Research improves accuracy of climate models – particularly for extreme events
Researchers have devised a new machine learning method to improve large-scale climate model projections and demonstrated that the new tool makes the models more accurate at both the global and regional level. This advance should provide policymakers with improved climate projections that can be used to inform policy and planning decisions.
“Global climate models are essential for policy planning, but these models often struggle with ‘compound extreme events,’ which is when extreme events happen in short succession – such as when extreme rainfall is followed immediately by a period of extreme heat,” says Shiqi Fang, first author of a paper on the work and a research associate at North Carolina State University.
“Specifically, these models struggle to accurately capture observed patterns regarding compound events in the data used to train the models,” Fang says. “This leads to two additional problems: difficulty in providing accurate projections of compound events on a global scale; and difficulty in providing accurate projections of compound events on a local scale. The work we’ve done here addresses all three of those challenges.”
“All models are imperfect,” says Sankar Arumugam, corresponding author of the paper and a professor of civil, construction and environmental engineering at NC State. “Sometimes a model may underestimate rainfall, and/or overestimate temperature, or whatever. Model developers have a suite of tools that they can use to correct these so-called biases, improving a model’s accuracy.
“However, the existing suite of tools has a key limitation: they are very good at correcting a flaw in a single parameter (like rainfall), but not very good at correcting flaws in multiple parameters (like rainfall and temperature),” Arumugam says. “This is important, because compound events can pose serious threats and – by definition – involve societal impacts from two physical variables, temperature and humidity. This is where our new method comes in.”
The new method takes a novel approach to the problem and makes use of machine learning techniques to modify a climate model’s outputs in a way that moves the model’s projections closer to the patterns that can be observed in real-world data.
The researchers tested the new method – called Complete Density Correction using Normalizing Flows (CDC-NF) – with the five most widely used global climate models. The testing was done at both the global scale and at the national scale for the continental United States.
“The accuracy of all five models improved when used in conjunction with the CDC-NF method,” says Fang. “And these improvements were especially pronounced with regard to accuracy regarding both isolated extreme events and compound extreme events.”
“We have made the code and data we used publicly available, so that other researchers can use our method in conjunction with their modeling efforts – or further revise the method to meet their needs,” says Arumugam. “We’re optimistic that this can improve the accuracy of projections used to inform climate adaptation strategies.”
The paper, “A Complete Density Correction using Normalizing Flows (CDC-NF) for CMIP6 GCMs,” is published open access in the Nature journal Scientific Data. The paper was co-authored by Emily Hector, an assistant professor of statistics at NC State; Brian Reich, the Gertrude M. Cox Distinguished Professor of Statistics at NC State; and Reetam Majumder, an assistant professor of statistics at the University of Arkansas.
The work was made possible by the National Science Foundation, under grants 2151651 and 2152887.
Journal
Scientific Data
Method of Research
Computational simulation/modeling
Subject of Research
Not applicable
Article Title
A Complete Density Correction using Normalizing Flows (CDC-NF) for CMIP6 GCMs
Article Publication Date
30-Jul-2025
How climate shapes soil fungal traits
Study reports on global distributions of microbial traits with applications for soil health
Dartmouth College
image:
Global distribution of 3,500+ study sites used in the analysis of AM fungal spore traits across diverse biomes.
view moreCredit: Map by Smriti Pehim Limbu.
Many soil microbes play a vital role in ecosystems, as they help plants access nutrients and water and assist in stress tolerance such as during drought and to defend against pathogens.
One such group of soil microbes are arbuscular mycorrhizal, aka AM, fungi. These important fungi are essential to plant health and are associated with the roots of approximately 70% of plant species on land. Through their symbiotic relationship with plant roots, the fungi contribute significantly to the carbon cycle and other processes that sustain ecosystem functioning.
A fungus's spores are responsible for fungal reproduction and dispersal. And spore traits, including volume, cell wall thickness, ornamentation such as projections or depressions in the cell wall, shape, and color, can affect how well fungi survive in different environments.
A new Dartmouth-led study reports on how global climate conditions affect AM fungal spore traits and the species biogeographic patterns. The study is the first to examine multiple traits of this kind on a global scale. The results are published in the Proceedings of the National Academy of Sciences.
