The intention of this writeup is to present the subject of global warming in a manner
understandable to an educated person who isn't a specialist in climatology. The writer
fits that description. The information comes from open sources, for which references
Global warming is simply an increase in the temperature in the Earth's average
atmosphere and ocean temperatures. That's vague enough that it doesn't describe the
phenomenon. Global warming reflects an increase in the amount of energy in the
Earth's complex, dynamic meteorological system. And, of course, global cooling would
reflect a decrease. What really matters is that either would cause climate change,
which can include many effects and some of the effects are unexpected, including
anomalous local temperature changes.
Properly speaking, our subject should be climate change. The Intergovernmental Panel on
Climate Change defines climate change as "change in climate over time, whether due
to natural variability or as a result of human activity." In this writeup, as in so many,
the terms "global warming" and "climate change" will be used interchangeably.
The particular concern is that certain "greenhouse" gases are building up in the
atmosphere. These gases admit visible and ultraviolet light from the sun but block
infrared light from the Earth to surrounding space. The result is a warming of the
The minimum effect would be more of what we've seen so far. The polar ice caps are
melting , plants and animals are migrating away from the equator and taking insects
and diseases with them , and rainfall patterns are changing around the world. As
long as global warming continues, those changes will increase.
We also can expect weather patterns to become more forceful and destructive. That is
because what drives global warming is the energy going into the Earth's climate system,
and it's the energy that drives storms and tornadoes.
Skeptics argue that more carbon dioxide will encourage plant growth, which will reduce
the amount of carbon dioxide as a self-regulating mechanism. That could work in the
short term, and may well be one of nature's self-regulators. But all plants die
eventually and return the carbon they absorbed, so at best plant growth can only slow global warming, not prevent it.
In the worst case, besides more destructive weather, global warming could cause large
amounts of land-supported ice to melt and rising water would flood densely-populated
parts of the world.
The worst case is more likely than you might suppose. As the planet warms up,
greenhouse gases can be expected to increase as a result. It's well known that
atmospheric water vapor increases with rising temperature. Water vapor is one of the
strongest of the greenhouse gases. Furthermore, we would expect dead vegetation to
decompose faster, adding to the load of methane and carbon dioxide. There are still
other predictable effects: as ice masses shrink, they will reflect less sunlight to space;
as dead, frozen tundra thaws, more carbon dioxide and methane will be released.
As greenhouse gases are added to the atmosphere, each increment has slightly less effect. In the extreme case, if the atmosphere were saturated enough that all of the infra-red radiation from Earth were trapped, then adding more greenhouse gases would have no effect. We can do rough calculations to show that the maximum additional temperature rise would be roughly 2.4 deg C. These calculations are crude in the extreme and shouldn't be taken literally. They merely show that there is an upper limit to how much global warming could take place. In comparison, the IPCC estimated a rise of 1.8-4 deg C (3.2-7.2 deg F) by the end of the century. Unless startling new information presents itself, there's no reason to worry about a runaway event that could turn Earth into Venus II.
Taking into account both the compounding effects and the limiting effects, we can put this in perspective. Although global warming won't cause total destruction, it nonetheless could lead to severe hardship. Furthermore, it's entirely possible that we could reach a tipping point after which there's no way to
prevent a compounding event that leads relentlessly toward the worst case. The catch is, no
one knows where the tipping point is.
People agree that all these factors contribute to climate change. What they don't agree
on is the relative magnitude of their contributions. It matters because if the main
causes are artificial, then it's possible for humans to mitigate the effects. Furthermore, it
also makes it necessary to mitigate the effects because all the indications are that the
world's population will increase and a larger portion of the population will be generating
greenhouse gases at the rate the wealthiest countries are generating them now.
The processes are so complex that they defy simple calculation. Climate scientists
have to use elaborate computer models to account for all the variables. Computer models can answer specific questions, but can't prove anything, because every model has limitations and there's no way to prove any model yields correct results.
It's better to compare the different factors in the historical record, but the records don't
go back very far. Scientists try to represent the historical record using proxy data, but
that's never reassuring. For example, a scientist might look at tree cores or ice cores
and find that some kind of data, maybe a ratio between the isotopes of some element,
corresponds to temperature over a few decades. In reality it never matches one-to-one.
But then he'll apply the correspondence over thousands of years. Or even longer.
