Cities are good subjects for study because they can invest heavily in large-scale experimental policies that could be scaled elsewhere (such as San Diego's advanced urban planning practices which could be applied elsewhere in the United States).[25][26] Multiple scholars approach this in different ways, but describe this "urban laboratory" environment for testing a wide variety of practices.[27][26] for example the book Life After Carbon documents a number of cities which act as "urban climate innovation laboratories".[28] These cities as laboratories offer an efficient way to detect climate change by looking at the effects of the greenhouse effect on rooftops, street trees, and other environmental variables within a city setting.[29] Though this method of looking at the heat waves effects in cities, it will offer a way of seeing the problem of the effect of heat that will be solved by cities within the future.[29]