In an effort to anticipate the future impacts of climate change, experts at Arizona State University are trying to gain a better understanding of extreme climate changes that occurred in the past.
The researchers are describing abrupt climate changes, what led up to these “tipping points,” and the consequences that followed.
“We’ve been putting a lot of chemicals into the atmosphere and changing the heat of the atmosphere for a long time, and really intensively for 150 years,” said study co-author C. Michael Barton.
“And, things are still chugging along. Temperatures are slowly going up globally, but we haven’t seen a huge, dramatic shift. However, complex systems are potentially vulnerable if you push too much.”
Barton studies the water cycle and other complex Earth systems, and looks at how drastically they have been altered by humans.
“People tend to look at how far you can push things before suddenly everything changes. And that’s what’s considered the tipping point.”
Earth’s major systems include the hydrosphere (water), the atmosphere (air) and the cryosphere (ice). All of these systems are interconnected.
The researchers focused their attention on tipping points across the history of these systems. They wanted to quantify small changes that can lead up to an abrupt, massive change, while also measuring how one abrupt change can trigger abrupt changes in other systems.
To understand what the planet was like hundreds of thousands of years ago, Earth system modelers turn to the prehistoric record that is available to them. This study, in particular, was focused on sediment cores from the Gulf of Alaska, dust records from North Africa, and ice cores from Greenland.
Scientists can also obtain prehistoric data from the ocean floor to measure changes in composition, circulation patterns, and influxes of fresh water from melting ice sheets.
The study authors point to past instances of extreme climate events that happened so quickly that humans either had difficulty adapting, or were not able to adapt.
For example, Europe experienced a period of abrupt cooling about 1,500 years ago, leading to major changes in vegetation. The researchers note that this cooling may have been caused by a natural phenomenon, such as volcanic activity. The changes were so extreme that people experienced famine and societal reorganization.
According to the study authors, climate events that occurred centuries ago triggered drastic changes or even collapse in ancient civilizations due to unforeseen societal vulnerabilities.
In the ancient city Angkor, humans altered the natural water cycle by diverting water to grow crops. As the city grew, the water system became too strained and reached a tipping point. Ultimately, the city of Angkor collapsed.
In Arizona, the last few years have been hotter and drier than usual. Barton said it’s not yet clear whether we have passed a tipping point in the Southwest region of the country.
While fluctuations in precipitation and temperature occur naturally from year to year, looking at the ancient climate makes Barton wonder if the drier weather patterns have become the new normal for our lifetime.
Barton also noted that researchers still don’t know why some weather systems change. For example, past monsoon rains have shifted without warning and for unknown reasons. This can be catastrophic for people who depend on the monsoon season.
The researchers are calling for new Earth system models to simulate future abrupt changes, and for more research on the interactions between environmental systems and human societies during past climate change events.
The study authors hope this paper raises awareness of the field, and that more people will understand how analyzing the long-term past could help us in the near future.
One component of tipping points research is identifying early warning signals – smaller fluctuations in a system before an abrupt change.
“All the components can change really, really fast,” said Barton. “The whole system can drop into a different state. How do we know when we’re getting too close?”
The researchers say these warning signals exist, but when the entire world is the focus, it can be challenging to trace how small changes in one system can warn of an abrupt change in another.
“As humans, we try to anticipate the future,” wrote the researchers. “We are now well aware that complex systems, including the coupled social and ecological systems that now dominate our planet, can undergo abrupt changes. If we cannot model abrupt change in the past, we cannot hope to predict them in the future.”
The study is published in the journal Nature Geoscience.