Here's a graph showing different temperature reconstructions scientists have made,
using different collections of proxy data :
Who's to say which one is right? Maybe none of them are.
The most comprehensive studies done so far were performed by the Intergovernmental
Panel on Climate Change. After reviewing all the information available, the panel
couldn't give a straight answer about how much the different factors contribute. In the
end, the different panelists voted on how much influence they thought each factor
would have, and how much confidence they had in their opinions. No criticism is
intended here: people have to do the best they can with what they have. Still, it's not
I've decided, since it's my writeup, to set some operating premises, as follows:
1) Computer models don't prove anything.
2) Proxy data don't prove anything.
3) Consensus polls don't prove anything.
First, let's look at the temperature data we have. One set of data comes from NASA
and the other is provided by Met Office Hadley
Centre for Climate Change in the UK.
The data don't agree exactly because (1) the NASA data shows the deviation from the 1951-1980 average and
the Hadley Centre data shows the deviation from the 1961-1990 average and (2) the calculations were done independently so small differences are expected. We should bear in mind that the older data comes from spottier readings and is less
reliable. The Hadley Centre data is shown both raw and smoothed. Now we'll look at the different factors that affect global average temperature, comparing them with the smoothed data.
Sunspots receive plenty of mention in the popular literature and we have more data to look at.
This is promising. Notice that the sunspots are lower in number, almost zero, in the
period 1650-1700. There is anecdotal evidence that Europe and China were cooler
then. There also is anecdotal evidence of the same thing happening in the early 19th Century, although the Tambora volcano could have contributed.
Looking more closely, we see that the low number of sunspots around 1900 fits the lower temperature then, and temperature and sunspot-count both rise thereafter. There was more activity around 1960 that shows up as a temperature bump, and also around 1980-1990, that fits with a slight, stretched-out bump. So it
seems clear that sunspot activity affects global temperature. Or, possibly, sunspots
affect the irradiance and it's the combination that affects global average temperature. A suggestion under review is that solar activity diminishes cloud formation by influencing the intensity of cosmic rays, as shown in this figure:
On the other hand, the temperature bumps are small compared with the upward
temperature trend since 1900. Furthermore, if solar activity was the main driving force,
then average temperature should drop after 1990 but instead it keeps going up. That means
something else has become a stronger driving force since 1900.
Solar irradiance is the intensity of solar energy striking the earth and
its atmosphere in watts/sq meter. It seems to follow sunspot activity, which seems reasonable. But it only matches the temperature changes about as well. 
The gas emissions from natural vegetation are an important part of the atmosphere's
loading, but the amount of land devoted to it hasn't increased. It's possible that
emissions have risen as a result of global warming. Either way, natural vegetation can't
be blamed for the temperature rise since 1900.
Volcanoes emit gases, too. We can do a quick calculation that shows volcanoes could never affect the atmosphere's CO2 concentration.
Volcanoes also emit particulates and aerosols, which reflect
heat away from the earth and cause more clouds to form, causing further cooling. Data
from the Mauna Loa Observatory shows the effects of volcanos since 1958.
We can see that volcanoes reduced solar transmission in 1982 and 1991, but they don't
affect the global-average temperature rise by much. The conclusion is that
volcanoes don't affect global warming either way.
One way the Earth's core could heat the oceans is by undersea volcanoes. We can do
a quick calculation that it would take around a half-million undersea volcanoes
equal in size to the one at Mount Saint Helens in 1980 every year to account for the
warming the oceans have seen since 1955. Even if the calculations are off by a factor
of ten, it would take around five thousand such volcanoes every year just to account for
ten per cent of the warming. And, there would have to have been no volcanoes before
1910. So undersea volcanoes aren't a major factor.
Another possibility is the extrusion of magma into the oceans at the edges of separating
tectonic plates. But the USGS has found that the rate tectonic plates have been
moving hasn't changed in the last thirty years from what it's always been. So
magma doesn't explain the recent warmup.
Landclearing has two important effects. One is the release of CO2 into the atmosphere, mainly from burning, which can make up a significant part of the total release. Another is to change the albedo, or light-absorbing capability, of the receiving surface. Landclearing usually has a cooling effect by lowering the albedo; for example, cropland or pasture absorbs less solar energy than forest. But a special situation exists in the Amazon rain forest, as determined from satellite data. Deforestation there has the effect of reducing cloud cover and for that reason it has a warming effect. If this effect is significant it should correlate with temperature data for the southern hemisphere. As we can see from this chart, though, it doesn't.
