We'll learn skills of quick and approximate (but surprisingly accurate) estimation of various useful and useless numbers. This can be very helpful when reading news and thinking about the environment and technologies: How large should be solar panels to charge your (self-driving) electric car? How much waste do we produce? How “carbon cleaner” is a horse than a car? If it better to stop eating meat, stop taking flights, or turn off your A/C to reduce your carbon footprint? How carbon-neutral are renewable energy technologies?