The basic proposition behind the science of climate change is so firmly rooted in the laws of physics that no reasonable person can dispute it. All other things being equal, adding carbon dioxide (CO₂) to the atmosphere—by, for example, burning millions of tons of oil, coal and natural gas—will make it warm up. That, as the Nobel Prize–winning chemist Svante Arrhenius first explained in 1896, is because CO₂ is relatively transparent to visible light from the sun, which heats the planet during the day. But it is relatively opaque to infrared, which the earth tries to reradiate back into space at night. If the planet were a featureless, monochromatic billiard ball without mountains, oceans, vegetation and polar ice caps, a steadily rising concentration of CO₂ would mean a steadily warming earth. Period.

But the earth is not a billiard ball. It is an extraordinarily complex, messy geophysical system with dozens of variables, most of which change in response to one another. Oceans absorb vast amounts of heat, slowing the warm-up of the atmosphere, yet they also absorb excess CO₂. Vegetation soaks up CO₂ as well but eventually re­releases the gas as plants rot or burn—or, in a much longer-term scenario—drift to the bottom of the ocean to form sedimentary rock such as limestone. Warmer temperatures drive more evaporation from the oceans; the water vapor itself is a heat-trapping gas, whereas the clouds it forms block some of the sun’s warming rays. Volcanoes belch CO₂, but they also spew particulates that diffuse the sun’s rays. And that’s just a partial list.

If your institution has site license access, enter here.