URBAN FORESTS Scientists and community planners are partnering to protect our vital city canopies - Eos.org
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VOL. 102 | NO. 6 Houston’s Rare
JUNE 2021
Winter Thundersnow
Aerosol Scientists
Pivot to COVID
Sea Cucumber Heroes
URBAN
FORESTS
Scientists and community planners
are partnering to protect our vital
city canopies.
FROM THE EDITOR
Editor in Chief
Heather Goss, Eos_EIC@agu.org
Growing Healthy City Canopies AGU Staff
Vice President, Communications, Amy Storey
Marketing,and Media Relations
W
Editorial
hen asked to imagine Washington, D.C., where AGU
Manager, News and Features Editor Caryl-Sue Micalizio
is headquartered, people who don’t live here prob- Science Editor Timothy Oleson
ably think of all our large, marble columns and Associate Editor Alexandra Scammell
monuments surrounded by lots and lots of concrete. But run- News and Features Writer Kimberly M. S. Cartier
News and Features Writer Jenessa Duncombe
ning right down the middle of the city is Rock Creek Park,
nearly 710 hectares (1,754 acres) of trees, trails, and streams Production & Design
Manager, Production and Operations Faith A. Ishii
that were designated a national park in 1890. This is an “urban Production and Analytics Specialist Anaise Aristide
forest” of perhaps the most obvious kind—a beautiful, pro- Assistant Director, Design & Branding Beth Bagley
tected piece of nature in the middle of a city. Senior Graphic Designer Valerie Friedman
Senior Graphic Designer J. Henry Pereira
These ecosystems are hugely important to city dwellers, but
Graphic Design Intern Claire DeSmit
they don’t need to be nearly as large as Rock Creek Park to pro-
vide benefits. Single trees planted along a street, small neigh- Marketing
Communications Specialist Maria Muekalia
borhood parks, and shrubs lining a thoroughfare can have sig- Assistant Director, Marketing & Advertising Liz Zipse
nificant impact on human health, local air quality and water systems, and even the economy.
In our June issue of Eos, we look at the growing body of research on this vital city greenery. Advertising
Courtney L. Peterson and colleagues walk us through the canopies of three U.S. cities—Albu- Display Advertising Steve West
steve@mediawestinc.com
querque, N.M.; Austin, Texas; and Durango, Colo.—and how local government is starting to Recruitment Advertising recruitmentsales@wiley.com
work with researchers to better manage and adapt their green spaces. As climate change exac-
erbates the urban heat island effect, among other issues, protecting local trees and their cool- Science Advisers
ing benefits is essential. Read more on page 20. Geomagnetism, Paleomagnetism, Julie Bowles
and Electromagnetism
Cities are, of course, made up of a complex amalgam of privileged and underserved com-
Space Physics and Aeronomy Christina M. S. Cohen
munities, with different levels of access to urban benefits. (Rock Creek Park, which runs Cryosphere Ellyn Enderlin
through the northern half of the city, is an excellent example; the households in D.C. with the Study of the Earth’s Deep Interior Edward J. Garnero
lowest median incomes are in the south and across a river.) If you’re wondering what that has Geodesy Brian C. Gunter
History of Geophysics Kristine C. Harper
to do with science, turn to page 34, where we report on researchers doing the hard work in Planetary Sciences Sarah M. Hörst
communities to create green infrastructure using equity-focused development strategies. Natural Hazards Michelle Hummel
Urban forests also face unique, c ity-dwelling dangers. On page 26, we report on trees in Volcanology, Geochemistry, and Petrology Emily R. Johnson
Societal Impacts and Policy Sciences Christine Kirchhoff
Boston, Mass., that neighborhood residents realized were dying from gas leaks in the pipes Seismology Keith D. Koper
under the street. Scientists partnered with local activists and have made real, legislative change Tectonophysics Jian Lin
that’s not only keeping their streets greener but playing a part in greening the state’s entire Near-Surface Geophysics Juan Lorenzo
Earth and Space Science Informatics Kirk Martinez
energy system. Mineral and Rock Physics Sébastien Merkel
We’re going to be talking more about scientists’ role in our communities this year—“Science Ocean Sciences Jerry L. Miller
Is Society” is the theme of AGU’s Fall Meeting 2021. Turn to page 18 to read about Raleigh Mar- Global Environmental Change Hansi Singh
Education Eric M. Riggs
tin’s experience as a geoscientist fellow on the Select Committee on the Climate Crisis in the
Hydrology Kerstin Stahl
U.S. House of Representatives. You don’t need to roll up to one of D.C.’s m arble-columned Tectonophysics Carol A. Stein
buildings to be part of effective change though—Martin offers several recommendations for Paleoceanography and Paleoclimatology Kaustubh Thirumalai
Atmospheric Sciences Mika Tosca
anyone interested in talking to their local policymakers about making good decisions sup-
Nonlinear Geophysics Adrian Tuck
ported by scientific evidence. Biogeosciences Merritt Turetsky
Is the weather nice where you are today? If so, I recommend heading outside and finding a Hydrology Adam S. Ward
lovely tree to read our June issue underneath. Diversity and Inclusion Lisa D. White
Earth and Planetary Surface Processes Andrew C. Wilcox
Atmospheric and Space Electricity Yoav Yair
GeoHealth Ben Zaitchik
©2021. AGU. All Rights Reserved. Material in this issue may be photocopied by
individual scientists for research or classroom use. Permission is also granted
to use short quotes, figures, and tables for publication in scientific books and
journals. For permission for any other uses, contact the AGU Publications Office.
Eos (ISSN 0096-3941) is published monthly by AGU, 2000 Florida Ave., NW,
Heather Goss, Editor in Chief Washington, DC 20009, USA. Periodical Class postage paid at Washington, D.C.,
and at additional mailing offices. POSTMASTER: Send address changes to Member
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Submit your article proposal or suggest a news story to Eos at bit.ly/Eos-proposal.
Views expressed in this publication do not necessarily reflect official positions
of AGU unless expressly stated.
Randy Fiser, Executive Director/CEO
SCIENCE NEWS BY AGU // Eos.org 1
CONTENT
26
20 34
Features
20 Community Forests Prepare 26 The Surprising Root
for Climate Change of the Massachusetts Fight
By Courtney L. Peterson et al. Against Natural Gas
In three U.S. cities, city managers are working with By Jenessa Duncombe
scientists to keep their trees alive and thriving.
