About 34 million years ago, Earth began to cool dramatically, transforming the climate from greenhouse to icehouse and causing sea levels to fall. As more land was exposed to weathering forces, copious amounts of sediment likely sloughed off continents into the oceans, bound for the deep seafloor.

So, when Montana State University assistant professor Zachary Burton, then a doctoral student at Stanford University, set out to see how that sediment had accumulated as submarine layers of sand and mud, he expected there would be much to discover.

To his surprise, he instead found—nothing.

The journal Earth-Science Reviews has published Burton’s findings, which reveal the existence of a global unconformity—or gap in the rock record—around the edges of every continent at the time of the pivotal greenhouse-to-icehouse climatic transition.

In addition to challenging conceptual models widely used for the past half-century about the relationships between sea levels and sediment movement in the deep oceans, Burton said his discovery has left him and his co-authors wondering: Where in the world did all the sediment go?

“This is something we weren’t at all expecting to discover,” said Burton, who recently joined the faculty of MSU’s Department of Earth Sciences in the College of Letters in Science. “We’d set out to find lots of deposition, lots of sand. Instead, we’re finding a gap in the rock record. That sediment is missing.”

The paper began as part of Burton’s doctoral thesis, for which he conducted a massive review of existing data on deep-sea sediments deposited during various extreme climatic periods in Earth’s history.

Last year, Scientific Reports published another article based on a different chapter of Burton’s thesis. It described the presence of large volumes of sand deposited along the margins of nearly all continents when sea levels were high during a very warm climate interval about 50 million years ago. It was another unexpected finding that didn’t conform to traditional ideas about how ocean sediments are deposited.

Burton said further research is needed to explain the results of both studies, and to expand understanding of global controls on marine sedimentary systems in the past, present and future.

“Why do we care about sand moving out in the ocean? It’s not only to understand what happened millions of years ago, but also to understand the contemporary world and what’s going on under the ocean surface,” he said.

For example, he said, geologists employed by oil companies study the distribution of sands in sedimentary basins, which often contain oil. Some scientists are investigating the suitability of sand deposits as reservoirs for sequestering carbon. And a better grasp of submarine processes and hazards is necessary to protect undersea cables, as well as to determine risks to other types of offshore infrastructure, such as wind farms or oil and gas platforms.

As a new MSU faculty member, Burton plans to continue studying the impacts of historic climate changes and other catastrophic events with his students. In the spring, he hopes to offer a special course for upper-level undergraduate and graduate students to investigate what happened after an especially notorious moment in Earth’s natural history: the Chicxulub meteor impact that killed the dinosaurs 66 million years ago.

Burton said the research-intensive seminar will follow a similar approach to his just-published paper. It will involve looking at data from marine settings along the world’s continental margins to compile a catalog of sediments centered around the dinosaur-killing impact.

“The motivation is to understand the responses of these sedimentary systems to catastrophic perturbations, such as extreme climate change or a world-altering meteorite impact,” he said. “For students, it’s an opportunity to contribute to a research question that hasn’t really been answered.”

As for the newly published paper, Burton said he expects it to capture some attention.

“We put out a paper that hopefully gets people scratching their heads,” he said. “It’s good to keep us all thinking.”

Any breach of what climate scientists agree is the safer limit on global warming would result in “irreversible consequences” for the planet, said a major academic study published on Wednesday.

Even temporarily exceeding 1.5 degrees Celsius before bringing temperatures back down—a scenario known as an “overshoot”—could cause sea level rises and other disastrous repercussions that might last millennia.

This “does away with the notion that overshoot delivers a similar climate outcome” to a future where more was done earlier to curb global warming, said Carl-Friedrich Schleussner, who led the study co-authored by 30 scientists.

The findings, three years in the making, are urgent, as the goal of capping global temperature rises at 1.5C above pre-industrial levels is slipping out of reach.

Emissions of heat-trapping greenhouse gases must nearly halve by 2030 if the world is to reach 1.5C—the more ambitious target enshrined in the 2015 Paris climate accord.

Currently, however, they are still rising.

Some kind of overshoot of 1.5C is increasingly being seen as inevitable by scientists and policymakers.

This new study, published in the peer-reviewed journal Nature, cautions against “overconfidence” in such a scenario when the dangers are not fully appreciated.

An overshoot could trigger impacts that last hundreds if not thousands of years, or cross “tipping points” that prompt large and unrepairable changes in earth’s climate system, the scientists warn.

It could mean the thawing of permafrost and peatlands, carbon-rich landscapes that would release huge volumes of planet-heating greenhouse gases if lost.

And sea levels could rise an additional 40 centimeters (16 inches) if 1.5C is exceeded for a century, the authors said, an existential difference for vulnerable low-level island nations.

“For most climate indicators, there are irreversible consequences due to the temporary exceedance of, for example, the 1.5 degree limit,” said Schleussner from the Austria-based International Institute of Applied Systems Analysis.

“Even if you brought temperatures back down again, the world that we are looking at is not the same as if you didn’t overshoot.”

Act now

Taken together, the world’s existing pledges for climate action would result in nearly 3C of warming by 2100, according to the UN.

To reach 1.5C, emissions must be at net zero by 2050, which means balancing the amount of carbon dioxide produced against the amount humanity can remove from the atmosphere via technology.

