Historic Global Temperatures
The isotopic composition of water, and in particular
the concentration of the heavy isotope of oxygen, O-18, relative
to O-16, is indicative of the temperatures of the environment.
During warm periods, the concentration of the slightly more nonvolatile
O-18 in the ice is lower than during cold periods. This reflects
the lower concentration of O-18 in the atmosphere available for
condensation into snow during warm periods due to little evaporation
of O-18 from the oceans.
A record of temperature variations over the last 160,000 years,
shown in the graph on the left has recently been constructed
by analyzing the O-18 to O-16 ratio in the Vostok ice core. The
numbers in this data set are recorded as differences from the
current average temperature (15 degrees C).
Starting on the left-hand side of the graph at about 140,000
years ago, the climate was about 6 C colder than it is today
- an ice age period. Then at about 130,000 years ago, there was
a quite rapid warming period until about 125,000 years ago, when
the climate was, perhaps, 1 C or 2 C warmer than today - an inter-glacial
period. From 120,000 to about 20,000 years ago, there was a long
period of cooling temperatures, known as the last Great Ice Age.
From about 18,000 or 19,000 years ago to about 15,000 years ago,
the climate went through another warming period to the next inter-glacial,
- the one we are now in.
Near Term Historical Temperature Records
Links to more Temperature Data Sets: Source: ChemConnections
CO2 and Temperature Data
it getting warmer?
there at temperature difference in trends for land vs. oceans?
How good are the computer models in predicting global temperature
Final Answer to Question: What is the evidence that temperature
is currently increasing?