The glaciers of the Alps, possibly the planet's most studied rivers of ice, are shrinking rapidly. They will be half gone in three decades, even if the world gets its act together on greenhouse gas emissions. If it does not, there will be little left by 2100.

Swiss scientists are worried about the future of the Alps' 3,500 glaciers, and not just for the effect on the tourist industry. Glaciers play an invaluable role in storing water and releasing it slowly, rather than in dangerous floods. Downstream agriculture and hydroelectric production suffer if glaciers vanish.

In The Cryosphere Professor Daniel Farinotti of ETH Zurich modeled the future of individual glaciers under three scenarios for climate change action. The findings are stark; winter is definitely not coming for Europe's largest mountain range. Mount Blanc may need renaming, its permanently year-round white status could be gone within many people's lifetimes.

Glaciers' sizes are affected by many things, of which air temperature is just one. The level of precipitation is an important factor, but ice flow processes determined by the terrain also matter, and have been neglected in much previous research. Farinotti confirmed his methodology by comparing his model with observed changes from 2003 to 2017. A handful of glaciers shrunk much more or less than he predicted, but many more were very close to the mark.

Farinotti found that for the years 2017-2050, most of the changes to the Alps' glaciers are baked in. Even scenarios where global emissions of greenhouse gases fall sharply after 2020 are insufficient to save much more than half of the alpine rivers of ice. This is because much of the existing ice is overhang – a remnant of past centuries' climates that is unsustainable even in current conditions. It only survives because large bodies of ice can take a long time to melt.

However, what we do over the next decade will matter much more later on. In the most positive scenario considered, glaciers will still be at 37 percent of their 2017 levels at the end of the century. Co-author Dr Matthias Huss said in a statement that in the most negative, where emissions keep rising unconstrained, “The Alps will be mostly ice-free by 2100, with only isolated patches remaining at high elevation, representing 5 percent or less of the present-day ice volume.” This would be less than a seventh of the ice expected under the optimistic scenario.

"Glaciers in the European Alps and their recent evolution are some of the clearest indicators of the ongoing changes in climate," Farinotti said. "The future of these glaciers is indeed at risk, but there is still a possibility to limit their future losses."