"As climate change continues, we expect shifts in these microbial traits that influence how these fungi survive, spread, and interact with plants, which could have cascading effects across ecosystems, and affect restoration efforts and food production," says lead author Smriti Pehim Limbu, a postdoctoral fellow in the Ecology, Evolution, Environment & Society Program and member of the Chaudhary Ecology Lab at Dartmouth.
For the study, the researchers synthesized data from different global databases of AM fungal species with climate data, to examine how climate affects the spore traits. These included TraitAM—a public database of the spore traits of more than 340 AM fungi, created by senior author Bala Chaudhary, an associate professor of environmental studies at Dartmouth.
"Our findings showed that spores that were bigger and darker in color were more common in warm, wet climates, but there was a trade-off between persistence and dispersal," says Pehim Limbu. "While being bigger helped the spores to persist in warm, wet conditions, these conditions were associated with a more limited geographical distribution."
Spores with more cell surface ornamentation were also more common in warm, wet climates but had smaller geographic distributions. Darker spores, which have more pigment, were more common in warm, wet climates. According to the co-authors, those attributes may help protect the fungi from ultraviolet radiation and fire.
Yet, cell wall thickness for spores decreased in warm, wet climates and was more robust in cooler, drier climates. Intermediate cell wall thickness was found to be associated with broader geographic distribution.
Global distribution of 3,500+ study sites used in the analysis of AM fungal spore traits across diverse biomes. Map by Smriti Pehim Limbu.
By understanding which AM fungal spore traits thrive in specific climates such as dry versus humid climatic conditions, the co-authors report that the findings could guide commercial applications of bioinoculants, microbial amendments used for soil restoration, through selection of AM fungi suited to the local environment.
"Ecologists since before Darwin have been studying the geographic distribution of species’ traits," says Chaudhary. "For example, we know that mammals with white fur are more likely to occur in cold climates. This study takes an important step in uncovering similar patterns for the traits of microbes, giving insight into the environmental adaptations of the majority of biodiversity on Earth," says Chaudhary.
Study co-authors Pehim Limbu (Smriti.Pehim.Limbu@dartmouth.edu) and Chaudhary (Bala.Chaudhary@dartmouth.edu) are available for comment.
Sidney Stürmer at the Universidade Regional de Blumenau in Brazil, Geoffrey Zahn at William & Mary, Carlos Aguilar-Trigueros at University of Jyväskylä in Finland, and Noah Rogers at Utah Valley University, also contributed to the research.
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Journal
Proceedings of the National Academy of Sciences
Article Title
Climate-linked biogeography of mycorrhizal fungal spore traits
Carbon 'offsets' aren't working. Here's a way to improve nature-based climate solutions
Utah-led research provides roadmap for harnessing Earth’s natural processes to reduce atmospheric carbon dioxide
image:
Climate-stressed forest in southwestern Colorado near Wolf Creek Pass.
view moreCredit: University of Utah
A lot of the climate-altering carbon pollution we humans release into the atmosphere by burning fossil fuels gets drawn into Earth’s oceans and landscapes through natural processes, mostly through photosynthesis as plants turn atmospheric carbon dioxide into biomass.
Efforts to slow the climate crisis have long sought to harness nature, often through carbon “offsets,” aimed at bolstering forests, wetlands, and agriculture, but have generally had only marginal success so far.
A new approach: contributions vs. credits
New research led by the University of Utah’s Wilkes Center for Climate Science & Policy offers a “roadmap” for accelerating climate solutions. To be published Thursday in the journal Nature, the paper analyses various strategies for improving such nature-based climate solutions, or NbCS, specifically exploring the role of the world’s forests in pulling carbon out of the atmosphere and storing it in long-lived trees and even in the ground.
“Nature-based climate solutions are human actions that leverage natural processes to either take carbon out of the atmosphere or stop the emissions of carbon to the atmosphere,” said lead author and forest ecologist William Anderegg, a professor of biology and past Wilkes Center director. “Those are the two main broad categories. There are the avoided emissions, and that's activities like stopping deforestation. Then there's the greenhouse gas-removal pathways. That's things like reforestation where you plant trees, and as those trees grow, they suck up CO2 out of the atmosphere.”
