What is a carbon footprint? Why does it matter? Short answer, it's how much you personally contribute to climate change. Since this is a widely misunderstood concept, here's an overview: energy arrives from the sun as visible light, plus infra-red/ultra-violet. This passes through the atmosphere, reaching the planet. Most bounces back into space as infra-red: this is why our planet isn't 800F like Venus. However, so-called greenhouse gases (GHG) in the atmosphere absorb that infra-red. Thus, instead of escaping, extra energy is retained in the atmosphere as heat. Some of this is good. The average daytime temperature on Earth is about 59F. Without GHG, we'd be more like Mars, whose average -55F is too cold for life.
The most famous GHG is carbon dioxide (CO2). Before 1750, our atmosphere contained about 280 parts per million (ppm). That tiny amount (plus some methane) took us from below zero to 59F - it's potent stuff. Since then, burning fossil fuels (coal, oil, natural gas) raised CO2 levels to 405ppm, a 50% increase and still rising. Resulting rising temperatures may make much of Earth too hot to farm, plus sea levels will rise 3+ feet this century alone (and up to 270ft in future). It doesn't have to be Venus-level bad to cause starvation, start wars, drown cities and wreck the economy.
Job-creating, economically viable solutions like solar/wind, electric cars/transit, and carbon sequestering (taking CO2 from the atmosphere with soils, trees, and tech) are set to displace fossils - but we're against the clock here. So until we can make the problem better, we should make it worse as slowly as possible. Hence, carbon footprint. How does yours affect the earth? Let's find out.