The heart of Europe: the effects of climate change in the Alps
For Europeans, the Alps are an uncomfortable reminder of the full toll of climate change, expected to close over half of all ski resorts, practically remove Alpine glacier from existence, and increase flooding, drought, and rockfalls significantly by the end of this century. In this report, we will explore the academia behind this complicated region, revealing what has happened, and what is likely to happen in the future, by examining: temperature, precipitation, glaciers, the fate of ski resorts, rockfalls, and the surprising vegetation changes occurring in high Alpine meadows.
It’s an often-touted fact that Alpine temperatures have risen at twice the global average rate. Drilling down into the academia reveals that this claim derives from a 2009 analysis (Brunetti et al) which found “an average warming of the GAR [Greater Alpine Region] of about 1.3 K per century … (1886-2005) … about twice as large as the global trend referred to by the IPCC (2007)”. 
What’s interesting, though, is that a French study has highlighted significant geographical variation: since 1950, the northern Alps has experienced a 1.8-2.1oC temperature increase, whereas the southern Alps have only experienced 1.5-1.7oC.  By 2050, the spring temperature are expected to rise by 1.2oC, and 1.6oC in summer and winter; by 2100 this may have risen to 2.7oC in spring, and 3.8oC increase in summer.  As climate models become more refined, and can deal with the deep incisions of mountain valleys and their corresponding mesoclimates, we can expect even more revealing data.
Explaining temperature rise, however, is much harder than modelling it, with several ideas at play. Firstly, changing patterns of global atmospheric circulation impact mountains to a greater extent as they are directly in the path of air currents. Secondly, the reduction in albedo, as virgin snow is replaced by dark rockface could amplify existing warming.  Thirdly, the continentality of the Alps in Central Europe could be at play. 
A 2012 study points toward strong warming at low elevations in autumn and early winter, preventing snowfall settling as easily, with the strongest warming in late summer. Another study cited in the same meta-review suggests the greatest reduction in snowfall to be in the spring, coinciding with the half-term holiday skiing season. 
the profound difference between bare rock and reflective ice can be clearly seen on this melting glacier, highlighting the importance of albedo feedback mechanisms within the Alps
How precipitation patters will change is another point of debate. Given warmer air can ‘extract’ more air at the air-sea interface, it would be expected that precipitation would increase; one study  models a 10% increase in precipitation per 2oC increase. Yet, historically, this doesn’t stand scrutiny: despite warming in the 1980s, there was a regime change to snowfall, and ever since less snow has fallen ; the 0oC isotherm rose by 400m by the end of that decade, with corresponding losses in snow . Moreover, the Alps sit at a transition zone within Europe: the south (particularly the south-east) will – and has already – become significantly drier, with less rain and snowfall, whilst the north has become only marginally wetter and foggier. 
The North Atlantic Oscillation – the decadal shifts in average Atlantic water temperature – could be at play, leading to decadal variability in precipitation. Alternatively, it could be misguided looking at total precipitation: one study analysing the intensity of precipitation found that it might increase by as much as 30% , making extreme flooding and avalanches much more likely. Under 2oC of warming, the risk of a once-in-100-years flood will reduce to a-once-in-20-years, in other words increasing the flood risk by five, although rivers with very high watersheds are less likely to behave in this manner. 
above : the increased flood risk under 2oC of warming, across Swiss rivers; the colour represents the number of times a formerly-once-in-100 year flood would now occur within a 100 year window
below : the changes in temperature (T), precipitation (P), radiation (G), relative humidity (RH), and wind speed (WS), in summer and winter from 2012-2050 on the left hand-side, and from 2069-2098 on the right
Alpine glaciers are amongst the longest-analysed, and, compared to 1850, only 50% remained in the year 2000. At a further 1oC increase, this figure will fall to 30%; at 3oC, only 10% will remain . Besides the issues detailed above, melting glaciers also rapidly produce proglacial lakes; large rockfalls into the lake are not infrequent, and cause lake outburst flooding, with the potential to send a torrent of water racing into nearby settlements. 
