Scientists Track the Tipping Points of Climate Change

Scientists Track the Tipping Points of Climate Change

By Chelsea Zhao

Crystal Rao, a geoscience graduate student at Princeton University, bases her research on the environmental changes and climate impacts on the species in clues from nitrogen isotopes in fossils.

Rao uses the ratio of two common forms of nitrogen as a standard, and compares it with the nitrogen inside the tooth of the megalodon shark. She has reconstructed a picture of when and where megalodon sharks topped the food chain in Arctic waters. Rao said this fierce predator could “basically eat anything in the ocean”.

Yet this 50-foot long shark, went extinct some 3.5 million years ago. Rao said the food source the sharks relied on to fuel their massive bodies caused their downfall.

“As climate shifts, maybe the production in the ocean could change,” Rao said. “And depending on what the ecosystem responded to, there could be less food availability” for marine life today just as those causing the demise of the megalodon sharks.

And that’s where the nitrogen fingerprint in the teeth comes in. The nitrogen isotope levels change in warm spells compared to ice ages so that Rao can track climate change in the distant past. Nitrogen isotopes from the Atlantic and Pacific Oceans mix during warm spells but ice ages lower sea levels, cutting off Atlantic from Pacific waters and and leaving a distinct isotope in each ocean. ,

Rao shared her research at the Comer Climate Conference this fall, an annual gathering of global climate scientists held virtually for the third year due to COVID-19. Comer conference veteran climate scientists, graduate students and post-docs investigate the effect of climate change from ancient life forms to theoretical models.

While Rao’s work examines a species belonging to an ancient era, another Comer scientist’s work takes estimations of the possibilities for the future.

Edmund Derby, a climate science Ph.D. student at Oxford University, utilizes simple models of Arctic sea ice from his past research in 2009 to examine the bifurcation or tipping point accompanying ice cover changes throughout the season.

Derby’s research presents climate from basic principles to its core behavior. In the scientific model, when atmospheric carbon dioxide exceeds a certain point, after all the Arctic ice melts, it is no longer possible to gain back the ice. His research presented at the conference investigates this tipping point under a model when the Arctic is covered in ice all year round.

“When you’ve reached this tipping point, you don’t get a reversible change once you’ve lost your ice cover,” Derby said.

The temperature of the Arctic is intrinsically connected with global warming across the rest of the world. In a phenomenon known as Arctic Amplification where the Arctic warms twice as fast as the rest of the world, which has warmed in excess of 1 degree Celsius (1.8 degrees F) with global warming due to emissions from human reliance on petroleum-based fuels.

The ice has the light reflective property that redirect the heat. But as it melts, the heat-absorbent ocean water takes its place, according to Derby.

With heat transport to lower latitudes, as the Arctic warms up, the transfer of heat to the Arctic would be expected to decrease.

However, in a changing climate, the transport of water vapor or clouds into the Arctic can counteract the cooling of the heat transport. The water vapor causes local temperature in the Arctic to rise.

In his research, Derby is adding more factors into the model to make it more realistic to the Arctic ice cover, and to investigate how the global rise of greenhouse gas will impact the ice melt at a local level.

Rao said, in her field of geoscience, the past informs the present and the future. Studying the ancient past of Earth’s environment builds a better understanding of the complex systems involved.

“Only when we can really understand or estimate the future better, then we can come up with better plans in terms of how we do climate adaptation and climate mitigation,” Rao said.

The numbers of climate change may seem small, but  a small change now may mean a colossal shift into the future. <The changes are occurring now – we don’t want to suggest this is a problem for the next millennium.

Through Rao and Derby’s research of both the past and the future, concerns of climate change continue to loom in both the vanishing fabric of the Arctic and the demise of a species.

Photo at top: Arctic water and the atmosphere help scientists reconstruct the past climate record and inform models for the future. (Photo by Kai Boggild, distributed via imaggeo.egu.eu.)


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