Arguments
The Fool's Gold of Current Climate
Posted on 4 April 2013 by dana1981
A frequent argument made by climate contrarians is that global warming hasn't yet resulted in unbearable climate change consequences, and therefore we have nothing to worry about. In a talk recorded by ReasonTV, Matt Ridley offers up several different examples of this line of thinking, arguing that climate change thus far has had some positive consequences and that fossil fuels are just great, implying that we should continue to consume them without worry.
However, this argument misses a key point – climate scientists aren't terribly concerned about the current state of the Earth's climate. If we were to stabilize atmospheric CO2 levels below 400 parts per million (ppm) – a level we are rapidly approaching – most people would be thrilled about that (especially if those levels eventually drop to somewhere around 350 ppm). The concern is that human CO2 emissions and the resulting global warming show no signs of slowing (Figure 1).
Figure 1: Estimated expected warming for the RCP scenarios in a most likely case world with 3°C equilibrium climate sensitivity (see this post for background and details).
The three higher warming scenarios in Figure 1 (red, green, and purple) describe the future that Ridley advocates for, where we see several more degrees of global surface warming over the next century. That is the future we are concerned about.
Ridley's Global Greenwashing
Most of Ridley's ReasonTV talk focuses on a claim that we've previously examined, that the planet is 'greening' and therefore more CO2 is great for plants. Overall the argument that CO2 is plant food is a gross oversimplification. It's true that when all else is held relatively constant, for example in a greenhouse, adding CO2 to the environment tends to increase plant growth. However, when we add more CO2 to the atmosphere, it changes the climate. More extreme weather results, like heat waves, bush fires, droughts, and floods - conditions which are obviously not favorable to plant growth. As John Mason has discussed,
"A key constraint of the carbon fertilization effect on the ground (and not in the controlled conditions of a greenhouse or laboratory) is that it would be operating in situations where other variables, essential to plant growth, may not play ball. It's a long list when one includes all the various minerals and trace-elements but key factors are major nutrients such as phosphorus, potassium, nitrogen and so on. CO2 is plant-food but so are these elements and they are essential, as any serious vegetable-grower will tell you."
It's just not as simple as 'more CO2 = more plant growth'; not even close. To argue otherwise, Ridley focuses on some studies of global Net Primary Production, which is essentially a measurement of plant growth. These studies have shown that over the past few decades, the planet has become greener. Great news, right? Well, that depends on where the greening is happening and which plants are thriving, but more importantly, Ridley fails to mention that the greening trend has already slowed down, and possibly even reversed (Figure 2).
Figure 2: Net primary production change measurements (in petagrams [1015 grams] of carbon per year) from Nemani et al. 2003 (blue), Zhao and Running 2010 (red), and Potter et al. 2012 (green).
The plants we're most concerned about are food crops, particularly staple crops like maize. On this subject, Ridley discusses the role technology has played in making agriculture more efficient and productive, which is indeed a very good thing. But again, we're concerned about what future climate change will do to that trend of increased agrigultural productivity. For example, Hawkins et al. (2012) examined maize yields in France and found that improved agricultural technology has increased crop yields, but hotter temperatures are taking a toll, and the increase has begun to slow (Figure 3).
Figure 3: French maize yields from FAOSTAT (black points) and empirical model predictions for the technology trend (grey shading) and expected yield (red shading) with total uncertainties (red lines), considering both temperature and precipitation. The black error bar indicates the forecast for 2011, assuming a flat technology trend since 2010. For the 2016-2035 periods, the boxes show the 25th-75th percentiles and the whiskers indicate the 5th and 95th percentiles. The yield projections assume a flat technology trend and are shown for both climatological precipitation (left) and precipitation constrained by historical correlations between temperature and precipitation (right).
In particular, note the low maize yield in 2003, associated with the major heat wave that summer. The projections for 2016—2035 in blue and red demonstrate that climate change is anticipated to decrease crop yields unless technological improvements can offset the effects of increased heat.
So what happens if monthly heat records become 12 times more frequent, as Coumou et al. (2013) predict will happen within 30 years unless we take serious action to reduce our greenhouse gas emissions? What happens when other types of extreme weather like droughts and floods increase? Will farming technological advances be able to offset the extreme weather impacts on crop production? Will the global greening trend be replaced by a browning trend?
