Pat'n Chip float by WUWT on a cloud of aerosols

Patrick J Michaels and Paul C. "Chip" Knappenberger have discovered a new blog article about aerosols. The article is by Dr Nicolas Bellouin from the University of Reading, who specialises in studying aerosols. He wrote about a preliminary estimate of aerosol-cloud forcing of -0.6 W m^-2, which is lower than the estimate in the latest IPCC report, of -0.9 W m^-2, but well within the range in the IPCC report, which is quite wide - from -1.9 to -0.1 W m^-2.

Pat'n Chip grabbed hold of the blog article as though it were precious gold, and published at WUWT (archived here).  Deniers haven't got much to grab hold of right now, so a blog article about a blog article will have to do. The first blog article is not yet a paper. That's promised for August this year. In fact, at the bottom of his article, Dr Bellouin wrote:

I thank Graham Feingold, Johannes Quaas, Annica Ekman, Leo Donner, and Ilan Koren for interesting discussions on current understanding of aerosol-cloud interactions. Note that they do not all agree that aerosol-cloud radiative forcing is weak: some argue that a value of up to −1.2 W m^-2 remains consistent with scientific understanding.

That value of −1.2 W m^-2 is higher than the lower end referred to in the IPCC report (−1.9 W m^-2), so it could be that the range has been better defined in the three years since the AR5 IPCC report.

Another point worth making is that there has been a lot of work on aerosol-cloud interactions over the past year or three. The published science is coming thick and fast. I've listed just a few of the many recent papers below, some of which are easier to follow than others. (That might be why Nicolas Bellouin decided to pre-publish in a blog.)

In a perspective article in Science a couple of years ago, Daniel Rosenfeld, Steven Sherwood, Robert Wood and Leo Donner described some ways in which aerosol-cloud interactions can affect climate, including cooling effects and warming effects:

...radiative forcing due to aerosol-cloud interactions may be limited by buffering mechanisms that result in compensation between different cloud responses to aerosols (3). Other situations may be hypersensitive to aerosols because aerosols have become extremely depleted by precipitation (4). In these ultraclean regimes, addition of aerosols can dramatically increase cloud cover, causing a large cooling (5). Another newly appreciated process is aerosol-induced invigoration of deep convective clouds that may transport larger quantities of smaller ice particles to the anvils of such clouds. The higher, colder, and more expansive anvils can lead to warming by emitting less thermal radiation to space (6).

Pat'n Chip as you'd expect favour studies that show that the cooling impact of anthropogenic aerosols on clouds is at the low end of the range. The way they put it was in the conspiratorial framing favoured by deniers. Pat'n Chip wrote:

In the absence of this presumed aerosol cooling effect, climate models predict that the earth should warm at a much faster rate than has been observed.  A large cooling effect from aerosols was thus introduced in the early 1990s as a way to “fix” the climate models and bring them closer in line with the modest pace of observed warming. 

I don't know for sure if Pat'n Chip think NASA faked the moon landing, or that Lizard Men rule the Earth, but as that passage shows, they definitely lean towards the "climate science is a hoax" end of the spectrum.

They are correct in that if aerosols exert less of a cooling effect than previously thought, then the "bring back smog" people at WUWT and CFACT don't have to be so scared of clean skies.

They are wrong when they talk about a "modest pace of observed warming". The observed warming is anything but modest. And if we don't take enough action, it will be much less modest very soon. As Stanford scientists worked out some time back, we are on pace for warming more than ten times faster than any seen in the past 65 million years.

What aerosol scientists are trying to work out is whether aerosols from human activity have been cooling the earth by 0.6 W m-2 or 0.9 W m-2. That's a difference of 0.3 W m^-2.  To put that into perspective, the radiative forcing from all the well-mixed greenhouse gases in 2011 was estimated at 2.83 W m^-2, so we're talking about a difference of around 11%. (The well-mixed greenhouse gases include CO2, CH4, N2O, CFCs etc.) There's also forcing from land use changes, as well as from natural causes like volcanoes and changes in solar radiation.

