Hormonal metaphors for rain and climate : Bioprecipitation III

Signalling systems, terpines, aerosols, and cloud creation

The smell of plants and trees - earthy and musky, herby and minty, peppery and spicy, sulfuric and unpleasant - has an intriguing connection with climate. These smells are made from a class of molecules called terpines that are ephemeral and volatile. These molecules react quickly in the atmosphere, transforming into different types of aerosols (which is a moniker for particles that stay aloft in the air). These aerosols nucleate water vapor into clouds, impacting land temperatures and rainfall.

The idea that plants and trees seed clouds and airborne water droplets was first proposed by Frits Went, a Dutch biologist. At Caltech university, in Los Angeles, he constructed some of the first greenhouses that could simulate different climates, with which he could study the behavior of plant emissions and aerosols. He pondered the origin of the blue haze that graced certain mountain ranges. In 1960, he proposed that blue hazes occur in places abundant in terpenes, such as the Blue Ridge Mountains of Appalachia, where terpene-rich coniferous oaks thrive. The terpenes react to form aerosols that seed tiny water droplets that hang in the air, scattering light into the blue part of the spectrum. [Went 1960]

An experimental measurement of terpenes turning into aerosols was made in 1978 by Dennis Schuetzle, an environmental engineer, who found limonene, a terpene responsible for the citrus smell of fruits, reacting with ozone to produce aerosols. [Schuetzle 1978] .

…..

In the 1970s, meteorologists conducted extensive research on aerosols and their impact on climate. Scientists researched how aerosols would impact the temperature of the earth, and how pollution circulated the earth’s atmosphere. But then in the 1980s interest in aerosols dropped, as climate scientists became much more interested in the carbon greenhouse effect.

Some scientists did continue to look at aerosols though. James Lovelock, who was working on his Gaia theory about how the earth behaved in ways similar to a living organism, proposed a provocative theory about how aerosols could help the earth self-regulate its temperature, in a similar way to how organisms could self-regulate their body temperatures. He, along with the atmospheric scientist Ray Charlson, proposed a feedback mechanism. As the planet warmed, algae would bloom more in the oceans. Since algae release into the air a sulfur aerosol called DMS that helps to seed clouds, then with more algae, more clouds would form, which would then cool the planet, and return it to its baseline temperature. [Charlson 1987]

Lovelock’s work may have played a significant role in guiding the larger meteorological community back to working on aerosols. Paul Crutzen, who won a Nobel Prize for his work on ozone hole, and who also did work on terpenes and aerosols, wrote with the biogeochemist Meinrat Andrae about how in the 1990s “Scientific interest in the climatic role of aerosols was rekindled after the proposal of a link between marine biogenic aerosols and global climate. This proposal, which was originally limited to the effects of natural sulfate aerosols, triggered a discussion about the role of anthropogenic aerosols in climate change which led to the suggestion that they may exert a climate forcing comparable in magnitude, but opposite in sign, to that of the greenhouse gas” [Andrae 1997]

…….

In the 1990s and the new millenia, scientists continued to decipher the connection between terpenes and clouds.

The molecular structure of terpenes gives it a volatility that enable it to metamorphize into new structures that attract water vapor molecules to nucleate on them. This molecular structure has the grouping of five carbon atoms and eight hydrogen atoms. When the molecular structure contains one group, they are called isoprenes; when there are two, they are called monoterpenes (despite the somewhat illogical naming); and when there are three, they are called sesquiterpenes, and so on. Isoprene alone has 30,000 different molecular forms, and countless biochemical pathways that can turn them into different types of aerosols. Terpenes belong to a category of molecules called BVOC’s( Biogenic Volatile Organic Compounds). Depending on atmospheric molecular concentrations, humidity, and temperature, the terpenes will undergo different biochemical pathways to turn into different types of aerosols with different water attraction properties.

[Bergman 2022] A map of isoprene emissions. Isoprene is the most basic terpene.

As research progressed, it became clearer that the huge amounts of terpenes forests of were releasing into the atmosphere, were creating enough second order aerosols that they were significantly affecting global cloud production. For example the small clouds/fog that hangs just above forests are often seeded from terpenes.

Terpines, fungi, and bacteria have been around before man. Scientists wanted to know what the aerosol profile was before humans altered the atmosphere. Deep in the Amazon jungle, the atmosphere still resembles its state before the onslaught of man-made aerosols—where clean water vapor from the oceans blows in, and the rain washes away the aerosol scars of the Anthropocene. Christopher Pöhlker, a doctoral student at the Max Planck Institute for Chemistry, led a study there in the Amazon in the 2010s. Working on a tower 80m up in the sky overlooking canopies of biodiverse green, his team collected samples of aerosols. Then peering through scanning electron microscopes, they made a surprising discovery. The aerosols contained potassium. The aerosols had two parts: a core containing potassium-rich salts and a gel-like coating made of volatile organic compounds derived from terpenes. It was a mystery why there should be potassium in the core. Then inspiration hit as the scientists realized that fungi use water containing potassium salts to launch spores into the sky. The potassium salts could, once in the air, then attract terpene-derived molecules onto them [Pöhlker 2012]. They had discovered the symbiotic poetry of fungi partnering with trees to make clouds.

