Recent extreme heat waves reinforce concerns that the slow pace of action against climate change is inadequate, raising interest in new fixes called geoengineering, but this warrants caution.
Proposed geoengineering fixes fall broadly between reflecting sunlight and heat back into space, or sucking carbon dioxide out of the atmosphere.
Perhaps the biggest concern among its detractors is the danger of distracting from the main task of cutting greenhouse gas emissions, given no geoengineering technique is guaranteed to work at scale and some can clearly make the problem worse.
The difficulty with that view is it presents the problem as a binary one, where humankind must choose between either entirely unassisted cuts in greenhouse gas emissions, or else rely on geoengineering.
In fact, techniques which remove carbon dioxide from the air can complement cuts in greenhouse gases and so buy time, although there are still huge uncertainties about whether they can be achieved safely and cheaply at scale.
And not all technologies are the same: climate fixes are a spectrum where some are clearly risky, such as spraying aerosols into space which at scale could cool the earth but also trigger unpredictable droughts.
More research clearly makes sense, with caution not to create a false illusion of climate action or embark on a slippery slope of deployment.
The notion of a slippery slope is related to that of "path dependence."
Stanford University economist Paul David gave that notion wide currency in his paper, "Clio and the Economics of QWERTY", published in the American Economic Review in 1985.
David explained the idea most simply as "one damn thing follows another", and used the example of how the sequence of letters on a keyboard, spelling "QWERTY" from the top left, has persisted since 1873.
Part of the origin of the keyboard's top row was simply a gimmick to help sales staff find all the letters of the name of the new contraption, "type writer", and type them quickly.
David found the top row of letters cemented itself, despite easier ("socially optimal") alternatives, after it became embedded in training manuals.
He pointed out that it was impossible to say with certainty in advance what technology or keyboard will eventually be dominant.
In the case of geoengineering, clearly a research program would make a climate fix a contender, but not for supremacy against emissions cuts or the development of low-carbon renewable energy.
In January David co-authored a paper on "Designing an Optimal 'Tech Fix' Path to Global Climate Stability."
The authors analysed the best timing for shutting down conventional fossil fuel energy, taking into account a growing risk of climate crisis and the greater productivity of fossil fuels versus the higher cost of low-carbon energy.
He and his co-author only briefly mentioned geoengineering as a potentially useful, back-stop insurance in case it was needed, with no suggestion it might exclude the development of low-carbon technologies.
Proliferating geoengineering research has followed a review by Britain's science academy, the Royal Society in 2009, which called for a publicly-funded program.
A United Nations panel of scientists, the IPCC, will assess geoengineering for the first time this year in its latest climate update.
The Royal Society report studiously toed a middle line between recommending research including field experiments, while stressing the need to pursue more ambitious emissions cuts.
"There is no credible emissions scenario under which global mean temperature would peak and then start to decline by 2100," said its report, "Geoengineering the climate: science, governance and uncertainty."
"Unless future efforts to reduce greenhouse gas emissions are much more successful than they have been so far, additional action may be required should it become necessary to cool the earth this century."
Broadly, it found techniques which reflected sunlight back into space were quick, impacting within a year or two, but risked creating new climate imbalances and did not address the root problem of rising atmospheric carbon.
Approaches which removed greenhouse gases from the atmosphere acted far slower, and so were no use as a plan "B" against unfolding catastrophe, but were also less risky.
Technical hitches centre on the difficulty of deployment at scale, given the volume of annual carbon dioxide emissions, where further research seems needed.
For example, one carbon removal approach is to expose natural or manufactured carbon absorbents to the atmosphere, called air capture.
The trouble with natural absorbents is the amount of quarried rock required to impact annual global emissions of more than 34 billion tonnes of carbon dioxide, equivalent perhaps to a mountain or two, while an industrial approach depends on an energy-intensive process to reclaim the CO2 from the absorbent.
The most discussed approach to reflecting sunlight is to inject sulphur dioxide into the atmosphere, creating reflective aerosols which mimic big volcanic eruptions known to have cooled the earth in the past, but which may also trigger droughts.
The Met Office Hadley Centre in the UK showed a link between more atmospheric aerosols, a cooler Atlantic Ocean and less rainfall over parts of Africa, in their paper "Aerosols implicated as a prime driver of 20th century North Atlantic climate variability" published in the journal Nature last April.
The paper illustrates how public support for geoengineering research must be extremely wary of engineers itching to try out a new toy.
This article was originally published by Reuters. Republished with permission.