New Scientist - USA (2019-08-31)

14 | New Scientist | 31 August 2019

Earth science

Chris Baraniuk

A MINI ice age that lasted for

125 years began in the middle of

the 6th century, helping to plunge

the world into an era of chaos. One

of the key events behind it was the

massive eruption of a volcano

somewhere in the southern

hemisphere. Now we may know

when and where it happened.

Huge eruptions fling so much

ash and debris into the atmosphere

that sunlight is partially blocked.

This can cool Earth and encourage

more ice to form at the poles, which

reflects more sunlight, further

cooling the planet. It has long been

thought that the eruptions of

volcanoes between AD 536 and

547 kick-started what is known

as the Late Antique Little Ice Age.

Robert Dull at California Lutheran

University and his colleagues have

now shown that the second of two

big eruptions during this time

appears to have occurred at the

Ilopango volcano in El Salvador.

The team found the remains of

three trees that “witnessed” this

event. Two of these were killed by

the volcanic activity.

Radiocarbon dating on multiple

tree rings inside the trunks revealed

their age – the trees died between

AD 503 and 545. Evidence from

ash deposits in nearby soil also

helped to confirm that a gigantic

eruption happened around this

time, most likely in late AD 539 or

540 (Quaternary Science Reviews,

doi.org/c9nk).

An earlier big eruption is thought

to have occurred in AD 536, but

researchers haven’t yet managed to

identify which volcano was involved.

“I think the Late Antique Little Ice

Age was started by these eruptions

here and prolonged by others,” says

Michael Sigl at the University of

Bern in Switzerland. The final

proof that would tie Ilopango to

the AD 540 eruption would be to

find debris from it in Antarctic ice

cores from that time, he says. ❚

Volcano that

led to little ice

age identified

News

A NEW study has added to the

mounting evidence suggesting

air pollution is linked to mental

health conditions. But it isn’t

clear yet how – or if – pollution

may be affecting our brains.

What has the latest study found?

Analysing data from 151 million

people in the US and 1.4 million

people in Denmark, researchers

discovered a strong correlation

between poor air quality and

higher rates of bipolar disorder,

schizophrenia, personality

disorders and major depression

(PLoS Biology, doi.org/gf6t7f).

This suggests there is a link, but

not necessarily that pollution is

causing these conditions.

How strong is the link?

When the researchers looked

at health insurance claims in

the US, they found that the

strongest predictor of being

diagnosed with bipolar disorder

(after ethnicity) was air quality.

Previous studies have

unearthed a correlation in

the UK between polluted

areas and teenagers reporting

psychotic experiences, and local

air pollution and psychiatric

disorders in Swedish children.

How good is the evidence?

“We don’t really know very

much overall. We’ve only got

a handful of studies and most

have methodological problems,”

says Helen Fisher of King’s

College London, who worked

on the UK teenager study.

One problem is a lack of data

on what an individual’s true

exposure to air pollution has

been, with some research

looking at city-wide air quality

measurements rather than

specific addresses. That is a big

weakness, given we know air

pollution exposure can vary

significantly from one street

to the next. In the new study,

exposure in the US was mapped

at county level, administrative

areas that can cover thousands

of square kilometres.

What else could explain the

associations between dirty air

and psychiatric conditions?

The study tried to take into

account confounding factors

where figures were available,

including income, ethnicity

and population density. But an

obvious factor that could be

linked to both mental health

and pollution is traffic noise.

This is known to increase stress

and disrupt sleep, which are

both linked to mental ill health.

In what ways could pollution

affect our brains?

Some of the smallest pollution

particles can pass through the

blood-brain barrier, potentially

affecting the brain. Air pollution

is known to cause inflammation

in the body, which may ignite

the brain’s stress response. Or

perhaps pollution can cause

epigenetic changes that affect

the levels of signalling chemicals

in the brain. But these are only

tentative ideas.

Why does it matter if air quality

affects our brains? Shouldn’t

we care because of the known

physical effects it has anyway?

Stronger evidence of a link to

mental health might not have a

huge impact on policy because

the case for action on air

pollution – such as it shortening

lives through lung and heart

problems – is strong. But if dirty

air was found to cause mental

illness, it would “open new

avenues to the prevention

and treatment of mental

conditions”, John Ioannidis at

Stanford University in California

wrote in a commentary in

PLoS Biology. ❚ Adam Vaughan

Briefing Mental health

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Why is pollution linked to

schizophrenia and depression?

Busy traffic in

Copenhagen, Denmark

“Air quality was a

strong predictor of

being diagnosed with

bipolar disorder”

More mental health news online

The latest research on depression and other conditions

newscientist.com/article-topic/mental-health