II. Mechanics
of Global Warming
“With the possible exception
of another world war, a giant asteroid, or an incurable plague, global
warming may be the single largest threat to our planet. For decades human factories and cars have spewed billions of
tons of greenhouse gases into the atmosphere, and the climate has begun
to show some signs of warming…If we don’t curb our greenhouse gas emissions,
then low-lying nations could be awash in seawater, rain and drought
patterns across the world could change, hurricanes could become more
frequent, and El Ninos could become more intense” says John Weier writing
in EarthObservatory.nasa.gov. Then some scientists (I believe in the minority)
believe global warming will result merely in “warmer winters and increased
plant growth.” John Weier states,
“In truth, the future probably
fits somewhere between these two scenarios.” i.e. What he’s saying is the future lies somewhere between totally
disastrous global warming side effects (i.e. The Day After Tomorrow scenario) and little more than warmer winters—which
is what?—a good amount of disastrous global warming side effects in
the middle of this PS (Pooch Screw) scale. [sorry, I couldn’t help myself.] He states, “To understand global warming we must understand the
science behind it.” I’ve given
you a lot of the side effects and what’s going on right up front. Now let’s take a look at the science of global
warming and simply how the earth is a stable and warm enough environment
to support life. Got to know
how a well functioning system works, before we can really understand
how it can get messed up. Right? So let’s go. [ http://earthobservatory.nasa.gov/Library/GlobalWarming/ ]
- The sun warms the Earth with a constant amount of
radiant energy which reaches the Earth at all times. The sun’s output has remained relatively
constant over millennia of time.
- About 30 percent of the sun’s total energy striking
the Earth reflects back into outer-space, and 70 percent is absorbed
in the form of UV, visible light and near infrared solar radiation. I say it is held, but this is only for
a period of time.
- The energy which is held doesn’t stay bound up on
Earth forever, but ends up being radiated back off into outer-space
at a near constant rate that leaves the Earth at a mean constant of
around 59 degrees Fahrenheit. As
the sun heats the Earth’s surface, land and oceans, it heats them,
and they in turn emit thermal radiation in the form of long-wave infrared
back into outer-space.
So what holds the Earth
at 59 degrees F? Some of this
long-wave infrared radiation being radiated back upwards from the earth’s
surface is re-absorbed by water vapor, C02 and methane and re-radiated
back toward Earth’s surface—trapped at the top of the troposphere. Without the greenhouse gases, Earth’s average surface temperature
would be a nice cold -18 degrees C (-0.4F), and life as we know it would
be impossible, the Earth would be essentially frozen.
But over the past 250 years, from 1750 to the present, human
activity has been raising greenhouse gas concentrations in the atmosphere
by our factories, power plants and vehicles, all burning coal, gasoline
and diesel fuel, and pouring C02 into the atmosphere in increasing
amounts. Once carbon-based greenhouse gases (C02 &
CH4) get into the atmosphere beyond the levels that maintain global
temperatures at a steady, even level, they stay there for decades, or
for C02, even longer, up to 100 years. The IPCC says since the start of the Industrial Revolution carbon
dioxide (C02) is up 31 percent, and methane (CH4) is up 151 percent. Paleoclimate readings from ice cores and fossil records show
these two gases are at their highest levels in the past 420,000 years
(i.e. one half million years). These
increased levels of greenhouse gases are preventing additional thermal
radiation from leaving Earth, trapping excess heat in Earth’s atmosphere,
causing a steady rise in the average mean temperature of the Earth.
Here are the facts: Most leading
researchers and scientific organizations project that the average mean
surface temperature of the Earth will increase along with emissions,
according to the IPCC, with surface temperatures (mean) raising anywhere
between 1.4 C and 5.8 C by the end of the 21st century. It only rose by 0.5 C, a lot in and by itself,
over the past 100 years. Now
in the next 100 years it is projected to rise 1.4 C (3 times as much
in the same time span) to 5.8 C (a whopping 11 times as much in100 years!). This is an exponential rise in global mean surface
temperature—from 56 F in 1900 to 59 F in 2000, to anywhere from 63 F
to 67 F by the end of the 21st century.
