12 | New Scientist | 25 January 2020
THUNDERSTORMS generated
by the intense heat of the
bushfires burning in Australia
have probably carried as much
smoke into the stratosphere as
a volcanic eruption.
Blazes across the country in
the past few weeks have been so
powerful they have generated
their own weather. They create
rising air that carries ash and
smoke and results in the
formation of thunderclouds
called pyrocumulonimbus
(pyroCbs) above the fires.
Some of these clouds are
strong enough and rise high
enough to have channelled
smoke into the stratosphere – a
stable layer of air between 10 and
50 kilometres up where particles
can get trapped and persist for
half a year or longer. Smoke from
the fires has moved eastward in
the stratosphere and made a
full circuit around the world,
according to NASA.
There were at least 20 pyroCbs
between 28 and 31 December, and
more on 4 January, some of which
put smoke into the stratosphere.
The scale of the smoke there hasnow been calculated by David
Peterson at the US Naval Research
Laboratory, who presented his
preliminary findings to the
American Meteorological Society
at a meeting in Boston last week.
“It’s very likely on a volcanic
scale,” he says. Peterson estimates
the effect is similar to a moderate
eruption, rather than on the
scale seen after the massive 1991
eruption of Mount Pinatubo in thePhilippines, the largest in modern
times. He has done similar work
on the impact of pyroCbs before.
He found that Canadian wildfires
in 2017 put as much smoke as
a volcano into the stratosphere.
While it is well known that a
volcanic eruption can put enough
particles into the atmosphere to
have a cooling effect, the different
chemistry of pyroCbs means the
impacts of the fires on global
temperatures aren’t yet clear.
They may have a warming or
cooling effect, and it isn’t known
how long the smoke will persist.Peterson says the biggest question
is what role pyroCbs are playing in
the climate system. Some of the
smoke plumes carried by these
clouds are also getting high
enough to affect the ozone layer,
which is usually at least 15 km up.
We may have a better idea of
the smoke’s impact soon, thanks
to NASA flying a plane earlier this
year through the upper level of a
pyroCb generated by US wildfires.
“It wasn’t as massive as these
Australia plumes but fortunately
at an altitude the aircraft could get
to,” says Peterson. That research
will reveal more about relevant
atmospheric chemistry in the
clouds. Combined with satellite
data, this should give us a clearer
idea of what to expect.
Alan Robock at Rutgers
University in New Jersey says if
the smoke has a cooling effect, it
is unlikely to be huge at a global
level, but could cause cooling of
several degrees C at a local level.
If the Australian pyroCbs produce
twice as much smoke as those
from Canada in 2017, “it still would
not be a large or long-lasting
impact on climate,” he says. ❚“ Your biological clock
doesn’t know it’s the
weekend. It gets confused
when you eat later”EnvironmentAdam VaughanNASANews
Smoke from the
Australian wildfires
has circled the globePhysiologyBrunch at the
weekend messes
with our bodiesEATING meals later on weekends
than during the week may cause
weight gain by disturbing the
body’s metabolic rhythms.
Disrupted sleep patterns are
linked to weight gain, probably
because our bodies aren’t used
to processing food eaten at night,
which seems to lead to the storage
of extra fat.
María Fernanda Zerón-Rugerio
and Maria Izquierdo-Pulido at theUniversity of Barcelona in Spain
wondered if eating meals later
on weekends might have similar
effects. “It’s common to sleep in
on weekends, so we end up having
breakfast later and then lunch and
dinner tend to be a bit delayed too,”
says Zerón-Rugerio. “We call this
eating jet lag.”
Their team surveyed more than
1100 university students in Spain
and Mexico to find out what time
they normally ate on weekdays and
weekends. Almost two-thirds had
an hour or more of eating jet lag on
weekends, meaning the midpoint
between their first and last mealwas at least an hour later on
weekends than on weekdays.
Breakfast was the most delayed
meal, tending to become brunch.
Students with greater eating
jet lag were more likely to be
overweight. Those who reported
more than 3.5 hours of eating jet
lag on weekends had higher body
mass indexes on average than those
with no eating jet lag, regardless of
their diet or how much they slept orexercised (Nutrients, doi.org/djsc).
The difference was equivalent to
4 kilograms in someone who is
170 centimetres tall and weighs
90 kilograms.
Eating jet lag is probably
linked to weight gain because our
internal biological clocks, known
as circadian systems, prepare
our metabolisms to process food
at specific times, says Izquierdo-
Pulido. If you usually eat breakfast
at 7 am, but at 9 am on weekends,
“your biological clock doesn’t know
it’s the weekend,” she says. “It gets
confused when you eat at 9 am.” ❚
Alice KleinAustralia’s fire-driven storms are
smoking up the stratosphere