AGU Advances: Clumped-isotope constraint on upper-tropospheric cooling during the last glacial maximum

Asmita Banerjee, Laurence Y. Yeung, Lee T. Murray, Xin Tie, Jessica E. Tierney, and Allegra N. Legrande


Ice cores and other paleotemperature proxies, together with general circulation models, have provided information on past surface temperatures and the atmosphere’s composition in different climates. Little is known, however, about past temperatures at high altitudes, which play a crucial role in Earth’s radiative energy budget. Paleoclimate records at high-altitude sites are sparse, and the few that are available show poor agreement with climate model predictions. These disagreements could be due to insufficient spatial coverage, spatiotemporal biases, or model physics; new records that can mitigate or avoid these uncertainties are needed. Here, we constrain the change in upper-tropospheric temperature at the global scale during the Last Glacial Maximum (LGM) using the clumped-isotope composition of molecular oxygen trapped in polar ice cores. Aided by global three-dimensional chemical transport modeling, we exploit the intrinsic temperature sensitivity of the clumped-isotope composition of atmospheric oxygen to infer that the upper troposphere (effective mean altitude 10–11 km) was 6–9°C cooler during the LGM than during the late preindustrial Holocene. A complementary energy balance approach supports a minor or negligible steepening of atmospheric lapse rates during the LGM, which is consistent with a range of climate model simulations. Proxy-model disagreements with other high-altitude records may stem from inaccuracies in regional hydroclimate simulation, possibly related to land-atmosphere feedbacks.

Plain Language Summary

Atmospheric temperatures at high altitudes determine the fate of montane glaciers and the energy balance of the planet. They change with Earth’s climate, but our knowledge of this relationship is poor: the few available temperature records for high-altitude cooling at the most recent ice age, which are limited to the tropics, disagree with model predictions for unknown reasons. Here we report a global-scale constraint for high-altitude temperature, applied to the last ice age, which yields results consistent with global climate model predictions. This new proxy―based on the isotopic variants of molecular oxygen trapped in polar ice cores―can be applied deeper in the past to understand the relationship between surface and high-altitude temperatures in different climates.

doi: 10.1029/2022AV000688

Companion piece from Seltzer and Tyne: Retrieving a “weather balloon” from the last ice age

Most but not all Texas coaches say they’ll plan for climate change

Mike Williams, Rice News – Aug. 1, 2022

Rice University survey suggests some aren’t considering dangerous conditions to come

A survey of coaches and athletic officials in Texas indicates many of them would be wise to think harder about the risks their students face as the climate changes, according to Rice University researchers who conducted the statewide study.

Rice climate scientist Sylvia Dee led a survey of Texas coaches, trainers and athletic directors showing that while many are aware of the risks of outdoor workouts during the height of summer, not all are on board with adjusting for hotter weather. Dee said that’s concerning in light of recent warnings that climate change is already making Texas’ summers hotter. For example, a 2021 report from the Texas State Climatologist’s office said Texans should expect the number of 100-degree days each summer to nearly double by 2036 compared to the average numbers from 2001-2020.

A survey of Texas college and high school coaches, trainers and athletic directors suggests many are not taking climate change into account as they plan their programs’ futures. (Credit:

“It’s one thing to send out a survey, but we need to think ahead and have the tough conversations about what to do if it’s too hot to play football in the summer in the near future (or even now),” said Dee, an assistant professor of Earth, environmental and planetary sciences. “I want to hope that just receiving this survey got these athletic staff thinking about the problem.”

The survey of hundreds of coaches and athletic directors at Texas high schools, colleges and universities found that most are aware of the dangers of intensive workouts and strenuous events when temperatures above 95 degrees Fahrenheit can put athletes at risk of heat-related illnesses.

They indicated they’re keeping a close eye on damaging heat, humidity and wet bulb temperatures and will adjust schedules as necessary. But surprisingly, some indicated they don’t acknowledge climate change or its implications for the health of athletes and their programs.

The results appear in an open-access paper in the American Geophysical Union journal GeoHealth.

The 22-question survey, organized and carried out by students starting during the COVID-19 pandemic in 2020, went to 4,701 email contacts, with complete responses from 224 Texas coaches and officials, 51% of whom coach football.

