As I write these words, much of North America is sweltering under near-tropical heat and humidity. Parts of the Middle East have set all-time high temperatures for the Old World, coming within a few degrees of Death Valley’s global record. The melting of the Greenland ice cap has tripled in recent years, and reports from the arctic coast of Siberia describe vast swathes of tundra bubbling with methane as the permafrost underneath them melts in 80°F weather. Far to the south, seawater pours through the streets of Miami Beach whenever a high tide coincides with an onshore wind; the slowing of the Gulf Stream, as the ocean’s deep water circulation slows to a crawl, is causing seawater to pile up off the Atlantic coast of the US, amplifying the effect of sea level rise.