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When physics meets biology there is poetry and music


Most of us working in the area of biological ice nucleation are intensely fascinated by and in love with this subject. Fascination drives research. And love for this subject does what love does: it can inspire art. Throughout the past decade of interacting with the various disciplines and persepctives about biological ice nucleation and how it could impact clouds, I have listened to expressions and explanations about mechanisms and processes in clouds that have sent me dreaming. This dreaming led to lyrics that emerged spontaneously in my mind as I was riding my bike to work in the countryside near my lab trying to avoid stray dogs and an occasional wild boar and her piglets. The lyrics were set to the melody from Joni Mitchell’s Both Sides Now, a song that begins with her impressions of clouds. After receiving positive feedback about the lyrics and encouragement to record it and share it online, I succumbed to this advice – as an experiment and as an opportunity to witness all of the “materials and methods” involved.  I suppose that this is ultimate interdisciplinarity.

You can read the lyrics are at the end of this posting, below. I was encouraged to copyright them, so I did. Likewise, a professional musician recommended that I obtain permission to publish what is known as a “cover”, i.e. my version of an existing song. This can be done via an agency that centralizes such requests and obtains permissions from the original author/artist. This is important if one intends to charge listeners for downloading – which is not my case. But I wanted the full experience of producing a cover, so I sought out the permission.


You can listen to the song Clouds: When Physics meets Biology via streaming on the Sound Cloud website (the name of this website is a nice coincidence).

This song could be a sort of educational tool, especially if it were accompanied by a video. I was afraid of only being able to conceive something full of cloud clichés that did not have the same artistic quality as the music and lyrics – so I did not even attempt to make a video.  If anyone has ideas for an artistic and informative video to accompany the song, please let me know.


Here is how the audio file of the song was produced:

The recording consists of 16 audio tracks managed with Logic Pro X software. Fifteen of the tracks were audio files (drums, organ, bass, guitars and voice) and one track was the “cloud impulse” program from a synthesizer pad. The main accompaniments were played on a 1991 Martin D41 acoustic guitar, a 1960 Fender Jazz master electric guitar, a handmade (“Elvis Presley Graceland” model) bass and a Hammond B3 organ. The guitar solo interlude between the second and third verses was played on a handmade (“License Plate” model) electric guitar. Guitars, bass and organ were played by Danny Mangold, a guitarist, guitar-maker and producer from Seattle, Washington, who also crafted the handmade guitars. The drum accompaniment was a track produced by looping a drum sample from a recording of Aaron Comess, drummer for the Spin Doctors band. Lyrics were sung by Cindy Morris and recorded with an ADK Hamburg microphone. Production of the audio file required 2 hours for production of an original demonstration version of the bed tracks and 5 hours of recording of the voice tracks and mixing. Lyrics were copyrighted by C.E. Morris on 30 Jan 2017 and permission for publication of a cover version of the original Both Sides Now song by Joni Mitchel was obtained on 28 Jan 2017 from the Harry Fox Agency before the .mp3 version of the audio file was uploaded to Sound Cloud. The .wav version was saved for use where listeners are likely to use excellent speakers beyond what their cell phones, computers and tablets permit. This file can be obtained from Cindy Morris.



The lyrics

Clouds: When Physics meets Biology

[cover version of Both Sides Now, Joni Mitchell]

Lyrics (except for first 4 lines of the first verse) by Cindy Morris, copyright 2017.


[Verse 1]

Rows and flows of angel hair

And ice cream castles in the air

And feather canyons everywhere,

We’ve looked at clouds that way.


But are they blankets or albedo shields?

Or lakes of rain for crops in fields?

Impressions in the painter’s dream

Meet a science theme.



We’ve looked at clouds that come and go

That surge or fade, or rain or snow

How can we hold them in our hands,

In hopes to one day understand?


[Verse 2]

Particles and drops so small

That billow in the clouds so tall.

Nucleate and aggregate

Will make the great rains fall.


They say that microbes are at the core

When crystals splinter and thunder roars.

When physics meets biology

Imagination soars.



We’ve looked at clouds superficially

But now we want to really see

The complex web of processes

Do we really know clouds at all?


[Verse 3]

Proteins in the dance of ice

Hold water bonds that they’ve enticed.

With such appeal, their fate is sealed

Encased in falling rime.


Leaf blades spring as drops rebound

And trickle deep into the ground.

To be absorbed and launched again

For yet another round.



Aerosols in masquerade

Take fleeting shapes in a white parade

Where Gibb’s free energy is king

We really shall know clouds someday.

The MILAF meetings


The MILAF meetings: Enabling early career scientists for interdisciplinary research on land-atmosphere feedbacks.

Mentoring of early career scientists is commonly an integral part of projects funded by the US National Science Foundation. In the context of the RAINS [i] project, setting-up a mentoring workshop was the responsibility of the two most senior of the RAINS PIs – David Sands (Montana State University, Bozeman) and myself. The workshop has turned into a series of meetings and has added a dynamic branch to the network of scientists working on bioaerosols and land-atmosphere feedbacks. Happily, the transformation of the initial workshop into a series of meetings and into a tight-linked community arose by popular demand. Nevertheless, it corresponds to our intention to create common goals for research on land-atmosphere feedback – launched with the 2006 Microbial Meteorology meeting – and to create a cohesive and cooperative community.


[i] Research on Airborne Ice Nucleating Species, NSF Dimensions: Collaborative Research Program, 2013-2016 The MILAF meetings were organized with funds from the RAINS project, from INRA’s Plant Health and Environment division and from the European Academy of Bolzano (EURAC).


