Washington: Of all the creatures on Earth, humans manipulate their environment the most. But how far can we push before something drastic happens? Scientists call for a better understanding of past extreme weather events in order to anticipate future changes.
Enter geoarchaeologist and anthropologist C. Michael Barton at Arizona State University. The School of Human Evolution and Social Change researcher, along with Foundation professor Sander van der Leeuw and an international and interdisciplinary team, published their analysis this week in the journal Nature Geoscience.
The paper describes the abrupt climate changes of the past, which led to the âtipping pointsâ of these events and what followed.
âWe’ve been putting a lot of chemicals in the atmosphere and changing the heat in the atmosphere for a long time, and very intensively for 150 years,â Barton said. “And, things are still moving forward. Temperatures are slowly rising around the world, but we haven’t seen a huge and dramatic change. However, complex systems are potentially vulnerable if you push too hard.”
Barton studies Earth’s many systems – especially the water cycle and landscapes – and how humans alter those systems.
âPeople tend to look at how far you can push things before everything suddenly changes,â Barton said. “And that’s what’s considered the tipping point.”
For a specialist in complex systems like Barton, almost anything can be thought of as systems or cycles. A tree grows and dies, and the decomposition returns nutrients to the soil. Water travels through the Earth in different forms such as rain, runoff and evaporation.
Some of the major systems on Earth include the hydrosphere (water), the atmosphere (air), and the cryosphere (ice). All of these systems are connected. This tipping point research examines the history of these systems to quantify small changes that can lead to abrupt, massive change, while also measuring how abrupt change can trigger abrupt changes in other systems.
The article explores previous research with sediment cores in the Gulf of Alaska, dust records in North Africa, and ice cores from Greenland. All of this prehistoric data gives modelers and scientists of the Earth system a better idea of ââwhat Earth actually looked like hundreds of thousands of years ago.
Scientists have also extensively studied the Earth’s oceans. This includes current levels of salt and oxygen, changes in circulation patterns, and inflows of fresh water from melting ice caps. Current ocean conditions can be compared to historical data collected from the composition of the ocean floor, to make inferences about past ocean currents.
The authors note past cases of extreme weather events occurring so quickly that humans have had difficulty adapting or have been unable to adapt to the new environment.
For example, about 1,500 years ago, a sharp cooling occurred in Europe, causing changes in vegetation. The authors note that the cooling may have been caused by a natural phenomenon – volcanic eruptions. The changes in vegetation and agriculture were so extreme that people experienced famine and the reorganization of society. This moment correlates with the transformation of the Eastern Roman Empire.
The authors note how the climatic events of centuries ago triggered drastic changes or even the collapse of ancient civilizations due to unforeseen societal vulnerabilities.
The ancient city of Angkor, located in present-day Southeast Asia, is an example. The people of Angkor have altered the natural water cycle by diverting water to grow crops. As the city grew, this region’s water supply system became so strained that it passed a tipping point. The system could not handle more intense droughts and floods, and the city of Angkor collapsed.
Arizona residents know the past few years have been drier and warmer than usual. Barton said it was not yet clear whether we had passed a tipping point in the southwest region.
It is normal to see slight fluctuations in precipitation and temperature from year to year. But recent studies of the ancient climate lead Barton to question whether drier weather conditions have become the new normal for our lives.
Barton also noted that researchers still don’t know why certain weather systems change. For example, past monsoon rains moved without warning and for unknown reasons. This can be catastrophic for human populations, as those who depend on the monsoon experience severe drought, while others lack the infrastructure to handle the influx of water.
There are still gaps in this area of ââresearch. More raw data needs to be collected and quantified, and some existing data lacks the precision and quality needed to create test models and simulate abrupt future changes.
Researchers are also calling for more analysis of the interactions between environmental systems and human societies during times of climate change.
Finally, improvements to Earth system models will help scientists simulate possible abrupt changes that humans might see in the near future. Current models are very good at simulating more gradual climate changes, but are not yet able to simulate well-documented past abrupt changes.
The authors hope that this article will raise awareness in the field and that more people will understand how analyzing the long-term past might help us in the near future.
For example, one component of tipping point research is identifying early warning signals. These are smaller fluctuations in a system before a sudden change. The authors say these warning signals exist, but when the entire world is the center of attention, it can be difficult to determine how small changes in one system can warn of abrupt change in another.
There is evidence of past warning signs. For example, there were anomalous changes in the climates of the North Pacific Ocean region and around Greenland before the major melting of Earth’s last Ice Age.
âAll of the components can change very, very quickly,â Barton said. “The whole system can fall into a different state … How do we know when we are getting too close?”
The authors leave the reader with this final thought: âAs human beings we try to anticipate the future. We are now well aware that the complex systems, including the coupled social and ecological systems that now dominate our planet, can undergo abrupt changes …. If we can’t model sudden changes in the past, we can’t hope to predict them in the future. “