Marine plankton brighten clouds over Southern Ocean
New research using NASA satellite data and ocean biology models suggests tiny organisms in vast stretches of the Southern Ocean play a significant role in generating brighter clouds overhead. Brighter clouds reflect more sunlight back into space affecting the amount of solar energy that reaches Earth’s surface, which in turn has implications for global climate. The results were published July 17 in the journal Science Advances.
The study shows that plankton, the tiny drifting organisms in the sea, produce airborne gases and organic matter to seed cloud droplets, which lead to brighter clouds that reflect more sunlight.
“The clouds over the Southern Ocean reflect significantly more sunlight in the summertime than they would without these huge plankton blooms,” said co-lead author Daniel McCoy, a University of Washington doctoral student in atmospheric sciences. “In the summer, we get about double the concentration of cloud droplets as we would if it were a biologically dead ocean.”
Although remote, the oceans in the study area between 35 and 55 degrees south is an important region for Earth’s climate. Results of the study show that averaged over a year, the increased brightness reflects about 4 watts of solar energy per square meter.
McCoy and co-author Daniel Grosvenor, now at the University of Leeds, began this research in 2014 looking at NASA satellite data for clouds over the parts of the Southern Ocean that are not covered in sea ice and have year-round satellite data. The space agency launched the first Moderate Resolution Imaging Spectroradiometer (MODIS), instrument onboard the Terra satellite in 1999 to measure the cloud droplet size for all Earth’s skies. A second MODIS instrument was launched onboard the Aqua satellite in 2002.
Clouds reflect sunlight based on both the amount of liquid suspended in the cloud and the size of the drops, which range from tiny mist spanning less than a hundredth of an inch (0.1 millimeters) to large drops about half an inch (10 millimeters) across. Each droplet begins by growing on an aerosol particle, and the same amount of liquid spread across more droplets will reflect more sunlight.
Using the NASA satellite data, the team showed in 2014 that Southern Ocean clouds are composed of smaller droplets in the summertime. But that doesn’t make sense, since the stormy seas calm down in summer and generate less sea spray to create airborne salts.
The new study looked more closely at what else might be making the clouds more reflective. Co-lead author Susannah Burrows, a scientist at the Pacific Northwest National Lab in Richland, Washington, used an ocean biology model to see whether biological matter could be responsible.
Marine life can affect clouds in two ways. The first is by emitting a gas, such as dimethyl sulfide released by Sulfitobacter bacteria and phytoplankton such as coccolithophores, which creates the distinctive sulfurous smell of the sea and also produces particles to seed marine cloud droplets.
The second way is directly through organic matter that collects at the water’s surface, forming a bubbly scum that can get whipped up and lofted into the air as tiny particles of dead plant and animal material.
By matching the cloud droplet concentration with ocean biology models, the team found correlations with the sulfate aerosols, which in that region come mainly from phytoplankton, and with the amount of organic matter in the sea spray.
“The dimethyl sulfide produced by the phytoplankton gets transported up into higher levels of the atmosphere and then gets chemically transformed and produces aerosols further downwind, and that tends to happen more in the northern part of the domain we studied,” Burrows said. “In the southern part of the domain there is more effect from the organics, because that’s where the big phytoplankton blooms happen.”
Taken together, these two mechanisms roughly double the droplet concentration in summer months.
The Southern Ocean is a unique environment for studying clouds. Unlike in other places, the effects of marine life there are not swamped out by aerosols from forests or pollution. The authors say it is likely that similar processes could occur in the Northern Hemisphere, but they would be harder to measure and may have a smaller effect since aerosol particles from other sources are so plentiful.
###
The research was funded by NASA, the U.S. Department of Energy and a graduate fellowship from the Air Force Office of Scientific Research.
Read the paper at Science Advances: advances.sciencemag.org/content/1/6/e1500157
Discover more from Watts Up With That?
Subscribe to get the latest posts sent to your email.
Thank you for this paper. This explains nicely the negative feedback mechanism that caps the temperature rise after coming out of an ice age.
Let’s hope there are some unknown positive feedbacks we discover as we dive into SC 25.
The positive feedbacks have been well researched and well funded by governments and other alarmists.
Dawtgtomis If there were any substantial positive feedbacks in the climate system you would not be around to ask that question and I wouldn’t be answering.
Matt, “If there were any substantial positive feedbacks in the climate system you would not be around to ask that question and I wouldn’t be answering.”
This statement is not precisely true.
Greenhouse gases cause substantial positive feedbacks, making the plant much warmer than it would otherwise be, but the effect is capped so there is no run-away warming.