This is how activism gets turned into science and
codified into state law.
On the Cover
Credit: Claire DeSmit 34 Growing Equity
in City Green Space
By Kimberly Cartier
Urban forest management requires a deep
understanding of the complex relationship residents
have with green spaces.
2 Eos // JUNE 2021
CONTENT
5 11
6 43
Columns
From the Editor Research Spotlight
1 Growing Healthy City Canopies 40 A 50,000-Year History of Current Flow Yields New
Climate Clues
News 41 An Innovative Approach to Investigating
Subduction Slip Budgets | Global Warming Causes
4 Turf’s Dirty Little Secret Uneven Changesin Heat Stress Indicators
5 Ancient Acidic Lakes May Have Harbored Life 42 The Gaps in Environmental Networks Across Latin America
6 Scientists Map Africa’s Groundwater Recharge 43 How Did Diatoms Evolve to Swap Zinc
for the First Time for the Toxic Metal Cadmium? | The Space Dust That
8 A Reminder of a Desert’s Past, Before Dingo Removal Causes Zodiacal LightMight Come from Mars
9 Rare Wintertime Thunderstorms Recorded 44 The First Angstrom-Scale View of Weathering |
over the U.S. Gulf Coast Earthquakes Can Acidify Groundwater
10 Aerosol Scientists Try to Clear the Air 45 Parsing Routes to Aquifer Recharge Along Mountain Fronts
About COVID-19 Transmission
11 Making the Universe Blurrier
13 Oak Trees Offer a Continuous Climate Record
Editors’ Highlights
for Central Europe 46 Dawn Storms at Jupiter | Cellular Radio Signals
14 Sea Cucumbers: The Excremental Heroes of Coral Provide New Data on Smoke Particulates
Reef Ecosystems
15 Aerial Photographs Uncover Bogotá’s Indigenous Positions Available
Hydraulic System
47 Current job openings in the Earth and space sciences
17 A Space Hurricane Spotted Above the Polar Cap
Opinion Postcards from the Field
48 Modern analogues for ancient stromatolites
18 How Scientists Can Engage to Solve the Climate Crisis
AmericanGeophysicalUnion @AGU_Eos company/american-geophysical-union AGUvideos americangeophysicalunion americangeophysicalunion
SCIENCE NEWS BY AGU // Eos.org 3
NEWS
Turf’s Dirty Little Secret
A
ustralian scientists have found that more gas production. Agriculture emits the bicide likely prohibits new growth and frees
grassy sports fields used for soccer, most nitrous oxide of any sector. up more soil nitrogen for hungry microbes,
cricket, and baseball can release a As the world urbanizes, scientists are researchers said.
potent greenhouse gas into the environment. studying how nitrous oxide emissions are Aerating, fertilizing, and watering for the
A yearlong study at La Trobe University in concentrated outside the agricultural realm. oncoming sports season also increased
Melbourne, suggests that mowing, fertilizing, A better understanding of how sports fields nitrous oxide emissions. Watering decreases
and applying herbicides to turfgrass sports contribute to emissions could help mitigate the microbes’ access to oxygen, making them
fields contributes to the release of large those emissions. Although the problem is produce more nitrous oxide.
amounts of nitrous oxide. relatively small, turf’s footprint may be large. Notably, the three sports fields’ emissions
“This study is another indication that In one study by Cristina Milesi of the NASA were 2.5 times higher than those of an unused
urbanization has complex impacts on our Ames Research Center, it was calculated that lawn nearby. Nitrous oxide averaged around
environment,” said Amy Townsend-Small, a turfgrass covers an area 3 times larger than 38 grams of nitrogen per hectare per day at
biogeochemist who was not involved with the any other irrigated crop in the United States the continuously monitored sports field (data
research. “Even though most cities are work- (bit.ly/turf-grass-cycle). at the other two were intermittent) versus
ing toward increasing their amount of green about 9 grams of nitrogen per hectare per day
space, this doesn’t always help meet climate Emissions Similar to High-Intensity at the lawn.
goals.” Farming “You do get these peaks of high emissions
In the latest study, David Riches, a research in the sports field, which you just don’t get in
A Greenhouse Gas That Eats Away fellow at La Trobe, and his colleagues installed the lawn,” Riches said.
at the Ozone Layer instruments to measure nitrous oxide and
Nitrous oxide is the third most emitted methane on campus fields used for soccer and
greenhouse gas, after carbon dioxide and cricket.
methane. Although it makes up only 7% of “What we found was, we got really quite
greenhouse gas emissions in the United high emissions in the sports field soils which The field’s emissions were
States, it has 265 times the global warming were comparable to [those] of the h igh- 2.5 times higher than those
capacity of carbon dioxide. The gas is also the intensity vegetable production systems we’ve
largest source of ozone-depleting substances previously been working in,” said Riches. The of an unused lawn nearby.
from humans. team monitored conditions for 213 days from
In soil, nitrous oxide is emitted by microbes autumn to spring on one sports field and
digesting chemical compounds for energy. intermittently on two others.
Although the process is natural, humans have Applying herbicide to the field caused the More Careful Management
cultivated soil conditions that encourage largest jump in nitrous oxide emissions. Her- Could Cut Emissions
One way to reduce emissions could be to water
only when a field needs it, Riches said.
Another idea might be to dial back the
amount of fertilizer and use a s low-release or
nitrogen-inhibiting product.
The study was published in Science of the
Total Environment (bit.l y/ s ports-f ields
-emission).
Extrapolating to the rest of Australia,
Riches figures that grass playing fields alone
do not have a significant impact on green-
house gas emissions. But the effect could be
greater if lawns, parks, gardens, turf farms,
roadside vegetation, and other intensively
managed green spaces are shown to emit as
much as sports fields.
“If you look at all the intensively managed
turf in total, then it might start to become
more significant,” Riches said. “Then you
might want to do something to mitigate it
when you can.”
By Jenessa Duncombe (@jrdscience), Staff
Writer
4 Eos // JUNE 2021
NEWS
Ancient Acidic Lakes May Have Harbored Life
F
or the early microbial colonists of Earth,
land was rather uninviting. In the
ocean, chemistry and temperatures
were relatively stable, and seawater provided
a shield against ultraviolet radiation. In com-
parison, the l ow-oxygen atmosphere of
freshly exposed land offered little protection.
