Climate Change

Instrumental Records

Instrumental records began generally in the 17th to 18th centuries, but early instruments were not well calibrated or were poorly exposed. Standard instruments and careful exposure became widespread in the mid 19th century, along with organized station networks and standard observing times. However, various temperature scales—Fahrenheit, Celsius, Reamur—were in use. Precipitation records remain one of the least consistent records due to the effects of airflow over the gauge, especially for solid precipitation, gauge characteristics (dimensions, rim design, and height above ground), shielding devices, and gauge siting. The frequency and time of gauge reading also introduces inhomogeneities. There are more than 50 different gauge types in use in national weather services, creating inhomogeneity in cross-border amounts. Sea surface temperatures are another problem area. Originally, readings were made with a thermometer inserted into a canvas bucket of seawater. Later, engine room intake temperatures were used. However, the changeover was gradual, and as ships increased in size, the depth of the water sampled by the engine room intake got deeper. Estimates of wind speed at sea, prior to the invention of anemometers, involved the use of the Beaufort wind scale (developed in 1805 by Admiral Beaufort), where categories 0 (calm) to 12 (hurricane) were based on the wind effects on wave state. In spite of the inhomogeneity problems, careful selection and adjustment of the records has enabled a consistent picture of climate variations over the period of instrumental records to be obtained. In the case of temperature, this reveals that temperatures were higher at the end of the 20th century than at the end of the 19th century in almost all locations on Earth.

The longest satellite climate record is of the Northern Hemisphere snow cover since 1966. Consistent global sea ice data began with passive microwave satellite measurements in 1979.

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