 One of our strongest pieces of evidence that the Earth is heating up is the balance of energy for our planet. The temperature of any object is the result of the amount of energy going into it and the amount leaving it. When the incoming energy and the outgoing energy are balanced, the object reaches a constant temperature. If we turn up the crank and add more energy, the object will heat up and also emit more heat to its surroundings until it reaches a new, warmer balance. It's very much like adding a blanket to block upcoming heat so that an object will warm up. The same process is true for the whole Earth suspended in space. And physics tells us that CO2 acts as a blanket for the Earth. Satellites now measure both the incoming and outgoing energy for the whole planet so we can measure the effect of our atmospheric blanket. The fact that more energy is coming in than going out must be rather vexing to people who promote the myth that there isn't enough CO2 to cause global warming, often stated as, CO2 is just a trace gas. This myth is jumping to conclusions. Just because there's a small amount of something doesn't mean it can't have a big impact. There are plenty of real-world examples that you're perfectly familiar with of small amounts having large impacts. For example, it doesn't take very much arsenic and drinking water to be hazardous to your health. And in this case, measurements show that trace CO2 is changing the energy balance of Earth. Satellites measure the sunlight reaching the edge of the Earth very accurately because they are outside of the influence of the atmosphere. About a dozen satellites have provided this data since about 1978. These satellites show that average energy to the Earth is about 340 watts per meter squared. So what happens when that energy reaches the Earth's outer atmosphere? This picture shows the energy budget for the surface. Energy is divided into shortwave radiation, which is the visible and UV light, shown in yellow, and the longwave radiation, which we think of as heat, shown in red. The sun's rays are high-energy shortwave radiation, which is visible light in all colors of the rainbow, along with the UV light that we can't see, but which causes sunburn. About 30% 100 watts per meter squared of the sun's energy is reflected directly back to space from the atmosphere clouds and the Earth's surface. All this reflected light gives Earth its lovely glow when seen from space. The red arrow shows the outgoing heat from the Earth, which is also measured by satellites. That energy is like the warmth you feel radiating from a hot stove. Four NASA series instruments are currently collecting the detailed energy pictures of the Earth. We can now see how much of the sun's energy bounces back to space and the amount of energy emitted by the Earth as heat. The data from these satellites, combined with measurements of the ocean heat, gives the net imbalance of energy for the Earth. This graph shows the five-year averages since the start of those measurements in 1985. The current energy budget for the Earth shows an extra 0.6 watts per meter squared coming in, then going out. So surprise, we're getting hotter. The claim that CO2 is only a trace gas is an example of a red herring. The fact may be true, but it is irrelevant to the discussion of its real effects on the planet. You're certainly familiar with lots of other substances where trace amounts have a big effect. A blood alcohol level of 800 parts per million means you're drunk. Ibuprofen works at 3 parts per million. The arsenic limit in drinking water is 0.01 parts per million. Even though each extra molecule of CO2 contributes only a tiny amount of warming, its effects add up over the whole Earth and grow each year.