In general terms, lighting research has been focused in the development of artificial light with the purpose of saving energy and having more durable lamps. However, the consequences that artificial night lighting could bring to the human being and living organisms have become an important issue recently. Light pollution represents a significant problem to both the environment and human health causing a disruption of biological rhythms related not only to the visible spectrum, but also to other parts of the electromagnetic spectrum.

Climate-induced range shifts have been detected in a number of European species for which long-term survey data are available. In North America, well-organized long-term data needed to document such shifts are much less common. Now observations made by ‘citizen scientists’ help to demonstrate that a major, climate-induced shift of North American butterflies is underway.

In their comment, Rodríguez-Sánchez et al. claim that our conclusions on the climatic debt of birds and butterflies are premature because introducing statistical and biological uncertainties in species-specific thermal tolerance (species temperature index, STI) would blur the temporal trend in the community temperature index CTI). Here, we show why our results are not affected by this uncertainty and further assess the STI uncertainty and its consequences. (Correspondence)