Article by Adrian Reid

28 August, 2021

The Earth's climate is warming so rapidly that in a few decades it could resemble the climate from millions of years ago. 3 million years ago, during the Pliocene period, trees grew in the Antarctic, sea levels were 25 metres higher than today, and the equator was unbearably hot. 50 million years ago, in the hottest point of the Eocene, the Earth went through a major mass extinction.

Article by Adrian Reid

28 August, 2021

New global climate by 2030

In just a few short years, we'll have said goodbye to the climate in which we have built civilisations, cultures, sciences and technologies for the last 10,000 years.

Instead, the Earth's climate is expected to resemble one that existed 3 million years ago, during the Pliocene period, and it could happen within the next few decades.

"Our study suggests that climates like those of the Pliocene will prevail as soon as 2030", says Kevin Burke of the University of Wisconsin, and lead author of a study on the Earth's changing climate.

But the changing climate doesn't stop there. Continuing greenhouse gas emissions could mean that by 2150, the Earth will have reverted to a climate that existed as far back as 50 million years ago, during the Eocene, not long after the end of the dinosaurs.

The Earth's new climate could be coming soon.

According to Dr Burke, "We are moving toward very dramatic changes over an extremely rapid time frame".

Past climates, future predictions

The researchers came to this conclusion after comparing computer models of the climate in the coming century against what is known about the climate millions of years ago.

They looked at two kinds of possible futures — one optimistic, the other pessimistic. In the optimistic future, known as RCP4.5, greenhouse gas emissions eventually come under control and even drop. In the pessimistic future, however, greenhouse gas emissions continue to rise. This is the RCP8.5 scenario, and it's the worst possible case.

How the Earth might have looked 50 million years ago Roberto Saltori, CC BY-SA 2.0

After running the data, a few matches came in. Under the RCP4.5 scenario, at around 2040, the Earth's climate reaches levels not seen since the Pliocene, but it then stabilises at this point, as emissions are brought under control.

But the RCP8.5 scenario was much worse. With increasing greenhouse emissions, we would be experiencing a Pliocene type climate as soon as 2030. Then, as the climate continues to warm in the years up to 2150, the Earth's climate turns into a climate that existed 50 million years ago, during the Eocene period.

And if we still let emissions rise, after 2150, the climate will change even more. At this point the scientists could no longer find a match. They labelled the climate at this point as "novel". A climate of this type had simply not existed before.

This new climate would first come to eastern and southeastern Asia, northern Australia and the coastal Americas.

The Pliocene climate

If scientists are correct, we've only got a few years to prepare for our next new climate — the Pliocene climate. So what should we expect?

The world 3 million years ago, in the Pliocene period, was still pretty familiar. If you ever got lucky enough to take a time travelling tour to this time, you would notice the layout of the oceans and continents was not so different to the present day, and most of the animals would be recognisable as the ancestors of today's animals.

You might even meet one of humanity's ancestors, Australopithecus africanus, still somewhere between ape and human.

Australopithecus africanus, humanity's ancestor from the Pliocene period, 3 million years ago.Tim Evanson, CC BY-SA 2.0

What might make life more difficult for any time travelling tourist, would be the weather. It was much hotter, wetter, windier, with worse storms and wildfires.

Average temperatures in the Pliocene were about 2 or 3 degrees Celsius (3.6 - 5.4 °F) warmer than today's temperatures. These were just average temperatures though. The Arctic and Antarctic regions were much warmer, with the Arctic as much as 19 degrees Celsius (34.2 °F) higher than today.

Those warmer temperatures made it possible for forests to grow across the Arctic and Antarctic. Scientists have found the remains of trees just 500 km from the South Pole. But the heat also meant these forests would burn in massive wildfires, across what we now think of as the "frozen north".

In these temperatures, permanent sea-ice was impossible, and the Arctic may have been totally free of sea-ice every summer. That meant sea levels 25 metres higher than today.

Cat 5 Hurricane Patricia from space, 2015. NASA Earth Observatory, CC BY 2.0

Closer to the equator, storms prevailed. Tropical cyclones were more frequent, more intense and they lasted longer. Computer modelling shows that they weren't limited to just around the equator and could move north or south. Chris Brierley, a climate researcher at Yale University estimated that there were twice as many cyclones in the Pliocene, and "they were all over the place".

This kind of weather sounds increasingly familiar. Arctic heatwaves, never-ending wildfires, and catastrophic tropical cyclones are all making the news.

We may be set for more of the same. By adding more CO2 into the atmosphere, it's like we've turned up the dial on the oven. Now we can only wait for the oven to heat up.

The Eocene climate

The climate doesn't stop changing once we've reached a Pliocene climate. By 2150, scientists expect the climate to resemble one of Earth's hottest climates in half a billion years — the Eocene climate.

Eocene temperatures were up to 13 °C (23.4 °F) hotter than now.

In the Eocene summer, the beaches off the Antarctic coast were warm, tropical, and lined with palm trees. Even winters in the Antarctic were a comfortable 10 °C (50 °F).

At the other end of the planet, the Arctic was nothing like the Arctic we know. It was wet, marshy, and home to alligators, turtles and hippo-like creatures known as Coryphodon. It was like someone had transported the Everglades of Florida to the top of the world.

What was left, along the equator, was unbearably hot. Computer modelling suggests summertime temperatures of more than 50 °C (122 °F).

The reason the Eocene was so hot was the way it started. A sudden burst in CO2 levels, which scientists are still unable to explain, pushed up the Earth's temperatures. It's known as the Paleocene-Eocene Thermal Maximum, or PETM for short. This was an extinction event which made the oceans more acidic and wiped out 50% of deep sea organisms, called foraminifera.

Hippo-like creatures in a marshy Arctic. edenpictures, CC BY 2.0

The PETM was an extinction event that we seem determined to outdo. According to a study by Professor Philip D. Gingerich of the University of Michigan, "current carbon emission rates are nine to 10 times higher than those during the PETM". The professor estimates that by 2159 we will have emitted as much carbon as all of the PETM.

We'll also have emitted the carbon 200 times faster, according to a separate article by Professor Martin Siegert of the Imperial College London, and colleagues. The PETM took around 20,000-50,000 years to bring CO2 levels over 1000 ppm, but current greenhouse emissions "will lead to around 1000 ppm in 80 years’ time", wrote the professor.

The Eocene climate started with some of highest temperatures in the last half billion years, and an extinction event. This is the climate that scientists predict awaits us in the next century, if nothing is done about climate change.