Microbes had to deal with fluctuating levels
of light, heat, minerals, and moisture.
Scientists have found what appears to have
been a suitable refuge from the harsh terres-
trial landscape: an acidic lake. In a recent
study, researchers identified sediments dat-
ing back billions of years that suggest a com-
munity of microbes that adapted to life in an
acidic lake that filled an ancient volcano. The
volcano’s hydrothermal waters could have
provided energy and minerals needed to sus-
tain life, according to the study, published in
Earth and Planetary Science Letters (bit .l y/
volcanic-lakes).
The researchers identified “a new environ-
ment for early life—that is, acidic volcanic
lakes—and could pinpoint specific organisms
based on their metabolisms,” said lead author
Andrea Agangi, a professor in the Graduate
School of International Resource Sciences at
Akita University in Japan. Ancient acidic lakes in volcanic cones, like this one at Ijen volcano in Indonesia, may have harbored microbial
The findings could help scientists under- life, a new study suggests. Credit: CEphoto, Uwe Aranas/Wikimedia, CC B Y-SA 3.0 (bit.ly/ccbysa3-0)
stand more about ancient life on Earth, as well
as aid in the search for extraterrestrial life in
the solar system. Similar volcanic lakes that
formed during the wetter, volcanically active spersed with layers of sediment rich in pyro- modern volcanic environments such as the
part of Mars’s early history, for example, may phyllite, known locally as wonderstone, a Yellowstone caldera complex. These proper-
too have harbored life—giving astrobiologists fine-grained mixture of light sandstone and ties include high levels of a luminum-rich
a promising new location to look. soft, black, carbon-rich shale. vanadium, arsenic, and nickel.
One of the first things Agangi’s group did “These are minerals you would associate
Identifying Wonderstone was identify the Dominion Group sediments with rocks that have been heavily altered by
Continental land emerged during the late as terrestrial. They analyzed samples of won- acids,” said Eva Stüeken, a lecturer in the
Archean, between 3 billion and 2.5 billion derstone taken from three sites. School of Earth and Environmental Sciences
years ago. There are a number of microfossils Distinguishing between ancient marine at the University of St Andrews who was not
from this period in Earth’s early history— and nonmarine sediments is tricky, but the involved in the research. If the South African
Archean microfossils are much rarer than positioning of volcanic rocks within the rocks were deposited in a marine setting, sea-
animal fossils—mostly in the form of stro- Dominion Group offered clues. When lava water would have likely neutralized the acidity.
matolites, ancient reefs formed by cyanobac- cools quickly in seawater, it hardens into Taken together, evidence offered by nearby
teria. Similar evidence of ancient life on land, tubular formations known as pillow struc- volcanic rock and mineral composition sug-
however, is very rare: Aside from the poten- tures. The wonderstone is sandwiched gests that the sediments studied were depos-
tial rarity of terrestrial-based life, tectonic between layers of volcanic rock that do not ited in an acidic lake.
activity and the rock cycle have altered many have pillow structures, which suggests that
Opposite: Unsplash/Lars Bo Nielsen
of the terrestrial rocks from the Archean. the lava erupted outside of the ocean, in the Looking for Life
Some of the world’s oldest crust lies in the open air. The sandwiched sediment was The hot, low-pH waters of an acidic lake may
Kaapvaal Craton in South Africa, which dates deposited out of the ocean, too, the authors have leached minerals from the rocks, Agangi
to around 3 billion years ago and is home to argued, washed down by a turbidity current to and his colleagues suggested. This process
the Witwatersrand Basin, a vast gold deposit settle at the bottom of a lake. would dissolve into water nutrients necessary
that has drawn miners since the late 19th In addition to being terrestrial in origin, the for biotic life, such as phosphorus and boron,
century. Here lies the Dominion Group, a South African wonderstone has properties and trace metals such as copper, selenium,
sequence of mostly volcanic rocks, inter- commonly found in hydrothermal pools in and zinc.
SCIENCE NEWS BY AGU // Eos.org 5
NEWS
“You have water, nutrients, energy—these
are the basic components people usually look
Scientists Map Africa’s Groundwater
for when looking for life,” said Agangi.
To search for signs of life, the researchers
Recharge for the First Time
used carbon isotopes. They found high ratios
of lighter isotopes in the wonderstone shale.
This isotopic signature suggested that the
carbon is organic, the authors concluded, as
it matches the signature of the modern pro-
duction of methane by s ingle-celled organ-
isms known as Archaea. Today these hardy
microbes are found in extreme environments
such as hydrothermal vents, Antarctic lakes,
and even the human digestive system.
“You have water, nutrients,
energy—these are the
basic components people
usually look for when
looking for life.”
Men and women collect water at a secured borehole in Moyale, Kenya, in 2019. Water security varies across
ecosystems in Kenya, often depending on groundwater storage and recharge rates. Credit: Munyaradzi Makoni
“I would think that low-pH acidic environ-
ments would be hostile to life, but these
T
researchers found good trends of carbon iso- he majority of people in rural Africa countries to provide information to sustain-
topes,” said Ilya Bindeman, a professor of and a large proportion in its urban ably develop water resources and overcome
stable isotope geochemistry at the University areas rely on groundwater for drinking, some of the most pressing issues countries
of Oregon who was not involved in the hygiene, and development. The rate at which often face, such as drought, deprivation, and
research. groundwater is replenished is often unknown, starvation,” said Seifu Kebede Gurmessa, a
“From all of this, we can say that it is very however, making regional water security dif- hydrologist at the University of KwaZulu-
possible—though not conclusively proven— ficult to assess. Natal, South Africa, and a study coauthor.
that methane-cycling microbes were living Now, for the first time, a study showing the “We estimate that the long-term ground-
in volcanically influenced lakes on Earth continent’s groundwater recharge rates may water recharge in Africa is approximately
3.1 billion years ago,” said Alexander Brasier, help policymakers decide how much water 15,000 cubic kilometers per decade and that
a senior lecturer in geology at the University can be drawn from aquifers without causing recharge can occur even in arid and semiarid
of Aberdeen not involved in the research. substantial depletion and impact on the envi- areas,” said MacDonald. “This is equivalent
Like Earth, Mars went through a wetter ronment. to more than half the annual rainfall in Africa,
volcanic period during its early life, and sim- “Groundwater recharge is like your which is replenishing the groundwater every
ilar acidic lakes may have formed on its sur- monthly or annual income,” said Alan Mac- decade.”
