Download How has Toronto*s climate changed in the last 150 years?

Clues to Past Climate
Change
A sampling of paleo-climate
reconstruction studies
How can we measure past
climate?
Because it is not possible to go back in time to
see what climates were like, past climate
cannot be estimated or measured using
ordinary methods.
In response to these challenges scientists
have developed a number of methods, which
are known as climate proxies.
What is a climate proxy?
Climate proxies are objects that can be measured
to create approximations of past climate patterns.
A climate proxy must possess a “climate”
component and a “date” component, which
together allow the reconstruction of the past
climate for that locale.
There are many climate proxies that can be used
but the four most commonly studied are; ice cores,
tree rings, coral, lake and ocean floor sediments.
World Data Center for
Paleoclimatology - Data Sets
Listing

This website contains the databases (collection of data from various
studies) a wide variety of climate proxies
http://www.ncdc.noaa.gov/paleo/datalist.html
Ice Cores
Ice cores have been one of the most valuable records of past climate
since they can provide information on temperature, atmospheric
characteristics, precipitation, and even volcanic activity from the past!
For example;
The thickness of each ice layer tells us how
much snow accumulated during the year , indicating
the general climate.
More information can be
extracted from chemistry-based
(CO2, SO4, even dust) ice core
studies which indicate higher
and lower air temperatures.
Although ice core records are
limited to areas where ice could
have existed at the time of
formation they still gives us a
general pattern of past climate.
http://www.iceandclimate.nbi.ku.
dk/research/past_atmos/ice_cor
e_impurities/dust_in_ice_cores/
Tree ring studies
(Dendrochronology)
Many tree species can live for several hundreds of years. However,
the Bristlecone Pine can live for up to five thousand years and so is
particularly useful as records of past climate.
Tree rings indicate not
only past air
temperature but
moisture and
cloudiness.
A narrow ring implies a
cold and dry season
while…
a wide ring indicates a
warm and wet season.
Coral studies
Corals also form
annual growth
rings.
As corals grow,
layers of calcium
carbonate
(CaCO3)are
deposited in its
skeleton.
Thicker growth recorded by the “coral rings” indicates a
warmer water temperature at that time.
Chemistry-based studies are possible because the calcium
carbonate skeleton absorbs 18O when the oceans are warm
but 16O when they are cooler.
Lake and ocean
sediments studies
Lake and ocean bottom
sediments, formed by
seasonal deposits, can also
act as a climate proxy thanks
to their layered structure.
The composition of each layer
of sediment changes
according to the climate
conditions at the time.
Fossils of sea animals
may reflect the
temperature of the
ocean at the time as
many sea animals live in
a narrow range of
temperatures.
Sediment layers formed
in warmer areas will
contain fossils with a
higher growing
temperature.
Putting it all
together
Glaciologists,
dendrochronologists,
oceanographers, and
sedimentologists assemble
these pieces of evidence and
reconstruct ancient climate
(paleo-climates) in order to
test climate models which are
then used to make
predictions about future
climate.