<
https://www.smithsonianmag.com/smart-news/forests-didnt-fare-well-during-an-ancient-global-warming-event-offering-a-cautionary-tale-about-todays-climate-change-180989353/>
"About 56 million years ago, Earth experienced one of its most intense periods
of global warming, known as the Paleocene-Eocene Thermal Maximum, or PETM. As
atmospheric carbon dioxide levels surged, forests suffered a massive decline in
canopy cover, and they took more than 100,000 years to recover, researchers
report in a study published on August 13 in the journal
Science.
The findings offer a sobering look into what our planet’s future might look
like because of ongoing human-caused climate change.
“The Earth has never experienced a carbon release at the pace we’re creating
today,” says Regan Dunn, a study co-author and paleobotanist at the Natural
History Museum of Los Angeles County, in a statement. “The PETM gives us our
best window into how Earth’s climate and ecosystems respond to a massive carbon
injection before humans began reshaping the planet.”
Humans are currently putting carbon dioxide in the atmosphere at an
unprecedented rate. Predicting the effects of the planet-warming greenhouse gas
on vegetation is complicated. Since plants need the gas for photosynthesis,
elevated carbon dioxide levels should theoretically lead to enhanced plant
growth. But too much heat and its consequences, like extreme weather events and
an increase in pathogens, can also stress and kill plants.
That’s why Dunn and her colleagues turned to the past to see what might happen
to today’s forests. They collected fossilized leaf fragments hidden in the
rocks of Hanna Basin in south-central Wyoming. The specimens preserve the
shapes of the leaves’ outermost cells, which can reveal how much sunlight the
leaf received as it grew.
“There’s this difference between sun leaves and shade leaves, even on the same
plant,” Dunn tells James Dinneen at
Nature. Leaves that grow in the shade
have longer cells that stretch out looking for light, while those exposed to
the sun are shorter and rounder.
The information helped the team calculate the density of the forest canopy,
which they tracked across the entire PETM. At first, the forest flourished
thanks to the elevated carbon dioxide. But that growth spurt didn’t last. The
canopy then quickly lost around 60 percent of its leaf coverage, and it stayed
around 35 percent thinner than it started through the rest of the PETM.
“This should be a concern because the rate of carbon release has never been
higher than now,” Dunn tells the
Guardian’s Oliver Milman."
Via Susan ****
Cheers,
*** Xanni ***
--
mailto:xanni@xanadu.net Andrew Pam
http://xanadu.com.au/ Chief Scientist, Xanadu
https://glasswings.com.au/ Partner, Glass Wings
https://sericyb.com.au/ Manager, Serious Cybernetics
