How big of a difference could a few degrees make?
As these words are being written, the temperature outside is 7.2ºC (45ºF) — a cool, late-winter day in New Jersey. Would it make a huge difference if it were 11ºC (52ºF)? Probably not — people might just unzip their jackets a little. Similarly, plenty of people wouldn’t feel a dramatic difference between 30ºC (87ºF) and 34ºC (94ºF) in midsummer — for a day or two, anyway.
Yet an average increase of 3.9ºC (7ºF) year-round and worldwide — more in some places, less in others — by the end of this century could cause significant impacts. Climate scientists think such an increase in temperature is most likely to come about given current trends in greenhouse gas emissions. They have determined that a temperature change of that magnitude would be enough to threaten coastal cities with rising seas; reduce freshwater availability in the western US, India, and many other places; turn some rich farmland arid; and force animals, insects — and the diseases they carry — and hundreds of millions of people to search for new places to live.
Even with just the .56ºC (1ºF) change that’s already occurred, we’re seeing a range of impacts around the globe. Many birds now head south for the winter several weeks later than they did a few decades ago, and return earlier — just one of many examples of how ecosystems are being disrupted. The oceans only have to rise a few more feet above their average 2-mile depth before low-lying coastal areas in North Carolina, Florida, and the Gulf Coast will be threatened. Heat waves in places like Phoenix, Arizona, are bad enough already; crank up the temperature by 3.9ºC (7ºF), and they will be close to unendurable. Wildfires in the American West are on the rise. There is a long list of impacts when you look at the effect of changing climate conditions, with multiple examples from every state and region.