Those future climate impacts are what we're concerned about. Arguing that so far the planet has become greener is irrelevant. It does not address climate scientists' concerns.
Polar Bears
At the end of his talk, Ridley discussed an anecdote which apparently makes him feel comfortable about advocating that we continue to rely on fossil fuels and accelerate the greenhouse effect. The anecdote dealt with an island in the Arctic that he visited several decades ago, which did not have any polar bears at the time, but which does now.
Ridley correctly noted that while there may be more polar bears now than there were several decades ago (their populations were not accurately monitored until fairly recently), that is because polar bear hunting is now strictly regulated, and was not in the past. However, according to a 2009 report by the IUCN Polar Bear Specialist Group, of the 19 recognised subpopulations of polar bears, 8 are in decline, 1 is increasing, 3 are stable and 7 don’t have enough data to draw any conclusions. This is a marked decline since just 2005 (Figure 4).
Figure 4: Subpopulation status of polar bears for 2005 and 2009 (Source: Polar Bear Specialist Group)
Again, the concern is not current conditions, it's future conditions. Arctic sea ice is critical for polar bears to hunt, and Arctic sea ice extent and volume are in the midst of a death spiral. That dangerous trend is why polar bears are considered a threatened species, and why an American court recently upheld that designation against a challenge by the State of Alaska and industry interests.
Ridley Has Company
Ridley has a history of being blindsided by events he did not foresee, for example when the bank he chaired failed and had to be bailed out by the British government. Ridley explained,
"We were hit by an unexpected and unpredictable concatenation of events."
Tacomic by RR Anderson
Of course, Ridley isn't the only climate contrarian to make the mistake of focusing on current impacts while ignoring those to come in the future. For example, Roger Pielke Jr. often focuses on the fact that according to the IPCC Special Report on Managing the Risks of Extreme Events and Disasters to Advance Climate Change Adaptation (SREX), certain types of extreme weather have not yet increased, like drought frequency in the USA. However, this misses the SREX conclusions about future climate impacts, which notes for example that droughts will likely intensify in the USA.
In a more recent example, just recently Anthony Watts said in an interview that "catastrophic predictions of the future just haven’t held up," but climate scientists don't expect catastrophic climate impacts to occur until later this century.
It's a common mistake among climate contrarians because it seems like a logical and reassuring argument – climate change hasn't yet resulted in terribly negative consequences, so maybe it's nothing to worry about. Unfortunately that conclusion flies in the face of a vast body of evidence indicating that if we continue on our current course, the climate consequences will be very bad, and potentially catastrophic.
The argument is like a diagnosed cancer sufferer claiming he's okay because he doesn't yet feel the effects. In truth there are a number of troubling things already underway – ocean acidification, the collapse of coral reefs, stronger and more frequent extreme weather events, sea level rise, sea ice and ice sheets melting, permafrost thawing, etc. We simply cannot allow these climate trends to continue just because we haven't yet felt the worst effects.
The part about greening by CO2 and limitation on it due to lack of nutrients made me wonder whether we know anything about how nutritous plants are wenn grown in artificially high CO2 concentrations? Do we know anything about the micronutrients in the plants (vitamins, minerals, phytochemicals, etc.)? Maybe from experiments in greenhouses comparing plants that were gassed with CO2 to normal ones.
In a nation where half the population has a religious aversion to simple evolution, the conversions when Mother Nature actually starts hitting us with the consequences are going to be extreme.
We will go from their climate disbelief to a climate inquisition... the religion they accuse us of having will finally exist... in them.
VictorVenema, I do not have close at hand links to help you get your ansewers but, free-air CO2 enrichment (FACE) studies have been done for a number of decades. I was involved a small bit in such studies at Biosphere II in the late 90s. Plant physiology is a well-known area, and there are thousands of papers on the subject.
Anthony Watts made the same mistake 3 years ago, commenting
Conditions in production greenhouses are monitored and modulated (drip lines, drainage, ventilation, etc). We can't simply open a 'space window' to let more heat escape!
Matt Ridley's talk reminds me of the Swedish politician who remarked--from his perspective--that a little global warming would be a good thing. He was later berated by an Israeli minister who called him self-interested twit.
So "Let's have a little bit of global warming"
is much like
"Let's get a little bit pregnant"?
