Where is the global warming? After a rather long and hard winter this year, many Europeans ask this question. The media have been spreading the terrible scenarios of a human-made global warming for years. But in Europe and many other parts of the Northern Hemisphere, in April there was still a lot of snow outside. Reason enough to become doubtful. Seemingly. Actually, however, the winter of 2013 is perfectly fitting the picture drawn by climate science. To understand why, we have to answer a few preliminary questions first.
First of all, we are talking about global warming. That it is cold here, in Europe, does not mean a thing – e.g., last year, we also had a really cold winter, while, at the same time, the Southern Hemisphere experienced an extraordinary hot summer. This is partly due to natural fluctuation, which is also the reason why the warming trend is not constant. Instead, there are years when the global mean temperature does not increase that much, while other years are pretty hot indeed. The main specific culprit is the Pacific ENSO (El Niño-Southern Oscillation), a climatic phenomenon that influences the temperatures all over the world on a regular basis – in El Niño years, it is particularly warm, La Niña years are colder than the average.
Much more important than the “overlooking” of the tiny word global, however, is the general semantic weakness of the term global warming. Would the only consequence of our greenhouse gas emissions be higher temperatures, we wouldn’t have to worry that much. But the temperature increase is only the first link in a chain of effects which change the whole climatic system of the Earth. Therefore, the term climate change is much better suited for the discussion since it does justice to the complexity of the problem in a much better way than global warming. What begins with globally rising temperatures, goes on with changing precipitation patterns, changes in the boundaries of vegetation zones, changes in frequency and severity of weather extremes and so on. To boil climate change down to the sole increase in global mean temperature is equivalent to underestimating the problem.
Back to Europe’s last winter. It should be noted first that, seen globally, it was not really cold at all (March was the 8th warmest in the history of temperature recording). But let us focus on Europe and the rest of the Northern Hemisphere: why is it so that we experience such a hard winter in a warming world? Paradoxically, those vast amounts of snow and low temperatures are an indirect consequence of climate change (which is the reason why climate scientists tell us to get used to them). Since Earth is getting warmer at a faster pace the closer to the poles one is, we experience the highest temperature increases in the Arctic, which also has a very strong feedback mechanism. Warming causes the Arctic ice cover to melt, light-coloured ice (which reflects sunlight) is being replaced by dark water (which absorbs sunlight), which amplifies the original warming via an albedo effect. The consequences of the ongoing melting of the Arctic are manifold. One of them is disruption of the winter climate of the Northern Hemisphere, including Europe. The airmasses reaching us via the Atlantic Oscillation (AO) carry today much more humidity than they used to (without the “protection” through an intact ice cover there is increased evaporation over the North Pole). Furthermore, pressure gradients are moving, which leads to generally more cold Arctic airmass reaching us than we are used from the past. These disruptions are supposed to have the potential to make the winter of 2013 the new normal in Europe and other parts of the Northern Hemisphere. Thus global warming becomes climate change.
Not only does the recent winter not counter the reality of anthropogenic climate change – indeed, it is completely compatible with the predictions of climate science. Pull your socks up, the world is getting warmer!