Carbon
Dioxide Rate Is At Highest Level For 650,000 Years
By Steve Connor
07 February, 2007
The
lndependent
Concentrations of carbon dioxide
in the atmosphere are at their highest levels for at least 650,000 years
and this rise began with the birth of the Industrial Revolution 250
years ago, according to the Intergovernmental Panel on Climate Change
(IPCC).
Carbon dioxide is the principal greenhouse gas responsible for global
warming and, in 2005, concentrations stood at 379 parts per million
(ppm). This compares to a pre-industrial level of 278 ppm, and a range
over the previous 650,000 years of between 180 and 300 ppm, the report
says.
Present levels of carbon
dioxide - which continue to rise inexorably each year - are unprecedented
for the long period of geological history that scientists are able to
analyse from gas samples trapped in the frozen bubbles of deep ice cores.
However, the IPCC points
to a potentially more sinister development: the rate of increase of
carbon dioxide in the atmosphere is beginning to accelerate. Between
1960 and 2005 the average rate at which carbon dioxide concentrations
increased was 1.4 ppm per year. But when the figures are analysed more
closely, it becomes apparent that there has been a recent rise in this
rate of increase to 1.9 ppm per year between 1995 and 2005.
It is too early to explain
this accelerating increase but one fear is that it may indicate a change
in the way the Earth is responding to global warming. In other words,
climate feedbacks that accelerate the rate of change may have kicked
in.
The IPPC's report points
out that, as the planet gets warmer, the natural ability of the land
and the oceans to absorb carbon dioxide from the atmosphere begins to
get weaker.
It is estimated that about
half of all the man-made emissions of carbon dioxide have been taken
out of the air and absorbed by natural carbon "sinks" on the
land and in the sea. Many computer models of the climate predict that
as the Earth continues to get warmer, these sinks will become less able
to absorb carbon dioxide from the atmosphere.
This means that more carbon
dioxide will be left in the air to exacerbate the greenhouse effect,
so leading to further temperature rises and more global warming, which
in turn will make the natural carbon sinks of the Earth even less efficient.
As the IPCC's summary says:
"Warming tends to reduce land and ocean uptake of atmospheric carbon
dioxide, increasing the fraction of anthropogenic [man-made] emissions
that remain in the atmosphere."
This is just one of several
"positive feedbacks" that could quickly accelerate the rate
of global warming over the coming century. One isa warmer world is causing
more evaporation from the oceans and a rise in water vapour - a powerful
greenhouse gas - in the lower atmosphere. Another is sea ice and snow
cover is shrinking at the poles and on mountains, leading to a further
increase in local temperatures.
Global warming: the final warning
According to UN report, the
world will be a much hotter place by 2100. This will be the impact ...
+2.4°: Coral
reefs almost extinct
In North America, a new dust-bowl
brings deserts to life in the high plains states, centred on Nebraska,
but also wipes out agriculture and
cattle ranching as sand dunes
appear across five US states, from Texas in the south to Montana in
the north.
Rising sea levels accelerate
as the Greenland ice sheet tips into irreversible melt, submerging atoll
nations and low-lying deltas. In Peru, disappearing Andean glaciers
mean 10 million people face water shortages. Warming seas wipe out the
Great Barrier Reef and make coral reefs virtually extinct throughout
the tropics. Worldwide, a third of all species on the planet face extinction
+3.4°: Rainforest
turns to desert
The Amazonian rainforest
burns in a firestorm of catastrophic ferocity, covering South America
with ash and smoke. Once the smoke clears, the interior of Brazil has
become desert, and huge amounts of extra carbon have entered the atmosphere,
further boosting global warming. The entire Arctic ice-cap disappears
in the summer months, leaving the North Pole ice-free for the first
time in 3 million years. Polar bears, walruses and ringed seals all
go extinct. Water supplies run short in California as the Sierra Nevada
snowpack melts away. Tens of millions are displaced as the Kalahari
desert expands across southern Africa
+4.4°: Melting
ice caps displace millions
Rapidly-rising temperatures
in the Arctic put Siberian permafrost in the melt zone, releasing vast
quantities of methane and CO2. Global temperatures keep on rising rapidly
in consequence. Melting ice-caps and sea level rises displace more than
100 million people, particularly in Bangladesh, the Nile Delta and Shanghai.
Heatwaves and drought make much of the sub-tropics uninhabitable: large-scale
migration even takes place within Europe, where deserts are growing
in southern Spain, Italy and Greece. More than half of wild species
are wiped out, in the worst mass extinction since the end of the dinosaurs.
Agriculture collapses in Australia
+5.4°: Sea levels
rise by five metres
The West Antarctic ice sheet
breaks up, eventually adding another five metres to global sea levels.
If these temperatures are sustained, the entire planet will become ice-free,
and sea levels will be 70 metres higher than today. South Asian society
collapses due to the disappearance of glaciers in the Himalayas, drying
up the Indus river, while in east India and Bangladesh, monsoon floods
threaten millions. Super-El Niños spark global weather chaos.
Most of humanity begins to seek refuge away from higher temperatures
closer to the poles. Tens of millions of refugees force their way into
Scandanavia and the British Isles. World food supplies run out
+6.4°: Most of
life is exterminated
Warming seas lead to the
possible release of methane hydrates trapped in sub-oceanic sediments:
methane fireballs tear across the sky, causing further warming. The
oceans lose their oxygen and turn stagnant, releasing poisonous hydrogen
sulphide gas and destroying the ozone layer. Deserts extend almost to
the Arctic. "Hypercanes" (hurricanes of unimaginable ferocity)
circumnavigate the globe, causing flash floods which strip the land
of soil. Humanity reduced to a few survivors eking out a living in polar
refuges. Most of life on Earth has been snuffed out, as temperatures
rise higher than for hundreds of millions of years.
© Copyright 2007 Independent
News and Media Limited
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