face. Not only does this correlation present a Donald, a hydrogeologist with the British So although l ong-term average rainfall
new ecological niche where researchers can Geological Survey who led the study. “It generally predicts groundwater recharge, the
search for past life on Mars, but also it estab- determines the amount of water that you can new study uncovers distinctions at local scales
lishes the Dominion Group as a good place to draw from your bank. If you draw more than due to differences in land cover. It also reveals
study the history of both planets. your income, you draw from your savings.” year-to-year differences associated with vari-
“What makes [the Dominion Group] a good With an international team from France, ability in the intensity of rainfall. The study
analogue is that it was deposited under an Nigeria, South Africa, the United Kingdom, was published in Environmental Research Letters
anoxic atmosphere,” Stüeken said. “The and the United States, MacDonald examined (bit.ly/africa-groundwater-recharge).
entire environmental setting was probably more than 300 different studies from 1970 to
more similar to Mars than the modern Earth. 2019 and developed a data set of 134 existing High Storage or High Recharge—
That’s very compelling.” recharge studies for Africa to create an over- Rarely Both
view of recharge patterns across the entire The new maps show that the majority of Afri-
continent. can countries have either high groundwater
By Richard Kemeny (@rakemeny), Science “This effort brought together extensive storage or high groundwater recharge—rarely
Writer African knowledge with expertise from other both and rarely neither.
6 Eos // JUNE 2021
NEWS
North African countries with little rainfall, to monitor and develop their groundwater State, in South Africa, agreed that although
including Algeria, Egypt, and Libya, have resources, the study authors said. the creation of a recharge map for the whole
considerable groundwater storage but very of Africa has merit when it comes to the avail-
low recharge rates. These regions are gener- Calculating Groundwater Recharge ability of groundwater, “the recharge is not
ally resistant to short-term drought but vul- Arnaud Sterckx, a researcher at the Interna- uniform for the whole of each country, as it is
nerable to long-term depletion of ground- tional Groundwater Resources Assessment highly dependent on the rainfall amount and
water resources. “In these areas, we can see Centre in the Netherlands, explained that intensity and on the geology.” Lukas was not
the groundwater is not connected to current estimating groundwater recharge is difficult. involved in the new study.
climate and that groundwater pumping MacDonald said his team estimated
slowly depletes a finite reserve,” MacDonald recharge from multiple data sets, including Next Steps
said. long-term variations in groundwater level “This study calls for more local-scale studies
African countries with smaller groundwa- measured in aquifers, the concentrations of of groundwater recharge, and it calls for
ter storage capacity but heavier rainfall and modern gases found in groundwater, ratios of decisionmakers at all levels to adopt appro-
a more reliable recharge rate include Burundi, different water isotopes, and the differences priate groundwater management measures
Côte d’Ivoire, and Liberia. These regions are in chloride concentrations between rainfall in line with the storage versus recharge prop-
more vulnerable to drought but more resil- and groundwater. The researchers also had to erties of aquifers,” Sterckx said.
ient to long-term depletion. find a method to scale up the individual stud- For MacDonald, the study provides a useful
Of the 50 African countries studied, five ies to provide maps that were useful for all of quantification of what researchers think
have both groundwater storage and recharge Africa. long-term average groundwater recharge is.
rates above the African average: Angola, the “The authors of this study have been cau- However, he admitted, it doesn’t tell much
Democratic Republic of the Congo, Guinea- tious, and they kept only the most reliable about the reasons for high and low recharge,
B issau, Nigeria, and the Republic of the estimates available in Africa,” Sterckx said. particularly at a catchment scale. To answer
Congo. These nations are generally consid- Considering the uncertainty inherent in the such questions, he said, several studies are
ered water secure. measurements, the results of this study are now looking at “what local factors affect
Five of the countries studied have storage meant not to directly guide local or national groundwater recharge, for example, forest
and recharge rates below the African average: applications but to provide an interesting pic- cover and agricultural practice.”
Eritrea, Eswatini, Lesotho, Zambia, and Zim- ture of how resilient groundwater resources
babwe. These nations are often water insecure are across the continent, Sterckx said.
and vulnerable to short-term climate hazards Eelco Lukas, director of the Institute for By Munyaradzi Makoni (@ MunyaWaMakoni),
and long-term depletion. Extra care is needed Groundwater Studies, University of the Free Science Writer
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SCIENCE NEWS BY AGU // Eos.org 7
NEWS
A Reminder of a Desert’s Past, Before Dingo Removal
A
s ecologist Mike Letnic trudged up gram has allowed for further analyses. A
and down the red-orange dunes of NASA satellite has been taking continuous
the Strzelecki Desert in South Aus- images of the Dingo Fence since 1988. Satel-
tralia, he noticed that his boots sank deep lite imagery, often used for crop or forest
into the sand and his equipment was more studies, traditionally looks strictly at photo-
likely to be covered in sand when he was on synthesizing vegetation, such as plants,
the northern side of what’s known as the trees, and grass.
Dingo Fence. A 5,614-kilometer barrier, the
fence stretches across southeastern Australia
and protects sheep flocks from the wild
dogs—dingoes are plentiful on the northern
“In Australia, we’ve been
side of the fence, but very few exist on the
southern side. pretty successful at
The contrast intrigued Letnic, a professor
at the University of New South Wales’s Centre
suppressing dingo
for Ecosystem Science, and he has studied numbers for more than 100
how the fence and the resulting lack of din-
goes on the southern side have affected the
years. And that memory of
desert’s ecosystem. He has documented, for what it was like before is
example, how the absence of the large pred-
ator has allowed populations of feral cats and
nearly gone.”
foxes to explode, which, in turn, has deci-
mated native herbivore populations. One
such creature is the hopping mouse, which
eats the seeds and seedlings of the native Here Fisher used a model to factor in non-
shrubbery. green vegetation, like shrubs, dry grasses,
In a 2018 study, Letnic and a coauthor flew twigs, branches, and leaf litter. According to
drones over the dunes and found that the Fisher, considering nongreen vegetation was
absence of mice on the southern side had necessary for an arid ecosystem. “Australia is
allowed shrubs to grow more densely, which mostly desert, and so to look at all that land-
altered the dunes’ shapes and sizes (bit.ly/ scape, we need a good way to factor in the
trophic-cascades). The denser shrub coverage brown vegetation, the dry stuff,” he said.