The RAINS project was motivated by the potential of ice nucleating microorganisms in the atmosphere to use precipitation as a dispersal strategy and the eventuality that this could result in feedbacks between land sources of these microorganisms and the atmosphere. The project was born in a period of growing concern that science needs to facilitate research on interdisciplinary questions of broad importance for society and for the environment (see Nature’s special issue on interdisciplinarity). The goal of RAINS’ mentoring workshops has been to enable a corps of early career scientists with passion for research about Microorganisms at the Interface of Land-Atmosphere Feedbacks (MILAF), with excellent disciplinary competences, and with strong wills to engage in interdisciplinary research in spite of the potential obstacles and inconveniences. Here is an account of how the MILAF meetings are becoming an important stimulus to setting and advancing a research agenda on land-atmosphere feedbacks.

Scouting and stimulating talent. As organizers, our goal was to create an open and informal forum for the exchange of ideas among i) talented early career scientists with high potential to contribute to the bioprecipitation research community in the future, ii) the Principle Investigators (PIs) of the RAINS project, iii) additional mentors with competences outside the expertise of the RAINS PIs, and iv) stakeholders representing perspectives from legal systems, land use and reforestation movements and enterprises, and the direction of research institutes. Early career scientists were selected through an application procedure that included, in addition to a CV, a 2-page essay on how they foresee themselves contributing to the theme of the workshop in the coming decade, the grand research challenges to which they want to contribute and how their participation in the workshop would facilitate achievement of their goals. After hours of discussion among four of the RAINS PIs during a pleasant train trip from Avignon to Switzerland, 14 early career scientists were selected. Although our selection criteria focused on excellence and the capacity to contribute to an interdisciplinary group, we also ended up with an equal balance of women and men from the physical and biological sciences.

The workshop format was initially perceived as unconventional by some of the RAINS PIs, but we felt that it would maximize discussion and interaction of participants.  We favored question sessions, ensuing discussions and break-out groups more so than formal presentations of each person’s research (Fig. 1).  To jump-start the process of getting to know each other, before the workshop everyone uploaded to the shared Dropbox folder a half-page brief CV with a photo. And to maximize the efficiency of our interactions, a reading list of 30 core papers was provided 3 months before the workshop (Fig. 1).


Figure 1. Participant list, program and the reading list for the first MILAF meeting (Oct 2014, Ste. Maxime, France). Click here for the full file


Creating a community with long-term goals. The format of the first meeting revealed that many of the participants were, themselves, inherently polyvalent, multidisciplinary and very skilled in interdisciplinary communication. Perhaps it was this realization among the participants and the solace and excitement of working with like-minded colleagues – a rarity in a world reigned by well-defined disciplines – that we rapidly moved to defining long term goals for our nascent community. We felt that our future interactions could focus on 5 types of activities:

  • Coordinating research activities that target the main scientific challenges that we identified for the upcoming decades
  • Promoting the cohesiveness of the bioprecipitation community, mentoring young scientists and fostering deployment of interdisciplinary competences
  • Creating a sense of urgency and educating the public
  • Identifying and engaging stakeholders
  • Translating research into practical applications to mitigate drought.

We specified the details underlying these activities in a more precise plan for the upcoming decades (Fig.2)

bioprecpvisionFigure 2. MILAF-2014 conclusions: Challenges for bioprecipitation research. Click here for larger pdf version


This plan oriented two subsequent videoconferencing meetings (21 May and 29 0ct 2015, ca. 15 participants each meeting) that were coordinated by Christopher Carr (MIT) and myself. These meetings revealed that participants had continued networking since the 2014 meeting. Videoconferencing also served to reinforce the desire for another in-person meeting. With contributions from a few outside sources, we managed to stretch the NSF funding to organize MILAF-2016 at the European Academy of Bolzano, Italy in March 2016. Additional early career scientists and mentors were brought in to re-inforce the activities of the working groups that were emerging from MILAF-2014. The program included formal presentations of research and also allowed several early career scientists to take leadership roles in pushing forward the main research themes (Fig. 3). It also included a stimulating visit to Bolzano’s South Tyrol Museum of Archeology and an overview of the research to identify the origin of the Helicobacter pylori strain in the stomach of the 5300 year-old Iceman mummy housed by this museum.


Figure 3. Participant list and program for MILAF-2016. Click here for the full file.

Achieving goals.  The MILAF meetings sparked camaraderie and cohesiveness of the participants and the budding of diverse initiatives to achieve the goals we identified. Here are our major achievements.

  • Coordinating research activities that target the main scientific challenges for the upcoming decades

Directly measure microbial flux and create relevant tools. Quantification of the flux of microorganisms or of ice nucleating particles (INPs) over land has stagnated since the publications of Lighthart and of Lindemann in the 1990’s because of the complexity of the required experimental field set-ups. Via the MILAF meetings a few scientists have joined forces and shared materials and competence to simplify the techniques and to obtain direct measurements of flux. During MILAF-2014, Yves Brunet (INRA-Bordeaux) led a really informative discussion about the physics underlying flux and different approaches to its measurement for microorganisms based on the gradient method and on relaxed eddy accumulation (see Yves’ work on REA flux measurements).  As part of his PhD thesis research, Federico Carotenuto (Univ. Innsbruck and CNR IBIMET – Florence, Italy) was attempting to measure microbial flux and simplify the task of the gradient method. He came to Avignon to hone his skills -and where I made an instructive video of his work.

After meeting Danny O’Sullivan (University of Leeds, UK) at MILAF-2016, they launched a collaboration to set up a field campaign to investigate emissions and characteristics of ice nucleating aerosols in England’s atmosphere (Fig. 4).  The campaign is bringing together expertise in the chemical, atmospheric, and biological fields needed to tackle this complex topic. And importantly, manuscripts are in the making.


