Sky & Telescope - October 2021 - 25

Studies at the Jet Propulsion Laboratory supports a number
of teams that search for life-threatening objects, and this
year a mission will launch designed to test technology that
could change the trajectory of an impactor in space. Although
astronomers have likely found 95% of kilometer-size asteroids,
they've discovered only a third of the medium-size
objects out there, Mainzer estimates. Those smaller ones
would bring region-level devastation.
Volcanism is not so preventable. Renne argues that something
like the Deccan Traps will almost certainly happen
again: On average, these colossal volcanic eruptions occur
roughly every 30 million years on land. The last one - which
released the Columbia River flood basalts across Washington,
Oregon, and Idaho - did most of its damage roughly 16 million
years ago.
Yet Keller argues that the next mass extinction will not
be caused by a volcanic eruption, but by us. And here, most
scientists finally agree. Myriad data, from ice core studies to
chemical analyses of our atmosphere's makeup, indicate that
Earth's climate is warming today due to the greenhouse gases
that we alone have emitted (see sidebar). Countless species
are staring down extinction. But if scientists can use the findings
from both the Chicxulub impact and the Deccan Traps
to better understand how much strain terrestrial life can
tolerate - specifically, the amount of greenhouse gases in the
atmosphere - then they will have a much better idea of what
to expect from the current crisis.
And that will help us truly focus on the defense of Planet
Earth, Keller argues. " Scientists can already see the end of the
world as we know it, not in thousands of years but just a few
generations as we speed into the sixth mass extinction. "
¢ S&T Contributing Editor SHANNON HALL is an award-winning
freelance science journalist who grew up traipsing around
the Columbia River flood basalts in the Pacific Northwest.
Climate Cliff Notes
While exactly how Earth's climate changed during the
K-Pg extinction remains under debate, scientists do know
that climate change today is both real and caused by human
activity. Often omitted from discussions is how they
know. Here are the key points leading to their conclusion:
* Air samples show that the atmospheric concentration of
carbon dioxide (CO2) is rising on Earth.
* CO2 absorbs infrared radiation (heat). Adding more
infrared-absorbing compounds, or greenhouse gases,
to Earth's atmosphere throws off its energy balance and
causes the planet to absorb more energy.
* This added energy should (among other things) raise
the global average temperature, increase ocean temperatures,
and spur more extreme weather. Absorbed
CO2 should also make the oceans more acidic. All are
happening.
* Both modern and ancient air samples - the latter from
air bubbles in ice cores reaching back several hundred
thousand years - confirm that the CO2 levels have
spiked since the Industrial Revolution.
* The rate of atmospheric CO2 increase matches that
released by human activities for the same time period.
* The relative amounts of carbon's three isotopes - carbon-12,
carbon-13, and carbon-14 - in the atmosphere
will be different depending on where the carbon in the
CO2 comes from. Volcanoes and the burning of fossil
fuels, for example, will lead to different proportions of
carbon-13 and carbon-14 relative to carbon-12. Chemical
analysis of Earth's atmosphere matches fossil fuels.
For a detailed discussion of these and other points, read
Jeffrey Bennett's A Global Warming Primer. Find more information
and resources for astronomers at https://is.gd/
astroclimate.-Camille M. Carlisle
FRACTION
FRACTION
OF SPECIES
ELIMINATED
GIANT
DRAGONFLY
90-95%
252
End-Permian
Volcanism
200
201
End-Triassic
Volcanism
75%
AMMONOIDS
100
66
CretaceousPaleogene
Volcanism,
impact
75%
TODAY
PTEROSAURS
OF SPECIES
ELIMINATED
FRACTION
OF SPECIES
ELIMINATED
sk yand tele scope .o r g * OCTOBER 2021 25
GIANT DRAGONFLY: ANDREY OLEYNIK / SHUTTERSTOCK; AMMONOIDS: ALZHAPARD /
SHUTTERSTOCK; PTEROSAURS: KATRINE GLAZKOVA / SHUTTERSTOCK
https://is.gd/astroclimate https://is.gd/astroclimate http://skyandtelescope.org
Sky & Telescope - October 2021

Table of Contents for the Digital Edition of Sky & Telescope - October 2021
