Geoengineering, early warnings, and a dash of Victorian science
A recent article on geoengineering in the New York Times sent me back to my aerosol roots – and research that dates back to Victorian times
This is not an article about geoengineering as such. But it is inspired by one.
And so that’s where I’ll start.
A couple of days ago, the New York Times published a long-form article on how the US is building an early warning system to detect attempts to “geoengineer” the climate.
The initiative is being spearheaded by the National Oceanic and Atmospheric Administration (NOAA), and consists of a global network of scientists who regularly send monitors up into the stratosphere to measure aerosol concentrations.
The idea is that, by measuring baseline aerosol concentrations, it’s possible to tell if a nation has unilaterally released plumes of fine sunlight-reflecting particles into the upper atmosphere — a relatively cheap and easy way to temporarily reduce the amount of solar radiation reaching the lower atmosphere.
It’s been known for some time that stratospheric aerosol plumes from volcanic eruptions can lead to temporary cooling effects. The eruption of Mount Pinatuba in 1991 for instance was estimated to decrease global temperatures by around 0.5 degrees Celsius. And previous massive eruptions have been associated with both local and global cooling effects.
Inspired by this, scientists have been actively looking at intentionally injecting aerosols into the stratosphere to take the edge of climate change — usually sulphate aerosols. But the ethics and politics of such geoengineering approaches are far from clear — especially when the global consequences of unilateral actions are highly uncertain.1
Given this, it makes sense that NOAA and other organizations are developing techniques and networks to monitor stratospheric aerosol concentrations, and flag anomalies that may indicate someone’s covertly trying to tinker with the climate.
As the New York Times article notes, this is currently being done by sending sophisticated aerosol monitors up into the stratosphere tethered to helium balloons. And this is where the aerosol physicist in me kicked in while reading the article — because while the global aerosol monitoring approach being pursued is new, efforts to measure concentrations of fine particles in the atmosphere date back to Victorian times.
In 1890 the Scottish scientist John Aitken presented a quite wonderful paper to the Royal Society of Edinburgh titled “On the Number of Dust Particles in the Atmosphere of certain Places in Great Britain and on the Continent, with Remarks on the Relation between the Amount of Dust and Meteorological Phenomena.”
The paper drew on several years’ work developing a device for measuring the concentration of fine particles in the atmosphere. These culminated in 1889 with Aitken taking a trip around Europe with a portable version of his “dust-counting apparatus”. While traveling he made meticulous measurements of aerosol concentrations in locations as varies as Cannes France, Bellagio Italy, Lucerne Switzerland, the Eiffel tower, and the peaks of Mont Fenouillet in France and Ben Nevis in Scotland (a link to his measurement notes are included in the postscript below).
Aitken’s research was some of the earliest to systematically monitor fine airborne particle concentrations and explore their correlations with human activities and climate, and his research still underpins approaches to measuring concentrations of fine aerosols used today.
Back in 2015 I wrote about his work in the journal Nature Nanotechnology in the context of modern day nanoparticle analysis. It remains a favorite paper of mine (despite a rather sad number of citations) as it shows how what we often think of as cutting edge innovation often has its roots in research that goes back decades —and over a hundred years in this case.
As I wrote back then, “Aitken's portable particle counter continued to be used widely for the next 50 years (3), and paved the way to its modern counterparts — including the portable condensation particle counters that now form the basis for routine workplace nanoparticle concentration measurements (4). And the condensation counting technique he invented is still used as the basis for measuring nanoparticle size distributions through techniques such as differential mobility analysis.”
This connection between the present and past of aerosol measurement still fascinates me — all the more so because the devices being deployed by NOAA are part of a monitoring provenance that dates back to the groundbreaking work of scientists like John Aitken and his contemporary Lord Rayleigh (aka John William Strutt, 3rd Baron Rayleigh).
But what I found even more interesting looking back at his work as I prepped for this article, was Aitken’s speculations on the associations between airborne particles and climate in his 1890 presentation to the Royal Society of Edinburgh.
In the paper of his presentation, Aitken speculates at length — based on his measurements — on the association between atmospheric aerosol concentrations and ambient temperatures. Because he was basing his theories on lower atmosphere aerosol concentrations, his ideas run contrary to what we now know about stratospheric aerosol. For instance, he strays at one point into considering whether an increase in cosmic dust in the atmosphere could lead to global warming, and a lack of it to global cooling. And yet, 135 years after he first presented his research, his thinking is nevertheless thought provoking.
Take this passage for instance:
“If dust increased the day temperature and decreased the fall at night, then the mean temperature will be increased by a large amount of dust. Can it then be proved from general meteorology that this is the case? Do inhabited countries have a higher mean temperature than uninhabited ones, other things being equal; or has the temperature of these islands [referring to the UK] risen since coal has come into such extensive use; or is the temperature of a place higher when the wind brings dust-laden air to it from a populous district than when it brings pure air; or has the temperature in the populous parts of New Zealand or Australia increased with the increase of population? Unfortunately this is a case where, while a positive reply might support the conclusion, a negative one does not weaken it, because the dust from human habitations keeps near the ground, and if there is no protection above it, its effect will probably be, not to keep up the night temperature, but rather to lower it, on account of the increased radiating power of the atmosphere caused by the dust.”
The effect Aitken speculates about is the inverse of that which proponents of geoengineering using stratospheric aerosols depend on. But the recognition of a connection between airborne particles and air temperature — and the likely impact of human activities on this — is relevant to the history of research on anthropogenic causes of climate change.
It’s a useful reminder that advances which sometimes seem innovative and cutting edge, often have their roots in research that goes back decades — and often more.
And on that note, it’s worth finishing with this quote from my 2015 Nature Nanotechnology article on Aitken’s work:
“A few years ago, while teaching a science communication class, I asked my students to write an article based on a paper of their choice that was published several decades ago. There was an awkward silence. Until someone chimed in “can we trust papers more than a few years old?” Admittedly, the student was in a programme where the state of agreed on understanding is somewhat 'fluid'. I was still taken aback though.
“I find myself having a comparable response when early research relevant to nanoparticle characterization is similarly discounted. Aitken's work may have preceded modern nanotechnology by a century and more, and early research on electron microscopy occurred decades before 'nano' was trendy. Yet this doesn't mean that this early work was irrelevant. To the contrary, it eloquently demonstrates that seemingly novel challenges don't always demand novel solutions, and sometimes, the key to moving forward safely, is to look back at what's already known.”
Postscript
The stand-alone published version of Aitken’s 1890 paper is, sadly, behind a paywall. However, it can be read for free in the Collected Scientific Papers of John Aitken, courtesy of HathiTrust.
For anyone interested in the history of science and the evolution of aerosol science, these papers are highly recommended reading.
I also thought I’d include the table of measurements from Aitken’s 1890 paper — more as a quite delightful record of observational notes on aerosol concentrations on a jaunt around Europe from 1889 than anything else:
And as I mentioned back in 2015, it would be fascinating for someone to replicate this set of measurements now!
I started writing about geoengineering and responsible innovation back in 2009, not around stratospheric aerosols (that would come later), but about one of the first large scale experiments to use ocean seeding to sequester carbon dioxide from the atmosphere.