Figure 4. Microbial flux platform set up by Danny O’Sullivan, Federico Carotenuto and colleagues from the University of Leeds (autumn 2016).


Build evidence from field campaigns for the impact of biological aerosols on precipitation. Hari Mix (Santa Clara University, California) and Jessie Creamean (NOAA, Boulder, Colorado) are collaborating on Hari’s NSF RAPID project on “Investigating the mechanisms driving extreme precipitation in atmospheric rivers with an integrated stable isotope and aerosol chemistry approach” where they will link isotope, INPs, and compositional measurements of rainwater samples in California during the CalWater 2015 field campaign. Their current analysis focuses on evaluating relationships between these parameters and air mass source and meteorology during atmospheric river events. The goals of the project include an examination of the rainout of bioaerosols on coast-to-interior transects in northern California. According to Hari, this work was largely motivated by the research of another MILAF participant Emiliano Stopelli (University of Basel, Switzerland) (viz., Stopelli et al 2015) and whom Hari was really happy to meet at MILAF-2016.

Elucidate and explicate component processes and limiting factors of bioprecipitation feedback. The process of bioprecipitation feedback implies an increase of cloud-active aerosols after rainfall and their effect on subsequent rainfall. To ferret out the component processes of bioprecipitation, we need to select cohorts of field sites where specific hypotheses about processes could be tested. Therefore, the task of developing criteria for creating these cohorts has become an important goal for bioprecipitation research. We developed these criteria as described in a previous blog post. The MILAF meetings contributed to this work by bringing to our attention the expertise of Jessie Creamean (NOAA, Boulder, Colorado) in atmospheric sciences and her capacity for teamwork in constructing the scientific arguments underlying the link between rainfall patterns and biological aerosols. She accepted our offer to participate in the development of these ideas and to interact mostly by email with statisticians, atmospheric physicists and microbiologists on several continents through multiple revisions of our manuscript to achieve publication of our method (Morris et al 2015).

Coordinate field campaigns. This goal is of utmost importance to account for geographic and land cover variability in the amount and types of bioaerosols in the atmosphere and their possible impact on atmospheric processes. To get the ball rolling, Pierre Amato (CNRS, Aubière, France) and Emiliano Stopelli and Franz Conen (mentor) (both from University of Basel, Switzerland) are verifying whether their recent observations in support of the bioprecipitation hypothesis from the Jungfraujoch observatory in Switzerland are valid more broadly. An observatory was set up in October 2015 in France (Fig. 5) for monitoring ice nuclei in precipitation, including meteorological and biological data, ice nuclei concentration and rain water atmospheric isotope ratios. One entire year of data (ca. 100 rain events) has been collected so far.

Figure 5. Site of the observatory in France to confirm bioaerosol observations made on the Jungfraujoch in Switzerland.


  • Creating a sense of urgency and educating the public

To address the need for outreach and educating the public identified during MILAF-2014, Renée Pietsch (Virginia Tech) developed a lesson on biological ice nucleation as part of her Ph.D. thesis work that was just published in the Science Teacher (Turning into ice: Teaching ice nucleation and the global water cycle).

Jessie Creamean (NOAA, Boulder, Colorado) has become the aerosol working group leader for the IASOA (International Arctic Systems for Observing the Atmosphere) and has been encouraging other MILAF participants interested in Arctic research to join the group.

Participation in the MILAF meetings pushed several of the mentors to become more engaged in creating a sense of urgency for understanding the land-atmosphere link. Jane Cohen (University of Texas School of Law, Austin), David Sands (Montana State University, Bozeman) and I participated in the conference sponsored by WeForest that led to the policy brief about the importance of vegetated land cover in the water cycle described in an earlier posting. The fruit of the interdisciplinary conference sponsored by WeForest has also become a manuscript that we hope will be accepted shortly (to be announced later).


  • Promoting the cohesiveness of the bioprecipitation community, mentoring young scientists and fostering deployment of interdisciplinary competences.

Strive to set up more collaborations relevant to bioaerosols and their impact on the atmosphere. There has been an exceptional flurry of efforts to continue working together on diverse subjects:

  • Jessie Creamean (NOAA, Boulder, Colorado), Erik Thomson (University of Gothenburg, Sweden) and Tina Santl-Temkiv (Aarhus University, Denmark) submitted a proposal on “Riders on the storm: Microbe-aerosol-gas interaction as a mechanism of active aerial cell dispersal” to the Human Frontier Science Program this year.
  • Jessie has also brought David Schmale (mentor) (Virginia Tech) on board to help analyze aerosol samples that she collected in summer 2016 on a cruise in the western Arctic Ocean in terms of the INPs, the overall aerosol composition and culturable bacteria.
  • Thanks to an announcement provided by Tina, Jessie (as PI), Christopher Carr and Brent Christner (mentor and PI of the RAINS project) (University of Florida, Gainesville) have a proposal pending with NSF Arctic System Sciences for the MOSAiC field campaign. It is a $3.2M project to understand aerosol properties in the context of clouds during a year-long trans-Polar drift cruise. They have proposed to deploy a series of aerosol and trace gas samplers and collectors to develop an unprecedented characterization of high Arctic aerosols over the course of an entire sea ice cycle. Franz Conen, Erik Thomson and Tina Santl-Temkiv will be external collaborators on the project.
  • To add on to her initiatives to exploit Arctic contexts to understand the interaction of bioaerosols and the atmosphere, Jessie (as PI) and Chris are constructing a proposal to the Arctic Natural Sciences program to conduct filter-based and real-time measurements on the upcoming joint US/SE summertime cruise on the Oden in 2018. This cruise will align with a cruise this coming summer and with MOSAiC, but focuses on biological and biogenic cloud nuclei in the eastern Arctic Ocean.
  • Christopher Carr  led up a proposal to NASA’s biodiversity solicitation – including colleagues in the MILAF network and other scientists – specifically geared to fund development of an exploration aerobiology sampling campaign for NASA.
  • Chris also set up a collaboration with Noelle Bryan (Louisiana State University, Baton Rouge) and Brent Christner  to sequence the genomes of bacterial strains that Noelle collected from the stratosphere and to perform de-novo genome assembly using single molecule sequencing.

