The declining areal cover and thickness of summer ice in the Arctic Sea continues, with 2012 shaping up to be another record-breaking year. Read the BBC summary here. These declines are of course predicted as a consequence of warming air temperatures due to anthropogenic global warming, but what really alarms me is the speed at which it is progressing. Basically, ice loss is accelerating every year, and has been since we noted a drastic speed-up in 2007. The consequences of an ice free Arctic will be far-reaching. First there are physical consequences. Losing the ice reduces the regional albedo, and creates a feedback that will continue the acceleration. Furthermore, thinner ice means that more light penetrates into the depths, warming the water beneath. The region's biology is also changing, and this too will accelerate. Warmer, brighter waters will most likely increase biological productivity in the Arctic Sea, which will be good news for some human industries, but isn't good news for all. The opening of the seaway, and increasing productivity, will change the ecology of the region, displacing many species, while allowing invasion from neighbouring waters in the northern Pacific and Atlantic. Geerat Vermeij and I wrote a predictive paper about this, oh, 4 years ago now. It is difficult to predict exactly what the consequences of those changes will be because of the problem's complexity, but they will be large. And finally, of course, opening the sea exposes many many resources of interest to humans, including fossil fuel deposits and shipping lanes. Let the wrangling begin. Noe note though is that the Arctic Sea ice melting will not contribute significantly to sea level rise; that ice is already in the ocean.

Our planet continues to change in response to global warming, and it seems that some of those changes are accelerating. I cannot be certain, and we will only know this in hindsight, but in my opinion we are beginning to cross thresholds. The time for discussion is long past. Now is the time for increased mitigation and implementation of adaptive strategies. I don't think that we are yet at the point where we need to consider drastic measures, such as extreme geoengineering. But, in the same way that a failure to agree upon and implement effective mitigating measures has brought us to this point, we may well be on our way to addressing this problem with technologically challenging, ecosystem-altering, economically difficult and socially painful actions.

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