"Every time we handle a sample, it’s terrifying - it only takes one mistake to ruin weeks of work.” 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. The ice core drilling station at Law Dome, 120 kilometres inland from Casey Station. Credit:AAP

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." Making that check has been no easy feat, and involved more than the odd "touch and go moment", he says. A savage round of cuts planned by CSIRO management, announced three years ago next week, brought the whole project within days of being axed. Public pressure at home and internationally ended up sparing many scientists from the chop, including possibly this project. Lately, the challenges have been mostly physical, including coping with the bitter cold - temperatures often drop below minus 20 degrees - and heavy snow drifts that come with working at Law Dome, some 120 kilometres east of Australia's main Antarctic base at Casey.

Etheridge has been involved in decades of atmospheric research and knew Law Dome had special qualities the scientists would need. In particular, the site happens to have some of the heaviest snow falls anywhere. “Right here, we have about 10 times the average snow in Antarctica - 120 centimetres a year versus five to 10 centimetres," Neff said. “It buries the ice much more quickly than anywhere else. It just piles and piles on top." Drilling ice cores to analyse the air trapped within the compacted snow has been routine for polar ice scientists for decades. In the case of a hydroxyl hunt, however, such air samples are particularly valuable. David Etheridge and colleague working in a blizzard at Law Dome. The researchers won't find the radical compound because hydroxyl is not stored for any length of time in a container, let alone for hundreds of years in ice. Rather, the scientists are after a proxy molecule - the carbon-14 isotope of monoxide - that indirectly will reveal the past abundance of hydroxyl.

Carbon-14 is produced by reaction with cosmic rays from outside the solar system, but the heavy snowfall at Law Dome acts "like a shield in an X-ray". The snow, then, protects the air in the deeper ice so that carbon-14 is not produced there by cosmic rays which would otherwise alter its level, compared with its original amounts in the atmosphere. Neff says there are no better places to drill. “It’s literally the only place on the planet where we can get large amounts of clean air that have not been compromised by this carbon-14 aspect that we are looking for," he says. Of course, getting to that evidence is hardly a ski in the back country.

Scientists typically sleep in mountaineering tents, tucked in a summer sleeping bag, inside a winter one. Snow drifts are such that staff have increasing difficultly over time fighting the snow drifts, Neff says. The crew have worked about 77 days straight to complete six drilling operations, extracting about 5 tonnes of ice. The average of the three deepest drills has secured the scientists ice dating from about 1875. That's early enough to capture the conditions of the air before the biggest surge in greenhouse gases kicked in. Methane emissions, for instance, have risen about 200 per cent since the late 1880s, Neff says. Inside the drill tent with the ice core. Credit:Joel Pedro

Humans have also released a host of industrial chemicals with various abilities to warm the planet, affect its stratospheric ozone layer, and contribute to local pollution over that time, all of which may have added to hydroxyl's cleaning load. So delicate are the experiments, though, the drills can't use drill fluids that would otherwise have allowed them to go deeper to, say, 1750 when the industrial era roughly began. That sensitivity to possible contamination also extends to placing the science tent some 50 metres upwind of the other buildings - basically modified shipping containers - to avoid pollution from the camp's diesel generator. The work can be intense not least because the ice has to be treated immediately it is extracted to preserve as much as possible the purity of the cores. “They become like hot potatoes, where all of a sudden they are at the surface and are being bombarded by the full cosmic ray flux,” Neff says.

Rather than ship the ice thousands of kilometres to distant labs, it is melted and the key evidence placed in stainless steel tanks. About 20 of them, weighing about 10 kilograms each, will make the journey to Casey and beyond when the camp packs up in coming days. Neff, who is also a geologist, says the work has gone better than expected. “We’ve got absolutely everything we wanted to get done," he says. The samples "have all been absolutely perfect and cleaner than we thought”. At least another year of testing awaits, however, including at the ANSTO nuclear facility on Sydney's south-west fringe. Etheridge, who helped provide the Sun-Herald and Sunday Age with a tour of CSIRO's world-renowned air archive at Aspendale in Melbourne's sandbelt last week, says his "gut-feeling" is that hydroxyl abundance will be shown to be on the skids.

"From my reading of the evidence and the chemistry, I would expect to see a decline over the industrial period of hydroxyl. I would expect it to have decreased," he says, stressing that the results from the current project have not been tested. “I’m looking forward to being found wrong." The findings would be strengthened by similar work in the northern hemisphere, such as drilling into Greenland's ice sheets although those cores are likely to be much dirtier than in the Antarctic. The implications, though, of proof of a reduced ability to destroy methane - which now has a life in the atmosphere of about a decade - would be profound, depending on the scale of any decline. Apart from raising the warming potential of methane - whether released from coal mines or natural gas fields - the potential for hydrogen to serve as a "clean fuel" could also be placed in doubt. (Labor this week floated a $1 billion plan to create hydrogen export zones in Queensland to be powered by a massive increase in renewable energy.)

"Hydrogen is a very leaky molecule and we’d have to expect that there’d be some leakage in its production," Etheridge says, adding that hydrogen itself has a greenhouse gas effect. “It may not be of any significance, but we don’t know.” Neff says that while being away from his family for 100 days is tough, he's proud that his work is going towards answering some of climate science's biggest questions. "We don’t want to be operating blindly, [about] how much of an impact we have on the entire earth system," he says. Etheridge likens his team's work to that of space exploration, where scientists pick up information that proves to be useful for something later on that can't yet be anticipated.