If the new claims are backed up by further experiments, the implications are literally cosmic. There are so many neutrinos in the Universe – about a billion in every cubic metre of space – that together they would provide more mass than all the visible stars and galaxies. Neutrinos would contribute about 20 per cent of the total mass required to make the Universe “flat� – balanced between eternal expansion and eventual re-collapse in a “big crunch�.

Physicists have long assumed that neutrinos are massless, but the Los Alamos team announced last year that their experiments suggested otherwise (New ĞÓ°ÉÔ­´´, Science, 12 November 1994). This meant that neutrinos could make up some of the mysterious dark matter which cannot be seen, but nevertheless seems to exert a gravitational influence on stars and galaxies. These claims were greeted with scepticism, but a further series of observations has convinced the experimenters they were right, and has revealed the range within which the neutrino’s mass lies.

Astronomers and cosmologists are delighted with the new results. “It’s almost too good to be true,� says Andrew Liddle of the University of Sussex. “If cosmologists could have ordered a neutrino to fit their models, this is exactly the mass range they would have specified.�

The reason is that if neutrinos were more massive than the upper limit suggested by the Los Alamos team, then the total mass of all the neutrinos in the Universe would be too great for galaxies to have formed. The influence of these particles hurtling through space would have smoothed out any irregularities in the young Universe’s primordial clouds of gas, giving no areas of clumpiness around which galaxies could form. “If more than 30 per cent of the stuff of the Universe were neutrinos, then we’d be in trouble,� says Martin Rees of the University of Cambridge.

In fact, the distribution of galaxies in chains, clusters and filaments across the sky indicates that they grew up under the influence of the gravitational pull of large amounts of “cold� dark matter. This is made up of hypothetical particles many times more massive than neutrinos, which would move slowly through space.

The computer simulations of galaxy formation which most closely match the observed pattern of galaxies suggest that the Universe’s dark matter is 80 per cent cold and 20 per cent hot. The new results suggest that the hot dark matter required by these models is composed of neutrinos.

The Los Alamos researchers, headed by Hywel White, have monitored a phenomenon called neutrino oscillation. They have not studied neutrinos directly, but have instead looked at their antimatter counterparts. Neutrinos and antineutrinos, however, must have the same mass. There are three flavours of antineutrino, one each associated with the electron, the muon and the tau particle. If they have mass, antineutrinos should flip, or oscillate, from one form to another. The Los Alamos experiment uses a beam of pure muon antineutrinos which passes through a tank filled with 200 tonnes of mineral oil. Muon antineutrinos cannot interact with the oil, but electron antineutrinos can. If some of the muon antineutrinos are converted into electron antineutrinos, a few of them will interact with the oil to produce flashes of light, which will be picked up by detectors surrounding the tank. That is exactly what happens, say White and his colleagues. And the rate of oscillation tells them that the antineutrinos involved have masses between 0.5 eV and 5 eV. For comparison, the mass of an electron is 500 000 eV.

The researchers will publish their results in full in a future issue of Physical Review Letters. But other scientists warn that that many more experiments will be needed before the controversy surrounding the neutrino’s mass can finally be settled. One of the teams best-placed to check the Los Alamos claims works with the Karlsruhe-Rutherford Medium Energy Neutrino experiment (KARMEN) at the Rutherford-Appleton Laboratory near Oxford (see below). Although the US experiment is bigger, KARMEN is now being upgraded (see Diagram).

Robert Oglesby and Barry Saltzman calculate that low levels of carbon
dioxide in the atmosphere were a key factor in triggering ice ages of the
past. During the most recent ice age, there was as little as 180 parts per
million by volume (ppm). The present concentration of carbon dioxide (CO₂)
in the atmosphere is roughly 350 ppm, and before the Industrial Revolution,
the concentration was about 280 ppm.

Oglesby and Saltzman used a computer model (a general circulation model),
to investigate how changes in carbon dioxide concentration are likely to
have influenced the climate. They calculated mean temperatures for a simulated
Earth with 100, 200, 330, 460, 660 and 1000 ppm carbon dioxide in its atmosphere.

