- Researchers write in a new study published in the journal Scientific Reports that “in order to preserve their annual mean temperatures, tropical populations would have to travel distances greater than 1000 km [about 620 miles] over less than a century if global mean temperature rises by 2 °C over the same period.”
- The rapid evacuation of the tropics that could occur under such a scenario would cause migrant species to concentrate in the margins of tropical zones and in the subtropics, potentially leading to population densities increasing 300 percent or more in those areas, which would have consequences not just for ecosystems but for human wellbeing, as well.
- Calculations by climate scientists have found that Earth could reach 2 degrees Celsius of global warming (about 3.6 degrees Fahrenheit) as soon as 2036.
The tropics are the warmest part of planet Earth, but as global temperatures rise, simply “staying put” and enduring additional warming may be extremely harmful to many tropical species and societies, researchers are warning.
Surface temperatures are nearly uniform near the equator, which means that species trying to migrate in order to find temperatures they are adapted to would have to travel extreme distances, even under relatively mild warming scenarios at the low end of current projections.
Researchers Solomon Hsiang of University of California, Berkeley and Adam Sobel of Columbia write in a new study published in the journal Scientific Reports that “in order to preserve their annual mean temperatures, tropical populations would have to travel distances greater than 1000 km [about 620 miles] over less than a century if global mean temperature rises by 2°C over the same period.”
The nearly 200 countries that negotiated the Paris Climate Agreement last December have agreed to limit global warming to 2 degrees Celsius (about 3.6 degrees Fahrenheit). Calculations by climate scientists have found that Earth could reach that threshold as soon as 2036 if we don’t sharply reduce greenhouse gas emissions.
The rapid evacuation of the tropics that could occur under such a scenario would cause migrant species to concentrate in the margins of tropical zones and in the subtropics, potentially leading to population densities increasing 300 percent or more in those areas, which would have consequences not just for ecosystems but for human wellbeing, as well, especially in contexts where alternatives to geographic displacement are limited.
“If populations were actually to concentrate this quickly in what are already exceptionally arid environments, we would expect there to be many adverse consequences in both natural and human systems, such as an accelerated transmission of infectious diseases or conflict over scarce resources,” Hsiang and Sobel write in the study.
The researchers found that 12.5 percent of the global human population would have to migrate more than 1,000 kilometers to stay in the temperature range they’re accustomed to — and the majority of those people currently live in the tropics. Just under 34 percent of the population would have to migrate more than 500 km.
“Imagining the tremendous cost of actually undertaking such massive spatial reorganization of the global population helps illustrate the potential importance of the dynamics we highlight here, although in the context of humans there are likely many local adaptations that are preferred to these displacements,” the researchers add.
Of course, not all populations can pick up and move as easily as humans — coral reefs and mature forests, for instance. It’s not clear at all that they can manage to move quickly enough to beat the heat.
“If maintaining their present environmental temperature is a critical adaptation to anthropogenic climate change, some tropical populations may have to migrate at unprecedented speeds over extreme distances in order to cope with relatively optimistic warming projections, given current emissions trajectories,” according to the study.
CITATION
- Hsiang, S. M., & Sobel, A. H. (2016). Potentially Extreme Population Displacement and Concentration in the Tropics Under Non-Extreme Warming. Scientific Reports, 6, 25697. doi:10.1038/srep25697