VictorVenema
There is a principle in agronomy called Liebig's Law of the Minimum. Essentially that growth of a plant is constrained by whichever resource is in shortest supply. Greenhouses manage what is happening so that everything is optimised so there is a benefit from extra CO2.
A CO2 fertilisation effect is real and is considered models of the Carbon Cycle. But it isn't nearly as simple as the 'CO2 is plant food' meme would paint it. And the higher temperatures that go along with the extra CO2 aren't good. For a range of major crops, yields increase slightly for modets temp increases. Beyond that they start to plummet.
Hmm, doesnt photosynthesis stop about 38C and slow down beyond 30? That cant be good for the tropics.
Hi Guys,
I believe there is an error in your article. In the paragraph under the cartoon of the falling Venture Banker, you say this:
Of course, Ridley isn't the only climate contrarian to make the mistake of focusing on current impacts while ignoring those to come in the future.
A 'mistake' suggest that Ridley makes an error of oversight. I would like to suggest that this is far from the truth. It is not a 'mistake' it is a deliberate distortion, and as such the sentence should read:
Of course, Ridley isn't the only climate contrarian to deliberately misinform the public by focusing on current impacts while ignoring those to come in the future.
I am not a chemist, physicist, geologist, or any other science directly related to the climate and climate change (which is one reason I am here to educate myself). But, I am a practicing biologist/naturalist that already holds an MS degree in Fisheries and Wildlife and will be starting another Master's program this year in Biological Sciences focusing on predator/prey relationships (wolves, bison and elk in Yellowstone).
Polar bears and their prey have survived both short term climate oscillations and long term glacial/interglacial periods over the last 100,000 years. I don't doubt they will survive the next 100,000 years now that overharvesting of both species has been controlled.
The polar bears success is predicated by the population size of its prey species, and one of their favorites is the ringed seal. Seal numbers drop during heavy ice winters and the polar bear numbers fall in response. The mothers and young are especially hard hit.
The graphic below shows this relationship.
[Sph] Image width reduced to fit in page.
Terranova,
I'm not dismissing your comment, but have you really considered how the Arctic ecosystems are likely to change, given the rate of warming and change that we currently see, which is only a fraction of what is inevitably in store?
As a trained biologist, do you think that you can really, rationally support the position that "you don't doubt" that polar bears will survive a change to their ecosystem that may well be more dramatic than anything experienced in the past half a million years?
Scaddenp … Quite right! There is a tendency to forget that plant (and animal) life is temperature sensitive and can only function within a limited range. That range is moving further north and south of the equator and plants will either do the same or adapt to higher surface temperatures. The problem is that the speed of temperature rise is too rapid for most plants to either adapt or move.
As Dana points out, even if Ridley is not concerned by present climate conditions produced by a surface temperature rise of 0.8°C since 1750, he – and we – should be very alarmed at the effects of a further increase of 2°C by 2100. Why should we be alarmed? Because the effects on climate are likely to be so severe that the ability of our own species to adapt and survive may well be compromised.
"The polar bears success is predicated by the population size of its prey species, and one of their favorites is the ringed seal. Seal numbers drop during heavy ice winters and the polar bear numbers fall in response. The mothers and young are especially hard hit."
My guess is that you're going to be very surprised next year when you start your masters program in predator/prey relationships. Let's just say that the model you present is ... overly simplistic.
Terranova:
Only anecdotal evidence, but I spent several summers in the Churchill area. The polar bears do little eating in the summer, on land. They fatten up on the ice, eating seals in the winter, and after the summer they are pretty hungry by the time the ice starts to form again in the fall. Although I can appreciate that in the past a heavy ice winter could lead to fewer seals and less to eat, I don't think that short winters and long summers with nothing to eat would be good for polar bear health in that area.
Also, terranova:
1. your graph discusses a study in one region, the beaufort sea.
2. the study is old, there's almost no data on the effect of the population resulting from changed sea ice conditions in the last couple of decades, and none for the last 15 years. If the winter ice were to disappear entirely from the region, so would polar bears.
Fortunately, scientists have continued studying polar bears in the Beaufort Sea. When working on your masters, I suggest you not restrict your literature search on past research on predator/prey relationships between wolves, bison and elk in Yellowstone to studies done before 1995. You'd miss an important event, the reintroduction of wolves in 1995 ... likewise, focusing on a study done in the arctic in the 1990s that concentrates on data from the 1960s-1980s misses significant changes in the arctic since then.