Thomas, I think he’s referring to the historical cycle of cooling followed by warming rebounds.allowing human populations to recover from the reductions caused by ice ages. We indeed would not have survived had there not been some positive forcings of the climate (heliospheric, orbital and oceanic in my perspective). I guess my comment was a flippant wish that we wouldn’t have to endure a repeat of the dalton minimum or worse.
Oops, sorry Matt, misread your comment. I see now that you were referring to the Venusian effect of runaway warming. Although, who’s to say what evolution might have done to develop a species that is at home in a dense, hot atmosphere. makes one imagine cockroaches or maybe chelonian reptiles…
Curious, Mods, what word threw my last comment into moderation?
Was it my careless punctuation and lack of capitalizations?
There seems to be a misunderstanding as to what a’positive feedback’ is. It doesn’t mean a feedback that increases temperature.
It is “the amplification of an effect by its own influence on the process which gives rise to it”.
A positive feedback refers, just as easily, to a decreasing temperature (and anything else.)
I don’t know whether this interpretation is universal.
Phytoplankton move in response to light. They move towards light (towards the surface) to increase photosynthesis and away from light (to greater depth) to avoid excessive destructive UV radiation. When phytoplankton are near the surface, the surface layer is warmer, because the plankton absorb sunlight and shade the water below. When the surface is warmer, air near the surface is also warmer. When phytoplankton move to depth, e.g. to avoid damaging UV radiation, the ocean surface is cooler and the air above the surface is also cooler. Solar UV varies by about 1.5% from minima to maxima whereas total solar radiation varies only about 0.1%. This could cause a dilemma for phytoplankton during solar maxima because photosynthetic light increase only slightly but UV increases. If phytoplankton are less productive, and further from the surface, during solar maxima, that could cause the surface to be cooler, but they would also produce fewer cloud nuclei, which would tend to make the surface warmer. It’s a fascinatingly complex process.
great insight, thanks!
…the surface to be cooler, but more total energy flux into the oceans yes?
…more total energy flux into the oceans for two reasons, less absorption in the near surface layers, and a decrease in cloud cover. We appear to be a long way from quantifying these things.
Others have mentioned it, but this post shows how the science is certainly not settled. Humanity is a long, long way from having a “settled” climate science. The one thing that we can demonstrate is that CO2 is not the “control knob”.
“The study shows that plankton, the tiny drifting organisms in the sea, produce airborne gases and organic matter to seed cloud droplets, which lead to brighter clouds that reflect more sunlight.”
Yea, I got a kick out of the brighter cloud thing. I never knew clouds came in different levels of brightness.
Would undersea volcanic activity improve the Fe nutrition available to plankton, helping facilitate a bloom?
There are often some glimpse of realism in such papers.
At least we now have a confirmation of what we could expect a priori:
“Aerosol processes remain a poorly understood influence on clouds (4). Processes regulating the concentration of naturally occurring aerosols, in particular, remain a major source of uncertainty, limiting our ability to quantify the magnitude of the human impact on climate from aerosols (5, 6).”
“Because of the complexity of chemical and physical interactions affecting sea spray production and processing in the atmosphere, experimental and observational studies have been unable to unambiguously determine whether marine organic aerosol derived from phytoplankton is associated with an increase or with a decrease in CCN and Nd in marine clouds.”
In the paper it is claimed:
“Aerosols influence clouds by acting as the cloud condensation nuclei (CCN) on which cloud droplets form, and the resulting concentration Nd of cloud droplets influences the amount of sunlight reflected by clouds (3). ”
Reference (3) is:
S. Twomey, Pollution and planetary albedo. Atmos. Environ. 8, 1251–1256 (1974).
For your convenience, here is a link to the paper:
http://www.clidyn.ethz.ch/ese101/Papers/twomey74a.pdf
I propose that you skim through this paper – which is referred to as basis for the above statement.
In my opinion, it does not even closely resemble a scientific approach to the issue.
Science or fiction? – I would say fiction!
If you disagree – please reply and let me know.
This is how IPCC summarized on aerosol-climate feedback:
“Aerosol-climate feedbacks occur mainly through changes in the source strength of natural aerosols or changes in the sink efficiency of natural and anthropogenic aerosols; a limited number of modelling studies have assessed the magnitude of this feedback to be small with a low confidence. There is medium confidence for a weak feedback (of uncertain sign) involving dimethylsulphide, cloud condensation nuclei and cloud albedo due to a weak sensitivity of cloud condensation nuclei population to changes in dimethylsulphide emissions. {7.3.5}”
(Ref. Working group I contribution; on the scientific basis; to the fifth assessment report by IPCC; TS.3.7 Climate Feedbacks)
To put the language straight: On this area there is no established theory which has been exposed to and stood up to rigorous testing.
Science or fiction? – I call it fiction!