Environmental Engineering Reference
In-Depth Information
ocean, increasing the temperature further, etc.). The tem-
perature spikes occur in both the warming phases and the
cooling phases,
indicating instabilities that we do not
understand.
What all of this tells us is that greenhouse gases and
climate are coupled. Throughout
years and many
ice ages, the greenhouse gas concentration has never been
as high as it is today.
.
The Recent Past
The temperature record for the past thousand years is
called the
“
hockey stick
”
curve because it looks like one:
roughly
flat except for the past hundred years, when it
swoops up like the end of a hockey stick. However, the
thermometer was only invented in
, and reliable
worldwide records exist only for the past
years.
Everything before that comes from what are called prox-
ies for the temperature
other things that are indirectly
related to the temperature. Unfortunately, all of the prox-
ies are affected by more than just the temperature. Tree
rings are one example of such a proxy. The width of the
rings does depend on the temperature, but also depends
on the amount of rainfall in the growing season, so the
temperature cannot be accurately determined by tree
rings alone. Many proxies are used together in the hope
that they will give a reasonable average. Here are a few.
The date of the grape harvest at wineries is a proxy for the
heat of summer: the earlier the harvest, the hotter the
summer. The length of glaciers serves to tell us something
about year to year temperature changes. The layer
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