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> And why is it that modifying such a small part of the atmosphere (0.04%) can cause such a huge problem? The modification is invisible to you, but not invisible to the photons which are supposed to leave the atmosphere and cool off the earth a bit. It it were visible to you, it would look like this: link Regarding the photons of thermal frequencies leaving the Earth atmosphere, or remaining there, the simplest you can imagine is a blanket: if it's cold outside the blanket keeps the heat not leaving the area under the blanket, keeping you warm. Here, the CO2 is actually a "one-way" blanket, it doesn't block the incoming radiation : The heat coming from Sun has other frequencies as it comes than the photons blocked that would cool off the Earth. The key is: CO2 is an ink-black "blanket" for exactly a part of the radiation that cools off the Earth. It's not too big, but big enough to make in sum that 0.8 C degree change since 1880. Or to produce even more warming in the coming years as we burn always more and we haven't managed to change that. A little more precise: "Energy arrives from the sun in the form of visible light and ultraviolet radiation . The Earth then emits some of this energy as infrared radiation . Greenhouse gases in the atmosphere 'capture' some of this heat, then re-emit it in all directions - including back to the Earth's surface." (There's of course infrared radiation coming from the Sun, but the one making problem is the radiation from the Earth) Scienti