The 330 ppm simulation settled to a steady temperature of around 16
Degree C, close to that on the Earth now, and the 660 ppm simulation settled
down at about 20 Degree C, in line with other simulations in which the concentration
of carbon dioxide doubles. But the simulation with only 100 ppm of carbon
dioxide showed no sign of reaching equilibrium, even after simulated years
of the model.

More importantly, the temperature difference between the 100 ppm and
200 ppm simulations is greater than that between the 460 ppm and 1000 ppm
simulations, even though the difference in concentration of carbon dioxide
is more than five times as great in the second case (Geophysical Re search
Letters, vol 17, p 1089).

Oglesby and Saltzman think that this nonlinear response of climate to
increasing carbon dioxide concentration could be linked with feedbacks in
the climate system. They point out that in their 100 ppm simulation, sea
ice extends far from the poles; Britain, for example, is almost entirely
surrounded by ice. In the 1000 ppm case, in contrast, there is virtually
no sea ice. Because ice reflects heat from the Sun back into space, removing
ice makes theL Earth warmer.

Water evaporating from the ocean as the world warms also traps heat.
But although there is a 100 per cent increase in atmospheric humidity between
the 100 ppm and 1000 ppm simulations, more than half of this increase happens
between 100 ppm and 330 ppm of carbon dioxide. So this feedback has less
effect as the world warms.

‘The most important implication of this study is that a decrease in
CO₂ relative to present-day values has a much larger effect than
an increase,’ say Oglesby and Saltzman. They suspect that the failure of
their 100 ppm simulation to reach equilibrium may be partly because their
model is imperfect. But they suggest: ‘The most important effect of natural
variations in CO₂ may be reductions that lead to a cooling and,
possibly, the inception of glaciation.’

Hardly a particularly insightful comment, given that the rains failed
in North America in 1988 and that for the past three years world food reserves
have indeed fallen – the first time that this has happened for three consecutive
years. But I wrote those words almost 10 years ago, in an article which
appeared in The Guardian in February 1981.

The first working group of the Intergovernmental Panel on Climate Change
has recently confirmed as established the scientific case that human activities
will cause the world to warm in the next few decades. But noises coming
out of the US, in particular, continue to stress the uncertainties in climate
forecasts, and the costs of reducing the consumption of fossil fuels. It
is all depressingly familiar for those of us who, unlike the present US
administration or the British government, have been following the story
for 10 years or more. But for the benefit of new readers, it is worth spelling
out yet again why the cautious approach is inappropriate.

The policy of inaction derives from our sense of natural justice, with
its key concept of ‘innocent until proven guilty’. But, as various recent
examples – such as CFCs – have shown, the burden of proof must lie the other
way round when it comes to protecting the global environment. There is even
a term for this approach, namely the ‘precautionary principle’. It is such
a blindingly obvious example of common sense that it is hard to see how
anyone who does not have a vested interest in pumping gases like carbon
dioxide and CFCs into the air can fail to accept it as a working hypothesis
for planning environmental policy.

Of course, there is uncertainty in the climate forecasts. We do not
yet know whether carrying out the equivalent of doubling the amount of carbon
dioxide in the air, which is likely to happen by 2030 on a ‘business as
usual scenario’, will increase global mean temperature by 2 Degree C or
by 4 Degree C.

Even the lower figure, however, represents an unacceptable increase.
According to guidelines established by the World Meteorological Office,
natural ecosystems can adapt to a rise in temperatures at a sustained rate
of no more than 0.1 Degree C per decade – half a degree Celsius, at most,
by 2030. A change in temperature of 1 Degree C corresponds to a shift in
climate zones of 100 to 150 kilometres in latitude.

What about the costs of reducing the emission of greenhouse gases? Huge
numbers are bandied about, frequently with the appearance of having been
pulled out of the air. A certain action, we are told, might cut X per cent
off the US GNP, or cost Y trillion dollars over the next five years.