Here's a piece that came out in 2006, noting changes in population structure in polar bears of the southern beaufort sea that are similar to those seen in the hudson's bay population before their numbers started declining significantly:
http://pubs.usgs.gov/of/2006/1337/
Glenn@6, Victor@1:
When I first read Victor's coment, I thought about nutrients limiting plant growth, but on more detailed reading, I realized Victor was asking about the nutrients available in the plants, after they grow to the point where we can eat them. Even if plants grow bigger, are they better for us? Or does a faster-growing plant provide little or no additional nutrients to us when we consume them?
An interesting question, for which I have no answer or knowledge on how to figure out an answer. Perhaps there is something in the plant breeding literature that discusses selective breeding for increased growth and evaluates the effect on nutrient levels in the resulting product.
Bob Loblaw:
"I don't think that short winters and long summers with nothing to eat would be good for polar bear health in that area."
Polar bear numbers in the hudson's bay population have dropped 22% from the 1980s, and is attributed to changes in sea ice coverage there.
Terranova
How does the ringed seal breeding cycle work? They have nests under the ice so heavy ice winters are easy to understand as being bad - maybe colder, harder to maintain air pockets, keep breathing holes open, whatever. What the graphic you show doesn't indicate is what they will do during extremely low ice winters, levels of ice unseen in historical times.
What is the minimum ice thickness they need to produce a den in the ice? How long does the ice need to be there for their breeding cycle? Can they delay their breeding pattern if the ice is late in forming?
On current trends the Arctic will be virtually ice free in September within 2-3 years. Ice free from August to October a couple of years later. Maybe ice free for 6 months a year within 1 - 2 decades. And all the ice that forms each winter will be first year ice - no more than 2+ meters thick, perhaps not as folded and misshapen as older ice and thus with worse conditions for creating dens.
What will the impact on the seals be then?
It's more likely that whatever numbers of Polar bears survive will be as a result of switching their hunting patterns to more land based prey.
An interesting study a year or so ago looked at the genetics of Polar Bears. Prior to this the conventional understanding seems to have been that the Polar Bear was only around 120-150,000 years old as a species, having emerged from a sub-population of Brown Bears near the previous inter-glacial.
This study puts them at around 3 million years old. However, what seems to happen is that the Polar Bear population declines hugely over the glacial cycle, effectively breeding back into the Brown Bear population (Brown & Polar Bears have been observed mating) then reappears as a distinctive population when temperatures turn colder again.
Perhaps they should be called The Great White Brown Bear.
"I don't think that short winters and long summers with nothing to eat would be good for polar bear health in that area."
Just found this, a layman's summary of a very recent study on hudson's bay polar bears:
http://www.csmonitor.com/Environment/2013/0320/Warming-Arctic-Receding-ice-leaves-Hudson-Bay-polar-bears-less-time-to-eat
Glenn: "whatever numbers of Polar bears survive will be as a result of switching their hunting patterns to more land based prey."
In the Churchill area, this probably means eating tourists instead of seals.... I'm sure the tourists will be glad the bears found an alternate food source. Working in the Churchill area was one of the few times in my life where I felt the need to own a gun, and carry it with me all the time. If the bears weren't on the ice, they were hungry.
It still amazes me that professional people can slander their name so much by twisting the findings in climate science so they can try and go against the consensus. They may have their moment in the spot light, but it’s a stain they are never going to get off them. I have to agree that a little warming from induced CO2 could be a good thing, which Dana also seems to suggest. Terra forming is an important process that we are going to have to better understand if we plan to live in this universe. I for one do not want to see the likes of an ice age in the future (be that if I find a way to keep myself a live for thousands of years).
Terranova
I am also a wildlife scientist, and I have to say that I am flabbergasted by your statements at post #9. You can't seriously be trying to tell us that the only factor which affects polar bear populations is the population size of their prey species. Perhaps I misread you, and the moderators cut off some of your explanation.
But then, your statements that:... I don't doubt they will survive the next 100,000 years now that overharvesting of both species has been controlled.... is the sort of statement that only someone would make if they were completely unfamilar with wildlife, and who was putting forward an ideological statement rather than a scientific one. So on that basis alone I have to wonder what you are trying to suggest - and if you really have the qualifications necessary to suggest it.
You do know that one of the most important factors influencing the population size of any species is habitat, right? So what do you think will happen to polar bears if their habitat is degraded?
