(a) Correlations between the 7-year high- and low-pass filtered fire–climate indices and the summer Arctic Oscillation, spring–summer PDO and winter El Niño Southern Oscillation indices for the period 1959–1999 (from table 2 in Macias Fauria & Johnson 2006). Fire–climate indices were obtained from the dominant upper air Northern Hemisphere height anomaly patterns during large fire events over several regions in the boreal forest of North America. Type 1 (2) fire–climate indices are positively (negatively) correlated with PDO at low frequencies and with ENSO at high frequencies. Type 3 (4) fire–climate indices are positively (negatively) correlated with AO at high frequencies. Significances were computed using a Monte–Carlo significance test, which generated 1000 pairs of series with the same autoregressive structure as the original series; *p<0.1; **p<0.05; ***p<0.01. (b) Correlations between total area burned in Canada and spring–summer PDO for the period 1918–2005. Filtered series and significances were computed as in a.
