Some solid research pointing to climate change being the primary factor driving this.[1] See other comments for details.
Also: “We have recently shown that B. dendrobatidis widely infects amphibian populations across Europe (Garner et al. 2005), suggesting that introductions of the pathogen are rather more ancient than were previously expected. However, mass mortalities are highly clustered within a relatively few high-altitude areas in Spain and France (S. Walker, M. C. Fisher & J. Bosch 2003–2006, unpublished data). These data are inconsistent with a wave-like front of introductions across Europe driving contemporary epidemics and suggest that environmental conditions influence host–pathogen dynamics in determining the outcome of infection within a site of introduction.”