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, posted Dec 29
Karl Zehr <karlzehr@y...> wrote:
There is a fourth and fifth feedback loop of global warming as well.
Forest dieoff will decrease carbon dioxide absorption from forests.
And increasing ocean temperature will decrease carbon dioxide
absorption and increase its release from the oceans.
Of our annual 27 billion tonnes carbon dioxide output;
7 billion tonnes are absorbed by oceans;
7 billion tonnes are taken up by forests, and;
13 billion tonnes accumulate in the atmosphere each year.
However, there's a complication to this neat little equation - in the
last two years, the accumulation of carbon dioxide in the atmosphere
has risen much faster than expected, from an average of 13 to 18
billion tonnes. Scientists attribute this increase to humans producing
more carbon dioxide and, ironically, to global warming itself - as the
Earth's temperature rises it decreases the ability of oceans and
forests to take up carbon dioxide.
As the planet warms, the ability of our oceans to dissolve atmospheric
carbon dioxide will decrease because of three key factors - the
increase in water temperature, slowing of the thermohaline current and
the role of phytoplankton.
On the whole, it's not good news. Climate models that take into
account changes in water temperature, the THC and phytoplankton
activity predict 14% less carbon dioxide will be absorbed by oceans by
Also, I know this is an energy list, but also in general emissions are
emphasized as a cause without including deforestation also as a major
factor. I read somewhere that global warming would be much less if
deforestation wasn't so rampant.
Clearing and burning rainforests release vast amounts of greenhouse
gases such as carbon dioxide, methane, ozone, and nitrous oxide into
the atmosphere. Each year deforestation contributes 23-30 percent of
all carbon dioxide in the atmosphere. Carbon dioxide, in turn, is
believed to be responsible for approximately half of global warming.
At present, the countries emitting the most carbon into the atmosphere
from tropical deforestation are, in order of importance, Brazil,
Indonesia, Burma, Mexico and Thailand. Tropical deforestation also
leads to global warming by destroying one of the Earth's only ways to
absorb excess atmospheric carbon. Through photosynthesis, forests
absorb and store so much atmospheric carbon that scientists refer to
tropical rainforests as "carbon sinks". Thus, while more and more
carbon is released into the atmosphere, there are less and less
forests to remove the carbon from the atmosphere. Deforestation both
releases huge amounts of carbon into the
atmosphere and destroys our means of absorbing and storing this
substance. And it is not only carbon that is released. Rainforest
canopies absorb nitrous oxide and ozone, which are released through
deforestation. The destruction of the Earth's rainforests not only
contribute to global warming, but, as noted, also undermines the
long-term ability of the Earth's atmosphere to neutralize greenhouse
gases. The Earth's defense mechanism against pollutants are called
"trace radicals:" gas molecules which interact with greenhouse gases,
making them harmless. There are limited quantities of these trace
radicals in the atmosphere, and as more greenhouse gases are released
more trace radicals are used up. This diminishes the Earth's ability
to stabilize the atmosphere.
janson2997 <janson1997@y...> wrote:
On Thinning Ice
Impacts of a Warming Arctic: Arctic Climate Impact Assessment ·
Cambridge, 139 pp, £19.99
The polar bears stare forlornly at Hudson Bay. It's late November and
they should be out on the sea ice hunting ring seals, but the ice
hasn't formed and the bears are starving. Ursus maritimus doesn't
hunt on land and normally fasts for months each summer. Now, however,
the summers are growing longer across most of the Arctic, and the
waters of Hudson Bay are ice-free for three weeks longer than they
were thirty years ago. In a decade or two, polar bears won't be found
this far south; by the end of the century, they might exist only in
In the two hundred years since industrialisation - a geological
millisecond - we've increased the concentration of carbon dioxide in
the Earth's atmosphere by 35 per cent; a third of that has appeared
in the last four decades. Carbon dioxide and other greenhouse gases,
such as methane, trap heat that would otherwise radiate into space.
As greenhouse gas levels rise, the lower atmosphere heats up and the
climate changes, sometimes in unexpected ways.
The global average temperature has increased by about 0.6°C over the
last two centuries. Most greenhouse gases remain in the atmosphere
for decades, and have an ongoing, cumulative warming effect. In 2001,
the UN Intergovernmental Panel on Climate Change, a group of 2500
scientists, predicted an additional increase during the 21st century
of between 1.4 and 5.8°C. In October, a body of nearly 300 scientists
completed the Arctic Climate Impact Assessment, a report based not on
worst-case scenarios but on observed changes to-date combined with
projected temperature increases that are below the middle range of
those anticipated by complex, increasingly accurate global climate
models. Despite this methodological caution, the predictions made in
the Assessment are terrifying. By the end of the century, annual
average temperatures in the north will rise between 3 and 5°C on land
and up to 7°C over the Arctic Ocean, with winter temperatures
increasing even more. Sea-ice cover will decline by 50 per cent, and
could disappear entirely in summer.
The Assessment expresses particular concern about `feedback loops'
exacerbating climate change. The first such loop is already
operating, as rising temperatures melt snow and ice and expose more
open water and bare ground each summer: these darker surfaces reflect
75 per cent less heat away from the planet's surface and this means
further warming, which melts more ice and snow, which reflects less
heat, and so on. In addition, the atmosphere is thinner at the
Earth's poles, and rising greenhouse gas levels therefore have a more
immediate impact on surface temperatures. In the Arctic the average
annual temperature has already increased almost twice as much as it
has globally: in Alaska and north-west Canada, average winter
temperatures are up by more than 3°C. In summer, across the Arctic,
the average extent of sea-ice cover is 15 per cent less than three
decades ago. More than two million square kilometres of highly
reflective sea ice has been lost, an area eight times the size of the
The second feedback loop involves fresh water from melting Arctic and
Greenland ice flowing south into the North Atlantic and disrupting
the Gulf Stream, the ocean current from the Caribbean that moderates
temperatures in Northern Europe. The Assessment reports a `tentative
indication from the North Atlantic of an initial slowing of the deep
ocean circulation'. Were the circulation to slow significantly, or
stop, the result would be a dramatic reduction in winter temperatures
and rainfall levels in Ireland, Britain and Scandinavia, at least for
a few decades. It is because of this possibility of localised cooling
that the term `climate change' is preferred to `global warming'.
The third feedback loop involves melting permafrost releasing huge
quantities of methane and carbon dioxide as the plant material in the
soil decomposes. Methane is 23 times more effective than carbon
dioxide at trapping heat in the atmosphere. As methane and carbon
dioxide from the melting permafrost reach the atmosphere, they cause
further temperature rises, which in turn cause more melting, and so
on. According to the Assessment the southern limit of permafrost is
liable to retreat several hundred kilometres northwards during this
century. Melting permafrost has already forced the Alaskan state
government to cut from 200 to 100 days the annual period during which
oil and gas equipment is permitted to travel on the Arctic tundra.
The impact of this third feedback loop may already be apparent:
measurements from Hawaii's Mauna Loa Observatory show that
atmospheric carbon dioxide concentrations increased by 2.08 parts per
million in 2002 and by 2.54 ppm in 2003, considerably higher than the
1.50 ppm average of recent decades.
Massive quantities of methane are also trapped on the frozen seabed
of the Arctic Ocean in the form of solid hydrates. As the temperature
of the seabed rises, these hydrates could decompose, releasing
additional methane into the atmosphere. Although the Assessment
describes this as `a less certain outcome', it warns that `if such
releases did occur . . . the climate impacts could be very large.'
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