The study relied on state-of-the-art simulations developed at the National Center for Atmospheric Research to compare temperature, heat index, humidity and wet bulb temperature in Texas over two key periods: 1976-2000 and 2076-2100. The projections incorporated estimates for high- and low-carbon emissions scenarios through the end of the century.

They projected average air temperatures, heat index values and wet bulb temperatures will all rise substantially in the future with heat index values regularly exceeding 113 degrees Fahrenheit in Houston, Austin and San Antonio, and exceeding 110 degrees in Dallas, even in the lower-emissions scenario. In West and North Texas cities, including Lubbock, El Paso, Midland/Odessa and Abilene, maximum heat index values could be 30 degrees higher than they are now.

Wet bulb temperature is the temperature of a parcel of air at 100% humidity, basically the point at which athletes — and everyone else — can no longer sweat to cool their bodies. According to one study, even the healthiest people would not survive a wet bulb temperature of 95 degrees for more than several hours in the shade.

Researchers at Rice University and elsewhere polled thousands of coaches and athletic directors at Texas high schools and colleges about how rising temperatures will affect their summer practices. From left: top row, Selena Guo, Beck Miguel Saunders-Shultz, Gargi Samarth and Emily Gurwitz; second row, Chelsea Li, Lizzy Gaviria, Karen Lu and Ebrahim Nabizadeh; bottom row, Kate Weinberger, Sylvia Dee, Jane Baldwin and Christine Nittrouer. Photos courtesy of The Climate and Water Lab/Rice University

“It’s quite rare that you would see the wet bulb temperatures on a newscast,” Dee said. “Although a weather forecast usually reports the heat index (the “feels-like” number that combines temperature and humidity), the wet bulb temperature is the one that matters for heat exhaustion, heat stroke and exertional heat illness.”

All of those responding to the survey reported they were aware of heat warnings issued by the National Weather Service, and 88% indicated they factor those warnings into decisions on whether to cancel practice. However, only 54% indicated they take humidity into account when making decisions.

“This discrepancy suggests that there may be a lack of understanding among athletic staff in how humidity affects the perceived temperature,” the researchers wrote.

They noted “athletic staff placed heavier emphasis on and were more concerned about the impact of temperature rather than climate change.” Fully 30% of those who responded were “not concerned at all” about the effects of climate change.

Dee noted there are state-level guidelines that discuss the risks of heat illness for various athletic activities. “But there’s certainly no acknowledgement of increasing risk in the future in any of these documents,” she said.

Dee said the Rice athletes among her intro-level students inspired the project. “I asked them what they do when it’s 100 degrees and humid outside. Where do you go? How do you handle that?” she said. “That got me thinking it would be a neat to start them thinking about the impacts of climate change on student athletes.”

The first pandemic summer of 2020 provided an opportunity to set them to work through online internships, gathering contact data for Texas coaches and officials. Along with designing the survey itself, she said that took nearly two years.

To better understand the responses, Dee and her Rice team collaborated with Christine Nittrouer, formerly a Ph.D. student of Mikki Hebl in Rice’s Department of Psychological Sciences and now a colleague at Texas Tech University who is accustomed to analyzing survey data, as well as colleagues who study extreme weather and epidemiology.

“It’s not surprising that it’s going to get really hot,” Dee said. “But it was a little frightening that, in relation to the physiological limit, there’s a lot of evidence that it’s already too hot for student athletes to safely play sports outdoors.”

She and co-author Nittrouer are interested in a follow-up collaboration that goes beyond the athletic field.

“There’s some interesting work to be done in this field,” she said. “A lot will rely heavily on our colleagues in the social sciences and humanities to think about how we communicate the risks to people in a way that will help them change their minds.”

Co-authors of the paper are Rice Ph.D. student Ebrahim Nabizadeh and undergraduates Chelsea Li, Lizzy Gaviria, Selena Guo, Karen Lu, Beck Miguel Saunders-Shultz and Gargi Samarth; Stanford undergraduate Emily Gurwitz; Jane Baldwin, an assistant professor of Earth system science at the University of California, Irvine, and an adjunct associate research scientist at the Lamont-Doherty Earth Observatory at Columbia University; and Kate Weinberger, an environmental epidemiologist at the University of British Columbia. Nittrouer is an assistant professor of management at Texas Tech.

The Rice Office of Undergraduate Research and Inquiry supported the research.