Create more opportunities to meet and to expand our community. To enrich the context that has been established by the MILAF meetings we are planning for future meetings. Erik Thomson and I have recently succeeded in obtaining funds through the University of Gothenburg, Sweden to organize a meeting in the same spirit as the previous MILAF meetings. So you should be hearing soon about the next MILAF meeting.

Below are photos from MILAF-2014 and MILAF-2016 to further illustrate the settings and ambiance of these meetings.
























Directory of participants in the network on biological ice nucleators and cloud processes


From the core of participants in the 2006 meeting in Avignon (described in the previous posting), the resulting network has grown and will continue to grow. Given that much of the communication among us is via the internet, it is becoming increasingly difficult to associate names with faces and expertise. Here is a directory of affiliations, addresses and expertise for participants in the network willing to provide such information.  This might help to keep us aware of who our colleagues are and their competences.


If you would like your name, photo, contact information and description of your expertise included in the directory, please let me know.

A decade of interdisciplinarity


Ten years ago this month, about 25 scientists from the Life Sciences and Earth Sciences convened in Avignon, France for the interdisciplinary meeting that set into motion the current international research dynamics on the role of microorganisms in atmospheric processes.  The meeting, funded by the European Science Foundation program for Exploratory Workshops, was romantically entitled Microbiological Meteorology: Working at the Intersection of Biology, Physics and Meteorology to Understand and Regulate the Microbial Component of Weather. (click here for the program, presentations and report).


Participants of the 2006 ESF workshop on Microbiological Meteorology.

Front row (from the left): Zev Levin, Gabor Vali, David Sands, Cindy Morris, Christel Leyronas, Tom Hill. Back row: Ottmar Moehler, Laurent Huber, Dominique Courault, Roland Psenner, Paul DeMott, Ulirich Pöschl, Ruprecht Jaenicke, Dimitri Georgakopoulos, Heidi Bauer, Berhard Vogel (peeking over Heidi’s head), Mihaly Posfai, Janine Fröhlich-Nowoisky, Marc Bardin, Laurent Deguillaume, Bruce Moffett.


This meeting was followed by a flush of other meetings that consolidated this initial group of researchers and drew in others. This included a session on Biological Ice Nucleators in the Atmosphere – at the Crossroads of Physics and Biology at the General Assembly of the IUGG (Int. Union of Geodesy and Geophysics) in Perugia, Italy in 2007, a special session on Biological Aerosols at the International Conference on Nucleation and Atmospheric Aerosols in Prague in 2009 and another session on Biological Aerosols in the Earth System at the IUGG General Assembly in Melbourne in 2011. Since those initial meetings, and as a consequence of the collaborations and publications that resulted, the surge of interest in this field has been remarkable.

What has this decade of effort to build an international and interdisciplinary network really changed concerning the tools for exploring the influence of microorganisms on atmospheric processes and the knowledge resulting from this exploration? And what are the major challenges that should be a priority for the next decade? To put together answers to these questions, I combined my own opinions with those of some of the scientists who have the most active hindsight on this subject – in particular Gabor Vali, Zev Levin and Keith Bigg.


We have expanded the scope of ice nucleation active particles of biological origin and confirmed their ubiquity. Various microorganisms, and especially numerous fungal species, have been added to the list of efficient (“warm-temperature”) ice nucleators. But, in addition, numerous studies have shown that particles with ice nucleation activity can be composed of various organic matter absorbed to inert mineral particles.  Rich, organic soils are one source of such particles.  This has led us to alter our vocabulary to adapt more generic expressions, such as Ice Nucleating Particles (INPs), to account for the variability in the nature of the particles. Furthermore, bio-INPs are ubiquitous: on plants, in fresh and marine waters, in precipitation, in leaf litter, in soils, and in clouds.

There has been a surge of proxies to identify INPs of biological origin. Based on the frequent use of heat sensitivity of ice nucleation activity in papers on biological INPs, it is clear that this has become the technical criterion for defining biological INPs. In parallel, particle fluorescence in UV-LIF spectrometers (such as the WIBS) has become a widely deployed criterion to identify biological particles in aerosols and in ice crystals. Probes (primers) for molecular detection (PCR) of the gene for the INA protein in Pseudomonas syringae and related bacteria have also been developed. But the sensitivity of this latter tool does not yet rival classical microbiological approaches.

Biological INPs have new rivals in the mineral world for efficient ice nucleation activity. Recently, the ice nucleation activity of feldspar was revealed, with the upper limits of the temperature of activity comparable to that for bio-INPs (near -5°C) making it the only mineral that rivals bio-INPs for this upper limit. However, in terms of the density of ice nucleation sites per surface of particles, bacterial INPs – and especially Pseudomonas syringae – still pack the greatest punch by several orders of magnitude.