Normal average mean temperatures over extended periods of time,
geologically speaking, are very stable. i.e. During the last ice age Earth was 5 C cooler. It has gradually increased to present levels, at a very slow
rise rate (1 C between every 1,000 to 4,000 years depending on when
you date the last major Ice Age—i.e. whether you view C-14 as an accurate
dating method or not). We’ve just experienced a rise of 0.5 C in a
very short 100 year time-span, and now the projected rise in average
mean surface temperature is between 1.4 C and 5.8 C within the next
100 years. The mid-range between 1.4 C and 5.8 C is a projected
3.6 C rise in 100 years or less. That’s
close to 68 F average mean surface temperature! [ http://earthobservatory.nasa.gov/Library/GlobalWarming/warming2.html ]
So, in review greenhouse
gases are gaseous components of the atmosphere that contribute to the
“greenhouse effect”. i.e. those
are the gases that help contribute to the trapping of solar energy in
the form of heat—the trapping of the suns infrared spectrum. With insufficient “greenhouse gases” the sun’s radiant energy
would escape back into outer-space, and earth would be a giant deep-freeze. Too much, and the climate warms, with all the
resultant side-effects we’ve been reading about. Now let’s learn about those gases.
Greenhouse Gases 101: The major green-house gases are
1) Water vapor. Yes, amazingly water vapor is a green-house
gas. Water vapor represents anywhere
from 36 percent to 70 percent of the greenhouse effect on earth.
2) Carbon dioxide, which represents anywhere from 9 to 26
percent of the greenhouse effect (G.H.E).
3) Ozone, 3 to 7 percent of the G.H.E.
Other gases:
4) Methane
5) Nitrous Oxide
6) Sulfur Hexaflouride
7) The Fluorocarbon’s (Freon: RF-12 & RF-22 from refrig
and ac units)
Water Vapor: Water vapor is a natural greenhouse gas and it accounts
for the largest percentage of the greenhouse effect. In climate models an increase in temperature
caused by the greenhouse effect do to a rise in C02 and methane levels
will in turn lead to an increase in evaporation and thus water vapor
content in the troposphere. This
in turn leads to a further increase in the greenhouse effect, and thus
a further increase in temperature, and thus a further increase in water
vapor until some equilibrium is reached (i.e. the atmosphere at the
higher temp becomes saturated with the amount of water vapor it will
hold (it’s dew point)). So we
see that water vapor acts as a positive feedback to the forcing provided
by human released greenhouse gases such as C02. Water vapor provides a powerful positive feedback
in the global warming sequence of events.
Carbon Dioxide: The C02 level
just as the industrial revolution began in 1750 was 280 ppm (parts per
million). It has steadily increased
without any real drop in ppm to 365 in the year 2000, a 31 percent increase. The problem with C02 is that although an actual molecule of C02,
if followed in its life-cycle, would remain in the atmosphere for only
a few years—before the ocean with its phytoplankton and zooplankton
absorbed it permanently from the atmosphere—the calculation of the dissipation
of a large increase in C02 levels would be measured in 100’s of years.
Methane: Methane in 1750 was
700 ppb (parts per billion). In
the year 2000 it has risen to 1745 ppb, a 150 percent increase. What happens to Methane in the air? Lightning and high intensity rays from the sun
“burn” it with the 02 in the atmosphere so it becomes water vapor and
C02, both greenhouse gases. So
the half-life on methane isn’t the true half-life of the greenhouse
effect it has, because it’s degrading down to water vapor and C02 continues
it’s effect.
Nitrous oxide in 1750 was 270 ppb, and in the year 2000 has risen
to 314 ppb.
