Astronomy and Global Warming
An Astronomical society friend has commented that there seem
to be fewer clear skies since he bought his telescope.
When I heard about global warming, I got an impression
(shared, I suspect, by many) of rising sea levels and the weather becoming more
prone to storminess. The main message, apart from “stop making CO2” was: “live
away from low ground”. And there was the bit about the conveyor belt turning
off and causing a mini-ice age around the British Isles.
The increasing propensity for flooding has shown (to me) an
unsuspected aspect: that of higher humidity and rainfall due to the warmer
atmosphere.
When the ice melted after the ice age, the air temperatures
were relatively low, so the extra liquid water stayed in the sea, raising sea
levels. At the relatively warmer air temperatures of today, the glacial melt water is evaporating, raising humidity
levels, increasing cloudiness and producing more rain; hence the flooding.
Also, I suspect, this process is maintaining the salinity of the oceans and,
with it, the operation of the conveyor belt.
So the message is not so much “stay away from low level” as
“stay away from rivers and valleys”. And councils need to make sure there is
good road drainage, especially on hilly roads. Last winter, when returning to
Sussex on a wet evening, I was appalled at the large puddles in the right hand
lane of the M4: a recipe for disaster.
I wonder how many people are aware of the latent heat of
fusion of ice. Ice doesn’t automatically turn into liquid water at 0 degrees
Celsius. The ice requires a further dose of heat to change state from solid to
liquid. That’s called the latent heat of fusion. It is possible for ice to be
raised to 0 degrees just before winter, then, effectively store heat until the
following spring, when it finally melts. This might help to explain why
unexpectedly large pieces break off from polar glaciers. The recent BBC TV
programmes Operation Iceberg showed that there is still a lot being learnt about
glaciers and icebergs
Longer term, the situation is more complicated, goes
further.
With the increased cloud coverage we will presumably see a
greater greenhouse effect, which implies accelerated global warming. Our “evil
twin” neighbour, Venus, is completely engulfed in cloud, and its surface
temperature is 560 degrees Celsius; not a comfortable place to be.
Venus is about two thirds of our distance from the Sun,
which means that, under the inverse square law, it gets more than double the
Sun’s radiant energy, compared with the Earth. I suspect that Venus has much
more internal heat than Earth: the extra radiation it gets from the Sun may
have delayed the radiation of its own heat. Not only that, but its clouds are
somewhat darker, (being sulphur dioxide-based) than our white water vapour
clouds. That means that a fully cloud-shrouded Earth could display a higher
albedo (the property of reflecting radiation) than Venus does. Currently
Earth’s is much lower than Venus’s. The higher albedo of a cloudier Earth would
deflect more of the Sun’s radiation, than currently, and could potentially
allow the planet to cool itself down again. Once the planet has cooled, the
polar ice could reform at the expense of the humidity and cloud cover, taking
us back to “normal”. So perhaps the
Earth is self-regulating in that respect.
Clever planet is the Earth. There’s more to the Goldilocks
zone than mere distance from the Sun!
Don’t hold your breath, though, it’s a very slow process.
Meanwhile, from an observational Astronomical point of view,
and in the short term, I see a continuing reduction in the number of clear-sky
nights for observing, and an increase in the need for dew management.
Reputedly, a hazy sky yields improved seeing, so, at least, we should get
clearer views when we can see the stars.
Conclusion: treat every clear night as if it’s the last!
