The Anthropogenic Signal: What the Record Shows and Who Emits

The idea

The exam's climate-change item asks what the record shows and what explains it, and the anchor's last chapter answers in a voice the course keeps attributed. The record first. Climate has never been stable over geologic time: the Cretaceous had no polar ice, the Pleistocene swung between glacial and interglacial, and the present interglacial is about ten thousand years old, with sea level up about one hundred twenty-five meters since the last glacial maximum. On shorter clocks, ENSO reshuffles heat across the Pacific every two to seven years, and over millions of years plate motions, supercontinents and volcanism have warmed and cooled the planet. Against that background the anchor sets the present: while temperatures have risen since the Pleistocene ended, most of the warming has come since nineteen hundred; the nine warmest years on record, at the anchor's writing, all fell after nineteen ninety-eight; two thousand ten to two thousand twenty was the warmest decade, the previous decade next; and sea-level rise, which had settled near zero point seven millimeters a year, began accelerating around eighteen seventy. The explanation second. Dastrup states, citing NOAA and NASA, that the scientific consensus among those who study climate is that the current warming is anthropogenic: more greenhouse gases are trapping heat, and the changes in their concentrations are due to human activity rather than natural processes, historic climates having tracked those gases all along. The emitters third, voiced with the anchor's own caveat. The United States was long the largest emitter, about twenty percent of the total; China's rapid growth carried its emissions past the United States in two thousand eight; and since the United States has about one-fifth of China's population, the average American produces far more than the average Chinese person. The anchor draws no policy conclusion from that comparison, and neither does the course.