Learning from the past to understand the future

The geological record reveals how past environments responded to broadly comparable climate changes. The mid-Pliocene (~3-5 million years ago) is perhaps the closest geological analogue for a future warmer world. CO2 levels in the atmosphere then were ~360-400 parts per million by volume [ppmv] (compared with 385 ppmv today and rising at ~2 ppmv per year), global temperatures were ~3°C higher and sea level was up to 25m higher. Because of lags in the climate system, warming in the pipeline is now ~2°C and approaching the 2-3°C level considered to represent a threshold for dangerous risks (e.g. leading to irreversible ice-sheet melting).

The landscape is always adjusting to climate. Although we cannot be 100% sure what will happen as global climate changes, we can make an informed guess as to what the most likely impacts might be, using analogues from the past and by applying our understanding of geomorphological processes. The weather, especially extreme events, are important in forcing readjustment in the landscape.