As is the case for natural particulates and
aerosols, artificial particulates and aerosols have a cooling effect by reflecting sunlight
and by causing clouds to form. The temperature graph shows a sharp drop around
1940 until almost 1950, then a slow rise until 1980 or so, and after that a sharp rise. That fits with our expectations: industrial production increased radically during the war. Virtually no attention was paid to the resulting pollution. The postwar period experienced some relaxation in both production and pollution.
About 1970, serious efforts were started to control particulate emissions from fossil-burning power plants, and the temperature graph clearly shows that global warming
There are a lot of these that can be important: carbon dioxide, methane, and nitrous
oxide are the most dominant. We need to consider their emission rates in order to compare their relative importance in the changing of the global average temperature.
The US Department of Energy has estimated their yearly emission rates and ranks them this
way (2005 data ). Global data comes from IPCC's report for 2001. All the rates are in million metric tons per year. These numbers are calculated, but show more precision than they should. Nonetheless, they show relative magnitudes.
US (CO2 Equiv)
World (CO2 Equiv)
Clearly, CO2 is the most important artificial greenhouse gas in respect to changing temperature.
The present CO2 content of the atmosphere is 3,036,000 MMT, so the emissions amount to almost 1% of what's presently in the atmosphere. The CO2 concentration is rising roughly 0.5% per year, so about half is staying in the atmosphere and the other half is going somewhere else, mostly into the ocean.
We have some measured
CO2 concentration data taken from ice cores.
This is our smoking gun. The CO2 concentration has risen from less than 300 parts per
million all the way up to 383 ppm in 2007. Of all the factors affecting global average temperature, it's the only one that's been increasing since 1980, so it's the only one that can explain the temperature rise during that time.
What is especially troubling is that, before 1850, CO2 concentration has not exceeded 290 ppm in over 400,000 years.
That's not to say that we can ignore the
other greenhouse gases, but controlling CO2 emissions is essential to limiting global
The evidence shows that solar activity and aerosols can influence global temperature. Before 1900, when greenhouse-gas concentrations were below 300 ppm, solar activity seems to have been the main driving force. Since then, greenhouse gases have become the main driving force.
The Skeptics: There are individuals who argue against these conclusions. Their claims been refuted many times but still get a lot of attention from media outlets. Read about their arguments.
Some mitigating steps are obvious: emissions of methane and nitrous oxide should be
minimized by adjustments in farming practices. Some other greenhouse gases can be
minimized by adjustments in industrial practices. But the big guy here is carbon
dioxide. The first step is to see where it's coming from. The following information
comes from the US Department of Energy, using data from 2005 for US emissions.
I wouldn't presume to tell residents of other countries how to deal with the problem.
The total emissions of CO2 for the US weighed in at 6009 million metric tons. The main
contributors that are amenable to replacement are as follows:
Electricity generation from fossil fuels
Residential use of natural gas
Gasoline motor fuel
The remaining 2291 MMT is spread over a large range of agricultural, residential, industrial, and
transportation applications and miscellaneous applications such as road pavements.
Some improvements can be sought here, but most of the users already are
economically motivated to reduce energy consumption, so we should only count on
modest improvements. Here's a plot that shows where all the greenhouse gases are coming from in the US:
Out of all these, electricity generation is where the greatest savings can be made,
accounting for 40% of the total CO2 emissions.
Taking CO2 emissions as a whole, there are four options available:
It is possible that the CO2 could be captured and stored in some geological formation.
The problems with sequestration are that it's very expensive to pipe the CO2 from the
power plant to the formation and pump it deep into the ground, and there's no way to be
sure the CO2 will stay there. The scheme du jour is to bubble the gas into saline
aquifers and hope the CO2 will form stable minerals there. No one knows what the
capacity of the available aquifers is, or how to find out.
Improving energy codes has gone a long way toward reducing greenhouse gases.
Americans are using only as much energy per capita as they were ten years ago and
twenty years ago. Meanwhile, energy consumption per dollar of domestic product has
dropped about 40% since 1980. Of course, the US has shifted away from
manufacturing toward services in that same period, which accounts for some of the
savings. Nonetheless, it's clear that energy codes can play a part in greenhouse-gas
Gasoline motor-fuel consumption could be cut by as much as half through higher fuel-efficiency standards. After all, there are cars made that get better than 50 miles per
gallon. The question is, would Americans accept the new standards?