But an advance copy of a report to be published in the autumn by the
US Environmental Protection Agency says fuel efficiency will actually strengthen
the economies of developed countries, including the US. Well, with a name
like that, they would say that, wouldn’t they? Except that, once again,
it is common sense. If industry is forced to use fuel more efficiently and
to save energy, its costs will be reduced. And the American experience has
now shown that in very many cases energy is being wasted so profligately
that it has been cheaper to provide consumers with insulation and efficient
machinery (such as low-wattage fluorescent light bulbs) than to build new
power stations.

The consumers will be happy; industry doesn’t have to build a new plant
with loans raised at high interest rates; and the environment benefits.

Who doesn’t benefit? Only the people who extract coal and oil from the
ground, and like to see it burned up as rapidly as possible. And last month,
when members of the George C. Marshall Institute, a privately funded think
tank based in Washington DC, were flown to London to present their maverick
views on climate change, it came as no surprise to find that the room at
the Hyde Park Hotel in which they gave their talks, under the auspices of
the Institute of Energy, had actually been booked by British Coal.

On the one hand, a team of 170 scientists who have been closely involved
in climate studies for years, and have been individually selected by the
World Meteorological Office, produces a definitive study pointing to a minimum
rise in global mean temperatures of 2 Degree C for a doubling of the carbon
dioxide equivalent of the atmosphere. On the other, four research scientists
best known collectively for a series of pamphlets on strategic defence say
there is no problem.

Giving the Marshall Report equal weight with the report of the Intergovernmental
Panel on Climate Change’s first working party, as the Bush administration
seems to have done, makes as much sense as instructing schools to give equal
weight in their teaching to ‘creation science’ and to the theory of evolution
by natural selection. The analogy is particularly apt, since one of the
images that sticks in the mind from a recent television documentary on global
warming was of a complacent American mineowner commenting that God had put
the coal in the ground, and he’d put it there so that it could be dug up
and burned.

Jim Hansen of NASA, one of the world’s leading climatologists and one
of the first to warn of the dangers of global warming, has made a telling
projection, using an analogy with the probabilities familiar to players
of dice games. In the 1960s, he points out, the chances of a summer that
was above average, average or below average, in terms of temperature, could
be demonstrated by rolling a die which has two faces painted red, two green,
and two blue.

In the 1990s, the same die could again be rolled to indicate the chances
of a hot summer – but now four faces must be painted red, with just one
green and one blue. And by the 2020s, if no action is taken, the summer
heat that used to come only twice every six years in the 1960s will be the
bottom of the new temperature range. Even the average craps players can
understand what this means; but, as I said, how long will it take for the
politicians to get the message?

John Gribbin is physics consultant to New ĞÓ°ÉÔ­´´ and author or Hothouse
Earth, recently published by Bantam Books

J. Chappellaz and his colleagues from the French Laboratory for Glaciology
and Geophysics, in St Martin d’Heres, near Grenoble, and from the Soviet
Arctic and Antarctic Research Institute, in Leningrad, have examined bubbles
of air trapped in an ice core. The core, drilled at the Vostok site in East
Antarctica, is 2083 metres long and covers the past 160,000 years (Nature,
vol 345, p 127).

The level of methane in the atmosphere changes due to natural fluctuations.
At the end of an ice age, for instance, both carbon dioxide and methane
increase their concentrations because of the increase in biological activity;
at the beginning of an ice age, they decrease. The effect of this is to
strengthen underlying temperature fluctuations that cause ice ages. These
fluctuations are caused by changes in the Earth’s orientation and orbit.

By examining the Vostok ice core, the Soviet-French team has found that
it takes several thousand years for the methane in the atmosphere to increase
from a low level to a high level and then decrease. The low levels occur
during an ice age, when the methane concentration is about 350 parts per
billion (ppb). This can increase to about 650 ppb during the warm spell
between ice ages, known as an interglacial. When the concentration is fluctuating
most rapidly, it changes at a rate of no more than 0.3 ppb per year.

