Warm Arctic, cold Britain

An email this morning from the UK parliamentary press office draws my attention to an Environmental Audit Committee meeting planned for next week. This evidence session will hear Met Office chief scientist Julia Slingo address the question of whether there is a causal link between warming of the Arctic and recent cold winters in the British Isles.

Such weather behaviour is understood as being due to disruptions in normal patterns of air flow at high altitudes, but we do not understand why these so-called blocking anticyclones develop in the first place. For a graphical illustration of the meteorological principles, I recommend watching the first episode of a new BBC science documentary Orbit, in which Kate Humble and Helen Czerski explore the relationship between Earth’s orbit around the Sun and the weather.

Weather forecasts have in recent years made increasing reference to the jet stream, and for good reason, as it is this narrow, high-speed, high-altitude air current that controls surface wind patterns beneath it. Recent icy winters in a region which is normally warm and soggy have coincided with an unusual southward kink in the jet stream. This disrupts the usual stratospheric flow, blocking the prevailing westerly winds, and allowing in colder, drier air from the east.

That much is known, but what we do not yet understand is how these often spontaneous weakenings of high-altitude flow arise. Such unpredictability plays havoc with weather forecasting, and the Met Office is unjustly slammed for failing to failing to get it right. And then the climate loonies claim that global warming is a fraud, and we are instead heading for a new ice age.

For those who are interested, and willing to explore beyond the usual click fodder sources, the Met Office regularly blogs about the science behind its work, and the practical challenges involved in weather forecasting. The truth is out there, as best we know it.