麻豆传媒

THE Arctic is in a . The top of our world is heating up faster than anywhere else on the planet, setting new records for the speed and area of ice melt. We are on track this year to have sea ice coverages so far. It is a huge problem, because what happens in the Arctic doesn鈥檛 stay in the Arctic.

What鈥檚 more, the Greenland ice sheet, which alone contains enough water to raise global sea levels by 6 metres, is disappearing. The frozen Arctic soil and sediment, or permafrost, is melting, releasing more and more carbon dioxide and methane into the atmosphere. This year, vast wildfires in the peatlands of Siberia have blazed for more than a month, and the Arctic warming is playing havoc with weather systems in the northern hemisphere too. But if you prefer to think simply in terms of money, the economic impact of unmitigated Arctic warming by the end of this century was recently estimated to be . As US congressman Jerry McNerney says: 鈥淲hen it comes to the Arctic, we鈥檙e in deep shit.鈥�

You鈥檝e heard the slogans: we are living in a time of climate emergency. But it is no good declaring an emergency without summoning help. So here it is: let鈥檚 refreeze the Arctic. There are several imaginative ideas to manipulate its climate system to get the ice back. They won鈥檛 be cheap or easy, but some researchers argue that the crisis in the north is too serious not to at least investigate ways to engineer the return of the ice.

Climate intervention in the Arctic might be more necessary than it first appears because the region鈥檚 death spiral is a feedback loop. As the shiny ice melts, models and satellite images suggest we could get a sea . When the ocean is exposed, instead of reflecting sunlight, the dark water absorbs more of the sun鈥檚 heat. Over the past 30 years, this change corresponds to a warming equivalent to released by human activity during that time. The warming is weakening the polar jet stream 鈥� the fast-flowing, high-altitude air current 鈥� in the northern hemisphere, resulting in more鈥漛locked鈥� weather patterns, and corresponding droughts, floods and heatwaves.

The global risks are huge. 鈥淎llowing the Arctic to change in unrecoverable ways poses an enormous safety risk to communities around the world and could move the climate system beyond our ability to recover,鈥� says Kelly Wanser, director of , a geoengineering NGO based in Washington DC.

鈥淚t is no good declaring a climate emergency without summoning help. So here it is: let鈥檚 refreeze the Arctic鈥�

Of course, we could have prevented the Arctic from warming as much as it has if we had cut global greenhouse gas emissions when scientists first started advising us to do so, decades ago. But we didn鈥檛, and nor are we now. 鈥淚t鈥檚 a pious hope and anyway it would take a while,鈥� says , head of the Polar Ocean Physics Group at the University of Cambridge.

This is why a growing number of scientists argue that, if we want to save the Arctic, we need to intervene directly by manipulating its climate system. There are three main proposals for doing this: increasing the extent of sea ice; artificially brightening the surface of the ice to reflect more sunlight; and cooling the Arctic air by brightening the clouds to deflect sunlight.

All three ideas are forms of geoengineering: intervention in the environment on a scale big enough to counteract climate change. The concept bothers many scientists because they fear that the idea of a technological fix will undermine efforts to cut carbon dioxide emissions. 鈥淲ell, we鈥檙e not making them anyway,鈥� says , a sea ice physicist at the University of Washington in Seattle. 鈥淢aybe intervention would be positive, showing that we have the capacity to improve the environment.鈥�

For those advocating such action, a big concern is the methane already streaming out of the seabed as microbes break down thawed organic matter. 鈥淭he fear is that this will grow from being a set of methane plumes to an outbreak,鈥� says Wadhams. 鈥淪o we need to bring back the ice around the coastal seas, and that might save us from a catastrophic methane burst.鈥� As well as this methane trapped under the sea, an estimated 1 trillion tonnes of carbon are in the top 3 metres of Arctic soils. If only a small fraction of this reaches the atmosphere, it will overwhelm any cuts in emissions we have made. 鈥淚t seems that nature offers us a choice: instant methane from the seabed giving us a huge immediate burst of warming, or longer, slower warming from complex chemical processes as terrestrial permafrost thaws. Except that it鈥檚 not an 鈥榦r鈥�, it鈥檚 an 鈥榓nd鈥�.鈥�

The first potential solution comes from Steve Desch, an astrophysicist at Arizona State University. His plan is to during the winter, where it will freeze, thickening the sea ice and extending its coverage. This method was recently proposed to prevent the collapse of the Antarctic ice sheet too.

鈥淎rctic sea ice may be restored by brightening ocean stratocumulus clouds鈥�

Sea ice moves around, so Desch鈥檚 idea is to locate the windmill-pumps on sea ice in the north of the Arctic. This would help thicken chunks of ice that are then protected from melting when they move south. 鈥淲hile that may seem like an impossible task, since the Arctic is a very large place, we outlined a mechanism, using simple, brute-force, steampunk technology that is not impossible, but enormous in scope,鈥� he says. 鈥淚t鈥檚 not like a space mirror larger than the Earth or something. It鈥檚 pretty simple, but just a big job.鈥�

Desch has calculated that we would need 10 million windmills across the entire Arctic to refreeze it, at a cost of $500 billion. That is a huge sum, but just a fraction of the estimated $67 trillion economic impact of Arctic warming if we don鈥檛 act. Bitz has evaluated Desch鈥檚 idea in a paper currently submitted for publication. 鈥淭he physics can work,鈥� she says. 鈥淭he basic principles make sense. To me that鈥檚 promising.鈥� But so far, Desch only has a prototype windmill that works in the lab. For a true test, field trials are essential.