The amount of methane in the air has increased from about 700 ppb in
1700 to 1700 ppb today. This concentration is now more than double the highest
level reached before AD 1700.

Up to 1900, methane increased at a rate of 1.5 ppb per year; now, however,
it is rising at a rate of 17 ppb per year. This is far greater than any
natural fluctuation found in the ice core record, according to the researchers.

The Soviet-French team says that such a build-up of methane can produce
disproportionately strong greenhouse warming. At the end of an ice age,
the change from 350 to 650 ppb would on its own produce a warming of only
about 0.08 Degree C. But the extra methane in the stratosphere – the upper
atmosphere – will cause stratospheric water vapour to increase as the methane
oxidises. Water vapour is a powerful greenhouse gas. The extra water vapour
will contribute a further warming of 0.06 Degree C at the Earth’s surface,
so that the overall warming is almost 0.15 Degree C. This is about 30 per
cent of the direct effect of carbon dioxide (0.5 Degree C) for the same
increase in methane at the end of the ice age. Together, the build-up of
the two gases causes a warming of 0.65 Degree C, about a quarter of the
total change, at the end of an ice age.

The most likely reason for natural changes in methane concentration
in the past, says the team, is a change in the patterns of monsoon rain.
This increases the area covered by low-latitude wetlands when the world
warms, and these wetlands harbour bacteria that release methane.

Today, human activities are increasing the amount of methane in the
atmosphere at a rate that is 50 times as fast as at any other time in the
past 160,000 years, according to the French and Soviet researchers. ‘The
fundamental link between methane and climate variations indicated by the
Vostok record,’ they say, ‘suggests that the natural methane cycle may provide
a positive feedback in any future global warming.’ Just as it has amplified
ice age cycles in the past, it may amplify global warming.

Two satellites, NOAA-6 and NOAA-7, which operated simultaneously between
29 June 1981 and 16 April 1983 collected data which show that over periods
of two days, the two satellites agreed with each other to within 0.05 Degree
C. For monthly averages, the variation was less than 0.011 Degree C. Data
collected from various satellites between 1979 and the end of the 1980s
correlated closely with global averages of temperature collected through
measurements made with instruments sited on the ground.

Roy Spencer of the Marshall Space Flight Center, and John Christy of
the University of Alabama say in Science (vol 247, p 1558) that the satellite
measurements now provide a more reliable guide to global temperature trends
than ground-based measurements.

Their data show that the global temperature changes in the 1980s were
dominated by two strong ‘El Nino’ events – dramatic switches in ocean currents
– in 1983 and 1987. Both events produced a sharp warming, with a colder
run of temperatures between 1984 and 1986. Of the ten years the researchers
studied, they classify nine as either ‘cool’ or ‘warm’, and just one as
‘a±¹±ğ°ù²¹²µ±ğ’.

Spencer and Christy, both based at Huntsville in Alabama, suggest that
although the measurements add little to the understanding of past climate
changes, they are of major importance in laying down a marker for investigations
in the future.

If MSUs are made the standard for monitoring global temperature changes,
say Spencer and Christy, they will provide ‘precise monthly determinations
of the locations and magnitudes of temperature change events,’ which ‘should
facilitate more informed policy decisions concerning the effects of (manmade)
greenhouse gas production’.

THE GREENHOUSE effect increases significantly as the sea surface warms
up, according to a study carried out by researchers at the University of
Chicago. This means that as the world begins to warm – because of heat trapped
in the atmosphere by greenhouse gases – each additional increment of such
gas will cause a bigger warming than the one before. Oceans are the key
to this feedback process, because they provide water vapour, one of the
most important greenhouse gases.

These gases allow incoming solar energy, chiefly in the visible band,
through to the surface of the Earth, but absorb radiation heading out from
the surface, which is chiefly in the infrared. The result is that the Earth
warms.

