Download LECTURE 17 Energy

CLASS LECTURE 17
What about Global Climate Change?
The Greenhouse Effect and Global Climate Change
The greenhouse effect occurs naturally. A large percentage of the
sun’s energy that reaches the earth is in the form of visible light.
Remember, visible light is just one portion of the electromagnetic
spectrum.
The earth’s atmosphere is largely transparent to visible light. About
30% is reflected back into space and never reaches the earth’s
surface. Of the 70% that does reach the surface, about 2/3 of that is
absorbed, warming the atmosphere, oceans, and continents.
The earth’s surface reradiates most of the absorbed energy in the
form of infrared. The atmosphere is not as transparent to infrared;
most of it is absorbed, holding warmth in the atmosphere. Think of a
greenhouse (for which the effect was named). Visible light passes
through the glass, but not the reradiated infrared, which remains
trapped inside. Greenhouses can stay warm, even during colder
weather. The same effect occurs with the interior of your car on a
sunny day. Even if the air outside is cool, you may find the inside of
your car to be uncomfortably warm if you parked in the sunlight.
www.usgcrp.gov/usgcrp/Library/nationalassessment/overviewclimate.htm
Water vapor and carbon dioxide are two gases that help to trap the
infrared. The greenhouse effect maintains the mild average
temperature (59 degrees F) at the earth’s surface.
Without this, the earth would be a frozen waste.
However, a runaway greenhouse effect is just as undesirable, the
surface of Venus is an oven. The rise in the surface temperature of
the earth caused by the increase in the greenhouse effect is known
as global warming. No one questions global warming; the
temperature data from the past 100 or so years confirms it. Most
climate specialists agree that earth’s average temperature will
increase about 1.0 to 3.5 degrees Celsius over the next century.
(Chemistry in the Community 4th Ed., American Chemical Society, p. 292)
The consequences of global climate include: major flooding in
coastal cities, regional climate changes, and more frequent weather
extremes. A warmer atmosphere can hold more moisture, making big
storms more likely but also drying out the land more quickly between
storms. Another consequence of this trend would be a tendency
toward shorter winters and more blizzards. (Chemistry in the Community 4th Ed.,
American Chemical Society, p. 292)
The real question is: how much does man contribute to global
warming? It does appear that man has some influence; the burning
of fossil fuels, which contain hydrocarbons, releases carbon dioxide
into the atmosphere.
In 1997, nearly 1500 scientists, including 97 of the 171 living Nobel
laureates in science, issued an urgent call for the nations of the world
to take strong, binding steps toward curbing global warming. Since
that time, the calls have become stronger and more visible as the
signs of climate change have already begun to appear. An excellent
link to follow is on the “Nature Conservancy” website
http://www.nature.org/initiatives/climatechange/activities/art19631.html
This particular page is dedicated to Facts about climate change and
has links to individual actions to help mitigate the problem posed by
climate change.
Enough political and scientific figures worldwide believed that man’s
influence was significant enough to warrant the Kyoto Protocol in
1997.
The European Economic Union pledged to reduce carbon dioxide
emissions to 8% below 1990 levels.
–Japan pledged to reduce levels to 7% below 1990 levels.
–The U.S. pledged to reduce levels to 6% below 1990 levels.
Then vice-president Gore signed on behalf of president Clinton.
However, as a treaty, Congress was required to ratify it. There was
stiff opposition to the plan from both parties, so the president never
sent it to Congress for a vote.
Much of the opposition came from those who felt it was unfair that
China and India were not pledging any reductions (these nations
argued that they should be allowed to achieve western economic
levels before being penalized- politics…).
President Bush halted any plans to put the treaty to a vote and
instead proposed searching for an alternative. An excellent
discussion on the issue of global warming is presented in the joint
Nova/Frontline program “What’s Up With the Weather?” on PBS.
