Our future on Earth may also be our past.
In a study published recently, researchers show that humans are reversing a long-term cooling trend tracing back at least 50 million years. And it’s taken just two centuries.
By the year 2030, Earth’s climate is expected to resemble that of the mid-Pliocene, going back more than three million years in geologic time. Without reductions in our greenhouse gas emissions, our climates by 2150 could compare to the warm and mostly ice-free Eocene, an epoch that characterized the globe 50 million years ago.
“If we think about the future in terms of the past, where we are going is uncharted territory for human society,” says the study’s lead author, Kevin Burke, who conducted the work while a graduate student in the lab of paleoecologist John “Jack” Williams, professor of geography at the University of Wisconsin–Madison. “We are moving toward very dramatic changes over an extremely rapid time frame, reversing a planetary cooling trend in a matter of centuries.”
All of the species on Earth today had an ancestor that survived the Eocene and the Pliocene, but whether humans and the flora and fauna we are familiar with can adapt to these rapid changes remains to be seen. The accelerated rate of change appears to be faster than anything living on the planet has experienced before.
The new study builds upon work Williams and colleagues first published in 2007, which compared future climate projections to historical climate data from the early 20th century. The new study relies on extensive data about climate conditions to probe much deeper in Earth’s geologic past and expand those comparisons.
“We can use the past as a yardstick to understand the future, which is so different from anything we have experienced in our lifetimes,” says Williams. “People have a hard time projecting what the world will be like five or 10 years from now. This is a tool for predicting that — how we head down those paths and using deep geologic analogues from Earth’s history to think about changes in time.”
During the Eocene, Earth’s continents were packed more closely together and global temperatures averaged 23.4 degrees Fahrenheit (13 degrees Celsius) warmer than they are today. Dinosaurs had recently gone extinct and the first mammals, like ancestral whales and horses, were spreading across the globe. The Arctic was occupied by swampy forests like those found today in the southern US.
In the Pliocene, North and South America joined tectonically, the climate was arid, land bridges allowed animals to spread across continents and the Himalayas formed. Temperatures were between 3.2 and 6.5 degrees Fahrenheit (1.8 to 3.6 degrees Celsius) warmer than they are today.
The models showed these deep-geological climates emerging first from the centre of continents and then expanding outward over time. Temperatures rise, precipitation increases, ice caps melt and climates become temperate near the Earth’s poles.