It’s not quite a “Planet of the Apes” moment, where humans suddenly realize (like Charlton Heston realizing he was on Earth all along) that they themselves were the cause of climate change. A new report in the recent edition of the journal Science is as sobering as it is simple: Humans didn’t used to be the main cause of glacier loss, but now they are.
The study, appearing in the August 22, 2014 issue of Science, covers glaciers during the period from 1851 to 2010. Though the worldwide glacier retreat began in the middle of the nineteenth century, people weren’t the primary driving force behind the ice loss until late 1970s. Prior to that point, the world was just coming out of a cooling period known as the Little Ice Age. Though not a true ice age, this cold period lasted roughly from the sixteenth through nineteenth centuries.
Researchers from the University of Innsbruck in Austria and Trent University in Canada used many different climate models to estimate snow accumulation verses snow and ice melt. From 1950 to 1980, natural climate change accounted for about three-quarters of glacial ice loss. From 1991 to 2010, humans were responsible for 70 percent of glacial retreat.
Of course, there are uncertainties in the study, as whenever models are used to infer what happened in the past. As climate models and measure techniques improve, so will the resolution of the numbers highlighted by the study.
“Glaciers are superb measuring sticks of climate, because they ignore the fluctuations of day-to-day weather,” wrote Shawn Marshall in Science‘s summary of the study.
The findings do not suggest that without the influence of humans, there would be no sea level rise or glacier retreat. “Our results indicate that a considerable fraction of 20th-century glacier mass loss, and therefore also of observed sea level rise, was independent of anthropogenic climate forcing,” wrote the study’s lead author, Ben Marzeion, associate professor at the Institute of Meteorology and Geophysics at the University of Innsbruck.
Measuring glacier loss certainly isn’t a new thing. The American Meteorological Society’s 2013 state of the world’s climate report singled out the dire situation mountain glaciers are facing: since 1980, glaciers have lost 50 feet of water. Glacier calving (breaking off into the sea) greatly contributes to sea level rise. Meltwater coming off mountains are browning rivers in California and causing ocean acidification.
Though the news seems dire, providing firmer measures of the extent to which humans contribute to ice loss may help build the impetus to find effective solutions to climate change. In the meantime, glaciers will continue to offer testimony to our species’ impacts on our planet.