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Why Was Winter 2015-16 so Mild?

Winter is on its way out. On 21st March spring begins again – flowers start to bloom, leaves appear on the trees and the temperatures increase. You’d be forgiven for thinking that 2015-16 was a year without winter. Despite some cold, wet weather in February and early March and some limited patches of snow, this season has been one of the mildest on record though, surprisingly, no temperature records were broken for December.

Playing Havoc with Nature

Nature lovers reported seeing butterflies, wasps and bees, and snowdrops and daffodils blooming in November and December as far north as Ayr. Most areas of the country have had little to no frost for most of the three months of winter. What are the reasons for this? Is it climate change or something else?

We’ve known for decades that increasing levels of greenhouse gases has pushed the global temperature up. These increases have been slow and barely noticeable from year to year, even though the records continue to bear out the fact of temperature rising due to these unnatural causes. However, climate change alone cannot account for the bizarre temperatures recorded in the period of November and December 2015.

winter daffodils_careco
Daffodils have bloomed much earlier than usual this year.

One major reason for this strange weather is El Niño, but it is not the only explanation.

What is El Niño?

Information on weather systems can be confusing; you have probably heard of El Niño but perhaps still don’t understand what it is or what it does. Every few years, warm water from the western South Pacific Ocean moves to the east, raising the average temperature of the water around the west coast of South America. This water imbalances the system along the coast; it evaporates as a result of natural process (creating clouds – most of our rain water comes from the ocean) and there is a noticeable increase in storms along the South American coast and lower activity to the west. This is how we know an El Niño event is occurring. The winds that carry the rain water from the area will also change strength and / or the direction. It’s amazing how much of an impact this can have on the global weather systems, but those impacts are profound.

The Effects of El Niño on UK Weather

The 2015 El Niño was recorded as one of the strongest on record; this is why we saw such extreme weather events – flooding along the west coast, the north and Scotland as well as the unusually warm temperatures across most of the country. There is no clear indicator of what causes El Niño, but we do know that it is a natural process that occurs roughly every five years though can be as few as two or as many as seven years apart.

The weather systems of the North Atlantic (which affect the weather patterns of the United Kingdom) become more stable as a result of El Niño. This means fewer hurricanes and drier periods of weather. Yet this did not happen in December as normal. The more powerful El Niño affected something else that reduced the possibility of snow and frost across the country. The extra wet air had to go somewhere and instead of evenly distributed snow, it became concentrated heavy rains.

What about the Jet Stream?

The particularly strong El Niño has also affected the Jet Stream from the South Atlantic. The Jet Stream is like a conveyor belt over the ocean, carrying warm tropical water and air from the south to the north. December is high summer in the South Atlantic so the air is already warm. Normally, this does not affect us beyond creating milder winters than continental Europe gets and provides truly warm temperatures only as far as southwestern Europe. However, November-December 2015 saw greater variation in the range of the Jet Stream; warmer air travelled farther north than it normally would and more so than most previous El Niño events.

The warm winter was a combination of direct El Niño impact and knock on effects from other systems. We can expect November – December 2016 to be a return to normal.