slows the velocity of the wind at ground level The dynamics of how humans alter the
and causes the dunes to become taller and the food webs of ecosystems is an urgent topic
sand to be more compact. “It’s a very windy and one that’s becoming even more difficult
place,” Letnic said. “And once the shrubs get to predict because of climate change, said
to a certain density, the wind actually skates Sinéad Crotty, an ecologist and project man-
across the top of the shrubs.” ager at the Yale Carbon Containment Lab who
A dingo trots by the Dingo Fence. Credit: Nicholas was not involved in the new study. Letnic and
Abundant Kangaroos Gobble Up Grass Chu Fisher, she said, “do a great job of utilizing
Letnic’s new study showed that the fence has multiple lines of evidence across spatial
also caused a different vegetation change— scales to demonstrate the effect of removing
one that is so pronounced it can be seen apex predators on vegetation and geomor-
from space (bit.ly/removal-predator). Using grew on both sides of the fence, but it did not phology.”
32 years’ worth of satellite imagery, Letnic grow as much or cover more land on the Letnic and Fisher said their work is an
and Adrian Fisher, a remote sensing special- southern side. important reminder of how the area’s ecosys-
ist at the University of New South Wales, “It’s a desert, so there’s not much growth tem used to be—one that’s easy to overlook
found that native grasses on the southern in plants. And then it will rain occasionally, because the fence has been around since the
side had poorer long-term growth than veg- and you get a lot of growth, and that’s when 1880s. “In Australia, we’ve been pretty suc-
etation on the northern side. we were able to see the difference in the graz- cessful at suppressing dingo numbers for
The difference stems from the overabun- ing pressure on each side of the fence,” said more than 100 years,” said Letnic. “And that
dance of kangaroos on the southern side, Fisher. memory of what it was like before is nearly
which has put tremendous grazing pressure gone.”
on the native grasses. Kangaroos are the pre- Reminder of the Past Landscape
ferred prey of dingoes. Letnic and Fisher Most dingo research has been conducted
compared the satellite images with weather using either drone imagery or field studies, By Nancy Averett (@nancyaverett), Science
data and found that after rainfall, vegetation but the U.S. Geological Survey Landsat pro- Writer
8 Eos // JUNE 2021NEWS
Rare Wintertime Thunderstorms Recorded
over the U.S. Gulf Coast
A
s fierce winter storms pummeled elusive, said Christopher Schultz, an atmo- ments are then fed into software that pin-
much of North America in February, spheric scientist at Marshall Space Flight points the altitude, latitude, and longitude
lightning danced over the Gulf Coast. Center in Huntsville, Ala., not involved in the of the lightning. “It gives you a t hree-
“Thundersnow”—thunderstorm activity new research. A “very conservative” guess is dimensional view of where the lightning ini-
during a winter snowstorm—is rare, and that they’re about a thousand times less com- tiates and how it moves through the atmo-
researchers are now poring over data from the mon than their w arm-weather counterparts, sphere,” said Logan.
Houston Lightning Mapping Array network he said. “It’s a rare phenomenon.” Logan and his collaborators focused on 835
to better understand this elusive phenome- But earlier this year, Logan and his col- flashes of lightning detected during the Feb-
non. leagues had the opportunity to study thun- ruary storms by the Houston Lightning Map-
Most thunderstorms tend to occur in dersnow occurring nearly in their own back- ping Array. The researchers found that the
spring and summer, and atmospheric sci- yards. flashes originated at an altitude of roughly
ence provides an explanation: Warmer con- 9 kilometers. That’s surprisingly high, said
ditions are conducive to lifting parcels of air, Thundersnow in the Lone Star State Logan. Ice, a critical ingredient of thunder-
which transport water vapor upward. This Starting just before Valentine’s Day, winter storms, would have been forming at lower
convection is critical to the formation of storms swept over a wide swath of North than normal altitudes during February’s
thunderclouds, said Tim Logan, an atmo- America. They dumped record amounts of storm, so it would make sense if lightning
spheric scientist at Texas A&M University in snow and ice, sent temperatures plummeting were also occurring at lower altitudes. “It was
College Station. “Storms need energy to to unprecedented lows, and left hundreds of actually at what’s considered a normal
develop.” thousands of people without power. The height,” said Logan.
Houston area was hit on 14 and 15 February.
A Boost from the Cold Logan, who was working from home in Col- More Positive in the Winter
Because temperatures are lower in winter, lege Station, monitored reports of thunder- The team also investigated the thunder-
there’s less convection, and that makes for far snow in the area. “There was lightning storms’ electrical nature using data from both
fewer wintertime thunderstorms. But they’re observed within 5 miles of my house,” he said. the Houston Lightning Mapping Array net-
possible if something physically forces air Logan and his colleagues are keen to work and the National Lightning Detection
upward, said Logan. Advancing cold fronts can understand how wintertime thunderstorms Network. Lightning can be classified as neg-
provide that boost because they tend to shove differ from the storms more commonly ative or positive: Negative lightning, by far
air out of the way—and upward—via dis- observed in the spring and summer. To do so, the most common, transfers a net negative
placement, he said. “Winter season thunder- they’ve been analyzing data from the Hous- charge. Positive lightning does the opposite.
storms need dynamical lifting.” ton Lightning Mapping Array. Logan and his colleagues found that
When a winter storm spawns a thunder- The network, directed by Logan, consists of roughly 30% of the lightning they analyzed
storm, the result is known as thundersnow or 12 s olar-powered sensors spread around was positive. That’s significantly higher than
thundersleet, depending on the type of pre- Houston. Antennas detect radio frequency the normal fraction of about 10%. However,
cipitation. Wintertime thunderstorms are emissions from lightning, and the measure- that result isn’t wholly surprising, Logan and
his collaborators suggested. Wintertime
thunderclouds often contain more ice crystals
than usual, and those particles tend to take
on a positive charge.
But there are downsides to positive light-
ning. It’s more likely to be associated with
severe weather like hail and tornadoes, and it
also often delivers a stronger punch, said
Schultz. “Positive flashes are generally more
powerful.”