When the world was pristine, there were far more terpenes, fungi spores, and bacteria in the atmosphere. Now in the Anthropocene, 10% of aerosols are man-made. Sulfate and other pollution based aerosols float in the sky.

Terpenes may play a role in helping regulate global warming. Moa Sporre, a physicist, modelled the feedback process of terpenes and other BVOC’s (Biogenic Volatile Organic Compoinds) to understand how they might help the climate self-regulate. The feedback process is reminiscent of the one Lovelock proposed for algae. When trees get hot and stressed, they release more terpenes. World-wide temperature rises means more terpenes. More terpenes means more clouds, which help cool the planet again. Sporre found this feedback loop helps significantly reduce global warming [Sporre 2019]. Their calculations though are very rough though because the aerosol picture is so complex.

Terpenes, signalling language, and hormones

It seems significant to me that a minuscule aerosol has such an outsize effect on clouds which are many orders of magnitude larger. Its seems important that tiny particles are able to regulate variables on a much larger scale, like that of temperature and rainfall, as Moa Sporre’s research demonstrates. This is reminiscent to me of how signalling molecules work in the bodies of organisms. For instance a hormone molecule is a signalling molecule that can trigger a much larger cascade of reactions in a cell, when it lands on the cell membrane receptors. The endocrine system releases different hormones to regulate blood sugar, or energy production. The existence of messenger molecules means organisms can regulate bodily functions without a large expenditure of energy. The existence of bio-aerosols means the earth can regulate its functions - providing the right amount of heat and water to its lifeforms - without a huge expenditure of energy. When systems get complex enough, they begin to develop a language and a messaging/signalling system. The endocrine system using hormones is an example of a messaging/signalling system.

Surprisingly, there exists a kind of universal language and messaging system across different species and kingdoms. You might think that fungi, the bacteria, the animals, the plants, would each only evolve a language for their own kingdom. But no, they have a universal language. That language is the language of terpenes. Nature uses terpenes to communicate and self-organize. Plants give off certain terpenes (odors) to attract pollinators, and different terpenes to warn other plants about attacking herbivores and insects. Ant colonies organize into a superorganism, not via one leader ant giving top-down instructions of what every ant should be doing, but rather with a bottom up system of messages that every ant can send. Their messages are written in the language of terpenes. The smell of the terpene gives ants information. Bacteria and fungi communicate across their respective kingdoms. Microbial ecologist Paolina Garbeva researches this phenomena and explains “A soil bacterium can smell the fragrant terpenes produced by a plant pathogenic fungus. It responds by becoming motile and producing a terpene of its own. Such fragrances are not just some waste product, they are instruments targeted specifically at long-distance communication between these minute fungi and bacteria.” Bacteria-fungi communication is written in the language of terpenes. [Schmidt 2017]. (For more info: the science channel Scishow hosted a piece about the universal language of terpenes.)

Why is the vehicle of this universal language, the terpenes, also involved in cloud formation? It seems intriguing to me that the instrument that nature uses to communicate between species is also the instrument used to create rain, trap heat, and block the sun. It seems curious that the protagonist of nature’s matrix of communication is also the protagonist of nature’s way to modulate the water cycle and the planetary heat. Perhaps this occurrence is just an evolutionary quirk, but maybe something more is going on here than the normative story of aerosols and climate would tell us.

Leopold Ruzicka, who won the Nobel Prize in Chemistry for his work on terpenes, proposed that many signalling molecules in the body, such as steroid hormones, evolved from terpenes.

So the molecules which regulate bodily functions are also related to the molecule that regulate atmospheric functions. If the earth behaves with a physiology similar to that of a living organism, as Lovelock’s Gaia hypothesis suggests, then perhaps the Earth has an endocrine-like system that sends hormone-like messenger molecules to regulate its global functions, such as temperature and water regulation, coordinating itself through a messaging system written in the language of terpenes.

