Insights & News

High Sensitivity of Snow to Climate Change in Temperate Maritime Climates

3rd December 2020

Maritime Climate… Boating Nations?

Not really, it’s a Köppen climate classification based on typical weather conditions and their seasonal patterns. Then again, these climates are associated with locations surrounded by ocean, so there’s some connection!

A maritime climate is defined as having generally mild summers and cool but not cold winters, relative to the average for that latitude (distance from equator). Atmospheric moisture tends to be abundant, which usually means plenty of rainfall too.

This climate type is largely found near oceans or large seas. These have a dampening effect on the temperature variability driven by the seasonal cycle of the sun. Meanwhile, evaporation from their surfaces provides ample moisture.

For this blog piece, we’re looking specifically at a sub-category known as ‘temperate’. This variety is mostly found in Northwest Europe and the far southeast of Australia, with a few patches scattered across South America. It features temperatures in the middle of the maritime climate range.

You can admire a detailed global climates visual on this Britannica page. The legend category ‘Cfb’ corresponds to the temperate maritime climate.

Northwest Europe – The Most Maritime of All

The north-western portion of Europe sports the largest continuous area of maritime climate, of any sub-type, in the world. This makes it the optimal focus region for studying what climate change has done to lying snow presence that have this climate type.

The (Relatively) Snowy Past

If you’re a long-term lowland UK resident born in the 1990s or 2000s, you’ve probably heard a lot along the lines of ‘back in my day it used to snow every winter!’.  This might well be true in many parts of northwest Europe, too.

Well, believe it or not, there’s some truth within that statement. In many parts of northwest Europe, it probably didn’t snow every winter, but it certainly snowed (and settled) a lot more often.

Let’s take a detailed look at just how much the daily chance of lying snow has changed for December to March. For useful weather stations in northwest Europe, observations have been split between 1989 or earlier and 1990 or later.

Map showing the average daily chance of snow for 1st Dec - 31st Mar in the years 1989 or earlier, for weather stations in Northwest Europe

During 1989 or earlier, even lowland areas of the region had an 8 to 10% chance away from the coasts. That’s equivalent to 10-12 days of the period!

Up on the hills, there used to be a 10 to 15% chance, up to 19 days with a covering of snow. The mountains of Wales tended to see up to about 24 days.

In the Lake District, North York Moors and northern mountains of Scotland, the chances range from 20-30%, an impressive 24-37 days of the period. You have to look to the higher mountains of mainland Europe to find higher snowfall tendencies. Parts of Alps far exceed the scale being used here (over 80% of days) – we’re focusing on lower elevations.

The Watery Present

Switching attention to the past 30 years, we find that lying snow has become scarcer across all low-lying areas. Even on higher ground, climate change has left its mark in numerous places.

Map showing the average daily chance of snow for 1st Dec - 31st Mar in the years 1990 or later, for weather stations in Northwest Europe

The Lake District has lost 5-10 days, the high ground of Wales 2-5 days. Lowland England and a large part of France now only experiences an average of 2-9 days of lying snow during December through March.

Further east, losses predominate in Belgium, The Netherlands, Denmark, and southern Norway. Some locations in Norway recorded their first completely snowless winter on record in 2019-20. Not one day of lying snow, in places where there used to routinely be at least 25 of them.

An Elevated Exception

In southern Germany, mildness of the maritime climate is tempered by greater distance from the ocean and generally higher terrain. The climate hasn’t warmed enough to reduce the number of lying snow days there. This is also true in the Alps of southeast France, except here it’s only elevation that’s keeping it so cold.

Believe it or not, a few locations have observed an increase in lying snow days. This can happen where typical temperatures are rising but still staying below zero. You see, the higher the air temperature, the more moisture it can contain. So, if it’s still cold enough, that means more snowfall, accumulating to greater depths and taking longer to melt away.

At lower elevation and nearer the ocean, conditions have tended to be only just cold enough in the past, so rising temperatures just lead to sleet or rain instead.

The Tumbling Trajectory

So far this century, lying snow days have continued to decline in many parts of northwest Europe.

Narrowing the most recent analysis period to 2010-2020 from 1990-2020, the average number of lying days reduces by 8. That’s a 45% reduction!

Slicing the data, the average reductions are 6 (50%) for locations below 300 m elevation and 12 (31%) for locations above.

Not even the high mountains are safe anymore; at 750 m and above we see an average loss of 7 days (26%). Important habitats are being lost as the snow line climbs higher and higher, the limited coverage of which makes many of the resident species inherently rare.

If you’d like to delve into snow trends in Europe further, this 2018 study by Bach et al. is a good place to start.

 

Most climate projections have mean temperatures rising further in most of Europe – and the world for that matter – in the decades to come.

It’s hard to see the overall snow cover trend heading any other direction than downward.

On the one hand, this means easier travel, reduced disruption to events and less strain on the health of vulnerable people.

On the other, cold, snowy weather plays a vital role in pest control (and pest aren’t just an annoyance – think agriculture). Lying snow also has direct benefits – for one thing, it’s an important water storage for some communities. It also slows the seasonal heat build of spring-summer.

There will inevitably be both winners and losers from this loss of snow cover. Are the gains worth the losses? That’s one to think about – it’s not for me to decide.

James Peacock MSc
Head Meteorologist at MetSwift

Speak to one of our experts and discover how our analytic platform can revolutionise your weather & NatCat insight. Request a meeting, a chat & demo, or a free trial. Developed via consultation & collaboration.