@mandas (22)
The point Terranova makes about "population size of prey species" also does not explain the availability of prey. Regards to polar bears there may be lots of seals but little ice for the bears to be able to access them. I also think an early breakup of the ice could cause the deaths of bears trapped out in the ocean.
Of cause the polar bears could just change their source of prey (-snip-)
(Rob P) -Inappropriate content snipped
There's a useful article here:
8 Tips From Scientists On Covering Polar Bears
It deals, among other things, with the myth that Polar Bears will just adapt to an ice-free Arctic, since ice is part of the ecosystem, like soil is in a forest and we would not expect trees to just adapt to a soil-free forest.
The climate conditions that Polar Bears will face by the end of this century with unmitigated warming will be unprecedented in the entire existence of the species over the last ~600,000 years since they split from brown bears. I hope I am wrong, but there seems every reason to doubt that they will be able to adapt to this very rapid change over just a few generations.
As someone else suggested, it seems likely that polar bears will continue only as a hybrid species crossbred with other bears if they lose their habitat. I'm not sure how a polar bear could 're-emerge' as a distinct species during ice ages, though. Once the DNA has been mixed, it can't exactly be un-mixed.
However, there are a lot more animals in the crosshairs of climate change than polar bears and penguins. How is climate change going to alter disease trajectories in different species, for example the white nose fungus that's decimating bat populations (is it possible even if not yet evident that it's linked to climate change?), or if climate change has a hand in the bee colony collapse (aside from the neonicotinoid pesticide link). What will climate change do with bird or swine flu? E-Bola? Rabies? Strep Throat? Are fish and cetacean populations experiencing mass die-offs as a result of climate change already? What if previous mass extinctions from climate change had disease explosions as their vectors? Is that possible to study in the fossil records?
To try to tie this back to the blog topic, it seems like these underlying things may already be happening, hardly what I would call benign or beneficial (not even bringing the physical effects of rising water and weather pattern changes into the discussion).
The article Andy Skuce linked to also includes a bit about the fact that we know from fossil remains that polar bears used to live in the Baltic sea off Sweden and Finland... but now they don't. Still plenty of ringed seals there, but no polar bears. Why? Because there is no longer sea ice in that region for polar bears to hunt from. The presence of their prey doesn't mean a thing if they can't catch it.
Andy Skuce already posted the article I was going to post. And CBDunkerson just highlighted the same point I wanted to highlight. And mandas gave the seasoned experienced wildlife biologist perspective, which is what I wanted to do. Then dhogaza trumped me with a couple of comments regarding Terranova's graph, and what Terranova will learn when he starts his new Masters.
I'm feeling quite redundant and rather useless here---think I'll go comment on a "skeptic" site where I'm outnumbered but at least can post relevant scientific information before anyone else. :)
It is far to flippant to call Riley's comments greenwash. If one can take his points as being valid, and I see no reason why he would lie about them, this is the other side of fossil fuels. We have increased growth of plant life due to increased carbon dioxide in the atmosphere and a reduced the use of resources from nature which were to the detriment of the natural environment. It is still, probably a valid point that if we continue to put ever increasing amounts of carbon dioxide into the atmosphere, we will very likely cause a climate flip and that would likely be disasterous. What comes out of his talk is that if we stop putting carbon dioxide into the atmosphere, it could reduce in the atmosphere rather rapidly. The other point is that the more we switch to wind, solar and other energy sources such as wave and tidal currents, the better off we will be all around. We won't be testing the theory of sudden climate change with gay abandon and we won't be putting a strain on the woodpeckers. I think we should take his comments seriously, examine them as scientists should and combine them into a bigger picture.
@Michael Whittemore(20) "...a little warming from induced CO2 could be a good thing, which Dana also seems to suggest", so there's the obvious corollary that humans this century using every last drip of coal & problem-recovery unconventionals is a tad selfish now we know that future humans might have used it to mitigate a glacial when it started rather than having it dissolved uselessly in oceans after a long hot spell.
william: What comes out of his talk is that if we stop putting carbon dioxide into the atmosphere, it could reduce in the atmosphere rather rapidly.
Actually, if we had stopped emissions dead, in 2010, the atmospheric concentration of CO2 would have declined to about 340 ppm by 2300. For comparison, that's the amount it was in 1980. The CO2 will reduce, over 190 years, at approximately one-sixth of the rate that we are currently increasing it. That's the most drastic case imaginable. Graph below is from Serendipity.