This process, known as carbon removal, would need to be massively scaled up to pull global temperatures back down in the event of an overshoot, something that is far from guaranteed.

“We cannot be confident that temperature decline after overshoot is achievable within the timescales expected today,” the authors wrote.

Schleussner said their findings reinforced “the urgency of governments acting to reduce emissions now and not later down the line, to keep peak warming as low as possible”.

“If you want to limit the climate risks in an effective manner, the race to net zero needs to be seen for what it is,” he said.

© 2024 AFP

Researchers from the Department of Earth Sciences at the University of Oxford have shown that weathering of rocks in the Canadian Arctic will accelerate with rising temperatures, triggering a positive feedback loop that will release more and more CO₂ to the atmosphere. The findings have been published in the journal Science Advances.

For sensitive regions like the Arctic, where surface air temperatures are warming nearly four times faster than the global average, it is particularly crucial to understand the potential contribution of atmospheric CO₂ from weathering.

One pathway happens when certain minerals and rocks react with oxygen in the atmosphere, releasing CO₂ via a series of chemical reactions. For instance, the weathering of sulfide minerals (e.g., ‘fool’s gold’) makes acid which causes CO₂ to release from other rock minerals that are found nearby.

In Arctic permafrost, these minerals are being exposed as the ground thaws due to rising temperatures, which could act as a positive feedback loop to accelerate climate change.

Up to now, however, it has been largely unknown how this reaction will respond to temperature change and much extra CO₂ could be released.

In this new study, researchers used records of sulfate (SO₄^2-) concentration and temperature from 23 sites across the Mackenzie River Basin, the largest river system in Canada, to examine the sensitivity of the weathering process to rising temperatures. Sulfate, like CO₂, is a product of sulfide weathering, and can be used to trace how fast this process occurs.

The results demonstrated that across the catchment, sulfate concentrations rose rapidly with temperature. During the past 60 years (from 1960 to 2020), sulfide weathering saw an increase of 45% as temperatures increased by 2.3°C. This highlights that CO₂ released by weathering could trigger a positive feedback loop that would accelerate warming in Arctic regions.

Using these past records from rivers, the researchers predicted that CO₂ released from the Mackenzie River Basin could double to 3 billion kg/year by 2100 under a moderate emission scenario. This change would be equivalent to about half the total annual emissions from Canada’s domestic aviation sector for a typical year.

Lead author, Dr. Ella Walsh (Department of Earth Sciences, University of Oxford at the time of the study) said, “We see dramatic increases in sulfide oxidation across the Mackenzie with even moderate warming. Until now, the temperature sensitivity of CO₂ release from sulfide rocks and its main drivers were unknown over large areas and timescales.”

Not all parts of the river catchment responded in the same way. Weathering was much more sensitive to temperature in rocky mountainous areas, and those covered with permafrost. By modeling the process, the researchers revealed that sulfide weathering was accelerated further by processes which break rocks up as they freeze and shatter.

Conversely, areas covered with peatland showed lower increases in sulfide oxidation with warming, because the peat protects the bedrock from this process.

Co-author, Professor Bob Hilton (Department of Earth Sciences, University of Oxford) said, “Future warming across vast Arctic landscapes could further increase sulfide oxidation rates and affect regional carbon cycle budgets. Now that we have found this out, we are working to understand how these reactions might be slowed down, and it seems that peatland formation could help to lower the sulfide oxidation process.”

There are numerous similar environments across the Arctic where the combination of rock types, high proportions of exposed bedrock, and vast areas of permanently frozen ground create conditions where warming will result in rapid increases in sulfide weathering. As a result, it is extremely likely that this effect is not restricted to the Mackenzie River Basin.

According to the researchers, the study highlights the value of considering sulfide weathering in large scale emission models, which are extremely useful for making predictions of climate change.

Records were provided by Environment Canada through their National Long-term Water Quality Monitoring Program. Sulfate concentrations were measured using ion chromatography, where liquid samples are passed through a column filled with a resin which attracts specific ions based on their charge.

The COVID-19 pandemic gave the global medical community the opportunity to take giant strides forward in understanding how to develop vaccines and implement public health measures designed to control the spread of disease, but the crisis also offered researchers the chance to learn more about another kind of contagion: ideas.

Mathematician and assistant professor of biology Nicholas Landry, an expert in the study of contagion, is exploring how the structure of human-interaction networks affects the spread of both illness and information with the aim of understanding the role social connections play in not only the transmission of disease but also the spread of ideas and ideology.

In a paper published this fall in Physical Review E with collaborators at the University of Vermont, Landry explores a hybrid approach to understanding social networks that involves inferring not just social contacts but also the rules that govern how contagion and information spread.

“With the pandemic, we have more data than we’ve ever had on diseases,” Landry said. “The question is, What can we do with that data and how much data do you need to figure out how people are connected?”

The key to making use of the data, Landry explained, is to understand their limitations and understand how much confidence we can have when using epidemic models to make predictions.

Landry’s findings suggest that reconstructing underlying social networks and their impacts on contagion is much more feasible for diseases like SARS-CoV-2, Mpox or rhinovirus but may be less effective in understanding how more highly infectious diseases like measles or chickenpox spread.

However, for extremely viral trends or information, Landry suggests it may be possible to track how they spread with more precision than we can achieve for diseases, a discovery that will better inform future efforts to understand the pathways of both contagion and misinformation.