The U-led study, which includes leading scientists from nine other universities as part of a Wilkes Center Working Group effort, identifies four components where nature-based climate actions have not lived up to their billing and proposes reforms to improve their performance and scalability.
Forests are the focus because of trees’ ability to store vast amounts of carbon that would otherwise be in the atmosphere exacerbating the climate crises. Conversely, deforestation, especially in the Amazon rainforest, is releasing carbon at an alarming rate.
About half the emissions associated with human activity are absorbed into plants, through photosynthesis, and oceans, with the rest building up in the atmosphere where these gases trap heat. Terrestrial ecosystems pull 31% of anthropogenic emissions out of the atmosphere, according to the study. While forests are seen as Earth’s most vital carbon sponge, current rates of deforestation release 1.9 gigatons of carbon a year, on par with Russia’s annual emissions. Thus, “actions to halt and reverse deforestation are a critical part of climate stabilization pathways,” the authors write.
The trouble with carbon offsets
Various programs are in place for companies to mitigate their emissions through purchasing “carbon offsets,” which fund projects aimed at preserving or restoring forests. But as currently configured, these programs are not delivering much in the way of climate benefits, according to Libby Blanchard, a postdoctoral researcher in Anderegg’s Utah lab.
“There are widespread problems with accounting for their climate impact,” said Blanchard, the paper’s second author who has extensively studied the impacts of offset programs. “For example, despite the potential for albedo to reduce or even negate the climate mitigation benefits of some forest carbon projects, calculating for the effect of albedo is not considered in any carbon-crediting protocols to date.”
To succeed, according to the study, a nature-based climate solution should
- lead to net global cooling;
- result in additional climate benefits;
- avoid carbon “leakage;”
- store carbon long enough to make a difference.
Finally, the study proposes structural reforms aimed at encouraging corporations to financially contribute to climate mitigation, as opposed to claim credit for something that may ultimately provide little climate benefit. A contribution approach would be more scientifically accurate and legally defensible than the current system, potentially resulting in higher quality projects, the authors argue.
The four critical factors explained
The first piece of the roadmap calls for accounting the various feedbacks to ensure that the NbCS results in an actual cooling effect on the climate. Planting trees can change a landscape’s albedo, that is its capacity to reflect the sun’s energy back into space.
“If you go in an ecosystem that is mostly snow covered and you plant really dark conifer trees, that can actually outweigh the carbon storage benefit and heat up the planet,” Anderegg said.
Next, the project must result in actions that that would not have otherwise occurred.
“You have to change behavior or change some sort of outcome,” Anderegg said. “You can't just take credit for what was going to happen anyway. One great example here is if you pay money to keep a forest from deforestation, but it was never going to be cut down to begin with, then you haven't done anything for the climate.”
The third problem is known as “leakage,” which occurs when a climate action simply pushes a land-disturbing activity from one place to another.
And the fourth component address climate actions’ durability, or how long they will keep carbon out of the atmosphere. This is particularly important given the longevity of carbon dioxide molecules. When fossil fuels are burned, carbon that was permanently locked in geological formations is released into the biosphere where it will cycle in and out of living things and landscapes for thousands of years.
A climate solution should always aim to keep carbon locked up for as long as possible, preferably at least a century. But drought, storms, insects, wildfire and other climate-related hazards can quickly negate any gains by killing trees.
“You have to know how big the risks are, and you have to account for those risks in the policies and programs,” Anderegg said. “Otherwise, basically you're going to lose a lot of that carbon storage as climate change accelerates the risks.”
The methods now in place, known as “buffer pools,” to account for these risks are not robust or rigorous currently, according to research by Anderegg’s lab, which expects to release a study soon highlighting potential fixes.
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The study appears July 30 in the journal Nature under the title, “Towards more effective nature-based climate solutions in global forests,” with contributions from several universities and nonprofits. Funding came from the National Science Foundation.
Journal
Nature
Method of Research
Literature review
Subject of Research
Not applicable
Article Title
Towards more effective nature-based climate solutions in global forests
Article Publication Date
30-Jul-2025
COI Statement
D.C. [Danny Cullenward of University of Pennsylvania] previously consulted for Isometric and is a member of the Milkywire Climate Transformation Fund Advisory Board, the UNFCCC Article 6.4 mechanism Methodological Expert Panel, and California's Independent Emissions Market Advisory Committee
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