ABSTRACT
Over the past 200 years, global average temperatures have increased by more than 1°C, and the impacts of this warming will worsen as temperatures continue to rise. In a major report released in 2021, the Intergovernmental Panel on Climate Change (IPCC) stated that human activities have “unequivocally” caused global warming. Reconstructions of Earth’s climate show that it has changed throughout its 4.6-billion-year history and has experienced intervals of extreme warmth and cold. Understanding how the climate has changed throughout Earth’s history allows us to provide meaningful context for the changes we are seeing today and also to analyse how resilient the Earth System is as we head towards a warmer future.
In this chapter, we explore the potential of the climate from ~3 million years ago to improve our understanding of the dynamics of the climate in a warmer world and consequently help us to better understand and prepare for our warmer future. We discuss how climate(s) from millions of years ago can be investigated and the role of geological proxy data and climate model simulations in developing our understanding. We also discuss the concept of palaeoclimate analogy, where elements of certain past time intervals present similarities to our projected climate future(s). No interval in Earth’s history is a perfect analogue of the future, but there are plentiful elements from which we can learn (e.g. which regions may experience the most warming). Throughout, we specifically focus on an interval ~3 million years ago, within the Pliocene epoch, which has been referred to as one of the best palaeoclimate analogues for our future.
Underlying this work is an appreciation that the relevance and usefulness of different past climates to our collective future depends upon the path humanity follows; the more emissions we produce, the more atmospheric greenhouse gas concentrations rise, the warmer the world becomes, and the further back in geologic time we would need to consider to see comparable warming. Our interval within the Pliocene, for example, is similar to projections of warming at the end of the 21st century under medium emission scenarios, but its usefulness may lessen if we follow a high emission scenario, where the overall level and rate of warming far exceed those of the Pliocene. Improving our understanding of a range of past climates, therefore, sets us in the best stead for using the past to inform our future.
