Science is an organized enterprise of inquiry which tries to tie together multiple strands of evidence to craft coherent explanations for disparate patterns in the natural world. Philosophers call this enterprise “inference towards the best explanation”. Such inferences at times depend upon detailed quantitative models, but at times one can rely upon the confluence of multiple strands of qualitative evidence. Humans are having unquestionable influences upon many aspects of the earth system at present, on land, in freshwater systems, and indeed the ocean, including devastating impacts on biodiversity. There are many patterns in the world at present – shrinking glaciers, shifting seasonal patterns in species’ life histories, and altered spatial distributions – which point to the signal of climate change, independent of the details of quantitative climate models. Yet, there are many other factors at play, often confounding clear assessment of the specific role of climate change in observed changes in the world. A deeper synoptic understanding of the drivers and impacts of climate change would be incredibly valuable and is urgently needed, even if in the end (though this seems increasingly unlikely) anthropogenic drivers were not the main factor underlying observed climate change.
A “green roof” is a roof on a structure created by humans, which has a plant community (and various hangers-on) established on it. There are many potential benefits of green roofs, ranging from moderation of local microclimates to modulations of storm runoffs, and green roofs may serve the enhancement of biodiversity conservation, as well. Green roofs would seem to be quintessential examples of a “novel ecosystem”. Here, I first outline some dimensions of the novelty that warrant more research. Green roofs can provide many opportunities for creative ecological research in the assembly, dynamics and functioning of novel ecosystems. Then, I briefly discuss some potential biodiversity hazards that are created along with green roofs. Recognizing these potential “shadows” of a green roof by no means belies the strong and compelling rationale for promoting green roofs, in terms of sustainability and livability of human structures; instead the points I raise are simply issues which should be evaluated and quantified when promoting green roofs broadly as a design strategy in new buildings or retrofitted existing structures.