Biological INPs have been “injected” into the realm of math and physics. Numerous models of cloud processes have included parameters that permit simulations of the effect of INPs having activities and abundances corresponding to those of biological INPs. This has led to the assessment of effects on cloud life-time, lightning, and precipitation.  Biological INPs have also been literally injected into cloud simulation chambers in order to catch these INPs in the act of inciting glaciation. The Snomax® product has proven to be a useful tool to allow scientists without access to microbiological labs to conduct such experiments.

Atmospheric microorganisms are also important in processes other than ice nucleation. The metabolic impact of microorganisms in the atmosphere has been a hotly debated subject because of the overriding importance of light-driven reactions in the chemistry of the atmosphere.  But, it has become established that there are conditions under which microorganisms surpass photochemistry or catalyze reactions not typical of photochemical processes.

A multitude of field observations have corroborated a role for biological INPs in precipitation. High altitude observatories and aviation-based sampling campaigns have provided much needed evidence that biological particles are guilty of being in the right places at the right time to be involved in processes leading to precipitation. The names of these sites and campaigns are becoming household words, such as Storm Peak, Jungfraujoch, Puy de Dôme, CalWater, etc. Results of these campaigns have revealed the possible importance of season and origin of air masses in the abundance of biological INPs.

Above all else, the atmospheric cycle of bio-INPs is now considered more seriously and a role for them in precipitation is assumed to be plausible.  A striking sign that this plausibility is being accepted is the more and more frequent use of the term “bioprecipitation” by physicists and biologists alike. The term is used mostly to describe the cycle in which microorganisms, mostly from plants, are transported to clouds, foster cloud glaciation and rainfall that deposits these microorganisms back on plants and also provides water for their subsequent multiplication. The past 10 years has seen an incredible complicity between Biology and Physics to provide evidence for the plausibility of some of the major processes of this cycle. Importantly, there have been several new reports about the rapid increase of INPs in the atmosphere shortly after rainfall and we have been reminded of the data on this phenomenon from as early as the 1950’s – all bolstering the occurrence of this important step of the bioprecipitation cycle. Mathematical tools have been made to assess the intensity of the feedback of rainfall in this cycle as a means to identify where rainfall is most sensitive to aerosols.



Another important outcome of the past decade has been the creation of a research community. This community is not only interdisciplinary but it also includes scientists from several generations of research on ice nucleation and bio-INPs. As Gabor points out, this community is critical to assure continuity in research.  The long term efforts that will be needed to attain certain goals about the role of bio-INPs in precipitation are difficult to get funded as single, full projects.  Therefore, as a community we will need to continue stitching together the patchwork of our results and to try to collectively define the subsequent goals. The visibility and interest that we have created has managed to attract young people who have smartly tackled relatively short-term projects that are contributing to the long-term goals.



The greatest challenge for the future is to provide solid, direct evidence for the importance of bio-INPs in precipitation formation. This will be very difficult mostly because of the inherent complexity of how the ice phase in general leads to precipitation in different cloud regimes. The nature and spectrum of action of bio-INPs is also highly variable and this adds on an additional dimension of complexity. Field observations have been one of the main foundations of the growing body of corroborative evidence and of the increasing plausibility of a role for bio-INPs in precipitation. But in the future will field experimentation be used to provide some of the needed solid evidence?  Would such field experimentation be another form of direct cloud seeding? Or rather, would we be able to deploy tools of modern molecular genetics and genomics to link sources, such as vegetation that harbors very specific types of microbial INPs, with these same microbial INPs in clouds, in ice crystals and in precipitation? The ubiquity of certain bio-INPs such as Pseudomonas syringae, Fusarium spp., lichens, etc. will, in fact, hinder such an approach. On the other hand, the extreme host specificity of rust fungi, that cause recurrent epidemics from clearly identifiable sources for which there are hundred-year historical records on most major continents, is one model of bio-INPs that could serve us well for this challenge. Because of the size of bio-INPs such as fungal spores, their action as giant cloud condensation nuclei (GCCN) might be a compounding factor in their role in precipitation. Keith points out that the interest in GCCN has not been proportional to their potential role in the bioprecipitation process and deserves more attention. Furthermore, ice nuclei are only important to rainfall production at temperatures below zero while GCCN can potentially stimulate precipitation in clouds at any temperature.

Another obstacle to advancing our understanding of the role of bio-INPs in the formation of precipitation is the continuing debate about the sufficient abundance of microbial INPs. Continued effort to expand the scope of biological INPs to include submicron-sized remnants of biological organisms, which are likely to be much more numerous than intact microbial cells and spores themselves, will probably greatly contribute to resolving this debate.

Unraveling the mechanisms and efficiency of transfer of bio-INPs from Earth’s surface to the atmosphere is also another important challenge. Methods to facilitate quantification of flux of bio-INPs from the ground into the atmosphere will be very welcome and will be an enormous technical leap.  In the meantime, mapping of the properties of near ground aerosols vs. the properties of bio-INPs on land surfaces across a wide variety of land covers and geographic sites might contribute to this challenge. Nevertheless, once bio-INPs are released from ground level sources, they age during transport in the atmosphere. Hence, questions about the transfer of bio-INPs into the atmosphere go beyond the basics of mass release as a function of wind, humidity and surface conditions and must address how the ice nucleation activity of bio-INPs is modified. Likewise, inert atmospheric particles with no inherent biological constituents might also pick up biological components during their transport. Zev reminds us that examples of such phenomena are starting to be suspected during the transportation of aerosols over oceans and during the flight of volcanic ash. In this light, there will be greater and greater need for techniques of detection and characterization of atmospheric INPs that can separate out the increasing range of classes of bio-INPs.

