Currents Magazine June 2016 Currents June 2016 | Page 4

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Currents

June 2016

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some locales. The years 1837 to 1844 were, generally speaking, years of deflation in wages and prices.

The Guardian - George Perkins Marsh
More than 160 years on, his speech seems
remarkably prescient today. It also shows that he was
decades ahead of most other thinkers on this subject. After all, he delivered his lecture a decade or
more before John Tyndall began to explore the thesis
that slight changes in the atmosphere's composition
could cause climatic variations. And it was a full half
a century before Svante Arrhenius proposed that carbon dioxide emitted by the "enormous combustion
of coal by our industrial establishments" might warm
the world (something he thought would be beneficial).
Yes, in his speech, Marsh talks about "civilised
man" and "savages" - and the language is turgid in
places - but let's cut him a little slack: this was 1847,
after all. It's about half way through he gets to the
bit that matters most to us today:
Man cannot at his pleasure command the rain
and the sunshine, the wind and
frost and snow, yet it is certain
that climate itself has in many
instances been gradually changed
and ameliorated or deteriorated
by human action. The draining of
swamps and the clearing of
forests perceptibly effect the
evaporation from the earth, and
of course the mean quantity of
moisture suspended in the air.
The same causes modify the electrical condition of the atmosphere
and the power of the surface to
reflect, absorb and radiate the
rays of the sun, and consequently
influence the distribution of light
and heat, and the force and
direction of the winds. Within
narrow limits too, domestic fires
and artificial structures create and
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diffuse increased warmth, to an
extent that may effect vegetation.
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The mean temperature of London

42 Years Experience

References Available

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