There has been much debate over the causes of excessive snow in the winter of 2009 and 2010. Much of northern European experienced a colder than average winter and many meteorologists have put this down to the El Niño phenomenon in the South Pacific. Others have argued that it was caused by climate change while still more have suggested that the winter is evidence that climate change is not happening. The difficulty in analysing the causes shows just how hard it can be to understand the complexities of the global weather system.
El Niño is the name given to a periodic event that affects temperatures in the South Pacific. Its exact causes are unknown, though it is generally preceded by a failure in Walker circulation. Walker circulation is the process that governs trade winds in the tropics; hot air rising near the equator diverges at high altitude and falls to Earth at a latitude of around 30N or 30S, before rushing back towards the equator over the surface to fill the gap left by the ever rising column of air there.
When this regular circulation of air begins to fail, it can lead to a build up eat over the normally cool South Pacific. The South Pacific is a massive reservoir for heat and changes there can have a massive impact on winds, and therefore weather conditions, around the world.
El Niño occurs on average once every five years, though it is not regular and gaps between its occurrence range from two to seven years. It generally lasts between nine months and two years and can cause unpredictable weather around the world. In January 2010 it was blamed for the unusually cold winter and large amounts of snow; yet others have offered other suggestions.
The winter has polarised views in the Climate Change debate. Some have emphasised the warming effect of the ocean on the northern European climate and have pointed to melting ice caps and suggested that the increased influx of cold, fresh water from the north has interfered with warm currents coming from the south, leading to a much colder winter.
Others have argued that the mere event of the winter disproves the global warming theory because if the planet was really getting hotter the winter would never have occurred.
The truth is that nobody really knows what caused the increased snows in 2010 and that the weather system is so complex it is unlikely to have been a single cause. Extreme weather events do occur periodically and it won’t be clear whether the cold winter marks a major shift in climate or was just a one off extremity until several more winters have passed and climatologists can perform some sort of regression analysis on the trends.