The past is the key to the future. When snow falls on polar ice sheets, in Greenland and Antarctica for example, air is trapped between the snowflakes. Year after year, the snow compacts under its own weight to become ice, and air is enclosed in small bubbles. These are the best atmospheric archives on Earth.
By analysing the air enclosed in polar ice, we can reconstruct past changes in the atmosphere’s composition. We have reconstructed past methane (CH4) variations back to the Roman Empire period, and discovered that humans emitted significant amounts of methane 2,000 years ago.