We actually mean two rather different things when we talk about
energy and conservation (this is because you're asking physicists,
whereas most people only talk about reducing energy consumption).
To a physicist, the conservation of energy is an observed feature
of the universe -- energy can be converted from one form into another,
and it can be neither created nor destroyed. Energy can be in the forms
of potential, kinetic, electromagnetic, chemical, thermal, and other
forms, including the energy of just being matter (E=mc^2). We describe
this elsewhere on the site (some of these categories of energy really
are overlapping descriptions of the same things).
But some kinds of energy are more useful than others in conducting
our daily business. The chemical potential energy stored in unburned
fossil fuels such as gasoline, oil, and natural gas are tremendously
important for moving us about, manufacturing our goods, heating our
homes, and generating electricity for doing a huge variety of other
useful tasks. The thermal energy in the air on a hot summer day is not
as useful for doing anything -- in fact, we often go to great lengths
to get rid of that kind of energy. When gasoline burns to make a car
go, some of the energy goes to heat up the exhaust, which just escapes,
and much of the rest of the energy ends up heating up the engine, the
brake pads, and the tires, through friction -- it becomes less useful
at that point. The energy in the fuel is much more valuable than the
same energy dissipated as heat after the fuel has burned and the work
has been done.
The big deal about conserving energy is really about conserving
fuels. There is a limited supply of oil underground and under the
ocean. By careless waste of this precious resource, we will use it up
more quickly than if we are careful about our use. Before then, of
course, the oil that we haven't yet pumped out of the earth will become
harder to find as we use up the easy-to-find stuff first. The price of
oil will go up as we have to dig deeper and deeper, and farther and
farther away. Countries with lots of oil reserves may use them as
political and economic tools to affect the welfare of countries that
use lots of oil but do not have natural reserves (or, more likely, just
to make themselves very wealthy).
Burning fossil fuels also has the unpleasant consequence of
increasing the amount of carbon dioxide in the atmosphere. Carbon
dioxide is a "greenhouse gas" -- it acts a bit like a blanket around
the earth, trapping solar heat in the atmosphere and the oceans and the
land, by reducing the rate at which this heat is reradiated back to
space. If the earth's temperature rises even by a few degrees, the
climate will change in many places, glaciers will recede, and the ocean
levels will rise. Deserts may expand in size. By reducing our
consumption of fossil fuels, we can delay the onset of global warming.
We can use coal instead of oil in many applications (such as
generating electricity, and various industrial applications, such as
making steel). Burning coal has unpleasant consequences too. In
addition to the carbon dioxide, coal burning also produces sulfur
dioxide, which combines in the air with water to make sulfuric acid.
Sulfuric acid (and nitric acid) dissolved in raindrops have lowered the
pH of many lakes in North America and Europe, in many instances killing
all the fish in them. Pollutants in the air caused by coal burning have
caused many people to have respiratory illnesses. Coal mining is also a
Nuclear-generated electricity is not without its hazards as well.
Spent fuel remains radioactive for tens of thousands of years and must
be disposed of properly. Nuclear power-plant accidents can cause
environmental harm -- the Chernobyl fire in Russia made a large area
uninhabitable (that reactor was particulary poorly designed). Reducing
consumption of electricity reduces the need to build more power plants
of all kinds -- coal, gas and nuclear ones. Even hydropower is not
without consequences. Rivers dry up below hydropower dams, and the
lakes created upstream flood previously useful land, and destroy
wildlife habitats. Salmon can no longer swim upstream where a
hydropower dam is put in place.
Handling energy in just about any form is hazardous, and reducing consumption can reduce the risks.
p.s. You may wonder whether the difference between 'useful' and
'useless' energy is just a matter of how clever our engineers are.
Actually, it is based on a deeper scientific distinction. There's a
quantity called 'free energy' which is what we're really trying to
preserve.Free energy depends not only on energy but on another quantity
called 'entropy'. Unlike energy, entropy is NOT conserved in an
isolated system. Entropy keeps increasing, by the Second Law of
Thermodynamics. That means that free energy keeps decreasing.
When certain politicians tell you not to worry about using up
energy because we can soon convert to hydrogen fuel, they're forgetting
that the hydrogen around is either in the fuels we were already using
or in water. To get hydrogen out of water, you ALWAYS need to use more
energy than you get out. That's not an engineering problem but a law of
physics. So those politicians would be lying, if they had any idea what
they were talking about.
Fortunately, the Earth isn't completely isolated. Sunshine provides a steady (but not enormous) influx of free energy.
(republished on 07/25/06)