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A Microwave Sounding Unit (“MSU”) is a device that has been installed on polar orbiting satellites to measure, from space, the intensity of microwave radiation emitted by earth’s atmosphere. Different “channels” of the MSU measure different frequencies of radiation which can, in turn, be related to temperature averages of the atmosphere over different vertical regions. Channel 2 measurements provide a vertically-weighted temperature estimate that emphasizes the mid-troposphere (with small contributions from the stratosphere), while Channel 4 largely measures temperatures in the lower stratosphere. Information from MSUs have been used to generate the “MSU Temperature Record“. More information on MSU can be found here.

This is a somewhat outdated term used to refer to a sub-interval of the Holocene period from 5000-7000 years ago during which it was once thought that the earth was warmer than today. We now know that conditions at this time were probably warmer than today, but only in summer and only in the extratropics of the Northern Hemisphere. This summer warming appears to have been due to astronomical factors that favoured warmer Northern summers, but colder Northern winters and colder tropics, than today (see Hewitt and Mitchell, 1998; Ganopolski et al, 1998). The best available evidence from recent peer-reviewed studies suggests that annual, global mean warmth was probably similar to pre-20th century warmth, but less than late 20th century warmth, at this time (see Kitoh and Murakami, 2002).

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Combinations of different channels of individual Microwave Sounding Unit (“MSU”) measurements have been used to generate a record of estimated atmospheric temperature change back to 1979, the “MSU Temperature Record”. The complex vertical weighting functions relating the the various channels of the MSU to atmospheric temperatures complicate the interpretation of the MSU data. Moreover, while MSU measurements are available back to 1979, a single, continuous long record does not exist. Rather, measurements from different satellites have been combined to yield a single long record, further complicating the interpretation of the MSU record. Direct comparisons of the MSU Temperature Record with the surface temperature record are therefore difficult. More information on the MSU Temperature Record can be found here.

Measure of the strength of the westerlies across the North Atlantic. Originally defined by Sir Gilbert Walker in 1932 as the difference in pressure between Ponta Delgada on the Azores and Stykkisholmur in Iceland. More information on the NAO can be found here. See also Arctic Oscillation (“AO”).

A pattern of variability in the ocean and atmosphere that appears to be centered in the extratropical North Pacific, which emphasizes decadal, rather than interannual, timescales. Term was introduced by Mantua et al. (1997). More information on the PDO can be found here.

Time history tied to a particular mode of time/space variance in a spatiotemporal data set (see “Principal Components Analysis”).

A procedure by which a spatiotemporal data set is decomposed into its leading patterns in both time (see ‘Principal Component’) and space (see ‘Empirical Orthogonal Function’) based on an orthogonal decomposition of the data covariance matrix.

A measure of the difference in sea level pressure between the western (e.g., Darwin, Australia) and central/eastern (e.g., Tahiti) equatorial Pacific, representative of the east-west changes in atmospheric circulation associated with the El Nino/Southern Oscillation phenomenon. Term was introduced by Sir Gilbert Walker (Walker and Bliss, 1932). More information on the SOI can be found here.

The instrumental record of surface temperature change is based on a combination of land air, marine air, and ocean surface temperature changes recorded over roughly the past century and a half. While several different datasets exist, the most widely used version has been produced by the Climatic Research Unit (CRU) of the University of East Anglia in the UK. Issues of consistency and homogeneity of the measurements through time have been taken into account in constructing this global surface temperature database, and measures have been taken to ensure that all non-climatic inhomogeneities (including Urban Heat Island effects) have been removed.

[Read more…] about Surface Temperature Record

An Urban Heat Island is a metropolitan area which is significantly warmer than its surroundings. As population centers grow in size , they tend to have a corresponding increase in average temperature. Not to be confused with global warming, scientists refer to this phenomenon as the “Urban Heat Island Effect” (UHIE). There is little controversy in the existence of the UHIE. What is more controversial is whether, and if so how much, this additional warmth affects the (global) temperature record. The current state of the science is that the effect on the global temperature record is small to negligible. More information can be found here.