For example, in 1955, the average domestic passenger car in the US got 16 miles per
gallon. In 1973 the average dropped to 12.2 and in 1979 it reached 19.3. But in 1979,
imported cars got 26.1 mpg, 35% better economy.
The American market wasn't impressed. In 1979, imported cars had 17% of the US
market, compared to 73% for domestic cars, and in 2004 they had 20%, compared to
29%. Light trucks and SUVs went from 10% to 51% in those same years.
Americans bought more imported cars than before, but they chose trucks and SUVs
over both imported and domestic cars. Are SUVs a fad? Will Americans switch to
economical cars? At this point, it's an imponderable.
Private cars are only one aspect of the issue. Americans, like everyone else, prefer affluent lifestyles over frugal ones. If the affluent lifestyles are supported by non-fossil energy sources, then the global-warming aspect of their environmental impacts is reasonably small. But, during the interim period while fossil fuels are being phased out, reducing greenhouse-gas emissions would require changing to lifestyles that are much less energy-intensive: smaller houses, less heating and air-conditioning, less residential lighting, etc. Even if people understand the problem, there are limits to how much conservation they'll tolerate.
Residential Energy Sources
Some important savings can be made by making greater use of natural energy sources.
Home heating and residential water heating could be switched almost entirely to solar
and solar-heat-pump systems. Passive solar heating techniques can be built into
homes. The remaining residential applications would mainly be cooking, which could
almost entirely be converted to electricity. These changes would reduce CO2
emissions by 367 million metric tons, or 6.1% of the total.
Wind power is already providing some electricity at a price which is only a little higher
than electricity from fossil-fired power plants. What limits wind power is the need for
storage, since neither homes nor businesses can stop functioning when the wind power
is unavailable. Currently, only one form of bulk storage is available for energy: existing
hydroelectric dams, which account for 6.6% of total US electrical capacity. There are limits to how much storage can be used, since dam operators have to
maintain minimum water flows and also have commitments to irrigators, but it's
conceivable that wind power could provide a few per cent of the country's energy.
If some sort of bulk energy storage could be developed, that could make wind energy practical. The storage method closest to practicality is pumped storage. In fact, there is a small amount of pumped storage in use now. A rough calculation shows, however, that there aren't enough places to install pumped storage for wind power to become the main electricity source.
A different strategy would be to have fossil-fired power plants standing by to back up wind
power. Since wind turbines have a load factor of 25 to 35%, that would seriously
hamper the effort to reduce greenhouse-gas emissions because the fossil-fired plants
would have to operate a large portion of the time. But the existing fossil-fired plants will be around for some decades while replacement capacity is built. In the meantime, they can be used as backup for wind turbines and other renewable sources. So, in the short term, wind power can be a major power source until replacement sources are constructed and the wind turbines wear out.
Solar photovoltaic systems are presently too expensive to compete with other energy
sources, but over the years can be expected to become cheaper. They already are
becoming popular in remote locations where connecting to the electrical grid is
impractical. If costs continue to fall, solar energy can complement wind power.
Geothermal energy presently supplies 0.34% of the energy used in the US. There
are two types of geothermal energy: wet and dry. The wet type is being exploited about
as much as it can be. There is a lot more available in dry form; unfortunately, there
aren't any practical ways of extracting it. If the cost problem could be overcome, MIT estimates it could produce as much as 100 GW of electricity, slightly more than nukes produce now.
Biofuels represent a possibility. To use them unblended as motor fuels would require
new engine designs, but that will be unavoidable with any change from petroleum-based fuels. Currently, the best estimate is that it takes 0.75 gallons of fuel to produce
the energy-equivalent of 1 gallon of conventional fuel. That's only true if credit is given
for the value of the leftover material as animal feed; once the demand for animal feed is satisfied, the payoff ratio won't be as good. It is believed that the fuel input
could be reduced to as little as 0.4 gallons with advanced technology that allows
agricultural waste to be used as the raw material. Agricultural waste is what
gardeners call mulch; it hasn't been determined what would be the adverse
consequences of diverting mulch away from fields. Research is being done on different biomass plants and chemical processes that could give better results.
