What is the story with global warming? Is it occurring or not?

Dear Tom,

What is the story with global warming? Is it occurring or not?

— StephaniamMcWillmotte

Dear Stephania,

The overwhelming consensus of experts in a wide range of fields in the earth sciences, and biological and environmental fields as well, is that global warming is a reality — a reality supported by direct observation and direct measurement. Here are some obvious examples: averaged across the Earth’s surface, glaciers are in retreat; icecaps are thinning; the sea level is rising (which means land ice is melting); ocean and air temperatures are increasing; spring arrives earlier and autumn lasts longer; and growing seasons are lengthening. The ranges of cold-loving flora and fauna are retreating northward, and the ranges of warm-loving species are expanding. The major debate: the role of people in that warming.