Re: {OT} Climate experts: Gore's movie gets the science right
- From: "Mike Hunter" <mikehunt2@xxxxxxxxxxxx>
- Date: Wed, 28 Jun 2006 16:05:19 -0400
I suppose it all depend on which scientist one chooses to believe. True
scientist believe the following. The environuts want us to believe it is
only the extra carbon dioxide produced by man.
Causes of Climate Change
The work of climatologists has found evidence to suggest that only a limited
number of factors are primarily responsible for most of the past episodes of
climate change on the Earth, like the one the earth is still going through
since the last ice age. These factors include:
a.. Variations in the Earth's orbital characteristics.
b.. Atmospheric carbon dioxide variations.
c.. Volcanic eruptions
d.. Variations in solar output.
Figure 7y-1 illustrates the basic components that influence the state of the
Earth's climatic system. Changes in the state of this system can occur
externally (from extraterrestrial systems) or internally (from ocean,
atmosphere and land systems) through any one of the described components.
For example, an external change may involve a variation in the sun's output
which would externally vary the amount of solar radiation received by the
Earth's atmosphere and surface. Internal variations in the Earth's climatic
system may be caused by changes in the concentrations of atmospheric gases,
mountain building, volcanic activity, and changes in surface or atmospheric
albedo.
A. Variations in the Earth's Orbital Characteristics
The Milankovitch theory suggests that normal cyclical variations in three of
the Earth's orbital characteristics is probably responsible for some past
climatic change. The basic idea behind this theory assumes that over time
these three cyclic events vary the amount of solar radiation that is
received on the Earth's surface.
The first cyclical variation, known as eccentricity, controls the shape of
the Earth's orbit around the sun. The orbit gradually changes from being
elliptical to being nearly circular and then back to elliptical in a period
of about 100,000 years. The greater the eccentricity of the orbit (i.e., the
more elliptical it is), the greater the variation in solar energy received
at the top of the atmosphere between the Earth's closest (perihelion) and
farthest (aphelion) approach to the sun. Currently, the Earth is
experiencing a period of low eccentricity. The difference in the Earth's
distance from the sun between perihelion and aphelion (which is only about 3
%) is responsible for approximately a 7 % variation in the amount of solar
energy received at the top of the atmosphere. When the difference in this
distance is at its maximum (9 %), the difference in solar energy received is
about 20 %.
The second cyclical variation results from the fact that, as the Earth
rotates on its polar axis, it wobbles like a spinning top changing the
orbital timing of the equinoxes and solstices (see Figure 7y-2 below). This
effect is known as the precession of the equinox. The precession of the
equinox has a cycle of approximately 26,000 years. According to illustration
A, the Earth is closer to the sun in January (perihelion) and farther away
in July (aphelion) at the present time. Because of precession, the reverse
will be true in 13,000 years and the Earth will then be closer to the sun in
July (illustration B). This means, of course, that if everything else
remains constant, 13,000 years from now seasonal variations in the Northern
Hemisphere should be greater than at present (colder winters and warmer
summers) because of the closer proximity of the Earth to the sun.
B. Atmospheric Carbon Dioxide Variations
Studies of long term climate change have discovered a connection between the
concentration of carbon dioxide in the oceans and the atmosphere and mean
global temperature. Carbon dioxide is one of the more important gases
responsible for the greenhouse effect. Certain atmospheric gases, like
carbon dioxide, water vapor and methane, are able to alter the energy
balance of the Earth by being able to absorb longwave radiation emitted from
the Earth's surface. The net result of this process and the re-emission of
longwave back to the Earth's surface increases the quantity of heat energy
in the Earth's climatic system. WITHOUT the greenhouse effect, the average
global temperature of the Earth would be a COLD as MINUS 18° Celsius rather
than the present 15° Celsius.
Researchers of the 1970s CLIMAP project found strong evidence in deep-ocean
sediments of variations in the Earth's global temperature during the past
SEVERAL HUNDRED THOUSAND YEARS of the Earth's history. Other subsequent
studies have confirmed these findings and have discovered that these
temperature variations were closely correlated to the concentration of
carbon dioxide in the atmosphere and variations in solar radiation received
by the planet as controlled by the Milankovitch cycles. Measurements
indicated that atmospheric carbon dioxide levels were about 30 % lower
during colder glacial periods. It was also theorized that the oceans are a
major store of carbon dioxide and that they controlled the movement of this
gas to and from the atmosphere. The amount of carbon dioxide that can be
held in oceans is a function of temperature. Carbon dioxide is released from
the oceans when global temperatures become warmer and diffuses into the
ocean when temperatures are cooler. Initial changes in global temperature
were triggered by changes in received solar radiation by the Earth through
the Milankovitch cycles. The increase in carbon dioxide then amplified the
global warming by enhancing the greenhouse effect and returning more carbon
dioxide to the oceans.