Study: Explosive volcanic eruption produced rare mineral on Mars

HOUSTON – (July 25, 2022) – Planetary scientists from Rice University, NASA’s Johnson Space Center and the California Institute of Technology have an answer to a mystery that’s puzzled the Mars research community since NASA’s Curiosity rover discovered a mineral called tridymite in Gale Crater in 2016.

NASA's Mars Curiosity rover
NASA’s Curiosity Mars rover snapped this low-angle self-portrait at the site where it drilled into a rock July 30, 2015, producing a powder (visible in foreground) that was later confirmed to contain the rare mineral tridymite. (Image courtesy of NASA/JPL-Caltech/MSSS)

Tridymite is a high-temperature, low-pressure form of quartz that is extremely rare on Earth, and it wasn’t immediately clear how a concentrated chunk of it ended up in the crater.Gale Crater was chosen as Curiosity’s landing site due to the likelihood that it once held liquid water, and Curiosity found evidence that confirmed Gale Crater was a lake as recently as 1 billion years ago.

“The discovery of tridymite in a mudstone in Gale Crater is one of the most surprising observations that the Curiosity rover has made in 10 years of exploring Mars,” said Rice’s Kirsten Siebach, co-author of a study published online in Earth and Planetary Science Letters. “Tridymite is usually associated with quartz-forming, explosive, evolved volcanic systems on Earth, but we found it in the bottom of an ancient lake on Mars, where most of the volcanoes are very primitive.”

Kirsten SiebachSiebach, an assistant professor in Rice’s Department of Earth, Environmental and Planetary Sciences, is a mission specialist on NASA’s Curiosity team. To suss out the answer to the mystery, she partnered with two postdoctoral researchers in her Rice research group, Valerie Payré and Michael Thorpe, NASA’s Elizabeth Rampe and Caltech’s Paula Antoshechkina. Payré, the study’s lead author, is now at Northern Arizona University and preparing to join the faculty of the University of Iowa in the fall.

Siebach and colleagues began by reevaluating data from every reported find of tridymite on Earth. They also reviewed volcanic materials from models of Mars volcanism and reexamined sedimentary evidence from the Gale Crater lake. They then came up with a new scenario that matched all the evidence: Martian magma sat for longer than usual in a chamber below a volcano, undergoing a process of partial cooling called fractional crystallization until extra silicon was available. In a massive eruption, the volcano spewed ash containing the extra silicon in the form of tridymite into the Gale Crater lake and surrounding rivers. Water helped break down the ash through natural processes of chemical weathering, and water also helped sort the minerals produced by weathering.

The scenario would have concentrated tridymite, producing minerals consistent with the 2016 find. It would also explain other geochemical evidence Curiosity found in the sample, including opaline silicates and reduced concentrations of aluminum oxide.

Curiosity rover's tridymite drill site
NASA’s Curiosity Mars Rover drilled this hole to collect sample material from a rock target called “Buckskin” on July 30, 2015. The diameter of the hole is slightly smaller than a U.S. dime. Rock powder from the drill site was subsequently delivered to a laboratory inside the rover and found to contain the rare mineral tridymite. (Image courtesy of NASA/JPL-Caltech/MSSS)

“It’s actually a straightforward evolution of other volcanic rocks we found in the crater,” Siebach said. “We argue that because we only saw this mineral once, and it was highly concentrated in a single layer, the volcano probably erupted at the same time the lake was there. Although the specific sample we analyzed was not exclusively volcanic ash, it was ash that had been weathered and sorted by water.”

If a volcanic eruption like the one in the scenario did occur when Gale Crater contained a lake, it would mean explosive volcanism occurred more than 3 billion years ago, while Mars was transitioning from a wetter and perhaps warmer world to the dry and barren planet it is today.

“There’s ample evidence of basaltic volcanic eruptions on Mars, but this is a more evolved chemistry,” she said. “This work suggests that Mars may have a more complex and intriguing volcanic history than we would have imagined before Curiosity.”

The Curiosity rover is still active, and NASA is preparing to celebrate the 10th anniversary of its landing next month.

The research was funded by NASA (15-MSLPSP15_2-0051, 15-MSLPSP15_0015, 80NSSC22K0732), the National Science Foundation (1947616) and Rice’s Department of Earth, Environmental and Planetary Sciences.