New Scientist - USA (2020-09-12)

12 | New Scientist | 12 September 2020

PLANTS could help investigators

find dead bodies. Botanists believe

the sudden flush of nutrients into

the soil from decomposition may

affect nearby foliage. If scientists

can understand those changes – for

instance, on leaf colour – they may

be able to identify where remains

are buried simply by studying

aerial images.

“If we’re able to use the plants as

sensors, at least first as indicators

or crude indicators, we can identify

whether a missing body may

be close by,” says Neal Stewart Jr

at the University of Tennessee.

Teams looking for human

remains often rely on aerial

searches, but these are difficult

if a cadaver is buried in a forest.

Although pedestrian surveys

or teams of trained dogs can

help in these situations, such

searches are impractical in

huge forests or war zones.

Forensic anthropologists

at the University of Tennessee

have been training members of

the FBI for 20 years, including in

rudimentary “forensic botany”.

Anecdotal evidence suggests that

visual signals can appear in the

leaves of trees and shrubs growing

near a body. For instance, a body

can affect the mix of plant species

growing nearby and plant leaves

may be visibly darker, indicative

of higher nitrogen uptake.

Now, the plan is to explore those

botanical effects more thoroughly

at a “body farm” at the university,

where researchers study the way

cadavers decompose (Trends in

Plant Science, doi.org/d7zc).

“We’ve actually built a whole

plant imager that can analyse

fluorescence signatures,”

says Stewart. “But the first steps

are going to be very fine scale,

looking at individual leaves

and measuring how their

reflectance or fluorescence

changes over time when plants

are near human remains.”

The average person in the

US contains roughly 2.6 kilograms

of nitrogen, much of which is

released and converted into

ammonium when their body

decomposes. That may see

nitrogen in the soil spike to levels

up to 50 times higher than when

a typical fertiliser is added. This

can increase soil toxicity or alter

leaf fluorescence or reflectance.

“That is why this study is

exciting, as we can quantify

exactly what is happening in the

foliage with hyperspectral and

chemical analyses even if we can’t

see a physical change,” says team

member Dawnie Steadman, also

at the University of Tennessee.

Currently, the research is at an

early stage. The team is focusing

on plants growing at the body

farm, which are predominantly

Amur honeysuckles, an invasive

plant found across much of the

eastern US. The results may be

translatable to different climatic

zones and ecosystems, but the

team is unsure how effects can

be generalised between species. ❚

Forensic science

Ian Morse

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Changes in leaf colour

could warrant further

investigation

“ If we’re able to use the
plants as sensors, we can
identify whether a missing
body may be close by”

Climate change

Flying is causing

twice the warming

effect it did in 2000

THE most comprehensive analysis

so far of how much warming is

caused by aeroplanes has found

that the amount of warming caused

by flying nearly doubled between

2000 and 2018.

“It is growing so rapidly,”

says David Lee at Manchester

Metropolitan University in the UK.

The study only goes up to 2018,

before the big decrease in flying

due to the coronavirus pandemic,

but this decrease is just a blip, says

Lee. “It’s not going to make much

difference in the long term.”

Flying has complex effects on the

climate. For instance, the soot from

jet engines triggers the formation of

contrails that, like clouds, can have

both a warming effect by reflecting

outgoing heat back down to Earth’s

surface and a cooling effect by

reflecting sunlight back into space.

Lee and his colleagues used

computer models to improve on

previous estimates of the overall

effect. These suggest that contrails

cause less than half as much

warming as previously thought.

Short-lived contrails still lead to

more warming than the long-lasting

carbon dioxide emissions from

aircraft. Overall, the team calculated

that flying is responsible for 3.5 per

cent of the global warming effect

resulting from human activities.

That is less than previous estimates

of around 5 per cent (Atmospheric

Environment, doi.org/d7x9).

This contribution of 3.5 per cent

has remained relatively constant

since 2000, but only because other

sources of warming have also

increased rapidly. Over this period,

the warming effect from flying has

nearly doubled due to the expansion

of the aviation industry.

Using renewable energy to

turn atmospheric CO₂ into synthetic

kerosene could reduce emissions –

but Lee doubts this will be adopted

so long as it is cheaper to remove

fossil fuels from the ground.  ❚

Michael Le Page

Around 3.5 per

cent of the global

warming effect

from human

activities is

caused by flying

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Trees and shrubs might reveal the

location of decomposing bodies