The defining feature of a technological civilization is the capacity to intensively “harvest” energy. But the basic physics of energy, heat and work known as thermodynamics tell us that waste, or what we physicists call entropy, must be generated and dumped back into the environment in the process. Human civilization currently harvests around 100 billion megawatt hours of energy each year and dumps 36 billion tons of carbon dioxide into the planetary system, which is why the atmosphere is holding more heat and the oceans are acidifying.

All forms of intensive energy-harvesting will have feedbacks, even if some are more powerful than others. A study by scientists at the Max Planck Institute in Jena, Germany, found that extracting energy from wind power on a huge scale can cause its own global climate consequences. When it comes to building world-girdling civilizations, there are no planetary free lunches.

By studying these nearby planets, we’ve discovered general rules for both climate and climate change (PDF). These rules, based in physics and chemistry, must apply to any species, anywhere, taking up energy-harvesting and civilization-building in a big way. For example, any species climbing up the technological ladder by harvesting energy through combustion must alter the chemical makeup of its atmosphere to some degree. Combustion always produces chemical byproducts, and those byproducts can’t just disappear