Geographic disparities and moral hazards in the predicted impacts of climate change on human populations

Aim It has been qualitatively understood for a long time that climate change will have widely varying effects on human well-being in different regions of the world. The spatial complexities underlying our relationship to climate and the geographical disparities in human demographic change have, however, precluded the development of global indices of the predicted regional impacts of climate change on humans. Humans will be most negatively affected by climate change in regions where populations are strongly dependent on climate and favourable climatic conditions decline. Here we use the relationship between the distribution of human population density and climate as a basis to develop the first global index of predicted impacts of climate change on human populations. Location Global. Methods We use spatially explicit models of the present relationship between human population density and climate along with forecasted climate change to predict climate vulnerabilities over the coming decades. We then globally represent regional disparities in human population dynamics estimated with our ecological niche model and with a demographic forecast and contrast these disparities with CO2 emissions data to quantitatively evaluate the notion of moral hazard in climate change policies. Results Strongly negative impacts of climate change are predicted in Central America, central South America, the Arabian Peninsula, Southeast Asia and much of Africa. Importantly, the regions of greatest vulnerability are generally distant from the high-latitude regions where the magnitude of climate change will be greatest. Furthermore, populations contributing the most to greenhouse gas emissions on a per capita basis are unlikely to experience the worst impacts of climate change, satisfying the conditions for a moral hazard in climate change policies. Main conclusions Regionalized analysis of relationships between distribution of human population density and climate provides a novel framework for developing global indices of human vulnerability to climate change. The predicted consequences of climate change on human populations are correlated with the factors causing climate change at the regional level, providing quantitative support for many qualitative statements found in international climate change assessments.