The difference between aerosol and other human forcings will widen further over time, as the amount of atmospheric CO2 increases. Anthropogenic aerosols will be expected to decline more over time as more countries make more efforts to reduce them, so their impact will decrease while that of greenhouse gases will continue to increase. According to the AR5 IPCC report, over the next 15 years or so, the radiative forcing is expected to be from 2.9 to 3.3 W m^-2. By 2050 it could 3.0–4.8 W m^-2, and by the end of the century could be from 2.7 to 8.4 W m^-2, depending on how much more CO2 we pour into the air.

In other words, if we continue to pour CO2 into the air at a great rate, then whether aerosols have a radiative forcing of -0.6 or whether it's -0.9 W m^-2 won't make much difference. The world will be very much hotter than humans have ever experienced, regardless.

I'm not wanting to play down the importance of understanding more about aerosol-cloud interactions. It remains one of the main uncertainties, and is important to know. What I am saying is that it's necessary to keep things in perspective. Deniers like Pat'n Chip try to argue that "climate change will not be catastrophic—that is, will not proceed at a rate that exceeds our ability to keep up." What they mean by "keep up" is anyone's guess.  It's a weird thing to say, particularly after the massive floods occurring simultaneously all around the world this past week or two.

Maybe they mean that "we" can afford to lose our beach fronts and a thousands of lives to heat waves, floods and storms. That it won't be catastrophic when drought causes famines, leading to starvation and civil unrest. That making vast tracts of land uninhabitable will be an acceptable price to pay to preserve the illusion of comfort of a few deniers in the USA.

From the WUWT comments

Latitude doesn't get out much. It's well known that some clouds warm and some clouds cool. He also seems to think that not knowing everything is the same as not knowing anything. Deniers aren't clear thinkers.

June 7, 2016 at 4:12 pm
I fully expect to see something…someday….that says clouds actually make it warmer…and it was the increase in clouds that upped the temp
I mean why not?….
I still can’t believe “scientists” created all these computer games…and just left out all the crap they know nothing about

I wonder does Claude Harvey know that the Earth has been through snowball phases as well as hothouse phases in the past?

June 7, 2016 at 5:34 pm
At some point, it seems to me that folks will have to accept that planet earth resists ANY temperature forcing function with “negative feedback” – period. If that were not true, the planet would long ago have either frozen or smoked life as we know it to oblivion.

Asp is more than a little bit nuts. (May I say that?)

June 7, 2016 at 8:39 pm
The introduction of the notion of aerosols as the agent for neutralizing the effect of GHG’s is just another twist in the rear guard action of climate alarmists, now increasingly evident. Of course it has to be anthopogenic? How else to continue the argument for world control, which is the basis of this massive fraud.

This comment from TonyN is my favourite for the day :)

June 8, 2016 at 1:49 am
Can we see photographs of their models, complete with aerosols?

References and further reading

The interaction between aerosols and clouds - blog article by Nicolas Bellouin at Weather and Climate @ Reading

Seinfeld, John H., Christopher Bretherton, Kenneth S. Carslaw, Hugh Coe, Paul J. DeMott, Edward J. Dunlea, Graham Feingold et al. "Improving our fundamental understanding of the role of aerosol− cloud interactions in the climate system." Proceedings of the National Academy of Sciences 113, no. 21 (2016): 5781-5790. doi: 10.1073/pnas.1514043113 (pdf here)

Lee, Lindsay A., Carly L. Reddington, and Kenneth S. Carslaw. "On the relationship between aerosol model uncertainty and radiative forcing uncertainty." Proceedings of the National Academy of Sciences 113, no. 21 (2016): 5820-5827. doi: 10.1073/pnas.1507050113 (open access)

Stevens, Bjorn. "Rethinking the lower bound on aerosol radiative forcing." Journal of Climate 28, no. 12 (2015): 4794-4819. DOI: http://dx.doi.org/10.1175/JCLI-D-14-00656.1 (open access)

Rosenfeld, Daniel, Steven Sherwood, Robert Wood, and Leo Donner. "Climate effects of aerosol-cloud interactions." Science 343, no. 6169 (2014): 379-380. DOI: 10.1126/science.1247490 (pdf here)

Stocker, T. F., D. Qin, G. K. Plattner, M. Tignor, S. K. Allen, J. Boschung, A. Nauels, Y. Xia, B. Bex, and B. M. Midgley. "IPCC, 2013: climate change 2013: the physical science basis. Contribution of working group I to the fifth assessment report of the intergovernmental panel on climate change." (2013). Link