This is a somewhat outdated term used to refer to a sub-interval of the Holocene period from 5000-7000 years ago during which it was once thought that the earth was warmer than today.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).
Archives for novembre 2004
MSU Temperature Record
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.
Oscillation Nord Atlantique (“NAO“)
) Mesure de l’intensité des vents d’ouest traversant l’océan Nord Atlantique. Définie a l’origine par Sir Gabriel Walker en 1932 comme la différence de pression entre Ponta Delgada aux Acores et Stykkisholmur en Islande. Plus d’informations sur la NAO (‘North Atlantic Oscillation’) peuvent être trouvées ici. Voir également ‘Oscillation Arctique’.
Oscillation décennale Pacifique (“PDO”)
) Mode de variabilité de l’océan et de l’atmosphère centré dans le Pacifique Nord extra-tropical et concentré aux échelles de temps décennales. Ce terme a été proposé pour la première fois par Mantua et al. en 1997. Plus d’informations sur la “PDO” peuvent être trouvées ici.
Principal Component (“PC”)
Time history tied to a particular mode of time/space variance in a spatiotemporal data set (see “Principal Components Analysis”).
Principal Components Analysis (“PCA”)
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.
Index de l’Oscillation Australe
) Mesure de la différence de pression atmosphérique au niveau de la mer, entre l’Ouest (ex. Darwin, Australie) et le centre/Est de la région Pacifique équatoriale. Cet index est représentatif des changements Est-/Ouest dans la circulation atmosphérique associés avec le phénomene d’El Niño-Oscillation Australe. Ce terme a été introduit par Sir Gabriel Walker (Walker and Bliss, 1932). Plus d’infos sur cet Index peuvent etre trouvées ici (en anglais).
Surface Temperature Record
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.
Urban Heat Island Effect (“UHIE”)
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.
Rétroaction de la vapeur d’eau
) La vapeur d’eau est un gaz a effet de serre puissant, qui absorbe les rayonnements de longueurs d’ondes élevées. Si la concentration atmosphérique en vapeur d’eau augmente a cause du réchauffement climatique, celle-ci va augmenter en retour l’effet de serre encore plus. Il est bien connu que le taux d’évaporation est lié a la température, et qu’une hausse des températures accroît la pression de la vapeur (équation de Clausius-Clapeyron). Ce processus est connu comme étant la rétroaction (positive) de la vapeur d’eau. Une différence importante entre la vapeur d’eau et les autres gaz a effet de serre comme le CO2 est que la vapeur d’eau ne passe qu’un temps très court dans l’atmosphère avant d’être précipité, alors que la temps de résidence du CO2 dans l’atmosphère peut dépasser une centaine d’années.