Scientists reveal how landmark CFC ban gave planet fighting chance
against global warming

Date:
August 18, 2021
Source:
Lancaster University
Summary:
New modelling by the international team of scientists paints a
dramatic vision of a scorched planet Earth without the Montreal
Protocol, what they call the 'World Avoided'. This study draws a
new stark link between two major environmental concerns -- the hole
in the ozone layer and global warming. The research team reveals
that if ozone-destroying chemicals, which most notoriously include
CFCs, had been left unchecked then their continued and increased
use would have contributed to global air temperatures rising by
an additional 2.5DEGC by the end of this century.



FULL STORY ========================================================================== Without the global CFC ban we would already be facing the reality of a 'scorched earth', according to researchers measuring the impact of the
Montreal Protocol.


========================================================================== Their new evidence reveals the planet's critical ability to absorb carbon
from the atmosphere could have been massively degraded sending global temperatures soaring if we still used ozone-destroying chemicals such
as CFCs.

New modelling by the international team of scientists from the UK, USA
and New Zealand, published today in Nature, paints a dramatic vision of a scorched planet Earth without the Montreal Protocol, what they call the
"World Avoided." This study draws a new stark link between two major environmental concerns - - the hole in the ozone layer and global warming.

The research team, led by a Lancaster University scientist, reveals that
if ozone-destroying chemicals, which most notoriously include CFCs, had
been left unchecked then their continued and increased use would have contributed to global air temperatures rising by an additional 2.5DEGC
by the end of this century.

Their findings, outlined in the paper 'The Montreal Protocol protects
the terrestrial carbon sink', show that banning CFCs has protected the
climate in two ways -- curbing their greenhouse effect and, by protecting
the ozone layer, shielding plants from damaging increases in ultraviolet radiation (UV).

Critically, this has protected plant's ability to soak up and lock in
carbon dioxide from the atmosphere and so prevented a further acceleration
of climate change.

The research team developed a new modelling framework, bringing together
data on ozone depletion, plant damage by increased UV, the carbon cycle
and climate change. Their novel modelling shows an alternative future
of a planet where the use of CFCs continued to grow by around three per
cent a year.



========================================================================== Their modelling reveals:
* Continued growth in CFCs would have led to a worldwide collapse
in the
ozone layer by the 2040s.

* By 2100 there would have been 60 per cent less ozone above the
tropics.

This depletion above the tropics would have been worse than was
ever observed in the hole that formed above the Antarctic.

* By 2050 the strength of the UV from the sun in the mid-latitudes,
which
includes most of Europe including the UK, the United States and
central Asia, would be stronger than the present day tropics.

The depleted ozone layer would have seen the planet, and its vegetation, exposed to far more of the sun's UV.

Plants absorb carbon dioxide (CO2) through photosynthesis and studies have shown that large increases in UV can restrict plant growth, damaging their tissues, and impairing their ability to undertake photosynthesis. This
means the plants absorb less carbon.

Less carbon in vegetation also results in less carbon becoming locked
into soils, which is what happens to a lot of plant matter after it
dies. All of this would have happened on a global scale.

The researchers' models show that in a world without the Montreal Protocol
the amount of carbon absorbed by plants, trees and soils dramatically
plummets over this century. With less carbon in plants and soils, more
of it remains in the atmosphere as CO2.



========================================================================== Overall, by the end of this century without the Montreal Protocol CFC ban:
* There would have been 580 billion tonnes less carbon stored
in forests,
other vegetation and soils.

* There would be an additional 165-215 parts per million of CO2 in the
atmosphere, depending on the future scenario of fossil fuel
emissions.

Compared to today's 420 parts per million CO2, this is an additional
40- 50%.

* The huge amount of additional CO2would have contributed to an
additional
0.8DEGC of warming through its greenhouse effect.

Ozone depleting substances, such as CFCs, are also potent greenhouse
gases and previous research has shown that their ban prevented their contribution to global warming through their greenhouse effect. By the
end of this century, their greenhouse effect alone would have contributed
an additional 1.7DEGC global warming. This is in addition to the newly quantified 0.8DEGC warming, coming from the extra CO2 that would have
resulted from damaged vegetation, meaning that temperatures would have
risen 2.5DEGC overall.

Dr Paul Young, lead author from Lancaster University, said: "Our new
modelling tools have allowed us to investigate the scorched Earth
that could have resulted without the Montreal Protocol's ban on ozone
depleting substances.

"A world where these chemicals increased and continued to strip away
at our protective ozone layer would have been catastrophic for human
health, but also for vegetation. The increased UV would have massively
stunted the ability of plants to soak up carbon from the atmosphere,
meaning higher CO2 levels and more global warming.

"With our research, we can see that the Montreal Protocol's successes
extend beyond protecting humanity from increased UV to protecting the
ability of plants and trees to absorb CO2. Although we can hope that
we never would have reached the catastrophic world as we simulated,
it does remind us of the importance of continuing to protect the ozone
layer. Entirely conceivable threats to it still exist, such as from
unregulated use of CFCs." The planet has already seen 1DEGC warming
from pre-industrial temperatures.

Even if we had somehow managed to get to net zero CO2 emissions,
the additional 2.5DEGC rise would take us to a rise of 3.5DEGC. This
is far in excess of the 1.5DEGC rise above pre-industrial levels that
many scientists see as the most global temperatures can rise in order
to avoid some of the most damaging effects of climate change.

Dr Chris Huntingford of the UK Centre for Ecology & Hydrology said:
"This analysis reveals a remarkable linkage, via the carbon cycle,
between the two global environmental concerns of damage to the ozone
layer and global warming." Background information The ozone layer is an essential barrier that protects us by filtering the sun's harmful UV --
when a hole in the layer was discovered above Antarctica in the 1980s,
it caused great alarm because of the damage UV can cause to human health through conditions such as skin cancers.

The Montreal Protocol, which was signed in 1987, is championed as an
exemplar in environmental diplomacy. By agreeing to a worldwide ban on
ozone depleting substances, including CFCs, international leaders were
able to save the planet's ozone layer. Thanks to the Montreal Protocol
the ozone layer is undergoing a long process of repair.

Funders: The research was supported by the Engineering and Physical
Science Research Council, Natural Environment Research Council, Lancaster University, the UK and New Zealand governments, NASA and the United
States' National Science Foundation.

The study brings together experts across atmospheric chemistry,
physicists, plant scientists, and land surface modellers from Lancaster
and Exeter Universities, the UK Centre for Ecology & Hydrology, NASA,
the National Center for Atmospheric Research, and the National Institute
for Water and Atmospheric Research.

========================================================================== Story Source: Materials provided by Lancaster_University. Note: Content
may be edited for style and length.


========================================================================== Journal Reference:
1. Paul J. Young, Anna B. Harper, Chris Huntingford, Nigel D. Paul,
Olaf
Morgenstern, Paul A. Newman, Luke D. Oman, Sasha Madronich,
Rolando R.

Garcia. The Montreal Protocol protects the terrestrial carbon sink.

Nature, 2021; 596 (7872): 384 DOI: 10.1038/s41586-021-03737-3 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2021/08/210818130504.htm

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