The upcoming generations of environmental scientists will be under considerable influence from the concern over climate change and its numerous ramifications. Sources of funding will probably mirror this concern with the likely consequence that research will be focused on macroscale processes. As much as such approaches are the path to direct evidence for the importance of bio-INPs in precipitation formation, understanding microscale processes will be needed to make better detection tools and for modeling. Gabor suggests that understanding the nature of nucleating sites and their permanent vs. transitory features is one aspect of microscale processes that should not be forgotten, in particular because of the dependence of quantitative laboratory analyses of ice nucleation activity on these features.

Future research should build on the past. Through online discussions in this network we have realized that there is a gold mine of research publications and competence from about 30-50 years ago that we probably have not build upon as best as we could have. Likewise for contemporary research findings, we need to use our convivial and dynamic network to anchor them into our collective knowledge, to frankly identify their strengths and deficiencies, and thereby continue building toward our ambitious long term goals.




Taming microbial ice nucleators: On the rough road from academic research toward policy and action


Working for a research institute that has recently taken on the moto « Science & Impact » has heightened my interest in how academic research is transformed into tools and behaviors that are adopted by society. I see this as bona fide impact, a natural extension beyond the numerical “impact factors” whose relevance is restricted to the sphere of academia.

Think about three seemingly unlikely Nobel Peace Prizes: one in 1970 for the plant pathologist and breeder Norman Borlaug who is considered to be the founder of agriculture’s Green Revolution, one in 2004 for the biologist Wangari Maathai who founded the Green Belt Movement, and one in 2007 for the Intergovernmental Panel on Climate Change. These prizes recognized individuals and organizations who put science and its results on a course of action that has helped society be sustainably peaceful. Yet, for many scientists those courses of action seem mysterious or elusive in spite of their importance for resolving world class problems such as feeding the growing human population, halting and reversing deforestation, or slowing emissions of greenhouse gases.

In the year leading up to the recent COP21  and for a few days during the weeks of this convention in Paris, I participated in activities that are helping to advance the concept that microorganisms play a role in land-atmosphere interactions and to push it into a trajectory where it could, one day, contribute to policy and action for adapting to and/or mitigating climate change.  I felt very lucky to see this first hand, so I would like to share what I witnessed and learned – and in the hopes of igniting the same passion in some of you.

From the perspective of climate change policy, plants are basically just a sink for CO2. Although the many other services of plants for the environment are known, the policies and actions that have issued from the climate change convention have focused on CO2. In the past few years numerous organizations (NGOs, companies, foundations, etc.) have intensified their lobbying for the recognition of these additional ecosystem services of plants – and of forests in particular – in policies for adaptation to and mitigation of climate change.  In 2010, I was invited to be on the scientific advisory board of several such organizations. One of them, WeForest, is particularly intent on influencing policy at national and international levels concerning reforestation and forest management. Recently they wanted to bring scientists and policy makers together to promote a range of issues.  However, I was unsure about the consensus in the scientific community concerning the importance of other ecosystem services of plants relative to climate change.  So in early 2015 following my advice, we launched the organization of a meeting to identify the consensus.

Our 3-day conference on Why Do Forests Matter for Water and Climate? Strategies for Sustainability took place in Leuven, Belgium in June 2015. In an effort to initiate the visibility of the meeting, it was announced as a partner event of the Common Future Under Climate Change conference held in Paris in July, one of the many events leading up to the COP21.  I don’t know how our meeting obtained this recognition, but it is likely due to the other organizers whom Victoria Gutierrez, WeForest’s chief science officer, had invited to work with me (Bruno Locatelli and David Ellison).  The conference format we chose was the fruit of hours of discussions among the four of us to overcome our disciplinary obstacles (social sciences vs. environmental sciences vs. political sciences vs. life sciences), to clearly establish the objectives of the meeting and to identify the people to invite.  The main objectives we agreed upon were:

  • To elucidate the current state of knowledge on the importance of forests for water and other Earth system processes and
  • To outline a policy brief on how this role of forests is or could be addressed in existing and potential policy frameworks

The 30 people we invited to attend the meeting represented institutes for research and/or development (CIRAD, CIFOR, INRA, ICRAF); universities in North America, Europe and Australia; the private sector and policy makers (FAO). They also represented a multitude of disciplines in the Life Sciences, Earth Sciences, Math and Physics, Social Sciences and Law. By the end of the 3 day meeting we had put together the skeleton of a white paper that has since blossomed into an in-depth manuscript soon be submitted for publication in a scientific journal.  By establishing the content of this manuscript we defined our consensus on the current state of knowledge.  Writing such papers is what we scientists know how to do. But the format and writing style are a far cry from a brief policy outline that can be grasped by policy makers. Importantly, in scientific papers we are long-winded, we hedge, we are vague and we rarely commit to definitive statements about “truths” because our task is to reject hypotheses – and there are always a slew of them still awaiting a test.

So in the months following the meeting in Leuven, Victoria Gutierrez of WeForest worked with incredible persistence to bring life to a policy brief and to obtain a venue to present it. The activities that were to take place around the upcoming COP21 meeting in Dec. 2015 would provide many options for a venue – in theory.  But most of them were inaccessible due to the cost for participating (over $20000 for a stand in a Pavilion at the Global Landscape Forum, for example) and the lack of space because most of the organizations in-the-know had been positioning themselves for many months in advance.  In the summer and fall of 2015 when we were considering all these options, I was a rather silent participant in the discussion because this sphere of events was really foreign to me and I felt lost.

