On last Friday’s (05/16/2014) Science Friday segment on “Antarctic Ice Sheet Slipping Into the Sea“, host Ira Flatow started off by stating that “It’s well known that global warming is having its greatest impacts at the poles”. I disagree. I strongly contend that while it is widely believed that global warming is having its greatest impacts at the poles, the greatest impacts are actually in the tropics – at least in terms of impacts to biota and the living world. The belief that impacts are strongest at the poles comes from the fact that the absolute rate of warming are indeed fastest at high latitudes and the impacts of this warming are very visible is the form of melting ice. In the tropics, the absolute rate of warming is lower but the relative rate of warming is much higher than anywhere else. This is because the climate of the tropics are naturally very stable and thus any change in climate, even very small changes, takes the climate outside of the envelope of normal variation, rapidly creating novel climates that we have never seen on earth before and that no species are adapted to. Similarly,as a consequence of the normally stable climates, tropical species have narrow thermal tolerances and small geographic ranges (ranges which are rapidly shrinking to due loss of natural habitats due to deforestation and land conversion) and consequently they are unable to persist in the face of even minor changes.
Making matter worse, tropical species have less options for migrating to stay at equilibrium with changing climate due to the absence of any latitudinal temperature gradient between 24 and -24 degrees latitude (meaning that while temperate and boreal species can shift their ranges to high elevations or higher elevations to escape rising temperatures, tropical species can only shift their ranges to higher elevations). The ability of tropical species to migrate is further impeded by the rapid rates of deforestation and habitat loss which is creating thousands of new hectares of inhospitable terrain every day.
We also simply have many more species in the tropics than in the temperate, boreal, or polar realms. So even a loss of just a small percentage of species will correspond to the extinction of thousands and thousands of species. Finally, we have a lot more people who directly depend on tropical systems for their livelihoods than we have people that depend on on polar systems. The loss of ecosystems services resulting from climate change in the tropics will directly impacts billions of people, many of whom are living in poorly developed countries with poorly developed support systems.
Global warming is doing more than melting ice – it is driving the extinction of thousands of tropical species and endangering the lives of billions of people.