Every month, researchers at Lamont-Doherty Earth Observatory and other parts of the Columbia Climate School publish work that deepens our understanding of the planet.
In October, we featured research on the chemical reactivity of microplastics, air quality shifts after NYC’s congestion pricing, how climate change stopped the next ice age, glacier stabilization by a massive ancient ice shelf in Antarctica and giant Martian canyons.
Here are additional studies by our researchers that are worth noting.
Delaying Emissions Cuts Could Tip the Arctic Into Abrupt Cooling
Even after carbon dioxide emissions stop, the Arctic could undergo dramatic climate changes if emissions reductions are delayed too long, according to a new study by Columbia climate scientists.
Using a global climate model, the researchers simulated what would happen if CO₂ emissions stopped at different levels of cumulative emissions. When emissions ceased earlier, Arctic temperatures generally stabilized or continued rising slightly. But under scenarios with much higher accumulated emissions, the model showed a striking reversal: Arctic temperatures fell by 2 to 3 degrees Celsius over the following century, while sea ice expanded.
The cooling was driven by a severe weakening or near-collapse of the Atlantic Meridional Overturning Circulation (AMOC), a system of ocean currents that transports heat northward.
“Stopping emissions doesn’t guarantee the climate simply settles down,” said lead author You-Ting Wu, a doctoral student at Columbia University. “If we delay cuts and overshoot the Paris 2 °C target, we raise the risk of pushing the Arctic and North Atlantic across an abrupt, hard-to-reverse threshold. So when we cut matters, not just whether we cut.”
Why it matters: The findings suggest that delaying emissions reductions could trigger disruptive climate changes even after emissions cease. The results come from simulations and do not predict whether or when the AMOC might collapse. The projected Arctic cooling would be a consequence of disrupted ocean circulation, not a reversal of global warming.
Other Columbia-affiliated authors: Michael Previdi, Lamont-Doherty Earth Observatory; Anastasia Romanou and Paul Lerner, NASA Goddard Institute for Space Studies; and Lorenzo Polvani, Department of Applied Physics and Applied Mathematics.
Listening to Tiny Earthquakes Deep Underground
Next-generation geothermal plants work by pumping water into hot rock at high pressure, cracking it open so water can circulate and carry heat to the surface. The fracturing triggers small earthquakes, and a new study shows how fiber-optic cables can give a detailed picture of those quakes and the rock around them.
Researchers used a fiber-optic sensing system installed in a nearly 3-kilometer-deep borehole at the Cape Modern geothermal field in Utah. The technology, known as distributed acoustic sensing, sends pulses of laser light through a fiber-optic cable. When seismic waves stretch or compress the cable, they alter the returning light, allowing researchers to measure ground vibrations at intervals of about two meters along its length. This effectively turns a single cable into thousands of seismic sensors.
The team analyzed roughly 1,800 small earthquakes triggered by fracturing rock at the site, measuring how seismic waves lose energy as they travel through the ground. They produced the first detailed measurements of how seismic waves lose energy at different depths, finding that the loss is greatest in the top few hundred meters and diminishes farther underground. How much that shallow layer absorbs is the piece researchers usually have to guess at.
The signal of small earthquakes at a few kilometers depth is largely muffled when it reaches the surface, making it difficult to determine the earthquakes’ true characteristics. By recording the waves closer to their source and measuring how much energy they lose, the team could better estimate the area that slipped and improve their estimates of how much stress was released.
“Our ability to observe small earthquakes is expanded by the dense network of sensors provided by downhole fiber-optic cables,” says lead author Hilary Chang, a Lamont postdoctoral research scientist. “This will help us understand how stress release varies among different types of earthquakes and ultimately improve seismic hazard assessments.”
Why it matters: Enhanced geothermal systems could provide a significant source of low-carbon energy. More precise monitoring of the small quakes that come with building them could help scientists understand how underground faults behave, improve hazard assessments and support monitoring at geothermal sites.
Ancient Arctic Ocean Held More Carbon During the Last Ice Age
Scientists have uncovered new evidence that the deep Arctic Ocean was more isolated from the atmosphere during the last ice age, potentially allowing carbon to accumulate in its waters.
Lead author Jesse Farmer, now at the University of Massachusetts Boston, began the research while a graduate student in Columbia’s Department of Earth and Environmental Sciences (DEES). Farmer, along with Lamont’s Bärbel Hönisch and Jannik Martens, analyzed boron isotopes preserved in the shells of tiny marine organisms recovered from nine sediment cores in the central and western Arctic. These chemical signatures allowed them to reconstruct changes in seawater acidity over the past 45,000 years.
During the last glacial period, roughly 45,000 to 11,000 years ago, the deep Arctic was substantially more acidic relative to surface waters in the nearby Nordic Seas than it was in the warmer millennia that followed. The researchers suggest deep Arctic waters were renewed more slowly then, allowing carbon from decomposing organic matter to accumulate. In the early and middle Holocene, the Arctic’s two deep basins also differed in chemistry, pointing to unequal exchange with surface waters.
“The Arctic is the least studied ocean basin, and it’s the one changing fastest,” says Hönisch, a paleoceanographer and DEES professor. “Few Arctic Ocean sediment cores have been collected to date and most are discontinuous. This new record allows us to see a snapshot of Arctic carbon chemistry back through the last ice age, which is something we haven’t been able to do before.”
Why it matters: The deep ocean stores enormous quantities of carbon, and ocean circulation shapes how much stays there rather than returning to the atmosphere. Understanding how Arctic circulation and carbon storage responded to past climate shifts could help scientists anticipate how the rapidly warming Arctic will take up human-produced carbon.
A More Accurate Timeline of Earth’s Magnetic Reversals
Earth’s magnetic field has flipped direction many times throughout its history, leaving a record in magnetized volcanic rocks and seafloor sediments. Scientists use these reversals as time markers to determine the ages of geological formations and reconstruct plate motions and major events in Earth’s past.
A new study by researchers at Lamont-Doherty Earth Observatory and the University of Wisconsin-Madison combines different sources of information to produce a more accurate timeline of the reversals that occurred between 83 and 33 million years ago.
The researchers drew on three kinds of data that capture time differently: magnetic stripes over spreading mid-ocean ridges, which record the relative length of each magnetic interval; radioactive dating of volcanic ash layers, which pinpoints a handful of absolute dates; and alternating sediment patterns that record Earth’s orbital cycles, which recur on a known schedule and can be counted like tree rings. Their resulting timescale, called MM26, sharpens the estimated timing of each reversal and attaches a quantified uncertainty to it. Combining all three data sources produced less uncertainty than relying on any one of them, offering a way to weigh and merge different geological timelines.
“The key implication is that we showed a way to combine different sources of information in a time scale that agrees with all the available data and has a quantified uncertainty,” says lead author Alberto Malinverno, a geophysicist at Lamont. “This approach can improve geological time scale construction in the future.”
Why it matters: Because the magnetic field flips everywhere at the same time, reversals act as a shared set of time markers in rocks all over the world. An updated record of when they happened sharpens the dates of everything scientists line up against them, including past episodes of dramatic climate change.