The International Energy Agency estimates fossil-fuel use at 388 exajoules per year worldwide, which may be expected to double or triple in this century. It also estimates that to supply 300 exajoules/year, a goal attainable with moderate effort, would require 7% of Earth's landmass, requiring forest clearing and insecticides and synthetic fertilizers.
In comparison, 13.3% of the landmass is arable, including 4.7% already under cultivation.
The IEA concludes that biofuels can be an important means of reducing greenhouse-gas emissions on a global scale. For the US and Europe, though, given their limited free agricultural land and their high dependence on liquid fuels, the main effect would be switching from oil-rich suppliers to land-rich ones. Presumably, the benefit of reducing global warming would justify the higher cost.
Many other systems have been proposed: wave engines, tidal engines, and ocean-thermal-gradient engines, to mention only a few. People have suggested micro-hydroelectric power, installing small turbines on thousands of creeks and streams, but
never have addressed the legal obstacles to extinguishing hundreds of species. Fusion
research continues apace, but no projections are made regarding when it could
become practical. Schemes have been suggested for energy storage, such as
compressing air in caves, or building mammoth flywheels. All of these ideas are exactly where they were over thirty years ago: nowhere.
But one idea has real potential: hydrogen. Hydrogen isn't an energy source, since it takes energy to produce it, but it could be a replacement for petroleum motor fuels. Presently, hydrogen use is hampered mainly
by the low energy efficiency (around 30%) of converting water to hydrogen at ordinary
temperatures. There are more efficient processes, but they require high
temperatures and are poorly suited to renewable energy sources. Alternatively,
research is going on to improve the efficiency of photosynthetic production, currently
around 2%. If the efficiency could be improved, then there is a real future for
There are three serious problems with hydrogen. First, onboard storage for vehicles still hasn't been made practical. Second, fuel cells have hit a technological dead end: they require catalysts; the only material that's been found to be satisfactory is platinum and the cost of platinum makes fuel cells too expensive. Third, if hydrogen is used in large amounts some of it will inevitably leak into the atmosphere where it will attack the ozone layer. What is needed is a way to turn the hydrogen into a hydrocarbon fuel.
There are two time-frames to consider. With present technology, renewable energy can displace a big part of fossil-fired electric power, but will lose that capability as the backup fossil-fired plants wear out. In the long run, the world must focus on non-fossil energy sources. Unless some form of bulk energy storage is invented, renewable sources will only be able to provide about ten per cent of the energy the US uses. Conservation, if pursued aggressively, could hold energy consumption to its current level. Now it's time to look at nuclear energy.
Nuclear Energy is the one non-fossil energy source available today that can provide bulk energy. It doesn't require storage or fossil-fired backup. Unless a new and better technology such as fusion becomes usable, nuclear is the only source that will allow us to stop using coal for energy.
Nuclear energy has the best safety record of any energy source. No member of the US
public has been killed or injured by any nuclear plant. This is a key point, because many
people are under the impression that nuclear plants are wildly dangerous. The
Chernobyl accident in Ukraine in 1986 showed what the actual scale of an accident
could be without normal safety provisions. After the accident, the World Health
Organization did an extensive investigation and continual followup; its findings were that
actual deaths have numbered less than 50 and there could be as many as 4000 fatal cancers in the future. As tragic as that is, it doesn't approach the
death rate due to burning coal. Even in the US, tens of thousands of people die every
year just from the pollution from generating electricity with fossil fuels. More
important, the accident at Three Mile Island in Pennsylvania in 1979 totally destroyed
the reactor but resulted in no adverse health effects, which validated the defense-in-depth designs used in all US reactors.
Nuclear energy is clean. Since reactors emit no pollutants they are as clean as any of the renewable energy sources that have been suggested.
Nuclear energy is abundant. At current usage, the world's known uranium reserves producible at less than US$60 per pound of U3O8 will last 85 years. Geologic data show that the supply is over 600 years. At higher prices, the supply is even greater. With advanced fuel cycles, the proven reserves would last over 2500 years.
Nuclear energy is economical. Presently, it is cheaper than any energy
source except hydroelectricity. Both of them are cheap because the capital costs have
all been paid back. Here are average operating costs in the US in 2005, in cents per KWH:
Gas Turbine and Small Scale
For new plants, of course, the cost would be higher because of the capital costs. Here
are comparisons for different energy sources . The costs are in UK pence/KWH.