The Houston Lightning Mapping Array—
and other lightning detection networks—will
continue to stand sentry for thundersnow.
It’s a fascinating phenomenon, said Logan,
but it’s unlikely to be spotted again over the
Houston area this century. “To see something
like this here over the Gulf Coast is a treat.”
Thundersnow is rare; this artist’s rendering shows a thunderstorm occurring during a winter snowstorm. Credit: By Katherine Kornei (@KatherineKornei),
Jeremy Bishop and Todd Helmenstine Science Writer
SCIENCE NEWS BY AGU // Eos.org 9NEWS
Aerosol Scientists Try to Clear the Air
About COVID-19 Transmission
A
tmospheric chemist Kimberly Prather
wants her day job back.
As a professor at Scripps Institu-
tion of Oceanography, she usually spends her
days looking at pollution in the ocean and its
effects on human health. But since the out-
break of the coronavirus, Prather has dedi-
cated herself to understanding the airborne
spread of the virus.
Because the airborne droplets that spread
coronavirus are chemically similar to sea
spray, Prather was well poised to pivot her
work. “We’re very interested in viruses and
bacteria that start out in the ocean, but when
waves crash, they get enriched into the atmo-
sphere,” explained Prather.
“I’ve been contacted by people in the
health care industry, including dental assis-
tants,” she said. “They’re desperate.”
In response, Prather and others created an
open-source document of frequently asked
questions (FAQ) about airborne spread (bit.ly/ Kim Prather stands next to a wave tank in San Diego, Calif. She pivoted from pollution research to C OVID-19 last
faq-aerosol-transmission). They’ve written year. “It’s so frustrating because we’re all scrambling…. We cannot keep doing this,” she said. Credit: UC San
letters to officials and called out medical sci- Diego Publications/Erik Jepsen
ence that they say is at odds with physics.
They’ve also repurposed their labs or work
spaces for COVID-19 research, like one scien-
tist in Colorado who repurposed instruments hence the need for these FAQs directly from basic physics, said Jose-Luis Jimenez, an
from his team’s airplane and coughed on the scientists” begins the 62-page document atmospheric chemist at the University of Col-
them in the lab. written by Prather and 11 other scientists. The orado Boulder.
FAQ sheet answers questions on ride-sharing, The WHO says that big droplets of human
elevators, masks, and air filtration, among exhalations are the primary mode of trans-
other topics. mission for the virus. The agency calls them
The WHO and Centers for Disease Control respiratory droplets and defines them as any-
Because the airborne and Prevention (CDC) did not respond to thing larger than 5 micrometers, about the
droplets that spread requests for comment on this article. size of a red blood cell.
In February, Prather and 11 colleagues sent But WHO’s definition of respiratory drop-
coronavirus are chemically a letter warning the Biden administration lets is wrong, said Jimenez. Cloud droplets are
similar to sea spray, that workers in health care, food processing, around 20 micrometers, and they don’t fall to
security, and prison populations aren’t ade- the ground, he said. That means that droplets
Prather was well poised to quately protected from the virus (bit.ly/letter of larger size could be airborne longer than
pivot her work. -biden). the WHO acknowledges.
They claim that although the CDC has “It’s just absurd,” said Jimenez. “This still
acknowledged that people could contract is the official statement of the WHO, and they
COVID-19 through inhaling particles, it has have refused to correct it for a year.”
been slow to update its guidance. In April The break in identifying transmission
“I’ve gotten a ridiculous number of thank- 2021, the WHO changed its guidance to droplets should be 100 micrometers, argued
ou letters from all over the world saying how
y acknowledge that transmission of the virus Prather in a letter published in Science last
many lives I’ve saved,” Prather said. “That’s can occur through inhalation at distances year (bit.ly/airborne-transmission-letter).
nice, but…I want this thing to end.” more than 6 feet from its source. The CDC fol- The argument isn’t just semantics: It directly
lowed suit one week later. affects safety measures.
Help to the Public,Appeals to Agencies But CDC and WHO guidelines emphasize
“We think that unfortunately, [the World At Odds with Basic Science that most transmission is passed through
Health Organization (WHO)] and CDC are Medical textbooks have descriptions of virus close contact, not airborne transmission.
being too slow to accept aerosol transmission, transmission that are not consistent with “The balance of attention must be shifted to
10 Eos // JUNE 2021NEWS
protecting against airborne transmission,”
Prather wrote.
Making the Universe Blurrier
Concerned for Family
At the start of the pandemic, atmospheric
scientist Jorgen Jensen repurposed a sensor
from an aircraft that his team uses to mea-
sure cloud particles. He wanted to know how
humidity in the air affected aerosols, so he
exhaled and coughed onto microscope slides
in his lab at the National Center for Atmo-
spheric Research in Boulder, Colo. He then
tweaked the humidity in the air surrounding
the slides.
Medical textbooks have
descriptions of virus
transmission that are not
consistent with basic The domes of the Very Large Telescope and smaller telescopes are reflected in the aftermath of an infrequent
rainfall atop Mount Paranal in Chile. Climate change could make the telescopes’ observations a little less crisp.
physics. Credit: A. Ghizzi Panizza/ESO, CC BY 4.0 (bit.ly/ccby4-0)
W
hen the European Southern specially relevant as ESO is building the
e
He found that humidity affects the sizes of Observatory (ESO) selected Cerro Extremely Large Telescope (ELT), a 39-meter
droplets over time. Droplets from human Paranal, a 2,6 64- m eter- h igh behemoth that will be the largest telescope in
exhalations are salty, and drying them out mountain in Chile’s Atacama Desert, to host the world, on a peak about 20 kilometers from
makes them increasingly uninhabitable to its Very Large Telescope (VLT), it touted the Paranal. ELT is expected to be a “workhorse”
viruses. But if a droplet dries out completely, location as “the best continental site known for decades, said Crewell.
the virus can remain viable for much longer. in the world for optical astronomical obser- Astronomers are just beginning to consider
While doing his research, Jensen thinks of vations, both in terms of number of clear how those changes are affecting observations
his father, living in a poorly ventilated nursing nights and stability of the atmosphere or might affect them in the years ahead.
