|
Best known for its
studies of the fundamental constituents of matter, the CERN
particle-physics laboratory in
Geneva
is now also being used to study the climate. Researchers in the CLOUD
collaboration have released the first results from their experiment
designed to mimic conditions in the Earth's atmosphere. The CLOUD
collaboration was set up to settle the question of whether or not there
is a link between cosmic rays and climate.
The experiment, which
has been running since the end of 2009, consists of a 3 m-diameter
stainless steel chamber containing humidified ultra-pure air and
selected trace gases, which is placed in the path of a charged-pion beam
that simulates ionizing cosmic rays. By varying the concentrations of
the trace gases, adjusting the temperature and humidity inside the
chamber, turning the beam on and off, and then measuring the
concentration of aerosols inside small samples removed from the chamber,
scientists can establish how changing atmospheric conditions affect the
rate of aerosol production. The fact that they can do this very
precisely and with extremely low levels of contaminants means that they
can make much cleaner and more controlled measurements than is possible
in the real atmosphere.
What they have
discovered is that cosmic rays could have a role to play in climate by
enhancing the production of potentially cloud-seeding aerosols.
Describing their findings in this week's Nature, the team has also found
that our current understanding of the chemistry of these aerosols is
inadequate and that manmade pollution could have a larger role in their
formation than previously thought.
Aerosols are tiny
liquid or solid particles suspended in the atmosphere that can warm or
cool the climate directly by absorbing or scattering radiation. They can
also act as surfaces on which water vapour condenses, leading to the
formation of cloud droplets and so tending to cool the planet. Around
half of all cloud droplets are thought to form on aerosols that are
injected directly into the atmosphere, such as dust particles, sea spray
or pollution from the burning of biomass. The other 50% form on aerosols
that are produced by the clustering of molecules of trace gases found in
the atmosphere. However, it is not well understood exactly how this
clustering takes place and precisely which kinds of molecules are
involved.
There has also been
much debate about the possible role of cosmic rays in the formation of
these aerosols. Henrik Svensmark of the National Space Institute in
Copenhagen
and colleagues hypothesize that the ions that are formed as (charged)
cosmic rays pass through the atmosphere act as a kind of glue that makes
it easier for molecules to stick together and form aerosols. This
hypothesis has proved controversial because it suggests a role for solar
variation, as well as human emissions of greenhouse gases, in climate
change – the idea being that the stronger the Sun's magnetic field,
the more cosmic rays are deflected away from the Earth, resulting in the
formation of fewer clouds and so a warmer Earth, with a weaker solar
magnetism having the opposite effect.
The researchers found
that when simulating the atmosphere just a kilometre above the Earth's
surface, sulphuric acid, water and ammonia – the components generally
believed to initiate aerosol production – were not on their own enough
to generate the quantities of aerosols observed in the real atmosphere,
falling short by a factor of up to a thousand, even when the pion beam
was switched on. They conclude that other molecules must also play a
role, and say that an organic compound or compounds are most likely. If
the missing substance is manmade, then human pollution could be having a
larger cooling effect than is currently believed (emissions of sulphur
dioxide are already known to generate the sulphuric acid that is vital
for aerosol production). If, however the missing substance comes from a
natural source, the finding could imply the existence of a new climate
feedback mechanism (possibly higher temperatures increasing organic
emissions from trees).
When simulating the
atmosphere higher up, the researchers found a stronger cosmic-ray
effect. They discovered that at altitudes of 5 km or more, where
temperatures are below –25 °C, sulphuric acid and water can
readily form stable aerosols of a few nanometres across and that cosmic
rays can increase the rate of aerosol production by a factor of 10 or
more.
More detailed
experiments required - and so the quest for what is really
causing our climate to vary continues.
Svensmark welcomes the
new results, claiming that they confirm research carried out by his own
group, including a study published earlier this year showing how an
electron beam enhanced production of clusters inside a cloud chamber. He
acknowledges that the link between cosmic rays and cloud formation will
not be proved until aerosols that are large enough to act as
condensation surfaces are studied in the lab, but believes that his
group has already found strong evidence for the link in the form of
significant negative correlations between cloud cover and solar storms
(which reduce atmospheric ionization). "Of course, there are many
things to explore," he says, "but I think that the
cosmic-ray/cloud-seeding hypothesis is converging with reality."
Other
scientists suggest a note of caution, however. Modelling
carried out in Canada shows that a 10–20% variation in atmospheric-ion
concentrations, roughly the variation associated with solar storms or
across a solar cycle, produces less than a 1% change in the
concentration of cloud condensation nuclei, with the diminishing returns
resulting from more aerosols having to share a given quantity of
molecular raw material and aerosols merging with one another. This
change is very likely too small to explain the effect on clouds reported
by Svensmark, and work is continuing to explore other potential physical
connections between cosmic rays and clouds.
As
stated above - the jury is still out and there is a lot more work to do
before we can really pretend to understand how the myriad of different
factors join together to produce the climate changes we are seeing.
In
the meantime, Mr Cameron would you PLEASE STOP dumping onto my power
bills the cost of your insane projects to build windmills all over my
country. We all know they will only ever produce a small fraction
of the power we need, and that we will have to build a costly network of
gas fired stations to back them up because they will only operate a
fraction of the time. Please could you recognise that carbon
dioxide emissions are very likely NOT causing global warming, and start
building nuclear or coal fired power stations before it is too late,
before we run out of power, and before we (you) drive the last of our
manufacturing industry out of the country. The Emperor is wearing
no clothes!! |