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CO2,
Earth’s Global Thermostat, Dials Up to Record 401.6 ppm Daily Value
on March 12
14
March, 2014
NASA
GISS, likely the world’s premier Earth atmospheric monitoring
agency has dubbed CO2 “The
Thermostat that Control’s Earth’s Temperature.”
So when human fossil fuel emissions keep cranking that thermostat
ever higher, it’s important sit up and take note. For, inexorably,
we keep forcing atmospheric values of this critical heat-trapping gas
up and up.
According
to reports from The
Mauna Loa Observatory and The Keeling Curve,
daily CO2 values for March 12 rocketed to a record 401.6 parts per
million. Hourly values rose briefly higher, touching 402 parts per
million. Levels fell back to around 400 ppm on March 13. But the
overall trend will continue upward through March, April and much of
May when the height of annual atmospheric CO2 readings is typically
reached.
By
comparison, during May of last year, daily
and weekly values hit just slightly higher than 400 parts per million
while measures for the month hovered just below this number. We are
now about two months away from the 2014 peak. So it appears possible
that daily values could rise to 404 ppm or greater with highs for the
month potentially exceeding 402 ppm (you can view a comparison graph
for May 2013 here).
Such
high levels of this gas have not been seen on Earth in over 3 million
years. A time when temperatures were 2-3 degrees Celsius warmer and
sea levels were 15-75 feet higher than today. And should CO2 levels
merely remain at the level currently achieved, we can probably expect
at least the same amount of warming long-term.
CO2
in Context
Annually,
the average rate of CO2 increase now is an extraordinary 2.2 parts
per million each year. This rate is about 6-7 times faster than at
any time in geological history. None of the vast flood basalts of the
ancient past, no period of natural vulcanism, can now rival the
constant and massive injection of this powerful and long-lasting
greenhouse gas by humans into the atmosphere.
Last
year, the rate of increase spiked to around 2.5 parts per million and
we can view this as mere prelude under a continuation of business as
usual. For if human fossil fuel emissions are not radically brought
into check, the ongoing economic inertia of existing fossil fuel
based infrastructure and planned new projects will likely shove this
rate of increase to 3, 4 even 7 parts per million each year by the
end of this century. As a result, CO2 levels alone have the potential
to reach catastrophic values of 550 parts per million by around
2050-2060 that, long term and without any of the added effects of
other greenhouse gasses, would be enough to eventually melt all the
ice on Earth and raise global temperatures to around 5-6 degrees
Celsius above current levels. A level that, through acidification
alone and not including damage through stratification and anoxia,
could drive up to 1/3 of ocean species to extinction.
CO2
accounts for much of the greenhouse forcing when taking into account
the feedbacks it produces on water vapor and clouds. NASA notes:
Because
carbon dioxide accounts for 80% of the non-condensing GHG forcing in
the current climate atmosphere, atmospheric carbon dioxide therefore
qualifies as the principal control knob that governs the temperature
of Earth.
All
other greenhouse gasses pale in comparison to both its total effect
and its current rate of increase. Methane, the next most potent
greenhouse gas, accounts for about 15% of the forcing and is rising
at a rate of 4 parts per billion (1/550 that of CO2), generating a
net effect equal to, in the worst case, an additional .4 parts per
million CO2 each year (.29 when aerosols drop out). A troubling and
dangerous increase itself. But still a mere shadow compared to the
overall rate of CO2 increase.
Only
in the most catastrophic of scenarios, when added atmospheric heat,
primarily generated through added CO2 and other greenhouse gas
forcing, triggers methane emissions equal to 2 gigatons each year in
the Arctic (a rate 25 times the current release), would the total
methane forcing approach the predicted value for CO2 by the end of
this century under current fossil fuel emissions scenarios.
More likely, paleoclimate scenarios tend to suggest that the natural
methane feedback, long-term, is roughly equal to 50% of the CO2
forcing and is largely governed by it. A dangerous amplifying
feedback driven by a devastating and long-lasting CO2 forcing.
CO2
is also the longest lived of the major greenhouse gasses with one
molecule of CO2 providing effective atmospheric warming for at least
500 years. By
comparison, the oxidation time for a single molecule of methane is
around 8 years.
What this means is that it takes an ever increasing methane emission
just to keep values constant while atmospheric CO2 takes much longer
to level off given even a constant rate of emission.
The
result is that heat forcing from CO2 tends to remain constant over
long periods while methane heat forcing values have a tendency to
spike due to rapid oxidation.
(Radiative forcing from a 10 gigaton release of methane in red compared to expected end century CO2 values of 750 ppm. Note how the methane heat forcing spikes and then rapidly falls off. Image source: RealClimate.)
Current
rates of CO2 increase, therefore, should be viewed as catastrophic to
climates that are both livable and benevolent to humans. A rate of
increase that puts at risk severe changes to Earth environments and
which provides a trigger for setting off a series of powerful
amplifying feedbacks through the medium and long term. These include
both loss of ice albedo and the potential for spiking methane
emissions from the widespread natural store.
Links:
Hat
Tip to Climate State
Kudos
to Mark Archambault for Looking Sharp
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