It is around this time every year that I start obsessively checking the National Snow and Ice Data Centre (NSIDC) website to look at the latest measurements of Arctic sea ice. I have no idea why I do this – I’m not an expert on ice, I have never been to the Arctic, and I certainly don’t like the cold. But there is something awe-inspiring about the dramatic changes taking place in this region, and I cannot help being struck by the idea that humans may play a dominant role in transforming this most hostile of environments. What is more, this year is already breaking the record for the lowest observed sea ice extent, and there are still some weeks to go before this melt season ends.
What does this phenomenon have to do with hydrology? On the surface, not much. But look down into the oceans, or higher up into the atmosphere, and the potential for a melting Arctic to affect other parts of the world becomes apparent. One of the main impacts is that the increased warming of the Arctic relative to the tropics will mean that the temperature gradient (the difference in temperature between the tropics and higher latitudes) will decrease, with this gradient being a major driver of atmospheric and oceanic circulation. Thus, circulation patterns in the northern hemisphere might change, affecting where it rains and by how much. A second impact is that although melting of the ice cap will not change sea levels directly, the increased temperatures in the region might cause an increase in the melt rates of the surrounding ice, including a possible acceleration of the melting of the Greenland ice sheet. This melting could in turn cause global ocean levels to rise, potentially increasing flood risk in many coastal regions.
It is therefore concerning that climate models have been poor predictors of the speed of the transformation which is taking place in this region. As can be seen in this figure which was presented on the NSIDC website several weeks ago, although climate models do tend to agree that the Arctic sea ice will melt, they have underestimated the speed of the recent change. Given that our projections of future rainfall patterns also come from these models, this might mean that the potential implications of the Arctic melt on the hydrological cycle might also be underestimated, or at the very least we must accept that we cannot understand all the possible effects of these remarkable changes.
Sometimes one can only stop and reflect on the power of humanity to modify our environment, where a region which was practically inaccessible to explorers as little as a century ago is now being transformed by us before our very eyes.