in initial conditions in a deterministic nonlinear system lead to progressively larger changes over time. The apparent randomness is just due to insufficient information and/or insufficient processing power to have perfect predictive value, but “sufficient information” for such systems may never be realistically achievable. Weather systems are a perfect example. In fact the “butterfly effect” used as a metaphor for chaotic systems is a weather metaphor.
That’s just a truism. Modeling feedbacks is the central issue in climate modeling. It’s the crucial component of climate sensitivity – how the climate responds to increases in GHGs. Otherwise the determination of climate sensitivity would just be a straightforward radiative transfer calculation.
I had essentially fallen for the mislabeling “business as usual”, when, as that article asserts, a more accurate term would be “No mitigation from the mid-90s & the world gets and stays especially stupid about burning max carbon.”
Although as they said, a few populist nationalist know-nothing governments in the wrong countries at the wrong time, or some unexpected carbon “burp” from nature could put us there. But those are low likelihood events.
Yeah. The idea that carbon credits are mere window-dressing and virtue signaling just means you aren’t imagining the optimal pricing of carbon credits/taxes.
If they pay anything close to a fair price for those carbon credits then their trip to Hawaii might be guilt-free but it wouldn’t be cost-free. People should absolutely be able to burn tons of kerosene in the atmosphere and jet off to Hawaii whenever they want to so long as they can pay the true price.
I don’t know what that would be once all the actual costs are figured… but I’m thinking at least $200,000 - $250,000 per seat? That’ll plant a lot of trees!
Put the proper price on electricity and water and folks will stop leaving their air conditioning, lawn sprinklers, and all 7 of their large-screen TVs on when they go to work.
You want a nice green lawn? How much green you got? That’ll set you back $10,000 / month in frivolous water-use penalties. Hope you’re rich!
Carbon taxes should become the ultimate, and ultimately the most expensive, sin tax.
