Temperature is the primary measure of climate and can be measured or reconstructed for the Earth's surface, and sea surface temperature (SST).
Precipitation offers another indicator of relative climate variation and may include humidity or water balance.
Biomass and vegetation patterns may be discerned in a variety of ways and provide evidence of how ecosystems change to adapt to climate change.
Sea Level measurements reflect changes in shoreline and usually relate to the degree of ice coverage in high latitudes and elevations.
Solar Activity can influence climate, primarily through changes in the intensity of solar radiation.
Volcanic Eruptions, like solar radiation, can alter climate due to the aerosols that are emitted into the atmosphere and alter climate patterns.
composition of air or water can be measured by tracking levels
of greenhouse gases such as carbon dioxide and methane, and measuring
ratios of oxygen isotopes. Research indicates a strong correlation between
the percent of carbon dioxide in the atmosphere and the Earth's mean temperature.
Climate forcing refers to specific
phenomena that directly influence changes in climatic dynamics. Forces
that influence climatic change can be broken down into those beyond the
Earth's environmental system (extraterrestrial) and those that relate
to internal forces (terrestrial).
Nature presents two basic measuring
units to which many plants and animals intuitively respond:
Years form the fundamental
measure of periods of time longer than a day. Using the exponential powers
of ten-- otherwise known as "log-ten" or "powers of ten
exponents"-- it doesn't take long to go from decades (10) and centuries
(102 or 10X10) to billions (109 ) and tens of billions
(1010) of years.
Time can be used to measure distance, as in the term "light year" which is the distance that light travels in a year (9.5 X 1012 kilometers.) Astronomers also use the term "parsec" so describe distances: one parsec is equal to 3.3 light years.
Between years and days are transition units that we call months, which are roughly the lunar cycle, though not exactly. The Mayan calendar, later incorporated by the Aztec peoples, was an elaborate combination of solar and lunar calendars as well as other astronomical cycles. According to some experts in the Mayan system, the current cycle of time ends December 23, 2012 according to the Mayan calendar, and a new cycle will begin thereafter.
From the unit of a day (which is actually 0.0027 of a year,) smaller units are developed with each day being divided into twenty four hours, every hour (roughly 10-4 year) subdivided into sixty minutes of sixty seconds in length. Some scientists use seconds as their primary measure and calculate the age of the universe as being a mere 1019 seconds old. The Swiss watch maker Swatch has recently divided the day up into 1000 beats that they are promoting as a universal time.
Days have obvious parameters
that can easily be observed, and lunar and annual cycles have physical
markers that can be tracked or can be intuited by animals and plants,
but all other measures of time (hours, weeks, seconds, light years, etc.)
are abstractions with no basis in nature other than being convenient frameworks
to organize time invented by human beings.
National Institute of Science and Technology's "A
Revolution In Timekeeping"and A
Walk Through Time website. Another resource is The
Origins and Implications of Time from Sanford University. Also
see the Why
Files' Time Timeline on the development of clocks and other timepieces.
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