The second proposal for geoengineering the Arctic has had some success outside the lab. It involves covering the ice with shiny, white beads. The idea is that these microbeads increase the reflectiveness, or albedo, of thin, young ice, so protecting it from the sun. The leading advocate is Leslie Field, an engineer at Stanford University in California, who also runs , a non-profit organisation exploring methods of restoring Arctic ice, mainly using hollow silica microspheres. These bright, non-toxic beads are chemically and physically similar to sand but smaller, more like powder, with a diameter of about 65 micrometres (0.065 millimetres).

Field and her colleagues have tested the idea, most notably on about 4200 square metres of North Meadow Lake in Alaska. They have shown that the albedo by around 20 per cent and slow the ice melting. To cover 25,000 square kilometres of the Arctic with the stuff would cost about $300 million for the materials alone, says Field. This represents just 0.7 per cent of summer ice coverage at its lowest extent on record: 3.4 million square kilometres in 2012. Yet many questions remain, not least whether it works on sea ice 鈥� so far it has only been tested on frozen lakes. And what happens to the beads when ice melts? Some sink and are incorporated into the mud on the lake floor, says Field.

There are, however, concerns about the biological hazards of this approach. Bitz says she is worried about the ecological impact of adding millions of tonnes of silica to the Arctic. 鈥淔or me this raises a red flag,鈥� she says.

Ken Caldeira, who researches geoengineering at the Carnegie Institution for Science in California, has doubts about the workability of modifying the surface of the ice 鈥� whether by the methods proposed by Field or Desch 鈥� and about whether this could be an effective tool against climate change. 鈥淚 am highly sceptical that this approach will prove feasible and desirable at scales required to be climatically substantial,鈥� he says.

For Bitz, Wadhams and several other climate scientists who spoke to 麻豆传媒, the most promising potential intervention is one that doesn鈥檛 involve tinkering with the ice directly. Instead, it entails brightening the clouds over the Arctic.

The idea dates back to the 1990s, when , now at the University of Manchester, UK, started thinking about ways of limiting the greenhouse effect by reducing the amount of sunshine reaching the planet鈥檚 surface. Latham was fascinated by something called the Twomey effect, which describes how the amount of solar radiation that clouds reflect back into space depends on the concentration of tiny particles around which cloud droplets form. He realised that you could increase this concentration over oceans by with tiny droplets of salt water.

We know from satellite images of ship tracks 鈥� the equivalent of the contrails left by airplanes 鈥� that clouds can be seeded by the sulphate emissions from ships. Latham and his colleagues have produced computer models showing how Arctic sea ice may be restored by brightening ocean stratocumulus clouds. These large, rounded clouds are by far the most common kind seen in the Arctic, and are usually found in groups covering huge areas.

On paper, it looks promising, but testing it for real is quite another matter. To do so will require a system that can spray an ultra-fine mist of sea water into the lower atmosphere over a large area of ocean. Stephen Salter, an engineer at the University of Edinburgh, UK, has well-advanced plans for this, having developed proposals for able to deliver the spray, which he presented to the UK government鈥檚 Environmental Audit Committee鈥檚 2017 inquiry into Arctic sustainability. The thing holding him back is lack of funding.

For the price of Neymar

Shortly after I started corresponding with Salter, he sent me a photo of Brazilian footballer Neymar, beaming as his transfer to Paris St Germain was announced in 2017 at a cost to the French club of 拢198 million. Salter鈥檚 point was made clear when he detailed the costs of his cloud-seeding project. For the price of Neymar, researchers could conduct all the preliminary trials and then run an entire fleet of ships for two years that might start to restore the damage done to the Arctic.

鈥淎mong ideas to prevent Arctic collapse, the most viable in terms of the scale and nature of the problem involve increasing the reflection of sunlight from the atmosphere,鈥� says Wanser, who is also an adviser to the University of Washington鈥檚 . 鈥淗owever, our effective level of investment in sunlight reflection is zero. This leaves us with an enormous exposure to near-term climate risk and not enough fast-acting options to keep warming within safe levels.鈥� Several scientific assessments have identified marine cloud brightening as one of the most promising methods to manage sunlight levels, says Rob Wood at the University of Washington.

We don鈥檛 yet know how effective cloud brightening might be. But there is another reason to do this research: it could help solve one of the biggest puzzles related to how warm our planet could get (see 鈥�Cloudbusting鈥�).

In the meantime, the region continues to turn from white to blue. Wadhams, who has led 40 expeditions to the Arctic, has seen enormous change in that time. 鈥淲hen I started going to the Arctic, you could think of the whole of the northern hemisphere as a solid continent,鈥� he says. 鈥淚ce connected Eurasia and North America. But now you have blue ocean. Physically and psychologically, the world is fragmented, and I think that is having an important change in how people think.鈥