Scientists are interested in the Earth's temperature change since the last glacial maximum, about 20,000 years ago. The first study to estimate the temperature change was published in 1980, and estimated a change of -1.5 degrees C, +/- 1.2 degrees C in tropical sea surface temperatures. The negative value means that the Earth was colder then than now. Since 1980 there have been many other studies. Different studies use different measurement techniques, or proxies. Some proxies can be used over land, others over water. The proxies are

proxy              code
"Mg/Ca"           1
"alkenone"      2
"Faunal"          3
"Sr/Ca"            4
"del 180"         5
"Ice Core"       6
"Pollen"           7
"Noble Gas"    8

Each study reports an estimate deltaT, a standard deviation of that estimate (sdev), the proxy used (coded 1 to 8), whether it was a terrestrial or marine study (T/M), which is coded as 0 for Terrestrial, 1 for Marine, and the latitude at which data were collected (latitude).

Source:  Data provided by Michael Lavine