(c) 2011 by Barton Paul Levenson
There is only enough sunlight to heat the Earth to 254 K mean global annual surface temperature ("Ts"), a fact first noticed by Jean-Baptiste Joseph Fourier in 1824. Water freezes at 273 K. The fact that Earth is not frozen over and lifeless is due to something called "the greenhouse effect."
This works because "greenhouse gases" in the Earth's atmosphere--mainly water vapor and carbon dioxide--mostly pass sunlight, but absorb infrared light from the ground and elsewhere in the atmosphere. Like asphalt in sunlight, they heat up when they absorb light. They then radiate IR of their own. Some of this goes back to the ground. This "atmospheric back-radiation" is what makes Earth's surface tolerably warm.
The more greenhouse gases in the atmosphere, the warmer the surface gets.
Burning fossil fuels puts carbon dioxide and water vapor in the air. The H2O rains out quickly. The CO2 does not. For the last 800,000 years, all through the cycles of ice ages and interglacials, the CO2 level stayed within 180 to 280 parts per million by volume. Since the industrial revolution started, it has climbed to 393 ppmv, a 39% increase. As a result, Earth's Ts has risen 0.8 K since 1900.
Our agriculture and economy are exquisitely sensitive to Ts, since ALL of it developed in the unusually stable climate of the current interglacial. Global warming will lead to sea level rise, more violent weather along coastlines, and--most immediately dangerous--greater drought in continental interiors. If we don't stop global warming, by 2056 (my estimate), we will have a year when no country in the world brings in a good harvest. At that point most of us die and human civilization collapses, possibly for good.
So burning more coal, oil, and gas is a really bad idea.