A recent study published in Nature Geoscience provides groundbreaking insights into long-term changes in tropical weather patterns that are leading to an increased frequency of extreme weather events such as heat waves and heavy rainfall in the Indo-Pacific. These changes are possibly driven by global warming, among other factors.

The paper, titled “Indo-Pacific regional extremes aggravated by changes in tropical weather patterns,” employs a recently proposed methodology that characterizes occurrence trends of weather patterns using atmospheric analogs, which are linked to the concept of recurrences in dynamical systems theory.

Unlike previous approaches, which have often focused on shifts in average behavior, the method used in the study can identify occurrence trends for each daily weather pattern, thereby enabling a direct study of their association with extreme events—something that was previously unachievable.

Thanks to this methodology, it was possible to identify the emergence of new large-scale atmospheric patterns, which are exacerbating regional weather extremes.

The study, led by doctoral student Chenyu Dong and Assistant Professor Gianmarco Mengaldo from the College of Design and Engineering (CDE) at the National University of Singapore (NUS), and a collaborative team of international scientists, uses advanced reanalysis datasets to analyze the tropical Indo-Pacific region’s evolving weather systems.

The researchers found that since the 1990s, previously rare weather patterns have become more common, while some others that were once prominent have nearly disappeared. These changes are linked to shifts in the Pacific Walker Circulation, a key driver of tropical weather and climate, whose future changes remain highly uncertain in current climate models.

Detecting long-term trends in the tropical Indo-Pacific has consistently been a challenge, especially on a daily time scale, due to the confluence of several modes of variability that tends to overshadow trend signals. This study is one of the first to investigate long-term changes in tropical weather patterns and their relationship with extreme events on a daily time scale.

“Critical changes in tropical weather patterns are significantly aggravating regional extremes, namely heat waves and extreme precipitation, in the tropical Indo-Pacific region. Our study is one of the first to disentangle trend vs. variability in the tropics, an aspect that has been historically challenging.

“We show that the changes identified cannot be fully explained by interannual modes of variability, and a possible culprit is anthropogenic global warming, though the influence of other factors may play a role.

“Further in-depth analyses are required to better inform climate modeling and climate adaptation strategies, especially in the tropical Indo-Pacific, where climate models still struggle to provide reliable projections.

“For Singapore, and other countries in Southeast Asia, improving climate projection capabilities and better understanding how tropical dynamics and regional extremes are evolving is of vital importance. This study is one step towards this direction,” said Asst Prof Mengaldo from the Department of Mechanical Engineering at CDE, NUS.

The study shows that new large-scale atmospheric configurations (or weather patterns) that were rare before the 1990s have emerged, while some others that were prominent have disappeared. These emerging weather patterns manifest as a stronger Pacific Walker circulation (or Walker cell) and are associated with wetter and warmer conditions in Southeast Asia and drier conditions in the equatorial Pacific.

The emerging patterns cannot be explained by interannual modes of natural variability, such as the El Niño Southern Oscillation (ENSO), the Indian Ocean Dipole (IOD), the Pacific Decadal Oscillation (PDO), and the Atlantic Multidecadal Oscillation (AMO), but they are instead likely driven by long-term trends from the 1940s to the present.

These trends and shifts of large-scale atmospheric dynamics in the tropical Indo-Pacific may be caused by global warming and other factors. Although these identified emerging patterns may be driven by the combined effect of different factors (excluding known modes of inter-annual variability), the implications for current and near-future climate are critical.

The emerging weather patterns are also strongly linked to increased regional weather extremes, namely heat waves and extreme rainfall. In certain regions, these extremes are up to four times more frequent than climatology when associated with emerging weather patterns.

For example, several regions, including parts of Indonesia, Singapore, South India, the Philippines and the western Pacific, exhibit markedly increased frequency of heat waves compared with climatology. The South China Sea and its surrounding areas, including Vietnam and the Philippines, the Malay Peninsula, Singapore, the tip of South India and a portion of the Indian Ocean off the coast of Australia, exhibit considerably increased frequency of extreme rainfall.

This increase in extreme weather is noteworthy, given that such changes are associated with long-term climate trends in a region that is highly vulnerable to weather extremes.

These findings are significant in the context of climate change as they reveal that new and emerging weather patterns are contributing to increasingly severe weather in a region home to more than a billion people, as well as unique and vulnerable ecosystems.

The increased occurrences of heat waves and extreme rainfall can lead to acute heat distress and flooding, respectively. With extreme weather events posing severe socio-economic and environmental challenges, understanding these changes is critical for improving climate models and informing future climate adaptation strategies.

This study was conducted by an international team of climate scientists from leading institutions, including NUS, Institut Pierre-Simon Laplace (IPSL), Uppsala University, Stockholm University, University of Cambridge, Columbia University, World Meteorological Organization (WMO), and the Center for Climate Research Singapore (CCRS). The team is committed to advancing climate research to better understand the impacts of a changing climate on regional weather patterns and extremes.

“The emergence of new tropical weather patterns is a key signal of how anthropogenic climate change is altering atmospheric dynamics on a daily scale. Our findings show a significant increase in heat waves and extreme precipitation in the Indo-Pacific, which may have profound consequences not only for the region but for global climate as well.

“This shift in weather patterns challenges our previous understanding of tropical variability and highlights the urgency to improve climate projections and preparedness for extreme events in vulnerable regions,” said Dr. Davide Faranda, Research Director at the Laboratoire de Science du Climat et de l’Environnement (LSCE) of Institut Pierre-Simon Laplace (IPSL), French National Center for Scientific Research (CNRS).

“Heat waves and extreme rainfall are two weather extremes that require careful and advance planning from policymakers to mitigate their effects. For instance, more frequent heat waves may lead to high peaks in electricity demand with possible power outages, many heat-related illnesses that would need enough hospital beds, and crop failure that could threaten food security.

“More frequent extreme rainfall may lead to floods, which in turn are a direct threat to human life, buildings and infrastructure. Extreme rainfall may also lead to crop failure, contamination of drinkable water, and landslides.

“Southeast Asia is a relatively research-scarce region in terms of extreme weather, and further efforts are required to better prepare policymakers and local communities for a changing climate,” said Asst Prof Mengaldo.

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.