I was really impressed and inspired by Victoria’s dedication and persistence. But it was becoming clear that there was little initiative among the participants of the meeting to write the policy brief; none of us really had experience. We considered the option of farming it out to professionals in communication, such as those associated with certain research and development organizations, but this was costly and we risked losing control of the message. Eventually, the participant from the FAO (Elaine Springgay) mentioned that the many policy briefs she had seen through her work gave her some ideas for the organization and format of ours.  That was the trigger for me to jump on the boat. In fact I felt compelled to do this because of my responsibility as one of the organizers of the Leuven meeting, but also because the scientific consensus was really exciting – as you can see below. In one week she and I created a document and figures that were validated by the other participants of the meeting and then sent off to the CIFOR communication service for the final beautification.  Here is the final version of the policy brief (that you can also find on the WeForest website).


To write the policy brief, we condensed in very short sentences the 5 points of consensus that dominated the meeting in Leuven and that were detailed in the manuscript.  The role that plants could play in rainfall via the ice nucleation-active microorganisms that they harbor was one of the points of consensus. This idea was identified by the participants as important and credible and needed to be promoted as a potential impact of vegetation on climate – beyond its role as a sink for CO2. The participants agreed that it should be integrated into the list of ecosystem services that vegetation could offer relative to the water cycle and climate – given the appropriate knowledge base.  Keep in mind that this point of consensus was proposed by several other participants of the Leuven meeting and was not due to any strong lobbying by David Sands or myself during the meeting.  When that consensus became clear – and importantly when it became clear that other scientists perceived this – I realized that the concept that we call “bioprecipitation” had moved from a wild idea hidden in the Journal of the Hungarian Meteorological Service, to ambitious but virtually unfundable projects for interdisciplinary research, to academic publications, to something that land managers in the future might reckon with if provided the appropriate tools and information. In my opinion, to witness this transformation first hand is a very scenic and thrilling ride on the rollercoaster of a career in science.

While the policy brief was being validated, beautified and printed, Victoria was tirelessly hunting for a venue.  When she finally announced the news that we had a place at the stand of ICRAF/FAO in the Pavilion on Achieving the Sustainable Development Goals at the Global Landscape Forum (GLF) and a 1-hour slot for a presentation on 6 December, we were stunned. I asked her to summarize the obstacle course of events that led to this unexpected opportunity. In a nutshell, it was the consequence of her professional network and of the activities in which she has been engaged over the past several years. Most notably, we were offered to share the ICRAF/FAO space free-of-charge and were provided a few entry tickets to facilitate the participation of the people presenting the policy brief. I think that this generosity reflects that Victoria’s colleagues perceive her strong sense of engagement for forest management, her persistence in achieving goals, her professional competence and her capacity for interdisciplinary work.  At least this is how I see the situation and it made me feel even more dedicated to helping Victoria achieve the initial objectives that we set.  So when she asked me to help present the policy brief at the GLF, I was ecstatically and enthusiastically on board.

My enthusiasm met head-on with the reality of the Pavilions at the GLF.  They were like a handicrafts fair that is set up right next to a museum of art with well-advertised expositions by major artists.  I don’t mean to be pejorative.  But the reality was that the time of our presentation was in competition with events that involved well-known policy makers and organizations.  Furthermore, the specific presentations at the Pavilions were not announced on the program. So with shiny policy brief in hand, we made publicity plugs every time we could get the microphone in the sessions we attended on 5 December.  This meant that we needed to come up with good questions at these sessions and insist on getting the floor. We distributed lots of copies of the brief, and attracted people to our presentation. And as a side benefit, I met many interesting people with whom I would otherwise never have had the opportunity to talk such as a director of a division of the World Health Organization, journalists from the European Plant Science Organization, economists, heads of start-ups and funding initiatives, etc. Something turned off my general reticence for social interactions leading me to even participate in the evening speed-networking session.  I was armed with calling cards specifically conceived for this event and copies of publications that were pertinent to the meeting – in addition to the policy brief.

About a dozen of the thousands of participants of the GLF attended the presentation of our policy brief and participated in the discussion afterwards. But I don’t think that is the real indication of the attention that we generated.  The notion that plants can influence rainfall not only because of evapotranspiration but also via the microorganisms they emit is now out of the closet of science and is tweaking the interest of organizations involved in development. Via the network that grew from the Leuven meeting and the launching of the policy brief I am hearing about future activities including fora for advocacy and initiatives to set up field research projects that would involve the 5 consensus points of the policy brief. Furthermore, a second complementary version of the policy brief was crafted in collaboration with ICRAF and presented at the Rio Pavilion activities at COP21 (see pg. 6 of the summary of activites at the Rio Pavilion) that will likely lead to interest that we have yet to measure.

While writing this post, I can hear some of you saying “Yes, but…..”  The contents of the policy brief make the subjects seem simple and resolved when there is so much that we don’t know and numerous details for which there is still discord within the scientific community.  Admittedly, in the policy brief the summary of the facts concerning the power of plant-associated microbes to influence rainfall is a short sentence that would be accompanied by much detail and several nuances if it were for an audience of scientists.  Wordsmithing for an audience other than scientists is a challenge.  But I am of the opinion that at some point we need to bring attention to novel scientific ideas when they reach a certain stage of maturity, a stage that is sort of like adolescence – with pimples but with clear potential.  When is the best time for this? If someone knows a general rule, then I would like to hear about it.

To prepare this post, I discussed with Gabor Vali who remarked that the dilemma of knowing when to talk to the public about potential applications of research in environmental sciences reminds him of the history of weather modification. Specifically he notes:

The lessons that I’d take from that, from my participation in weather modification research and policy making, are (1) that the prospect of weather modification has been the basis for getting attention and funding to much research and engineering over the past ~66 years; (2) that unrealistic promises have stained the credibility of science and scientists in serious ways, (3) that enormous amounts of money have been spent on trying to prove and/or improve the potential for weather modification, (4) that even today the degree of certainty is minimal about being able to beneficially apply cloud seeding, and (5) that the large potential benefit/cost ratio continues to give rise to both research and operational programs.