The mild average temperature (15 degrees C, or 59 degrees F) at
Earth’s surface is determined partly by the balance between the
inward flow of energy from the sun and the outward flow of
transformed solar energy into space. However, certain properties of
earth also help determine how much thermal energy the planet can
hold near its surface- where terrestrial life resides- and how much
energy it radiates back into space. The combination of these factors
helps create a balance of energy that leads to a hospitable climate on
earth. (Chemistry in the Community 4th Ed., American Chemical Society, pp. 279-280)
About 30% of incoming solar radiation never reaches earth’s surface
but is reflected directly back into space by clouds and particles in the
atmosphere. Solar radiation is also reflected when it strikes such
materials as snow, sand, or concrete at earth’s surface. In fact,
visible light reflected in this way allows earth’s illuminated surface to
be seen from space. (Chemistry in the Community 4th Ed., American Chemical Society, p. 280)
Of the remaining 70% of solar radiation that reaches earth’s surface,
about two-thirds is absorbed, warming the atmosphere, oceans, and
continents. Another one-third of this energy powers the hydrologic
cycle- the continuous cycling of water into and out of the atmosphere
by evaporation and condensation. This energy causes water to
evaporate from the oceans, forming clouds, which then release the
water as precipitation. (Chemistry in the Community 4th Ed., American Chemical Society, p. 280)
Earth’s surface reradiates most absorbed solar radiation, but not
necessarily at its original wavelengths. Some incoming UV and
visible radiation is re-emitted at longer wavelengths – in the infrared
region of the spectrum. This reradiated energy plays a major role in
Earth’s energy balance. Some molecules in the air absorb lowenergy infrared photons rather than the original radiation, thus
holding warmth in the atmosphere. (Chemistry in the Community 4th Ed., American Chemical
Society, p. 280)
Carbon dioxide and water readily absorb infrared radiation, as do
methane (CH4), nitrous oxide (N2O), and halogenated hydrocarbons
such as CF 3Cl and other chlorofluorocarbons or CFCs. Because
clouds consist of droplets of water or ice, they also absorb some
infrared radiation. Energy absorbed by these molecules in the
atmosphere is reradiated in all directions. Thus energy can pass
back and forth between Earth’s surface and molecules in the
atmosphere many times before it finally escapes into outer space.
(Chemistry in the Community 4th Ed., American Chemical Society, pp. 280-281)
This trapping and returning of infrared radiation by carbon dioxide,
water, and other atmospheric substances is known as the
greenhouse effect because the process resembles the way thermal
energy is held in a greenhouse on a sunny day. Atmospheric
substances that effectively absorb infrared radiation are known as
greenhouse gases. (Chemistry in the Community 4th Ed., American Chemical Society, p. 281)
Without water and carbon dioxide molecules in the atmosphere to
absorb and reradiate thermal energy to Earth, the planet would have
an average temperature of about – 18 degrees Celsius (about 0
degrees Fahrenheit). This temperature is quite close to the average
surface temperature on Mars. At the other thermal extreme is the
planet Venus, an example of a runaway greenhouse effect. Its
atmosphere is composed of 96% carbon dioxide (and clouds made of
sulfuric acid!), which prevents the escape of most infrared radiation.
As a result, the average temperature on Venus (450 degrees Celsius)
is much higher than on earth (15 degrees Celsius). Although some of
this difference is due to different planetary positions relative to the
Sun, Venus (the second planet from the Sun) is actually hotter than
Mercury (the planet nearest the Sun). (Chemistry in the Community 4th Ed., American
Chemical Society, p. 281)
So, assuming you buy into arguments that for whatever reasons we
should limit our use of fossil fuels, the question becomes: how do we
do this?
Alternative Energy Sources
An alternative energy source is any that does not rely upon the
combustion of fossil fuels. (although some would exclude nuclear
power from this category even though it dose meet the criterion of the
definition).
Solar Power
Solar power is derived by harnessing the energy of the sun’s visible
light that falls upon the earth’s surface. The light is collected in “solar
panels” and is used to either heat water directly or is converted to
electricity.
Consider a risk vs. benefit analysis.
Pros
There is essentially a limitless “fuel” supply.
