Even if humans completely halt greenhouse gas emissions starting today, more than a third of the world’s remaining glaciers will melt before the year 2100, according to a new study by climate scientists from Germany and Austria.

Researchers at the Universities of Bremen and Innsbruck used a climate model – the CMIP5, developed by the Intergovernmental Panel on Climate Change (IPCC) – to project the effects of present-day conditions onto global glacier mass in the future.

Their analysis, published in Nature Climate Change, predicted that 28 to 44 percent (an average of 36 percent) of current glacier ice will be lost even if humans undertake “the most ambitious measures,” said lead author Ben Marzeion.

This volume of melted ice will lead to an impactful 11.2 centimeters (4.41 inches) of sea level rise after water flows into the oceans. And the complete picture is even bleaker, naturally, because these calculations are only for glaciers, and do not explore what will happen to sea ice (such as the remaining 13.95 million square kilometers, or 5.39 million square miles, of ice that makes up the Arctic) and ice sheets (the Antarctic and Greenland ice sheets contain 142 and 18 times more stored water than the glaciers and ice caps).

Preventing this outcome, the authors estimate, would require a magical reversion back to the global temperature range from between 1850 and 1879.

"Glaciers react slowly to climatic changes. If, for example, we wanted to preserve the current volume of glacial ice, we would have to reach a temperature level from pre-industrial times, which is obviously not possible," said co-author Georg Kaser. "In the past, greenhouse gas emissions have already triggered changes that can no longer be stopped. This also means that our current behaviour has an impact on the long-term evolution of the glaciers – we should be aware of this." 

Translating the glacier melt into more understandable terms, Kaser, Marzeion, and colleagues infer that every additional kilogram (2.2 pounds) of carbon dioxide released into the atmosphere from this moment forward will lead to the loss of 15.8 kilograms (35 pounds) of glacial mass – this is on top of the ice melted by pre-existing greenhouse gas-driven warming. 

And although we are resigned to witness substantial melting during the coming decades that stems from past emissions, what humans choose to do now will begin to have differing effects on glaciers by the end of the 21st century.

If we can stick to the Paris climate agreement's proposed maximum global average temperature rise cut-off of 1.5 °C (2.7°F) above pre-industrial values, a significantly smaller proportion of glacier ice will be lost than if we adopt the less ambitious 2°C (3.6°F) cut-off.

In summary, the model shows that the lag time between rising temperatures and glacier melt means that "more ambitious climate change mitigation measures [taken now] will have a disproportionately greater impact on the long-term preservation of glaciers than less ambitious measures," thus lessening the climate disaster inherited by future generations.