It is the mark of wisdom to also consider the Temperature Change portion of Andy's graphic above. And note that this is the result of a complete cessation of human-sourced emissions (brought to zero and held there for 300 years).
Questions, anyone? Bueller?
Serendipity graphs above are also on a hopeful site, because they consider the A-O CO2 exchange only. They do not consider the earth system response. So far, what is known about it, is that we can expect only positive feedbacks: methane release from clathrates and permafrost, decreased albedo from melting arctic ice, warmer ocean degassing CO2 because warm water can hold less of it.
The only problem is that the quantity of those feedbacks are unknown (maybe with the exception of ice albedo). I expect those figures (abstractive and outdated already, we need to update the starting level to 400ppm) to become more pessimistic (more warming in the pipeline) once those positive feedback are quantifiable.
"Significant contribution to climate warming from the permafrost carbon feedback" – Andrew H. MacDougall, Christopher A. Avis & Andrew J. Weaver.
In figure 3, the paper suggests that even with a hypothetical complete cessation of anthropogenic CO2 and sulphate emissions in the year 2013, atmospheric CO2 would not fall by more than about 10ppm for hundreds of years, if climate sensitivity is ~3C per doubling. That seems very worrying if true – doesn’t it mean that they expect permafrost carbon release to have offset all natural carbon sinks within the next decade or two? The usual scenario is that land and ocean sinks would quickly start to draw down atmospheric CO2 if we stopped emitting it (e.g. in the ‘Climate change commitments’ RealClimate article from 2010).
Icarus, we know that human industry emits about 30 billion tons of CO2 per year and that the atmospheric content of CO2 is increasing by about 15 billion tons (2 ppm) per year. Thus, we know that natural sinks are removing about 15 billion tons more than natural sources are emitting. If human emissions suddenly dropped to zero natural sinks still take about 15 billion tons (2 ppm) out per year... at first. That would rate would decline as the atmospheric and ocean surface carbon levels came into equilibrium. This kind of decline can be seen in the red line of graph A of Andy Skuce's post #29 above.
The alternate view, as with the MacDougall paper, is that we will soon see a shift in the balance between natural sources and natural sinks as permafrost and other sources release long held carbon. If that does happen then atmospheric CO2 levels might remain raised, or even continue to increase, even without human emissions. There is still a great deal of debate about the temperature at which this shift in natural emissions vs sinks would take place and how large an impact it would have. As you note, MacDougall seems to predict that we have already passed the point at which natural emissions will grow to offset natural sinks. If true then we're looking at a 'best case scenario' (i.e. immediate zero human CO2 emissions) matching the blue line in charts A & C from Andy Skuce... with level atmospheric CO2, temperatures would continue slowly rising for centuries.
However, that difference between 'flat' temperatures if atmospheric CO2 levels fall and slowly rising temperatures if atmospheric CO2 remains stable is relatively insignificant in comparison to the real danger... which is the currently upward rocketing temperatures as atmospheric CO2 levels climb. The sooner we get to 'flat' atmospheric CO2 levels the better. If we can then go further and actually decrease atmospheric CO2 that'd be good to, but we have got to stop the level from increasing ASAP.
I have a post in the works (out later this week) that will discuss the recent Matthews and Solomon paper in Science and which refers to the MacDougall et al paper on permafrost that Icarus mentioned. I did a blogpost a few months ago on that paper. Figure 3 from that post is similar to Figure 3 in the MacDougall paper and I have reproduced it below.
Figure 3. Showing the atmospheric concentration of CO2 following a shutdown of human emissions in 2013(left) and, after following DEP 8.5 for 39 years, a shutdown in 2050 (right). The dotted blue line shows the results at a climate sensitivity of 3.0°C and the upper and lower lines 4.5° and 2.0° respectively. Selected and modified from Figure S8 in the Supplementary Information.
The Matthews and Solomon paper appears to depend on the earlier Matthews and Caldeira paper. However, as far as I can see neither this nor the earlier Matthews and Weaver paper dealt with effects of aerosol reduction which must surely also accompany emissions.
On the other hand, that paper references Montenegro et al 2007 which surely gives lie to those who think CO2 levels in the atmosphere are short-lived.