Migration adds another layer of complexity to the scenario. In the 21st century the world could see substantial numbers of climate migrants—people displaced by either the slow or sudden onset of the effects of climate change. The United Nations’ recent Human Development Report stated that, worldwide, there are already an estimated 700 million internal migrants—those leaving their homes within their own countries—a number that includes people whose migration is related to climate change and environmental factors. Overall migration across national borders is already at approximately 214 million people worldwide, with estimates of up to 20 million displaced in 2008 alone because of a rising sea level, desertification, and flooding.
One expert, Oli Brown of the International Institute for Sustainable Development, predicts a tenfold increase in the current number of internally displaced persons and international refugees by 2050. It is important to acknowledge that there is no consensus on this estimate. In fact there is major disagreement among experts about how to identify climate as a causal factor in internal and international migration.
But even though the root causes of human mobility are not always easy to decipher, the policy challenges posed by that movement are real. A 2009 report by the International Organization for Migration produced in cooperation with the United Nations University and the Climate Change, Environment and Migration Alliance cites numbers that range from “200 million to 1 billion migrants from climate change alone, by 2050,” arguing that “environmental drivers of migration are often coupled with economic, social ad developmental factors that can accelerate and to a certain extent mask the impact of climate change.”
The report also notes that “migration can result from different environmental factors, among them gradual environmental degradation (including desertification, soil and coastal erosion) and natural disasters (such as earthquakes, floods or tropical storms).” (See box on page 15 of the report for a more detailed definition of climate migrants.) Clearly, then, climate change is expected to aggravate many existing migratory pressures around the world. Indeed associated extreme weather events resulting in drought, floods, and disease are projected to increase the number of sudden humanitarian crises and disasters in areas least able to cope, such as those already mired in poverty or prone to conflict.