Earth’s temperature naturally warms and cools cyclically throughout time, and warmer periods are typically more conducive to human thriving than colder periods. While human addition of greenhouse gases, particularly carbon dioxide (CO2), to the atmosphere may slightly raise atmospheric temperatures, observational studies indicate that the climate system responds more in ways that suppress than in ways that amplify CO2’s effect on temperature, implying a relatively small and benign rather than large and dangerous warming effect. Rising atmospheric CO2 benefits all life on Earth by improving plant growth and crop yields, making food more abundant and affordable, helping the poor most of all. Abundant, affordable, reliable energy, most of it now and in the foreseeable future provided by burning fossil fuels, which are the primary source of CO2 emissions, is indispensable to lifting and keeping people out of poverty. Mandatory reductions in CO2 emissions, pursued to prevent dangerous global warming, would have little or no discernible impact on global temperatures, but would greatly increase the price of energy and therefore of everything else. Such policies would put more people at greater risk than the warming they are intended to prevent, because they would slow, stop, or even reverse the economic growth that enables people to adapt to all climates. They would also harm the poor more than the wealthy, and would harm them more than the small amount of warming they might prevent.