uppose
that over the next decade or two the forecasts of global warming
start to come true. Color has drained from New England's autumns
as maple trees die, and the Baltimore oriole can no longer be
found south of Buffalo. The Dust Bowl has returned to the Great
Plains, and Arctic ice is melting into open water. Upheavals in
weather, the environment and life are accelerating around the
world.
Then what?
If global warming occurs as predicted, there will be no easy
way to turn the Earth's thermostat back down. The best that most
scientists would hope for would be to slow and then halt the
warming, and that would require a top-to-bottom revamping of the
world's energy systems, shifting from fossil fuels like coal, oil
and natural gas to alternatives that in large part do not yet
exist.
"We have to face the fact this is an enormous challenge," said
Dr. Martin I. Hoffert, a professor of physics at New York
University.
But interviews with scientists, environment advocates and
industry representatives show that there is no consensus in how to
meet that challenge. Some look to the traditional renewable energy
sources: solar and wind. Others believe use of fossil fuels will
continue, but that the carbon dioxide can be captured and then
stored underground. The nuclear power industry hopes concern over
global warming may help spur a revival.
In an article in the journal Science last November, Dr. Hoffert
and 17 other experts looked at alternatives to fossil fuels and
found all to have "severe deficiencies in their ability to
stabilize global climate."
The scientists believe that technological fixes are possible.
Dr. Hoffert said the country needed to embark on an energy
research program on the scale of the Manhattan Project that built
the atomic bomb during World War II or the Apollo program that put
men on the moon.
"Maybe six or seven of them operating simultaneously," he said.
"We should be prepared to invest several hundred billion dollars
in the next 10 to 15 years."
But to even have a hope of finding a solution, the effort must
begin now, the scientists said. A new technology usually takes
several decades to develop the underlying science, build pilot
projects and then begin commercial deployment.
The authors of the Science paper expect that a smorgasbord of
energy sources will be needed, and they call for intensive
research on radical ideas like vast solar arrays orbiting Earth
that can collect sunlight and beam the energy down. "Many concepts
will fail, and staying the course will require leadership," they
wrote. "Stabilizing climate is not easy."
The heart of the problem is carbon dioxide, the main byproduct
from the burning of fossil fuels. When the atmosphere is rich in
carbon dioxide, heat is trapped, producing a greenhouse effect.
Most scientists believe the billions of tons of carbon dioxide
released since the start of the Industrial Revolution are in part
to blame for the one-degree rise in global temperatures over the
past century. Carbon dioxide concentrations are now 30 percent
higher than preindustrial levels.
With rising living standards in developing nations, emissions
of carbon dioxide are increasing, and the pace of warming is
expected to speed up, too. Unchecked, carbon dioxide would reach
twice preindustrial levels by midcentury and perhaps double again
by the end of the century. That could force temperatures up by 3
to 10 degrees Fahrenheit by 2100, according to computer models.
Because carbon dioxide is colorless, odorless and disperses
immediately into the air, few realize how much spills out of
tailpipes and smokestacks. An automobile, for example, generates
perhaps 50 to 100 tons of carbon dioxide in its lifetime.
The United States produces more carbon dioxide than any other
country by far. Each American, on average, generates about 45,000
pounds of carbon dioxide a year. That is about twice as much as
the average person living in Japan or Europe and many times more
than someone living in a developing country like Zimbabwe, China
or Panama. (Even if the United States achieves President Bush's
goal of an 18 percent reduction in the intensity of carbon dioxide
emissions by 2012, the output of an average American would still
far exceed that of almost anyone else in the world.)
Even if all emissions stop, levels of carbon dioxide in the air
will remain high for centuries as the Earth gradually absorbs the
excess.
Currently, the world's energy use per second is about 12
trillion watts — which would light up 120 billion 100-watt bulbs —
and 85 percent of that comes from fossil fuels.
Of the remaining 15 percent, nuclear and hydroelectric power
each supply about 6.5 percent. The renewable energy sources often
touted as the hope for the future — wind and solar — provide less
than 2 percent.
In March, Dr. Hoffert and two colleagues reported in Science
that to limit the temperature increase to 3.6 degrees Fahrenheit,
non-carbon-dioxide-emitting sources would have to generate 7
trillion to 25 trillion watts by midcentury, 4 to 14 times as much
as current levels. That is roughly equivalent to adding a large
emissions-free power plant every day for the next 50 years.
And by the end of the century, they wrote, at least
three-quarters and maybe all of the world's energy would have to
be emission-free.
No existing technology appears capable of filling that void.
The futuristic techology might be impractically expensive.
Developing a solar power satellite, for example, has been
estimated at more than $200 billion.
Energy Secretary Spencer Abraham cited the Science paper from
last November in a speech at the American Academy in Berlin two
months ago. Mr. Abraham said that merely setting limits and
timetables on carbon dioxide like those in the Kyoto Protocol
could not by themselves solve global warming.
"We will also need to develop the revolutionary technologies
that make these reductions happen," Mr. Abraham said. "That means
creating the kinds of technologies that do not simply refine
current energy systems, but actually transform the way we produce
and consume energy."
Too Far Away
Some long-hoped-for options will almost certainly not be ready.
Fusion — producing energy by combining hydrogen atoms into helium,
the process that lights up the sun — has been heralded for decades
as a potentially limitless energy source, but scientists still
have not shown it can be harnessed practically. Experimental
fusion reactors do not yet produce more power than they take to
run.
Increased energy efficiency — like better-insulated buildings,
more efficient air-conditioners, higher mileage cars — is not a
solution by itself, but it could buy more time to develop cleaner
energy.
The much-talked-about hydrogen economy, in which
gasoline-powered engines are replaced by fuel cells, is also not a
solution. It merely shifts the question to what power source is
used to produce the hydrogen.
