Category: Factual
& Arts TV
Date: 13.01.2005
Printable version
BBC TWO's Horizon
- broadcast today at 9.00pm - reveals for the first time the devastating
affects of a phenomenon that scientists are calling 'global dimming'.
It may already have led to the terrible famine in Ethiopia in the
Eighties and, perhaps even more worryingly, it may have masked the full
effects of global warming.
According to work revealed exclusively on the programme by Dr Peter
Cox of the Met Office's Hadley Centre - Britain's leading institute
for climate research - in the next hundred years temperatures worldwide
could rise by as much as ten degrees Celsius, twice as quickly as previously
thought and enough to turn tracts of Britain into a desert.
Furthermore Dr Cox fears that unless action is taken swiftly, an unstoppable
chain of climatic disasters may be set in motion in just 20 years.
The story of the unmasking of global dimming is as good
as any thriller.
Two years ago climatologists noticed that the heat of
the sun had been dropping dramatically for several decades – for
example by up to 10% in the USA and 16% in parts of Britain.
No-one had noticed because the loss of heat from the
sun had been offset by global warming.
The dimming is a bizarre by-product of the fossil fuels
that cause global warming. It is caused by tiny
airborne particles of soot, ash and sulphur dioxide reflecting back
the heat of the sun.
But it is the effects of dimming that have really alarmed
scientists. The heat of the sun is vital for seasonal
rains like monsoons.
Recent work shows a direct link between dimming and
the failure of the rains in Sub-Saharan Africa in the Eighties –
the terrible droughts that afflicted Ethiopia, and led to the creation
of Band Aid.
In other words, that African catastrophe may have been
partly caused by western air pollution from cars and power stations.
Professor Veerabhadran Ramanathan of the University
of California now believes that the same thing could affect areas populated
by billions of people, eg India, where in recent years the monsoon has
been coming later and later.
The worry is that one day it won't come at all.
Fortunately, the cure for the problem is relatively
straightforward: simply clean up our emissions.
Scrubbers in power stations and catalytic converters
in cars – things many people are doing anyway – cut particle
pollution and remove the cause of global dimming.
But there is a catch: as we tackle the dimming, the
full power of global warming will be revealed. This was the discovery
of Dr David Travis of the University of Wisconsin.
In the days immediately after 9/11 the entire United
States commercial airfleet was grounded for three days.
Dr Travis believed that aircraft vapour trails were
themselves a significant contributor to solar dimming, and he found
that their three day absence alone resulted in a massive jump in the
daily temperature range – the difference between the highest daytime
temperature and the lowest night time temperature.
This important climatic variable increased by more than
one degree Celsius over the three days of the grounding.
The unforeseen climatic effects of 9/11 suggest that
if we remove other causes of dimming, the impact on global temperatures
could be huge.
Dr Cox now believes the cooling effects of dimming may
be the reason that, so far, global warming has been relatively muted,
despite the rapid rise in greenhouse gases.
In effect, two different forms of pollution – the
airborne particles that cause visible air pollution, and invisible greenhouse
gases like carbon dioxide - have been cancelling each other out, leading
scientists to underestimate the power of global warming.
Dr Cox has now factored global dimming into the models
for global warming and the effect is dramatic.
If nothing is done to tackle global warming then in
just 20 years, Dr Cox believes, the globe could see a two degree increase
– enough to begin the irreversible melting of the Greenland ice
sheet and start the flooding of our cities.
Within 40 years, temperatures could be four degrees
higher – enough to ignite the rainforests.
And, by the end of the century, if Britain does nothing
about greenhouse gases, it will have a climate like that of North Africa,
and our green and pleasant land will have become a desert.
Horizon: Global Dimming is a DOX production for
BBC TWO.
The producer is David Sington and editor is Matthew
Barrett.