Climate models were originally physics-based. After the significance of chemical reactions in the atmosphere was better understood, climate models also became chemistry-based. If this framework of messenger-molecule-based earth regulation is correct, then maybe we will also need to make our climate models biology-based. In this biological framework we would see the earth in terms of functions. (We would get on the path to lessening global warming, droughts, fire and floods, by restoring the various ‘biological’ earth functions.) Different facets of the earth play different biological roles. The forests are the lungs because it produces oxygen. The forests are the heart, because of its ability to pump water into the sky above. The atmospheric rivers are the arteries, and the rivers are the veins. The wetlands are the kidney.

Still to be figured out is what is the earth’s endocrine system. An endocrine system would know when to send ‘hormones’ (terpenes) to create a more useful distribution of clouds. We might expect this endocrine system to span large distances since terpenes and aerosols released in one region can get blown by winds to affect cloud formation hundreds of miles away. There are mycelia networks over a mile long that connect forests, funnelling nutrients and water between trees and coordinating various species. But they are too small in scale for the purposes of an endocrine system. Since we know bacteria and fungi can talk via terpenes wafting through the air, maybe there is the possibility of a kind of Terpene Coordination Matrix over continental scales forming if they are all linked up, enablng an endocrine system. Could this matrix better know when to release terpenes to affect continental water and heat distribution?

There is still much to learn about terpenes, a fragrant language of universal communication, and how their emission by plants and trees affect our global climate system.

=============================================================

Here is Bioprecipitation part I, and part II if you want to read the preceding essays.

This is a reader supported publication that runs on terpene emissions and fungi sporing.

References

Andreae, Meinrat O., and Paul J. Crutzen. "Atmospheric aerosols: Biogeochemical sources and role in atmospheric chemistry." Science 276, no. 5315 (1997): 1052-1058 https://sci-hub.ru/10.1126/science.276.5315.1052

Bergman, T., Makkonen, R., Schrödner, R., Swietlicki, E., Phillips, V. T. J., Le Sager, P., and van Noije, T.: Description and evaluation of a secondary organic aerosol and new particle formation scheme within TM5-MP v1.2, Geosci. Model Dev., 15, 683–713, https://doi.org/10.5194/gmd-15-683-2022, 2022.

Burrows, Susannah M., Wolfgang Elbert, M. G. Lawrence, and Ulrich Pöschl. "Bacteria in the global atmosphere–Part 1: Review and synthesis of literature data for different ecosystems." Atmospheric chemistry and physics 9, no. 23 (2009): 9263-9280

Charlson, R., Lovelock, J., Andreae, M. et al. Oceanic phytoplankton, atmospheric sulphur, cloud albedo and climate. Nature 326, 655–661 (1987). https://doi.org/10.1038/326655a0

Crutzen, Paul J. "Global tropospheric chemistry." In Low-Temperature Chemistry of the Atmosphere, pp. 465-498. Berlin, Heidelberg: Springer Berlin Heidelberg, 1994

Pöhlker, Christopher, Kenia T. Wiedemann, Bärbel Sinha, Manabu Shiraiwa, Sachin S. Gunthe, Mackenzie Smith, Hang Su et al. "Biogenic potassium salt particles as seeds for secondary organic aerosol in the Amazon." Science 337, no. 6098 (2012): 1075-1078 https://www.science.org/doi/abs/10.1126/science.1223264

Ruth Schmidt, Victor de Jager, Daniela Zühlke, Christian Wolff, Jörg Bernhardt, Katarina Cankar, Jules Beekwilder, Wilfred van Ijcken, Frank Sleutels, Wietse de Boer, Katharina Riedel, Paolina Garbeva. Fungal volatile compounds induce production of the secondary metabolite Sodorifen in Serratia plymuthica PRI-2C. Scientific Reports, 2017; 7 (1) DOI: 10.1038/s41598-017-00893-3

Ruth Schmidt et al, Fungal volatile compounds induce production of the secondary metabolite Sodorifen in Serratia plymuthica PRI-2C, Scientific Reports (2017). DOI: 10.1038/s41598-017-00893-3

Sporre, Moa K., Sara M. Blichner, Inger HH Karset, Risto Makkonen, and Terje K. Berntsen. "BVOC–aerosol–climate feedbacks investigated using NorESM." Atmospheric Chemistry and Physics 19, no. 7 (2019): 4763-4782. https://acp.copernicus.org/articles/19/4763/2019/Dennis Schuetzle & Reinhold A. Rasmussen (1978) The MolecularComposition of Secondary Aerosol Particles Formed from Terpenes, Journal of the Air Pollution Control Association, 28:3, 236-240, DOI: 10.1080/00022470.1978.10470595

Sesartic, A., and Tanja N. Dallafior. "Global fungal spore emissions, review and synthesis of literature data." Biogeosciences 8, no. 5 (2011): 1181-1192.

Went, Frits W. "Blue hazes in the atmosphere." Nature 187, no. 4738 (1960): 641-643.