Glaciers are natural archives of data on the climate and environment of the past, essential to interpret how the climate is changing today. By studying ice cores – like the one I am carrying in this photo, drilled at the Grand Combin glacier in the Swiss Alps – we can journey back hundreds or even thousands of years.
One way to do this is to analyse the hydrogen and oxygen stable isotopes found in the water molecule. While their ratio is constant in sea water, it changes in rain and snow, depending on atmospheric temperatures. This means that we can indirectly observe the temperature of the atmosphere at the time the ice sheet was formed, and thus infer how the climate evolved in the past.
The ice layers, however, also store other types of environmental data that show the impact of humans. Layer by layer, in a sample from an Alpine glacier we can point to traces left behind by historical events, both global and local. For example, lead pollution spiking around the 1970s. Polonium residues resulting from military nuclear testing during the Cold War. A fall in pollutant emissions during the Great Depression. Even traces of local mining activity in medieval times. Pollen encapsulated in ice shows the arrival of maize crops in Europe, as well as the spread of chestnut cultivation by the Romans.
The layers of ice are like pages in a book that we are just now learning to read. Sadly, these precious records are disappearing due to rising temperatures in the atmosphere. I am currently working on Ice Memory, a project that aims to preserve these records for future researchers. We are creating an archive by sampling two cores for each chosen site: we analyse one and send the other to a sanctuary in Antarctica, a snow cave with a stable temperature. The Antarctic continent is a natural freezer, as well as a supranational territory, and we want these ice records to be available to future research teams of any nationality.
Understanding how the climate has changed in the past is crucial for making predictions about the future. Glaciers are sentinels of climate change: what is now happening in the high mountains is a sign of the impacts we will see at lower altitudes. The unprecedented melting of ice sheets that we are witnessing now is tragic for the loss of water resources, but also because of the loss of the knowledge and memory enclosed in the ice.
Preserving these ice cores has a scientific purpose, of course, but it is blurred with an historical one.For me, holding a sample that was frozen during medieval or Roman times is always a thrilling, emotional moment. When you realise that the ice has been trapped for thousands of years, your mind wanders. The stories that ice tells are captivating and can raise awareness about the loss of glaciers, wonderful environments that we see deteriorating day after day.
