Climate change is a major contributor to migration and displacement. Persistent drought forced as many as 1.5 million Syrian farmers to move to overcrowded cities, contributing to social turmoil and ultimately a civil war that drove hundreds of thousands of people to attempt to cross the Mediterranean into Europe. Drought also worsened refugee crises in the Sahel, the Horn of Africa and other parts of the continent. Climate change can cause displacement in multiple ways. No reliable estimates exist of the number of people who will be displaced partly or wholly by climate change, due to uncertainties concerning the rate of climate change, the ability of different societies to cope with this change, and other factors. However, several estimates put the number of people in the hundreds of millions in the latter part of this century. It is well documented that displacement leads to a considerable increase in human trafficking.