Human activities produce greenhouse gases such as carbon dioxide or
chlorofluorocarbons (CFCs), and their effect is to make the world a little
warmer still. The extra warmth causes more water vapour to evaporate from
the oceans, and this traps more heat, intensifying the greenhouse effect.
At the same time, the spectrum of the outgoing radiation changes as the
surface warms. This means that as the surface warms, proportionately more
heat is trapped.

Atmospheric scientists have long understood all this in principle. Indeed,
the British researcher John Tyndall noted the importance of water vapour
as a greenhouse gas in the 1860s. But until now climatologists have lacked
the hard numbers with which to quantify the effect.

Now the numbers have been providedby Ameet Raval and Veerhabadrhan Ramanathan
in Chicago. They have used satellite measurements of the flux of outgoing
radiation from the oceans (Nature,vol 342, p 758).

Since 1985, the radiation escaping into space has been monitored by
the Earth Radiation Budget Experiment (ERBE). Measurements of sea surface
temperatures are collated by the US National Center for Atmospheric Research,
and researchers can use them to calculate the upwardflux of radiation at
the surface. The distribution of this radiation with wavelength isknown
to resemble that of a perfectradiator, known as a ‘black body’. Thedifference
between this theoretical curveand the actual measurements from space(see
Figure) is a direct measure of the greenhouse effect.

Without the presence of clouds in the skies, the Earth’s atmosphere
traps 146 watts of heat for every square metreof ocean surface. Clouds trap
a further33 W/m². The total absorption of the natural greenhouse
effect is, therefore, comparable to the total energy absorbed from the Sun,
which averages 237 W/m².

Raval and Ramanathan have measured the way the greenhouse effect increases
with increasing sea surface temperature. They have done this by looking
at different parts of the ocean. They find that the effect is small and
linear – that is, the greenhouse warming is proportional to the sea surface
temperature – up to a temperature of about 27 Degree C. At higher temperatures,
however, the effect increases sharply. At the moment, this enhanced warming
is largely restricted to the tropics.

The steady increase found by Raval and Ramanathan fits the trend expected
for the change in radiation from a warmer surface. But the researchers do
not understand why there should be an upturn at high temperatures.

It is possible to put the figures in perspective by looking at the effect
on the atmosphere of a hypothetical doubling of the amount of carbon dioxide.
In itself, this would trap an extra 4 W/m². At temperatures below
27 Degree C, the temperature feedback would increase this level to 5.9W/m²,
and the extra water vapour released from the oceans as a result would add
a further 3.6 W/m² to the warming, almost as much as the original
effect of the carbon dioxide.

So if we allow for the sensitivity of the greenhouse effect to surface
temperature, our estimates of global warming over the next few decades will
now have to increase. Raval and Ramanathan say that if governments take
no action to reduce the emissions of greenhouse gases, the cumulative effect
of these gases over the next 50 years will be to trap directly an extra
2.5 W/m². Simple models of the atmosphere have suggested that
this will be enough to make the Earth between 2 Degree C and 4 Degree C
warmer by 2040. But because of the feedbacks that Raval and Ramanathan have
now quantified, the effective increase in the greenhouse effect is likely
to be between 9 and 15 W/m².

The two researchers describe the process as ‘a strong positive feedback
on any perturbations to the present climate’. They believe that the changes
will be detectable long before that point is reached, by the instruments
now being used to monitor the Earth’s radiation ‘budget’ from space. That
should give the first unambiguous identification of the greenhouse warming
that results from human activities, which most experts believe has already
started to occur.

But the upturn in the feedback processes at temperatures above 27 Degree
C has the alarming implication that as the oceans warm, a band of the atmosphere
which carries an enhanced greenhouse effect may spread out from the tropics.
‘Both the cloudy and clear-sky greenhouse effect,’ say Raval and Ramanathan,
‘increases rapidly at temperatures characteristic of the tropics. It is
at present not known whether this nonlinear rise is simply a climatological
feature of lowlatitudes.’ If it is not, then the greenhouse threat facing
us is worse than any forecaster has yet dared to imagine.