Forecast of the Century
Before we venture out into deep time, let’s look in on the forecast for the next one hundred years. Our interest is not totally selfish; a lot of the action will actually take place on timescales of centuries.
The fossil fuel era could potentially last until about the year 2300, when coal begins to run out. After the CO2 is released to the atmosphere, it takes a few hundred years, perhaps a thousand, for the CO2 to dissolve in the ocean, as much as is going to. The atmospheric CO2 concentration will spike upward and relax back downward, on a timescale of centuries. When this centuries-long climate storm subsides, it will leave behind a new, warmer climate state that will persist for thousands of years. That’s the basic outlook.
If CO2 emissions continue and climate responds as expected, then the surface of the Earth will be about 3–5°C (5–9°F) warmer by the year 2100. This doesn’t sound all that impressive, really, on the face of it. The daily cycle of temperature is larger than this, and so is the seasonal cycle. A change in the long–term average, however, is a very different thing than a cold morning or a warm day. The climate in my home city of Chicago is expected to come to resemble that of present–day Texas or Arkansas by 2100. That sounds noticeable to me.