ECONOMIC CONSEQUENCES OF CLIMATE CHANGE
Although the physical effects of climate change in the Alps are worrying, the economic effects are arguably a larger talking point. What’s most concerning is the winter snowline: it dictates whether the town can remain a ski resort, particularly whether it can advertise itself as a resort in which tourists can ski to the door of their apartments for après-ski. For every, 1oC rise in temperature, the snowline will rise 150 m up the mountainside  ; by the late 21st Century, the snowline is projected to have retreated to an altitude 1500m and 2000m, a shift of 300-600 m .
2oC rise in temperature is largely unavoidable in our current situation, under which an OECD study claims 39% of currently-viable resorts would have to close; at 4oC of warming, this would be a 70% decrease. At only 1oC of warming, 60% of German resorts would be forced to close, according to the OECD study . For small ski resorts perched in picturesque yet isolated mountain passes, winter income is critical, even existential. A 2008 study estimates that, by as soon as 2030, tourist numbers will have fallen by 10.2% . Looking at the snow-sparse winters of 1987-90 to model what future winters could be like, the revenue for cable car companies fell by 20%. 
Even today, recreation is not just inviable but plain dangerous: as anecdotes from climbers attest, the thawing of permafrost is causing slope failure and rockfalls. (see here for a more in depth consideration) The rocks once held together by ice in their pores now fracture and can no longer bear the load of even a small volume of climbers. Historic trails, such as the Hörnli Route up Matterhorn, are eroding to the point of closure; paths are increasingly more difficult and expensive for local authorities to maintain . The effects of this are wide-spread, with expensive ramifications: ski-lift foundations must be sunk deeper, tourist infrastructure will become unsafe, refuge huts may tilt precariously. The increased frequency of rockfalls – as has been proven by a French study  – may have disastrous economic repercussions if they block road access to ski resorts.
According to this French review, whilst climate change has reduced the threat of avalanches closer to the valley floor since 1980, at higher altitudes, the risk has increased. Studies equivocate over whether precipitation is a cause, but there has certainly been an increase in wet-pack snow : snow which has been subject to rain, causing it to become denser and more prone to collapse .
the fracturing Hörnli Ridge and hut are clearly visible in this photograph
Although it is often-ignored, climate change has the potential to cause radical shifts in vegetation, changing the landscape of the particularly fragile Alps. The vegetation of the Alpine region is striated up the mountainside according to individual vulnerability to snow, wind, slope angle, and altitude. Climate change is happening a rate too fast for plants to genetically adapt to the changing conditions; instead they are migrating up the mountainside, invading and reducing the habitat ranges of even more vulnerable species . Already, this has been quantified as a staggering 11% increase per decade in the vascular plant richness of the alpine-nival ecosystem , a figure which comes at the expense of the endemic species. It is suggested that by 2100, 31-51% of Alpine plant species will have lost 80% of their habitat ranges .
A fascinating 2015 study, published in Nature, has artificially recreated the conditions of 3oC warming. When they transplanting 4 typical Alpine plants into meadows downslope, they found that a 52-84% reduction in survival, and a 48-61% decrease in biomass for the poor transplanted species .
The issue is that the treeline is unlikely to migrate northwards, despite these rapid vegetation shifts across fragile Alpine meadows. A review of studies into treeline changes found no evidence for upward migration as saplings cannot tolerate the invariable winter snow at higher altitudes, with episodic stresses (drought, pests, frost) much more significant than climate change . This phenomenon is known as ecotonal shift: the boundary between habitats has shifted, but the core ranges haven’t.
Arguably, most significant for plant life is a phenomenon called melt-out, when snow melts and exposes plants for growth. One study places melt-out as occurring 6-26 days earlier than historical expectations ; another concludes the growing season has increased by 10.8 days, 6 in the spring, 4.8 in the autumn . More worryingly than increased growth, is that frost damage is much more likely, plus coordination with insect pollinators is upset . Meadows may potentially become carbon sources rather than carbon sinks because warmer conditions will stimulate more microbial soil activity, releasing carbon dioxide  (see Thawing permafrost).
Alpine kidney vetch – one of the transplanted species
a typical Alpine meadow, showing the graduation in species uphill
The Alps are threatened by climate change in complex ways that academia is only just catching up with as climate models become more sophisticated and able to deal with their topography. But what is abundantly clear is that the Alps have been – and will be – the barometer of climate change in the heart of Europe, reminding its leaders of what they stand to lose if they do not act soon.
 Climate change and natural hazards in the Alps, Journal of Alpine Research, Einhorn et al., 2015