EEE会議（地球温暖化とエネルギー問題：米国の科学者たちの見方）.......................................2003.11.05


本日（米国時間で11/4）付けのNew York Timesの科学技術欄に、地球温暖化とエネル
ギー問題に関する次のような注目すべき記事が載っています。　あいにく小生、目下
時間的余裕が無く、全文を要約してご紹介しかねますので、どなたかヴォランティア
で内容を簡単に紹介してくだされば幸いです。

ちなみに、原子力関係（記事の中段に）については、カリフォルニアにある米国電力
研究所(EPRI)の初代・名誉理事長Chauncey Starr博士が「将来は原子力発電所で水素
を作り、電気と水素を全米に供給するのが最も有利な方法であり、そのようなシステ
ムが今後３０〜５０年以内にできるだろう」と述べているのが注目されます。　
また、別の科学者は、「米国は、かつてのマンハッタン原爆開発計画やアポロ月面着
陸計画のような大規模なエネルギー研究開発計画に乗り出すべきだ」と提唱していま
す。ご参考まで。
--KK

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As Earth Warms, the Hottest Issue Is Energy
By KENNETH CHANG

Published: November 4, 2003


Suppose 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.