According to the notions of weather modification and of bioprecipitation, weather and climate effects are expected from influencing ice nucleation in clouds. This led Gabor to wonder if the application of knowledge about biological ice nucleating particles to land management will progress more rapidly than the application of knowledge of other INPs to cloud seeding. Cloud seeding was advocated as early as the 1950’s by Irving Langmuir (Nobel Prize in Chemistry, 1932 ), inspired by the work of Bernard Vonnegut, yet there is still important controversy. But we have the good fortune to have this historical perspective as a reference. Furthermore, the economic incentives driving the interest in weather modification via cloud seeding are very different from the interest in climate benefits expected from land management. And perhaps most importantly, we are in an epoch where we can deploy the powerful tools of the internet to facilitate a collective debate that might foster efficiency in application of knowledge, reduce controversy and inhibit overselling.

Ice nucleators from vegetation in the Sahel: the impact of overgrazing


The search for ice nuclei with remarkably efficient activity has been a pre-occupation of the atmospheric sciences long before the recent interest in biological ice nucleators propelled this search into the limelight.  Some of the data and observations that constitute the collective knowledge about these ice nucleators are not available in accessible publications.  Russ Schnell has contributed some more of the gems from the collection of observations that he has amassed during his long career.  (For more information about Russ, see the post from 2015/03/04). The following observations concern sources of ice nuclei in the Sahel.

In 1973 at the height of the great Sahel Drought of the early 1970s, Russ noticed a satellite photo that showed a fenced area of some 50,000 hectares in central Niger, Africa, (black & white photo, lower center section) where vegetation was growing much better inside the fenced area than outside.  Outside of the fence the land was heavily overgrazed and even shrubs and trees cut down to feed goats (color photo, taken southeast of the place on satellite photo labeled “photo here”) The fenced property was later identified as the “Ekrafane Ranch”.


Russ suspected that that overgrazing had removed the most active biological ice nuclei and thus reduced precipitation that in turn exacerbated the drought. To test this hypothesis he sought and obtained funding from the Rockefeller Foundation and then for about a month in August-September 1974 traveled alone across the Sahel area of Niger, often on foot, collecting vegetation and soil samples.  He tested them for ice nuclei content using the method described by Schnell and Vali in 1976 (1) (referred to as the Univ. Wyoming report AR111 in Russ’s report to the Rockefeller Foundation).

In his report to the Rockefeller Foundation (2), Russ presented a series of freezing spectra for the vegetation, litter and soil samples illustrating that vegetated areas contained more active immersion freezing ice nuclei than nearby less-vegetated areas.  Interestingly, the most active ice nuclei (active at -7° C) were from vegetation closer to the Sahara Desert where all of the cattle and goats had died the two years before and vegetation was recovering. The results in the report were based on a partial analysis of the samples; a more comprehensive analysis of the data led to the same conclusions.

The drought ended in October 1974 and the Rockefeller Foundation lost interest in the project. It was particularly frustrating for Russ to not be able to assure the Foundation that the local source of active ice nuclei was possibly important in the precipitation process. Without any assurance of this importance, the Foundation was not interested in funding any further work.  Also, soon after Russ moved to Kenya, Africa to work for the UN in a different orientation – but he has kept all of his precious log books that contain the data from this trek in the Sahel.

Almost 40 years later, drought and desertification are rampant and are threatening major world economies as well as the developing world. If, as a scientific community, we needed to provide guidance for the best ways to exploit natural reservoirs of the most active ice nucleators to help fend off disaster, what would we say?  What key observations would we need to assure ourselves and to assure the end users of such guidance?



  1. Schnell R.C. and Vali G. 1976: Biogenic Ice Nuclei: Part I. Terrestrial and Marine Sources. J. Atmos. Sci., 33, 1554–1564. (see the Mendeley data base for the link to this paper).
  2. Schnell R. 1974. Biogenic and inorganic sources for ice nuclei in the drought-stricken areas of the Sahel – 1974.  Interim report to the Directors, Rockefeller Foundation, New York

Rainfall Feedback Maps: a website to explore rainfall patterns that might involve bioprecipitation


Recent research has led to the development of a time series analysis to assess feedback in series of daily rainfall data.  This analytical tool was applied to rainfall data from Australia and revealed that rainfall on one day can be significantly correlated with the probability of rainfall on subsequent days for up to 20 days.  Patterns of positive rainfall feedback mirror the patterns of accumulation of ice nucleation active particles that have been observed to occur after a rainfall.  Taken together, these observations are consistent with the phenomena involved in bioprecipitation whereby biological ice nucleation-active particles are enriched as a consequence of rainfall and then have the possibility to influence subsequent rainfall events.

The time series analysis used for this work provides a tool to characterize sites for their propensity for bioprecipitation. Hence, it offers criteria for selecting geographical sites for research  to understand the processes that underlie bioprecipitation and rainfall feedback – either via direct field measurements or via meta-analyses of how land use and geography can influence rainfall feedback. In light of the ready availability of daily rainfall data for certain continents and the automation of the calculation and mapping procedures for rainfall feedback indices that has been achieved, we have made maps of rainfall feedback indices across 1250 sites in the western states of the USA.  The new website makes these maps available, explains how to interpret the maps, will allow you to access the data resulting from our analyses, and provides information on how to make maps of other regions.

The website address is:

I encourage you to visit the website and deploy it as much as possible.

Happy navigating