CSIRO Team Exploring Critical Question Through Ice Core Data - Can Atmosphere Remove Non-CO2 GHGs
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In fact, the findings of the six-year project - led by senior CSIRO atmospheric scientist David Etheridge and Vas Petrenko from the University of Rochester in the US - may carry their own measure of terror, depending on how they turn out. The role of carbon dioxide, the primary greenhouse gas, has been known for more than a century, including how it is eventually removed from the atmosphere by absorption into the oceans or by terrestrial plants.
But what has actually happened to some 40 other gases, including methane, hydrofluorocarbons and ozone-depleting chemicals, over the decades since industrialisation turns out to be rather less well understood. "We know pretty well how [these gases] are produced. We need to know how quickly they are removed," Etheridge says from the rather warmer confines of Melbourne this week. "Without that, we’ve only got part of the puzzle, part of the equation.”
The quandary in question goes something like this. We know hydroxyl radicals - which bond oxygen and hydrogen - act like atmospheric scrubbers, destroying non-CO2 greenhouse gases such as methane. Those gases contribute about a third of the extra warming we're inflicting on our planet by trapping additional heat from the sun in our atmosphere. Hydroxyl is naturally produced in the atmosphere but so reactive that a radical lasts only about a second before destroying a pollutant molecule, and itself.
"Because hydroxyl is so variable, with such a short lifetime and so variable in time and space, it’s actually hard to quantify even in the modern atmosphere,” he says. More to the point, though, we have little notion of whether this critical cleanser has increased or decreased in abundance since pre-industrial times - with implications for future emissions. The oxidation process involving hydroxyl is actually crucial at keeping methane “in the supporting role that it’s in, rather than actually becoming the leading troublemaker for warming the atmosphere", Neff says. The implication - depending how the results play out - could include requiring a recalibration of the major climate models that underpin the Paris climate agreement that almost 200 nations have signed up to. "All of [the models] are making an assumption about the fundamental reactivity [of hydroxyl in] the atmosphere before the year 1990," Neff says. “This is the first actual check on that part of those models."
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https://www.smh.com.au/environment/climate-change/terrifying-scientists-dig-deep-for-missing-piece-of-climate-puzzle-20190125-p50tjs.html