Ecosystem collapse could occur "surprisingly quickly," study finds

On the heels of several consecutive record-breaking "hottest days ever," it has become increasingly clear that there is an urgent need to address human-caused climate change. After all, a recent study published in the scientific journal PNAS revealed that the types of so-called compound drought and heatwaves that humanity is currently experiencing — these are known as CDHW events — are projected to become what co-author Dr. Michael E. Mann labelled a "new abnormal."

By the late 21st century, the PNAS authors contend, approximately one-fifth of the species will endure CDHW events roughly twice a year, each one lasting approximately 25 days, with all of the wildfires and blistering, scorching heat they entail.

Yet humanity may not need to wait until the late 21st Century for climate change to bring about real-world apocalyptic conditions. This will especially be so if ecosystems undergo abrupt changes after too many extreme weather events occur, one after another after another. According to a new study in the scientific journal Nature Sustainability, that scenario might indeed occur sooner rather than later.

"We previously knew that ecosystems can undergo very abrupt changes," Professor Simon Willcock of Rothamsted Research and Bangor University, who co-authored the study, told Salon by email. He added that this knowledge had been derived from past observations of small increases in stress on particular ecosystems. As one example, deforestation in one tropical region might turn a rainforest into a "savanna-type system," which is a drier, grassier ecosystem with far fewer trees.

Prior to this study, much of our understanding of these vast changes "[came] from focusing on a single stress at a time," according to Willcock. By contrast, the new paper examines how ecosystems respond when there are multiple simultaneous stresses, such as climate change, deforestation and pollution caused by mining.

"We show that the combination of additional stresses and/or the inclusion of noise [such as variables like El Niño] brings ecosystem collapses substantially closer to today by ~38–81%," Willcock explained. "We also show that, if you were focused on just one stress – because it was easier to measure, for example – the ecosystem collapse may occur at stress levels you thought were safe (i.e. due to the pressure of the stresses you are not observing)."

To reach these conclusions, the scientists performed experiments on four models to simulate what would happen after abrupt changes in areas such as the Chilika lagoon fishery and the Easter Island community, as they comprise "ecosystems with a range of anthropogenic interactions." In addition to finding that ecosystem collapses occur much sooner when there are multiple stresses, the paper also determined that they collapse faster if the primary stress is particularly powerful.

"As the strength of a main driver increases, the systems collapse sooner," the paper concludes. "Adding multiple drivers brings collapses further forward, as does adding noise, and the two effects can be synergistic."

Does this mean people should expect catastrophic consequences due to climate change in the near future?

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"I think that, with climate change and its associated extreme events, [they] will put additional stress on the world's ecosystems, which are already under tremendous pressure," Willcock wrote to Salon. "This might cause some ecosystems to collapse surprisingly quickly."

For instance, the study warns that the Amazon region may transition from a rain forest into a savanna-type region earlier than predicted by the United Nations' Intergovernmental Panel on Climate Change, which is currently projecting that to occur in the year 2100. Instead, it may occur about 20 years earlier.

At the same time, Salon pointed out that the basic premise of the scenario described in this paper — climate change being linked to rapid, cataclysmic changes in our environment — sounds analogous to the premise of a climate change-themed blockbuster like the movie "The Day After Tomorrow." Willcock sounded a slightly more reassuring note.

"That is a very extreme tipping point (i.e. triggering an ice age!!)," Willcock replied, adding that "I think the rapidity of that change remains in the realms of Hollywood." He said that anything which happens in real life "will be at a smaller scale and, by comparison, more gradual."

This doesn't mean there won't be a global impact to some of those relatively smaller events, such as the aforementioned possibility of the Amazon hitting a "tipping point" by 2030 and turning into a savanna by 2080. If this process were to unfold, it would release so much carbon that it could on its own "trigger other tipping points (e.g. the melting of the ice sheets)," Willcock explained. "But again, these would take some time to melt. When they did, sea levels would rise, which could affect cities across the world, as well as biodiversity."

In the PNAS study released earlier this week, scientists predicted that CDHW events will occur with increasing frequency from eastern North America and eastern Africa to Central Asia, Central Europe and the American southwest. According to Dr. Ashok Mishra, a professor at Clemson University's School of Civil and Environmental Engineering and Earth's Science and co-author of the study, "compound drought and heatwaves severely threaten socio-ecological systems, leading to greater impacts — e.g., wildfires, crop failure, and heat-related mortalities — than individual extremes."

Mishra later added that there are ways to prepare for these impending calamities, such as by "implement[ing] sustainable water management strategies, including water conservation measures and investments in water infrastructure, to ensure a reliable water supply during CDHW events."

Similarly, Willcock told Salon that "there is still hope! Obviously, we want to try to avoid collapsing ecosystems as that would have huge consequences for many species, including us. By reducing emissions and using ecosystems more sustainably, we can hopefully avoid putting ecosystems under pressures they can't bear. Also, if any ecosystems do collapse, in future, we hope to learn how to apply pressure in a positive direction to trigger rapid ecosystem recovery."