The cold wave that swept through parts of Europe, especially Ukraine, Czech Republic, Russia and Poland wreaked havoc killing more than 600 people. This may seem unusual during a time when everyone is talking about ‘global warming’, but it is really a powerful reminder that these events still continue even as the global temperature rises. While it appears unknown as to whether this cold snap was in any way directly attributable to human-induced climate change, the primary culprit – Arctic Oscillation – isn’t unfamiliar to scientists as it plays a large role in global climate change. According to NASA, the Arctic Oscillation is basically ‘a see-sawing pressure system over the North Pole’ and recently it has been responsible for driving cold air from north to southern latitudes, hence the reason why it was snowing heavily in Tripoli, Libya.
The Arctic Oscillation definitely has a major influence over the Earth’s climate system(s) capable of causing extreme weather events in many different parts of the world. Here are some satellite images from NASA of Korea, the UK and US taken during the extremely cold weather they experienced in 2010.
The Arctic Oscillation (AO) has a negative and positive phase. The negative tends to favour colder weather in Europe and the US, but it is currently not known how it switches from one phase to another. When this switch does occur it fundamentally changes the circulation of the atmosphere and the way winds blow, according to Mark Serreze with the NSIDC. When it is in a negative phase pressure is higher than normal in the Arctic and lower than normal over mid latitudes and when it is positive (you guessed it) air pressure is lower than normal in the Arctic and higher than normal at mid latitudes. Some decent graphics that illustrate how this process works are available here.
But the AO isn’t the only factor, unusual jet stream activity has also been blamed. There is however an interesting coincidence between these cold waves caused by the AO and the rapid loss of sea ice in the Arctic. Sea ice loss may actually encourage winters during predominately negative phases of the Arctic Oscillation. If this is the case then ice loss in the Arctic could actually lead to warming there while causing colder winters in Europe and elsewhere. Whether this is indeed the case will be interesting to see in the future, but also useful for understanding how to prepare for these kinds of extreme events.