Aside from water vapor near the earth’s ocean surface—which has
a residence time of a few days—most greenhouse gases take a very long
time to dissipate from the atmosphere [see http://www.sciencedaily.com/encyclopedia/Greenhouse_gas . Look up NOAA Paleoclimatology
Program-Vostok Ice Core, go ahead, do a Google search on your own.]
A must see, with good explanations
and clear charts, log onto NOAA CMDL CCGG Interactive Atmospheric Data
Visualization, NOAA C02 Data at: http://www.cmdl.noaa.gov/aggi/ .
“NOAA issued the Annual
Greenhouse Gas Index (AGGI) today, its benchmark measurement of gases
in the atmosphere that affect the Earth’s climate. This year’s AGGI reflects an increase in carbon dioxide (C02)
and nitrous oxide (N20) but a leveling off of methane (CH4), and a decline
in two chlorofluorocarbons (CFCs), gases that contribute to the cause
of the Antarctic ozone hole. Overall,
the AGGI shows a continuing, steady rise in the amount of heat-trapping
gases in the atmosphere…The AGGI is referenced to a baseline value of
1.00 for the greenhouse gas levels that were present in the atmosphere
in 1990. The value of the AGGI for 2005 is 1.215. This reflects a continuing upward trend in the accumulation of
greenhouse gases, as well as the change in the amount of radiative forcing. Radiative forcing indicates the balance between
radiation coming into the atmosphere and radiation going out. Positive radiative forcing tends on average
to warm the surface of the Earth, and negative forcing tends on average
to cool the surface. Radiative
forcing, as measured by the index, is calculated from the atmospheric
concentration of each contributing gas and the per-molecule climate
forcing of each gas…Most of the increase in radiative forcing [positive]
since 1990 is due to C02, which now accounts for approximately 62 percent
of the radiative forcing by all long-lived greenhouse gases. Global C02 increased from an average of 376.8 parts per million
(ppm) in 2004 to 378.9 ppm in 2005. This increase 0f 2.1 ppm means that for every one million air
molecules there were slightly more than two new C02 molecules in the
atmosphere. The pre-industrial
C02 level was approximately 278 ppm. [Probably determined from ice-core samples,
fairly accurate.] [taken from http://www.publicaffairs.noaa.gov/releases2006/may06/noaa06-050.html ] 
As we have just seen, the
National Oceanic and Atmospheric Administration, NOAA, has said that
for this year of 2006, in May, there was a continuing rise in carbon
dioxide and nitrous oxide, though methane leveled off. There was also a decline in chlorofluorocarbons, gases that contribute
to the ozone hole over the Antarctic. Currently the concentration of carbon dioxide in the atmosphere
has climbed to a record 381 parts per million last year…the reading
up 2.68 ppm according to NOAA’s David J. Hofmann. In addition to C02, the 2004 data from WMO calculated nitrous oxide,
which has been steadily rising since 1988, totaled 318.6 ppb. Methane has risen the most dramatically over
the past two centuries, with the total amount in 2004 at 1,783 ppb,
but its growth has been slowing down, according to the World Meteorological
Organization. Said Leonard Barrie of WMO, “If
you have that much more energy being trapped, where does it go? [keep
that question in the back of your mind, it’s important]...Given the
lifetime of carbon dioxide in the atmosphere is 50 to 200 years depending
on how you calculate it…it doesn’t take a nuclear scientist to state
that we’re going to have this problem for a long time…If we stop now
C02 emissions to the atmosphere, it would take 50 to 100 years before
we were starting to see approaches to pre-industrial levels.” Scientists
worry that overall warming will melt glaciers and the polar ice caps,
raising sea levels enough to damage many low-lying islands and cities
around the world. In addition, warmer climate could lead to changes
in weather patterns, agriculture and even allow some diseases to expand
into new areas. [March 15, 2006, Associated Press]
[ http://www.cmdl.noaa.gov/ccgg/trends/co2_data_mlo.php ]
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