home in Denmark. He wants to know what above.” Potential problems include reduced “see-
humidity range nursing homes could use to Cerro Paranal remains one of the best ing”—the clarity with which a telescope
minimize person-to-person transmission. He observing sites on the planet. Yet it’s not as observes the universe—plus greater risk from
said his preliminary research shows that there pristine as it was at the time of its selection, forest fires and a need for more p ower-
is a Goldilocks spot of air—not too humid and in 1990. A study released last September consuming a ir-conditioning to keep tele-
not too dry—that could thwart airborne showed that temperatures have climbed and scope mirrors cool.
viruses faster. jet streams are more troublesome, making “Long term, we’re concerned about how
Jensen partnered with aerobiology engi- the VLT’s observations of distant stars, gal- climate change will affect the viability of cer-
neer Mark Hernandez at the University of axies, and exoplanets a tiny bit fuzzier (bit.ly/ tain observing sites,” such as Paranal and
Colorado Boulder to test the viability of virus astronomical-observations). others in Chile, said Travis Rector, an astron-
particles. “The main motivation of this study was to omer at the University of Alaska Anchorage
“We were all baffled that [public health raise awareness among the astronomical and chair of the American Astronomical Soci-
agencies] didn’t take aerosol transmission as community that climate change is impacting ety Sustainability Committee. “Will we enjoy
being more serious to begin with,” said Jen- the quality of observations,” said Faustine the same quality observing conditions many
son. Cantalloube, an astrophysicist at Laboratoire years down the road?”
“There were people who were hammering d’Astrophysique de Marseille and lead author
that, and they were not being heard for many, of the report. Evaluating the VLT as a Test Case
many months,” said Jenson. “And my per- “As atmospheric conditions influence the Paranal is the first observatory for which sci-
sonal feeling is that was a tragedy.” astronomical measurements, it is important entists have studied that question. Can-
to be prepared for any changes in the cli- talloube’s team compiled more than 3 decades
mate,” agreed Susanne Crewell, a coauthor of weather observations made at the site,
By Jenessa Duncombe (@jrdscience), Staff and a professor of meteorology at the Uni including temperature, wind speed and direc-
Writer versity of Cologne. These preparations are tion, and humidity. The study also included a
SCIENCE NEWS BY AGU // Eos.org 11NEWS
reanalysis of information from two European
climate databases that date to 1980.
The records revealed a temperature
increase of 1.5°C over the study period. The
change is important because the VLT’s domes
are cooled during the day to match the
expected ambient temperature at sunset. If
the telescope mirrors are warmer than the air
temperature, heat waves ripple above them
like those above a desert highway on a sum-
mer afternoon, blurring the view.
“Long term, we’re
concerned about how
climate change will affect
the viability of certain
observing sites.”
The aftermath of a fire at Siding Spring Observatory in Australia shows up as brown in this false-color image
The VLT’s current cooling system was from NASA’s Terra satellite. The observatory forms a small patch of red speckled with white dots near the center.
designed to maintain a temperature no higher The image was snapped in February 2013, 3 weeks after the fire. Credit: NASA Earth Observatory image by
than 16°C because when the telescopes were Jesse Allen; data from NASA/METI/ERSDAC/JAROS, U.S./Japan ASTER Science Team
designed, sunset temperatures exceeded that
value roughly 10% of the time. In 2020,
though, they did so roughly 25% of the time.
As a result, Cantalloube said, air-conditioning advance the atmospheric humidity content, forest fires can be very difficult,” Rector said.
capacity, as well as cooling capacity for many we can schedule observing programs accord- “They’re the most vivid threat.”
telescope instruments, will need to be ingly.”
increased in the future as the temperature Cantalloube said her team is continuing to Proposed Solutions
continues to rise (perhaps by up to 4°C by the evaluate the Paranal data while expanding One proposed solution to climate change
end of the century, according to some mod- its work to study conditions at major obser- could actually cause more problems for
els). vatories in Hawaii, Arizona, and the Canary astronomy, Rector said. Some climate scien-
The study also found that changes in the Islands. tists have suggested that injecting aerosols
jet stream cause periodic increases in wind into the upper atmosphere could reduce the
shear in the upper troposphere, particularly Threats on the Ground amount of sunlight reaching the surface, per-
during El Niño events, creating a blurring Rector noted that climate challenges aren’t haps reversing the warming trend. However,
effect known as a w ind-driven halo. The limited to the quality of the view. “The most that would also reduce the amount of light
VLT’s four component 8-meter telescopes obvious threat is forest fires,” he said. “In from stars and other astronomical objects
are equipped with adaptive optics, which use recent years we’ve seen several major fires reaching Earth’s surface. “Aerosols are prob-
lasers and deformable mirrors to create and come near observatories, especially in Cali- ably best saved as a last-ditch Hail Mary,”
focus an artificial “guide star” in the upper fornia.” Rector said.
atmosphere, compensating for most of the Last August, for example, a fire on Califor- Cantalloube and others said that astrono-
blurring. But turbulence from the wind shear nia’s Mount Hamilton burned one residence mers also must reduce their own carbon foot-
is making it tougher for the system to work. and damaged others at Lick Observatory and print by reducing travel, cutting back their
That’s particularly troublesome for efforts to barely missed some of the telescopes. A reliance on e
nergy-guzzling supercomputers,
image exoplanets, which require both high month later, another fire threatened Mount and taking other steps. “Technological devel-
resolution and high contrast, the study Wilson Observatory, near Pasadena. Siding opments can cope with these subtle effects
noted. Spring Observatory in Australia lost its lodge due to climate change,” Cantalloube said.
“Monitoring meteorological parameters for visiting astronomers and other structures “I’m more concerned about the way round:
on site is one way to make the best out of the in 2013, and the country’s Mount Stromlo How can we make our observatories greener?”
telescope time, thanks to an adapted observ- Observatory lost several major telescopes in
ing schedule,” said Cantalloube. For example, 2003.
