Dr. Christine Jones is raising some ire. Her contention is that because carbon dioxide comprises just 0.4% of the atmosphere, while water is 80% by mass and 95% by volume, the former is trivial while we really need to be focusing our climate-change efforts on water vapour. Walter Jehne and Peter Donovan also make similar claims.
At first glance, I found her logic intriguing: it does seem, at first, appealing to equate ‘most abundant’ (i.e. water) with ‘most important’. So I brought it up at our lab meeting and everyone was pretty adamant that because water vapour is so variable – basing the argument on differences in humidity – it can’t possibly be considered the most important greenhouse gas, and that whatever science she was citing was bunk, or misunderstood. That still didn’t really satisfy, because I wasn’t clear if we were all (me, the lab, Christine) referring to atmospheric concentrations, e.g. partial pressures, relative volumes or masses, or local concentrations, e.g. percent humidity, or what, and I wasn’t clear for myself whether it mattered or not. So I left it ‘for now’ and continued writing up my article summarizing the weekend’s workshop. I brainfarted out a place-holder paragraph to note the controversy without landing my foot in either boat, for now:
“One point of Christine’s work, though, raises a lot of eyebrows, and that’s her contention that water vapor, not carbon dioxide, is the critical greenhouse gas that we need to be working to mitigate. A quick read through the literature reveals this is anything but a settled question, and the controversy has been going on for over a decade, with American Chemistry Association, NASA, NOAA, Yale Climate Connections, and other climate research bodies weighing in.”
The ‘over a decade’ remark alludes to a number of articles written in 2008, namely on those websites listed above, but also one in 2004, in addition to others in 2011 and 2016. Clearly the conversation has been going on for awhile; Forbes, The Guardian, New Scientist, Skeptical Science, and Regeneration International (via the AgJournal article) have all weighed in since.
The gist of the counterargument, i.e. water vapour isn’t the gas we need to worry about, lies in the distinction between forcing and feedback. The Yale Climate Connections was the best layperson review for me on this topic, if you’re not clear already. So reducing water vapour, which has been increasing since the Industrial Revolution along with other key greenhouse gases carbon dioxide, methane, and nitrous oxides, could be advantageous in reducing the feedbacks, it won’t do anything to impact the forcing effects of increasing the other (non-compressible) gases.
Here’s the rub, though: surface warming due to loss of vegetation and desertification is increasing both the amount of water vapour entering the atmosphere by evaporation, and the temperature of the air, allowing it to hold more water as vapour (increased humidity with rising temperature). What Christine Jones is proposing – keeping soils covered year-round with green, growing plants – has enormous capacity to greatly reduce surface soil temperatures. (Here’s a good overview of the surface cooling effects of vegetation on climate). Furthermore, those actively growing plants are busy taking up carbon dioxide and, if her claims are accurate, stacking that carbon deep in the soil, locking it away in soil biology and organic complexes, i.e. humus.
I’m not going to say that it doesn’t matter if her science on the carbon dioxide vs. water vapour is right or wrong; it does, because if she gets that wrong it throws into question her expertise and credibility on all of the other work she speaks on, including the roles of quorum sensing, epigenetics and self-organization in soil microbial communities. The water vapour conversation is controversial, for sure, and for all intents and purposes from what I have read and gleaned from colleagues working in climate-related fields, she’s got it wrong: the greenhouse gases carbon dioxide, methane and nitrous oxides, are the ones we need to be worrying about in terms of emissions reduction, changes to cultural norms and technology, and agricultural reform. We can impact water vapour patterns and distribution by revegetation, especially in trees, which is what Walter Jehne and Peter Donovan (also) actively support; but we ignore the other gases at our peril (see Yale’s discussion on forcing and feedbacks).
However, the impacts of heeding her advice for keeping soil covered year-round, while adding and supporting existing soil biology and plant biodiversity, are good for both the climate and agriculture, in terms of capturing and storing carbon dioxide through the liquid carbon pathway, while reducing surface temperatures, evaporative water losses, and nutrient loss due to run-off and leaching. All these lead to productive gains for farmers, reduced inputs (less pollution, less money, less time), improved ecological health, greater soil water storage (less irrigation), and so on.
For now, I’m going to have to be content to pick and choose through the information she’s offered us. None of us get it right all of the time; most of us get it wrong more than we think; and maybe the best we can hope for, is to get it right when it counts the most.