The chart below depicts deviations about 57 F of earth average temperature over the past 4500 years. The chart below that goes back 450,000 years, and is from ice core samples at various locations, showing deviations from present day temperature.
The Figures below show at temperature history progressing from a narrow time span (1979-2014) . NOTE: Most of the Figures in these charts are of “anomalies” about a specified or arbitrary reference temperature range.
The plot below is also for global average temperature changes
UAH = Satellite data base from University of Alabama – Huntsville
Analysis (plot) courtesy of C. Bruce Richardson Jr., Houston, TX.
The light blue line indicates little temperature change over past 14 Years.
Orange lines represent atmospheric CO2 levels.
Red line is linear regression since 1979.
ANNUAL AVERAGE EARTH SURFACE TEMPERATURE
In the climate change debate, the most important parameter is Surface Temperature. Usually annual average surface temperature, averaged over the planet is the topic. Presently the annual average earth temperature is 15oC = 288oK = 59oF. Often the degree (o) symbol is dropped and only the unit C, K or F is used.
Temperature has been measured in three ways:
- Hundreds of thousands of years ago to the 18th century by ice core samples.
- From the 18th century to the present by surface thermometers.
- From 1979 to the present from space by weather satellites.
An ice core (see http://en.wikipedia.org/wiki/Ice_core ) is a core sample that is typically removed from an ice sheet, most commonly from the polar ice caps of Antarctica, Greenland or from high mountain glaciers elsewhere. As the ice forms from the incremental buildup of annual layers of snow, lower layers are older than upper, and an ice core contains ice formed over a range of years. The same samples also yield historic CO2 levels. Due to the indirect method of determination of temperature and the uncertainties in age of the layers, ice core temperatures have the poorest accuracy.
In earlier times, thermometers were the glass-liquid type, with alcohol (dyed red) or mercury as the liquid). Later electronic thermometers have also been used, including thermocouples, resistance thermometers, and solid state thermometers.
Since the oceans cover about 70% of the earth’s surface, sea surface temperature (SST) is very important. See http://en.wikipedia.org/wiki/Sea_surface_temperature . SST is presently measured by battery powered “floats”. These floats transmit temperature and salinity data, at various depths to 2,000 meters, to satellites. See http://www.argo.ucsd.edu/How_Argo_floats.html .
Satellites are best the method of thermometry for averaging large areas. Several countries have deployed climate satellites. These satellites are in a polar orbit (north-south), circling the earth twice a day, and taking data for segments of earth surface from 1o longitude wide and 1o latitude high. They measure temperature at various altitudes by infrared thermometry, see http://en.wikipedia.org/wiki/Satellite_temperature_measurements. Infrared thermometry includes very long wavelength infrared, or microwave radiation.