Chapter 4 reports on waves of human migration precipitated by climate change as regions of the Earth can no longer support existing populations and people leave their homes because they have no alternative. Reinforcing national boundaries is not likely to stop climate change refugees as rising seas flood coastal areas uprooting millions of people; as scorching heat waves force sub-Sahara Africans to make the dangerous trip to Europe; and as Central Americans, whose farms have become unsustainable, try to enter the United States through the southern border.