3 November 2018 | NewScientist | 7IT IS the forgotten famine. A
global drought in the 1870s led to
starvation in South America, Asia
and Africa, but the event doesn’t
even have a Wikipedia page.
At last we are shedding light
on its causes. The drought was
triggered by a combination of
climate events never seen before.
While rare, this was entirely
natural, so could happen again.
Between 1875 and 1878, severe
drought ravaged India, China
and parts of Africa and South
America. The result was a famine
that struck three continents.
“It is one of the worst
humanitarian disasters in human
history,” says Deepti Singh at
Washington State University.
The resulting famine was
described by Mike Davis at the
University of California, Riverside
in his 2001 book Late VictorianHolocausts. He estimated that
50 million people died.
Now Singh and her colleagues,
including Davis, have examined
the drought in detail. The first
step was getting weather datafrom a time before records were
kept. Fortunately, in 19th century
India a network of rain gauges was
set up. For other places, like China,
the researchers estimated rainfall
from tree rings.
Singh says the results suggested
the events of the 1870s were
unusually severe. By looking at
estimates of rainfall based on tree
rings and other proxies, the team
estimated that the drought at thistime was the most severe in Asia
for 800 years.
The researchers identified
several factors that may have
helped trigger the catastrophe.
The most obvious was a big El
Niño from 1877 to 1878. During an
El Niño, warm water spreads over
the Pacific, releasing heat into the
air. This affects weather across the
world, bringing storms to some
places and drought to others.
But that’s not all. In 1877, a
second climate cycle, the Indian
Ocean Dipole, was active, which
meant the western Indian Ocean
was warmer than the east. This
typically weakens India’s rain-
generating monsoon. “It was the
strongest Indian Ocean Dipole on
record,” says Singh. Finally, there
is evidence of unusual warmth in
the Atlantic from 1877 to 1879.
To check which of these events
may have played a role in the
drought, the team ran a climate
model in two ways. One used
global sea surface temperatures.
The other used just Pacific
temperatures, simulating the
El Niño alone. They found they
could only explain the drought
using the global sea temperatures
(Journal of Climate, doi.org/cwb7).
The study has impressed
climatologist Isla Simpson of the
National Center for Atmospheric
Research in Colorado. “It’s pretty
unusual to be able to go into this
much detail on an event that far
back,” she says.
This pattern of climate events
was natural, beyond our control,
and so could be repeated. The
good news is the world is more
resilient to droughts today, thanks
to better crops and extensive
trade, says Olivier Rubin at
Roskilde University, Denmark.
“If we had a drought like this
today, there would be devastating
effects on hunger, devastating
effects on poverty,” he says. But
while people would go hungry, it
should be possible to avoid such a
deadly famine. Michael Marshall ■CANNABIS use really does weaken
your memory. People who gave up
smoking the drug saw their cognitive
abilities improve after just a week.
Though cannabis has a reputation
for making people less mentally sharp,
it is hard to know if the drug causes
the problems reported or if users
have a worse memory to begin with.
The only definitive way to find out
is a randomised trial in which some
people who don’t normally smoke
cannabis take it up for months,
but this wouldn’t ever get past an
ethics board. So Randi Schuster at
Massachusetts General Hospital in
Boston hit on the idea of a trial that
asks existing users to stop and
compares them with a control group
who continue.
Schuster’s team recruited 88
people in the US aged between 16 and
25 who used cannabis at least once a
week. Two-thirds of them, chosen at
random, were incentivised with cash
to quit for a month, with regular urine
tests to keep everyone honest. At the
start of the trial and then once a week
they took tests of memory.
The quitters scored significantly
better in these tasks in the first week,
and stayed at that level for the rest
of the month (Clinical Psychiatry, doi.
org/cwd2). Those who continued
using cannabis only improved their
scores slightly over the month,
probably because they were getting
used to the tests, says Schuster.
Brain-scanning studies have shown
that regular cannabis users have
lower amounts of a receptor in the
brain that binds chemicals in the drug.
This receptor is normally found at high
levels in the hippocampus, part of the
brain involved in memory, says Tom
Freeman at the University of Bath, UK,
who wasn’t involved in the study.
“It makes sense that this is where we
are going to see the impairments.”
Brain scans have also shown that
cannabis receptor levels return to
normal within two or three days of
quitting. Clare Wilson ■
Freak climate event that
killed millions explained
© ILLUSTRATED LONDON NEWS LTD/MARY EVANSFor daily news stories, visit newscientist.com/news
“If we had a drought like
this today, there would be
devastating effects on
hunger and on poverty”Smoking a joint
makes your
memory hazy
A depiction of the impact of famine
that hit India in the 1870s