Today, most hydrogen is made from natural gas, a process that
produces carbon dioxide that is then released into the air.
Hydrogen can also be produced by splitting apart water atoms, but
that takes more energy than the hydrogen will produce in the fuel
cell. If the electricity to split the water comes from the
coal-fired power plant, then a hydrogen car would not cut carbon
dioxide emissions.
Exploiting What's Here
A fundamental problem remains: how to produce electricity
without carbon dioxide.
Hydroelectric power has reached its limits in most parts of the
world; there are no more rivers to dam.
Nuclear power is a proven technology to generate large amounts
of electricity, but before it could be expanded, the energy
industry would have to overcome longstanding public fears that
another accident, like those at Three Mile Island or Chernobyl,
will occur. Solutions also need to be found for disposing of
radioactive spent fuel and safeguarding it from terrorists.
Marvin Fertel, senior vice president of the Nuclear Energy
Institute, an industry group, said warming had become such a worry
that some environmental groups were becoming amenable to new
nuclear plants. "In private, that's what we get from them," he
said.
Researchers at the Electric Power Research Institute in Palo
Alto, Calif., espouse a major expansion of nuclear power, coupled
with a switch from gasoline to hydrogen to power cars and trucks.
Electricity from the nuclear plants would split water to produce
hydrogen, and then cables made of superconductors would distribute
both electricty and hydrogen, which would double as coolant for
the cables, across the country.
"I think in 30 to 50 years there will be systems like this,"
said Dr. Chauncey Starr, the institute's founder and emeritus
president. "I think the advantages of this are sufficient to
justify it."
In the short run, fossil fuels will still be widely used, but
it is still possible to control carbon dioxide.
In his Berlin speech, Mr. Abraham highlighted two projects the
Energy Department was working on: carbon sequestration — the
capturing of carbon dioxide before it is emitted and storing it
underground — and FutureGen, a $1 billion prototype coal power
plant that will produce few emissions. The plant will seek to
demonstrate by 2020 how to convert coal to hydrogen on a
commercial scale that will then be used to generate electricity in
fuel cells or turbines. The waste carbon dioxide would be captured
and stored.
The technology for injecting carbon dioxide is straightforward,
but scientists need better knowledge on suitable locations and
leak prevention.
Sequestration, however, will probably not be cost-effective for
current power plants. The filters for capturing carbon dioxide
from the exhaust gas will by themselves consume 20 percent to 30
percent of the power plant's electricity.
Renewing Renewables
Solar is still a future promise. The cost of energy from solar
cells has dropped sharply in the past few decades. One
kilowatt-hour of electricity — the energy to light a 100-watt bulb
for 10 hours — used to cost several dollars when produced by solar
cells. Now it is only about 35 cents. With fossil fuels, a
kilowatt-hour costs just a few cents.
But solar still has much room for improvement. Commercial cells
are only 10 to 15 percent efficient. With much more research, new
strategies to absorb sunlight more efficiently could lead to cells
that reached 50 to 60 percent efficiency. If the cells could be
made cheaply enough, they could produce electricity for only 1 or
2 cents a kilowatt-hour.
Dr. Arthur Nozik, a senior research fellow at the National
Renewable Energy Laboratory in Golden, Colo., said the advanced
solar concepts were scientifically feasible. But, echoing Dr.
Hoffert, Dr. Nozik said: "We need like a Manhattan Project or an
Apollo program to put a lot more resources into solving the
problem. It's going to require a revolution, not an evolution. I
wouldn't expect to get there in 2050 if we're going at the same
pace."
But if scientists succeed with a cheap, efficient solar cell,
"you'd be on Easy Street," Dr. Nozik said.
Wind power is already practical in many places like Denmark,
where 17 percent of the electricity comes from wind turbines. The
newest turbines, with propellers as wide in diameter as a football
field, produce energy at a cost of 4 or 5 cents a kilowatt-hour.
Further refinements like lighter rotors could drop the price by
another cent or two, making it directly competitive with natural
gas.
Dr. Robert W. Thresher, director of the National Wind
Technology Center at the energy laboratory, envisions large farms
of wind turbines being built offshore. "They would be out of
sight," he said. "There's no shortage of space and wind."
Solar and wind power will be hampered because the sun doesn't
always shine and the wind doesn't always blow. The current power
grid is not well suited for intermittent power sources because the
amount of power produced at any moment must match the amount being
consumed. To exploit the sun and wind, utilities would have to
develop devices that could act as giant batteries.
One concept is to pump compressed air into an underground
cavern. When electricity was needed, the air would be released,
and the air pressure would turn a turbine to generate electricity.
The Big Ideas
Then there are the big ideas that could change everything. To
get around the problem of the intermittency in solar power, solar
arrays could be placed where the sun shines 24 hours a day — in
space. The power could be beamed to the ground via microwaves.
Another big idea comes from Dr. Klaus S. Lackner, a professor
of geophysics at Columbia University: what if carbon dioxide could
be scrubbed out of the air? His back-of-the-envelope calculations
indicate it may be feasible, although he is far from being ready
to demonstrate how.
But if that were possible, that would eliminate the need to
shift from gasoline to hydrogen for cars. That would save the time
and cost of building pipelines for shipping hydrogen, and gasoline
is in many ways a superior fuel than hydrogen. (Hydrogen needs to
be stored under very high pressure or at very cold temperatures.)
Owners of gas-guzzling S.U.V.'s could assuage their guilt by
paying for the scrubbing of carbon dioxide produced by their
vehicles.
Eventually, the captured carbon dioxide could be processed to
create an artificial gasoline, Dr. Lackner said. Then the world
would discover, much to its surprise, that everything old would be
new and clean again.
"Carbon may actually be just as clean, just as renewable," Dr.
Lackner said.