C. Volcanic Eruptions
For many years, climatologists have noticed a connection between large
explosive volcanic eruptions and short term climatic change (Figure 7y-4).
For example, one of the coldest years in the last two centuries occurred the
year following the Tambora volcanic eruption in 1815. Accounts of very cold
weather were documented in the year following this eruption in a number of
regions across the planet. Several other major volcanic events also show a
pattern of cooler global temperatures lasting 1 to 3 years after their
eruption
At first, scientists thought that the dust emitted into the atmosphere from
large volcanic eruptions was responsible for the cooling by partially
blocking the transmission of solar radiation to the Earth's surface.
However, measurements indicate that most of the dust thrown in the
atmosphere returned to the Earth's surface within six months. Recent
stratospheric data suggests that large explosive volcanic eruptions also
eject large quantities of sulfur dioxide gas which remains in the atmosphere
for as long as three years. Atmospheric chemists have determined that the
ejected sulfur dioxide gas reacts with water vapor commonly found in the
stratosphere to form a dense optically bright haze layer that reduces the
atmospheric transmission of some of the sun's incoming radiation.
In the last century, two significant climate modifying eruptions have
occurred. El Chichon in Mexico erupted in April of 1982, and Mount Pinatubo
went off in the Philippines during June, 1991 (Figure 7y-5). Of these two
volcanic events, Mount Pinatubo had a greater effect on the Earth's climate
and ejected about 20 million tons of sulfur dioxide into the stratosphere
(Figure 7y-6). Researchers believe that the Pinatubo eruption was primarily
responsible for the 0.8 degree Celsius drop in global average air
temperature in 1992. The global climatic effects of the eruption of Mount
Pinatubo are believed to have peaked in late 1993. Satellite data confirmed
the connection between the Mount Pinatubo eruption and the global
temperature decrease in 1992 and 1993. The satellite data indicated that the
sulfur dioxide plume from the eruption caused a several percent increase in
the amount of sunlight reflected by the Earth's atmosphere back to space
causing the surface of the planet to cool.
D. Variations in Solar Output
Until recently, many scientists thought that the sun's output of radiation
only varied by a fraction of a percent over many years. However,
measurements made by satellites equipped with radiometers in the 1980s and
1990s suggested that the sun's energy output may be more variable than was
once thought (Figure 7y-7). Measurements made during the early 1980s showed
a decrease of 0.1 percent in the total amount of solar energy reaching the
Earth over just an 18 month time period. If this trend were to extend over
several decades, it could influence global climate. Numerical climatic
models predict that a change in solar output of only 1 percent per century
would alter the Earth's average temperature by between 0.5 to 1.0° Celsius.
Scientists have also link sunspots to climatic change (also see the link
www.sunspotcycle.com). Sunspots are huge magnetic storms that are seen as
dark (cooler) areas on the sun's surface. The number and size of sunspots
show cyclical patterns, reaching a maximum about every 11, 90, and 180
years. The decrease in solar energy observed in the early 1980s
correspond to a period of maximum sunspot activity based on the 11 year
cycle. In addition, measurements made with a solar telescope from 1976 to
1980 showed that during this period, as the number and size of sunspots
increased, the sun's surface cooled by about 6° Celsius. Apparently, the
sunspots prevented some of the sun's energy from leaving its surface.
However, these findings tend to contradict observations made on longer times
scales. Observations of the sun during the middle of the Little Ice Age
(1650 to 1750) indicated that very little sunspot activity was occurring on
the sun's surface. The Little Ice Age was a time of a much cooler global
climate and some scientists correlate this occurrence with a reduction in
solar activity over a period of 90 or 180 years. Measurements have shown
that these 90 and 180 year cycles influence the amplitude of the 11 year
sunspot cycle. It is hypothesized that during times of low amplitude, like
the Maunder Minimum, the sun's output of radiation is reduced. Observations
by astronomers during this period (1645 to 1715) noticed very little sunspot
activity occurring on the sun.
During periods of maximum sunspot activity, the sun's magnetic field is
strong. When sunspot activity is low, the sun's magnetic field weakens. The
magnetic field of the sun also reverses every 22 years, during a sunspot
minimum. Some scientists believe that the periodic droughts on the Great
Plains of the United States are in someway correlated with this 22 year
cycle.
Man has no contol over any of those factors
mike hunt
"ToMh" <tlhumm@xxxxxxxxxxx> wrote in message
news:1151519116.011470.326110@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
WASHINGTON (AP) -- The nation's top climate scientists are giving "An
Inconvenient Truth," Al Gore's documentary on global warming, five
stars for accuracy.
http://www.cnn.com/2006/TECH/science/06/27/gore.science.ap/index.html
.
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