The sun is not scheduled to enter its red giant phase for another 5
billion years. By that time, humanity will have passed on or evolved
to the point at which it doesn’t need energy from our sun.
There are no sulfur dioxide (contributes to acid rain) or carbon dioxide
emissions (contributes to global warming).
There are other forms of pollution that must be considered, as well as
the technological hurdles that face this technology.
Cons
Sunlight is needed. Obviously there is a night/day cycle, and some
areas, such as the Pacific Northwest, New England, or the British
Isles have many overcast days.
The efficiency is low. Only about 15% of the energy absorbed as
sunlight is converted to electricity. This is “bottom-of-the-barrel”.
Panels must cover tremendously large areas to generate appreciable
quantities of electricity. Even in the desert southwest, would square
miles of panels impact the environment?
There are still very high initial costs with long payback times.
Suppose the initial investment required to save $5,000/year is
$100,000; you won’t break even on your outlay until the 20th year.
The business environment typically demands quicker returns.
Subsidies and/or tax breaks could remedy this problem; there may be
other priorities could help with this. Visual pollution is also a potential
drawback. An ugly solar array on top of your roof will also need to be
cleared of snow. This is not a cheap and easy solution for everyone.
It also demands changes in your lifestyle that limits how and when
you use things like water pumps, air conditioning and lighting.
The balance of plant for a PV systems requires that a complex
inverter be included in the design. This inverter can double the cost
of the installation and come with service requirements that go beyond
most normal homeowners ability, requiring expensive specialized
electrical contractors. The images below are of the balance of plant
systems at UML CEC they include batteries and inverters for
converting the power into a form for use in electrical equipment. This
equipment services the wind generators on the roof of Ball Hall.
Hydroelectric Power
Water cascading through dams drives turbines by pushing them
directly. Lowell was founded on the existence of the Merrimack River
and its hydro power capability. This is a picture of the actual dam,
the power generation facility is located a ¼ mile down stream of the
dam.
http://www.clemson.edu/caah/history/FacultyPages/PamMack/lec323/lowelldam.
JPG
Pros
There are no sulfur dioxide (contributes to acid rain) or carbon dioxide
emissions (contributes to global warming). The efficiency is high
(about 80%).
Cons
There are a limited number of sites suitable for damming.
Hydroelectric power is not a solution in and of itself, only a
supplement. Currently hydroelectric power represents about 10% of
our nation’s electricity.
Wind Power
Moving air can push windmill turbines directly.
Pros
There are no sulfur dioxide (contributes to acid rain) or carbon dioxide
emissions (contributes to global warming).
Cons
Wind is a highly variable power source. Similar to solar, wind power
is at the mercy of weather patterns. Large-scale power generation
isn’t currently viable.
Many windmills could be built, but visual pollution might become a
concern.
Visual pollution is a concern.
Will the public want their hillsides dotted with huge windmills? Think
of the reaction in Vermont or New Hampshire if large-scale wind
projects were proposed for the Green Mountains or the White
Mountains. There is definitely a potential for “Not In My Backyard”
(NIMBY).
Other issues also pose concerns; the Columbia Gorge project was
sidelined because of the potential for disruption of bird migrations.
Geothermal Power
Underground water supplies are heated to steam by geological heat
sources; the steam can escape to the surface and drive a turbine.
Pros
There are no sulfur dioxide (contributes to acid rain) or carbon dioxide
emissions (contributes to global warming).
The efficiency is high. The steam has already been created, so a
step is eliminated from the process.
The initial costs are low.
The steam has already been created, so there is no need to purchase
steam generation equipment.
Cons
There are a limited number of sites where geological conditions
permit natural steam generation.
Geothermal power simply will never be more than a supplement due
to the small number of sites available.
This doesn’t mean it’s not a viable option, it simply means that it is
not “the answer”.
There is no “silver bullet for getting the people of the world the power
they want and need. Other sources that do not pollute must be part
of the larger mix of energy generation in our county and the world.