Nuclear fission plant
Coal-fired pulverised-fuel (PF) steam plant
Coal-fired circulating fluidized bed (CFB) steam plant
Note that the coal-fired electricity costs more than nuclear, which no doubt is because
advanced-technology plants are being considered in order to minimize pollution. If
older-technology plants were being priced, the cost would be somewhat less, probably
less than any of the costs shown.
Nuclear energy is effective against climate change. Comparing life-cycle greenhouse-gas emissions, nuclear ranks with the cleanest of all electric-energy sources in tonnes CO2-equivalent per GWeh.
Combined-cycle natural gas
Furthermore, most of the solutions to replacing petroleum-based motor fuels require hydrogen and
the most efficient way to convert water to hydrogen is with high-temperature processes,
at temperatures nuclear reactors can provide. In particular, hydrogen can be added to biomass to triple the output of biofuels; that could make biofuels a major alternate fuel. The nominal efficiency is over 45%.
But the heat left over from the conversion can be used to generate electricity, so the
hydrogen production is nearly 100% efficient.
The waste materials from nuclear energy are at most a hypothetical concern. No person has ever been harmed by them. Despite that, people who oppose nuclear energy do so mainly because the wastes stay
radioactive for a very long time, even hundreds of thousands of years. It's odd that the
same people don't have problems with coal wastes, which pile up in vast heaps and sludge ponds that stay
Until recently, the plan was to bury the wastes in geological structures where they would be safe until
the radioactivity decayed away. But now the plan is to reprocess the wastes to separate out the valuable uranium and transuranic actinides to use as fuel. The remaining wastes are only 3% of what was there before and lose their toxicity in much less time, hundreds of years instead of hundreds of thousands. Many geologic places, such as caves or abandoned mines, could store those wastes safely. Besides that,
proven technology exists to irradiate the wastes into other, shorter-lived
materials. To deal with the wastes this way doesn't require any technological breakthroughs, just a political decision.
There is a common misunderstanding that nuclear power plants are a requirement for making bombs. That is not the case, as explained by Hans Blix, a former Director of the IAEA, the United Nations agency responsible for preventing proliferation :
A phasing out of nuclear power in some or all states would not lead to the scrapping of a single nuclear bomb.
States can have nuclear weapons without nuclear power though it is not common today. Israel is a case in point. It has no nuclear power but is assessed to have some 200 nuclear warheads. For a long time China had only the weapons. Indeed, most nuclear weapons states, including the US, had weapons before they had power.
Despite that, people have a concern that nuclear fuel could be diverted
and used to make a bomb by someone who shouldn't have one. This concern
overlooks the fact that, even assuming someone could defeat the security measures for
protecting the material and somehow ship it to his own facility, the material has to be
treated with chemical separation and isotope separation and enrichment. This is a
major industrial operation. In every case where it has been done, it required a nation's best
minds and vast capital resources. And there still remains the problem of learning how
to make a bomb go off. If a nation decides to make a bomb and is willing to make the
investment, it can make it from natural uranium; stealing fuel is not a
A possibility of dirty bombs comes up in some discussions. The concern is that a
terrorist could get his hands on spent fuel and blow it up with conventional explosives.
That is a possibility, and puts it in the class of other threats, such as chlorine or
ammonia or explosives made from fertilizer. But spent fuel is unattractive to terrorists
for several reasons. One is that it's monitored in shipping and it's highly likely that the
thieves would be caught and the terrorist plot would be exposed. Another is that it has
to be heavily shielded so it would take a huge explosion to spread the waste. Another
is that the radioactive material is easy to detect; people who are contaminated can be
decontaminated quickly and cleanup crews can clean up the contaminated area. Of all
the things we have to concern ourselves with, dirty bombs don't rank very high.
38. P.J. Meier, Life-Cycle Assessment of Electricity Generation Systems and Applications for Climate Change Policy Analysis, Ph.D. Dissertation, University of Wisconsin – Madison, 2002 http://merllc.com/ab4.htm
53. Potential environmental impact of a hydrogen economy on the stratosphere. Tracey K Tromp, Run-Lie Shia, Mark Allen, John M Eiler, Y L Yung. Science. Washington: Jun 13, 2003. Vol. 300, Iss. 5626; p. 1740 (3 pages)