Review article. Studying climate effects on ecology through the use of climate indices: the North Atlantic Oscillation, El Niño Southern Oscillation and beyond

Abstract

Whereas the El Niñ o Southern Oscillation (ENSO) affects weather and climate variability worldwide, the North Atlantic Oscillation (NAO) represents the dominant climate pattern in the North Atlantic region. Both climate systems have been demonstrated to considerably influence ecological processes. Several other large-scale climate patterns also exist. Although less well known outside the field of climatology, these patterns are also likely to be of ecological interest. We provide an overview of these climate patterns within the context of the ecological effects of climate variability. The application of climate indices by definition reduces complex space and time variability into simple measures, 'packages of weather'. The disadvantages of using global climate indices are all related to the fact that another level of problems are added to the ecology-climate interface, namely the link between global climate indices and local climate. We identify issues related to: (i) spatial variation; (ii) seasonality; (iii) non-stationarity; (iv) nonlinearity; and (v) lack of correlation in the relationship between global and local climate. The main advantages of using global climate indices are: (i) biological effects may be related more strongly to global indices than to any single local climate variable; (ii) it helps to avoid problems of model selection; (iii) it opens the possibility for ecologists to make predictions; and (iv) they are typically readily available on Internet.

Lagged influence of North Atlantic Oscillation on population dynamics of a Mediterranean terrestrial salamander

“…Coulson et al 2008). In the S. strinatii population, the negative winter NAO values that are indicators of humid and warm weather in the Mediterranean (Stenseth et al 2003) may have increased the salamander survival in particular of eggs, newborn or first year juveniles, all of these stages being small-size and therefore highly sensitive to unfavourable dry weather conditions (Hairston 1987).…”

“…The North Atlantic Oscillation (NAO) is a global climatic index that describes the temporal variability in the atmospheric pressure measured along a north-south gradient, from the subpolar region of Iceland to the Azores in the subtropical part of the North Atlantic Ocean (Hurrell 1995;Hurrell and van Loon 1997;Stenseth et al 2003). The differences in atmospheric pressure determine the direction and speed of the westerly winds that cross the Atlantic Ocean, blowing from North America towards Europe.…”

“…As a consequence, the NAO affects the quantity and strength of the weather storms that hit the northern regions of the European subcontinent and the western areas of the Mediterranean basin (Hurrell 1995). The effects of the NAO on local weather are observable throughout the year, but this index shows its greatest level of variability during wintertime, when the air masses that cross the Atlantic embed their highest energy content (Stenseth et al 2003). For these reasons, the NAO is mainly considered a winter climatic index, although it may influence weather conditions of western Europe (Hurrell and van Loon 1997;Stenseth et al 2003) and the Mediterranean basin (Rubolini et al 2007;Cañellas et al 2010) all over the year.…”

“…The effects of the NAO on local weather are observable throughout the year, but this index shows its greatest level of variability during wintertime, when the air masses that cross the Atlantic embed their highest energy content (Stenseth et al 2003). For these reasons, the NAO is mainly considered a winter climatic index, although it may influence weather conditions of western Europe (Hurrell and van Loon 1997;Stenseth et al 2003) and the Mediterranean basin (Rubolini et al 2007;Cañellas et al 2010) all over the year. In the Mediterranean, the influence of the NAO on local weather has been demonstrated in relation to air and sea temperatures, precipitations and river discharges (e.g.…”

“…Usually in southern Europe, positive values of the winter NAO index are associated with cold and dry weather conditions, while the opposite (i.e. rainy and warm weather) is observed during prevalent negative NAO years (Stenseth et al 2003;Brandimarte et al 2011).…”