Action to cool the Arctic is a common sense response to what is happening: the beginnings of abrupt climate change.
The long spell of wet weather here in the UK this winter is due to a stuck pattern of the polar jet stream, such that it frequently passes over us. Meanwhile the mid-US has been experiencing an extreme cold spell, as the jet stream meanders southwards in a gigantic loop.
Strong scientific evidence suggests that this jet stream behaviour, producing an increasing frequency of weather extremes at mid-latitudes, is primarily driven by Arctic warming; global warming is only a secondary, compounding factor.
Abrupt climate change under way?
If this is true, then as the Arctic continues warming much faster than the rest of the planet, we can expect weather disruption tantamount to abrupt climate change.
As crops fail there will be increasing food shortages, with worsening famine and conflict for many parts of the world. Food prices are already a factor in Middle East unrest.
Arctic warming is occurring in lock step with sea ice retreat, in what can be considered a vicious cycle. The sea ice has been retreating over the past thirty years, with a minimum extent in September 2012 down about 50% and the minimum volume down about 80% over that period.
The retreat of the sea ice exposes open water to absorb more sunshine, heating the water and causing further retreat from year to year, in a vicious cycle. Once the cycle has got going, both the warming of the water and the retreat of the sea ice accelerate.
Dramatic sea level rises
Thus another consequence of Arctic warming is a loss of the habitat for polar bears and other creatures which depend on sea ice for hunting. The efforts of Greenpeace to protect the Arctic ecosystem will come to nothing if the warming continues and the sea ice disappears.
A third consequence of Arctic warming is the ultimate disintegration of the Greenland Ice Sheet, creating a sea level rise of 6 or 7 metres.
As the sea level rises, the footings of the West Antarctic Ice Sheet will be unseated, resulting in further sea level rise in sympathy. The rate of glacier ice mass loss has been increasing over the past few years at both ends of the planet.
Methane emissions set to increase
Finally the Arctic warming will cause massive amounts of methane to be released, as the permafrost on land and below the seabed thaw.
Vast plumes of the gas have been seen arising through the water of the shallow East Siberian Arctic Shelf, and methane levels in the Arctic have been growing.
Methane is a potent greenhouse gas, with a global warming effect about a hundred times greater than CO2 over twenty years, weight for weight.
If the apparent exponential growth in methane continues, then methane could dominate over CO2 as the driver of global warming within 20 years.
It's already happening
These four effects of Arctic warming are starting to happen already. As the warming accelerates, so do these consequential processes.
Can a reduction of greenhouse gases help to prevent a rapid deterioration in the situation? Definitely not! The main 'positive forcing' agent is CO2 and it has a long life-time, of the order of hundreds of years.
The warming for existing CO2 in the atmosphere will last well beyond 2100, unless it is removed from the atmosphere, e.g. by rock crushing (see article by Schuiling).
But even with the most ardent efforts at CO2 removal, it will take decades to halt global warming.
On the other hand we need to halt Arctic warming in the Arctic on a much shorter timescale - before the sea ice practically disappears at the end of summer, which could happen within a few years.
How can we cool the Arctic quickly?
So how can we cool the Arctic quickly and effectively to save the sea ice? It is suggested that several methods can be deployed in conjunction, each utilising effects which occur naturally.
The cooling effect of volcanoes such as Mount Pinatubo when it erupted in 1991 has been well researched. It is known that ejected sulphur dioxide (SO2) forms an aerosol reflecting sunshine back into space.
Pinatubo sent megatons of SO2 into the stratosphere, with a global cooling effect of about half a degree over two years. Deliberately creating an aerosol in the lower stratosphere at mid to high latitudes should have a cooling effect in the Arctic.
If SO2 is used - and there are promising alternatives - the pollution effect will be negligible compared to what we have from coal-fired power stations in terms of health and acid rain.
By creating the aerosol well below the ozone layer, there is minimal danger of ozone depletion and enlargement of the ozone hole over the Arctic.
Modelling suggests that stratospheric aerosols may have an effect on the monsoon precipitation, but any such effect is likely to be dwarfed by the effect of jet stream meandering - implicated in the 2010 floods in Pakistan, the worst for decades.
It is this meandering that one would expect to reduce by cooling the Arctic with the aerosols.
Another way of reflecting sunshine before it reaches ground level is to brighten clouds with cloud condensation nuclei (CNN) of the right size. One way of producing the CNN is by creating a fine spray of seawater droplets which evaporate leaving tiny crystals of salt.
Professor Stephen Salter has suggested spraying from autonomous vessels which could be powered by wind and deployed in the North Atlantic to cool the ocean currents flowing into the Arctic.
A key advantage of this approach is that it uses only harmless natural materials - sea water and sea salt. It can also be stopped rapidly. Tell the boats to stop spraying, and the droplets are all gone within a week.
Ice thickening and snow brightening
The sea ice itself could be thickened in the autumn and winter so that it takes longer to melt in the following spring and summer. We know that multi-year ice takes longer to thaw than single-year ice.
One way of thickening the ice is to spray water on the surface; the water would freeze in the cold air.
We know that snow retreat is producing as much warming as sea ice retreat. So any method to produce, promote or preserve snow will help cool the Arctic. A simple method of treating snow has been proposed which will make the snow melt much slower while also brightening it.
Finally we can change the net heat energy balance in the Arctic by increasing the outgoing radiation, especially by removing those clouds which have a net heating effect.
An international effort is needed
None of these techniques is particularly expensive, but an international effort will be required to deploy them effectively.
The dramatic retreat of sea ice in September 2007 and 2012 are like wake-up calls from the climate system, indicating that the Arctic situation is changing rapidly, and if we don't act quickly it may be too late to prevent disaster.
We are prepared to contemplate the potential disaster for future generations which we are creating through CO2 emissions, but now we have a potential disaster for ourselves.
Action to cool the Arctic is a common sense response to what is happening: the beginnings of abrupt climate change. This is a rare opportunity for international collaboration, as was dealing with ozone depletion.
Everyone interested in preserving ecosystems and biodiversity should now support the necessary action.
John Nissen is Chair of the Arctic Methane Emergency Group.