This process often has trees and forests metaphorically
characterised as the lungs of the world.
Normally, when we are healthy, our breathing is a
relatively quiet activity. However, when we get sick or develop a disease of
some sort, especially one that affects our lungs, we cough. Coughing is a
symptom of some illness.
What if trees get sick? What if the normal process of
photosynthesis becomes diseased?
Do trees also “cough”?
It seems that – metaphorically at least – they do?
A study released in November 2023 by a team of earth
and planetary scientists from Pennsylvania State University reveals a
disturbing trend. When trees get stressed by high temperatures and/or limited
water then the process of photosynthesis gets impeded, and a reverse process
commences.1
This reverse process, known as photorespiration, means
that trees no longer take up carbon dioxide; rather they begin to send CO2
back into the atmosphere.
The lead author of the study, Max Lloyd (Assistant
Research Professor of Geosciences) says that “Trees
in warmer, drier climates are essentially coughing instead of breathing.”
This is a worrying condition. Continuous
coughing in humans can be a sign of asthma. To stretch the analogy of trees
breathing a little further we might ask: Is the Earth becoming asthmatic?
There is no known cure for human asthma.
Is there one for an asthmatic Earth?
Not likely.
Plants and trees presently absorb around
25% of the carbon dioxide emitted by humans. If these “lungs” become diseased,
and the world becomes “asthmatic” then the ability of trees to absorb this
carbon dioxide will diminish.
Consequently, a positive feedback loop in
the carbon cycle of Earth becomes established. Humans pump CO2
into the atmosphere, trees absorb that, thus sequestering it. But now, a positive feedback loop gets launched, whereby trees no longer sequester the CO2 –
they contribute to the rising emissions. This form of “positivity” is not good
for trees, it is not good for humans, it is not good for Earth.
Just as asthma sufferers worldwide find
ways to cope with asthma, so will we as a species have to find ways to cope
with an increasingly asthmatic world.
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