“some observations are less affected by “Many observatories are remote, they have By Damond Benningfield (damond5916@att
humidity and some more, so if we know in limited access, so defending them against .net), Science Writer
12 Eos // JUNE 2021NEWS
Oak Trees Offer a Continuous Climate Record
for Central Europe
F
or decades, the widths of tree rings have Worst Summer Droughts Unlike pooled samples, which reduce cost
offered a precise window into past in 2,000 Years and analysis times, nonpooled samples, like
regional environmental conditions. The The team obtained 21 cores from living oak the method detailed in this study, reflect the
oxygen (δ18O) and carbon (δ13C) isotopic sig- trees from seven locations across the Czech nuance of the stable isotopic record in indi-
natures of wood cellulose provide an addi- regions of western Bohemia and eastern vidual trees. The team found that older oak
tional, nuanced environmental fingerprint Moravia. wood samples can be combined to improve
that records subtle shifts in temperature, stable isotope chronologies for l ong-term,
precipitation, and drought conditions. i sotope- b ased paleoclimatic reconstruc-
Despite the power of this approach, ques- tions.
tions remain as to how tree species, site ele-
vation, tree age, and preservation techniques
“To reconstruct “Such multimillennial reconstruction
would be impossible without previous confir-
could affect the stable isotopic values cap- multimillennial mation of the suitability to combine separate
tured in the individual samples. wood samples,” said Urban. “Our data set can
“To reconstruct multimillennial chronol-
chronologies, samples from further be used as a part of a larger archive for
ogies, samples from living trees, historical living trees, historical regional to large-scale dendroclimatic inves-
timbers, archaeological remains, and sub tigation with the possibility to extend the data
fossil materials have to be combined,” said
timbers, archaeological set into the past when new samples are avail-
Otmar Urban, a scientist at the Global Change remains, and subfossil able.”
Research Institute, Czech Academy of Sci- To prove this point, the researchers applied
ences, and lead author of a new study on the
materials have to be this approach in a subsequent study in Nature
value of stable isotopes in individual trees. “It combined.” Geoscience using 147 samples from living and
could bring problems, because [this informa- dead European oaks (bit.ly/recent-drought).
tion] is usually unknown.” They were able to reconstruct hydroclimate
To address these uncertainties, the conditions in central Europe over the past
researchers developed a new method to eval- 2,110 years. In particular, they found that
uate the variability in the stable isotopic The samples consisted of two species of oak, recent summer droughts, between 2015 and
record in individual trees. They leveraged a English oak (Quercus robur) and sessile oak 2018, have been the most severe throughout
multimillennial tree ring chronology estab- (Q. petraea), spanning the natural elevations of the past 2 millennia.
lished in the Czech Republic consisting of each species across central Europe. The “The study from Otmar Urban contributes
about 4,000 core samples obtained from liv- researchers grouped samples at low elevation valuable methodological insights in the
ing oaks and historical timbers of the same (170-250 meters above sea level) and high ele- development of nonpooled chronologies of
species. This database provides a mechanism vation (450-495 meters above sea level). In tree ring stable isotopes. From my personal
to reconstruct climate conditions across addition, samples were grouped at young (NEWS
Sea Cucumbers: The Excremental Heroes
of Coral Reef Ecosystems
bation rates—that is, how much each sea
cucumber pooped in a given day. On average,
each sea cucumber produced about 38 grams
of poop in 24 hours. Using this information,
along with their estimates of the reef’s sea
cucumber population, the researchers deter-
mined that on a single reef, sea cucumbers
produced more than 64,000 metric tons of
poop per year—more than the weight of five
Eiffel Towers.
The Importance of Excrement
Scientists think that all of that poop plays an
important role in ecosystem health and in the
biogeochemical cycles of the reef.
“Sea cucumbers can be considered like a
long sausage, almost,” said Williamson.
“Sediment goes in and sediment comes out….
By eating the sediment and then pooping it
out again, they’re actually aerating the sedi-
ment, which makes the sediment a healthier
place for other animals to live, like small
crabs or polychaetes, which are worms, or
small mollusks that live inside the sediment
By measuring how much individual sea cucumbers pooped per day and estimating the number of sea cucum- in the surface layer.”
bers on the reef using drones and satellite images, researchers determined how much poop sea cucumbers con-
tributed to the Heron Island Reef. Credit: Williamson et al., 2021, https://doi.org/10.1007/s00338-021-02057-2
Sea cucumbers could even
help protect coral reefs
O
n its own, a single sea cucumber sea cucumber numbers, said Williamson. But
may not be very impressive. But get boats stir up the water, making it difficult to against one of the harmful
enough of these floppy, faceless see the animals, and divers can collect infor-
creatures together, and they—or, more spe- mation over only relatively small areas, side effects of climate
cifically, their poop—can physically and bio- resulting in a high degree of uncertainty when change: ocean
chemically reshape a coral reef habitat. their observations were used to extrapolate
In a recent study, an Australian research the population of the entire reef. acidification.
team used drone surveys, satellite imagery, So Williamson and her team, which
and observations of individual sea cucumbers included coral reef geomorphologist Stepha-
to estimate how much poop the sea cucum- nie Duce, remote sensing expert Karen Joyce,
bers of Heron Island Reef produced per year and marine ecologist Vincent Raoult, wanted Sea cucumbers are also involved in the
(bit.ly/sea-cucumber-poop). Heron Island to try a different method. Using images cap- nitrogen cycles of the reef ecosystem. As sea
Reef is part of the southern Great Barrier Reef tured by drones, the team surveyed sea cucumbers eat and excrete sediment, “they’re
system off the coast of Queensland, Australia. cucumbers over tens of thousands of square releasing nitrogen that’s trapped in between
Historically, one of the major problems meters in two different geomorphic zones the sediments,” said Williamson. “So this is
scientists have faced when trying to assess (the inner and the outer reef flats). Research- really important because nitrogen in partic-
the importance of sea cucumbers (and their ers then used satellite imagery to determine ular is a limiting nutrient on coral reefs…. The
excrement) in the reef ecosystem is the dif- the area of each of these geomorphic zones corals need nitrogen, and the algae need
ficulty in assessing just how many sea cucum- and extrapolate the number of sea cucumbers nitrogen, everything sort of locks it up really
bers there are in a given area, said Jane Wil- present on the entire reef. These methods quickly when it’s available, so the sea cucum-
liamson, the study’s lead author and head of indicated that there were more than 3 million bers are doing them a big favor in terms of the
the Marine Ecology Group at Macquarie Uni- sea cucumbers on the flats surrounding growth rate of these organisms.”
versity. Heron Island Reef. Sea cucumbers could even help protect
Previous research used footage from boats The team also collected dozens of individ- coral reefs against one of the harmful side
or information collected by divers to estimate ual sea cucumbers to observe their biotur effects of climate change: ocean acidifica-
14 Eos // JUNE 2021You can also read
