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Hi all, The PIOMAS sea ice volume trend for the month of September indicates a zero in January 2015. Thus we can expect the ocean to be free of ice for September of that year, according to that trend. http://www.guardian.co.uk/environment/2012/oct/03/track-ice-free-arctic-ocean-2015 The repercussions of allowing the sea ice to disappear are terrifying. In the letter I focus on food security. Urgent action is needed by the G20 governments to cool the Arctic, which will involve cooling technology called SRM geoengineering. Without rapid action, to cool the Arctic in spring and prevent further collapse of sea ice next summer, we risk passing a point of no return because of the non-linear trend. We have no option but to intervene as quickly as possible. But will our government face up to what is happening and call a G20 summit to deal with this emergency? Your support is needed - we have a petition to world leaders, which you can sign. You should find it on our web site: www.ameg. me. For the kind of action we envisage, see footnote [1]. Cheers, John [1] The action needed is not intrinsically dangerous, as some would have you believe.We have been geoengineering for years, producing both cooling and heating effects. The greenhouse gases produce a heating effect, whereas aerosols have tended to produce a net cooling effect, also known "global dimming".There are several technologies that have been suggested for countering global warming, but could be used more specifically to counter Arctic warming and sea ice retreat. They are either based on aerosols or on cloud brightening. And they are based on observed phenomena -- not rocket science.Hopefully several techniques would be used in conjunction, so that the combined effect can be optimised geographically. The marine cloud brightening technique is particularly benign as it relies on sea salt spray, as produced round the coast. It can provide cooling effect in specific places.All potential side-effects can be avoided by modelling the deployment.Salt water is sprayed into the atmosphere from ships or islands.For cooling the Arctic, marine clouds over the North Atlantic and North Pacific would be brightened, to cool the surface water beneath, such that ocean currents would carry the cooled water into the Arctic and allow sea ice to form (also strengthening the global conveyer).In theory such cooling could be scaled up to produce several petawatts of cooling power. However the technique has not yet been subject to experimental trials, so the efficacy has not been established.A determined programme could bring such technique into full-scale cooling by spring 2014. The most rapid means of cooling the Arctic is by producing a reflective haze, to reflect a proportion of sunshine back into space. One could either increase the existing burden of reflective aerosol haze in the troposphere (lower atmosphere), where it washed out in a few weeks, or put a lesser amount in the lower stratosphere, where it could last for a few months.A simple way of increasing the haze in the troposphere is by creating longer-lasting contrails from commercial aircraft.It is well-known that global warming increased after 9/11 as thousands of aircraft were grounded.However this is not going to have nearly enough effect; so the aerosol burden has to be increased by direct injection of a particulate (such as a fine TiO2 "white paint" spray) or an SO2 precursor, ideally into the lower stratosphere. Mount Pinatubo injected enough SO2 into the stratosphere to cool the planet 0.5 degrees C over two years. We would not have to put so much into the stratosphere, as we just need to cool the Arctic.As for cloud brightening, the technique is unsuitable for the Arctic itself. The injection has to be such as to cool the currents and rivers flowing into the Arctic, thereby cooling the Arctic indirectly. It is certainly doable, but requires the mentality of a war effort to be sure of success.