[MUSIC] The third way of measuring temperatures, is by satellite. And at first blush, this would seem like it is the ideal way of making measurements, because it is out in space and nobody is touching it and it's covering the whole world. It's actually not the best way to get a time-series measurement of temperature, because orbits of the satellite can decay and over the time span that we're talking about there were several satellites that flew. And so they all had to be calibrated against each other in order to come up with a time series. So the satellite is really good at making a map, an instantaneous snap shot of surface temperatures. But for a time series, it's a bit more work. And for a long time, the satellites didn't show the same warming as the land and the sea surface temperature records were showing and so this seemed like it could be a major problem. So the way the satellites work is they measure microwave radiation that comes from molecular oxygen. And just like greenhouse, black body radiation, these wavelengths of light are more intense when the oxygen is warmer. The difficulty is that the satellite is sensitive not just to the temperature right at the ground, but it's sensitive to temperatures throughout a range of altitudes in the atmosphere. And so if there's cooling higher up that can pull the temperature the satellites sees down and so you don't get the full signal from the ground, which is what we're interested in. So after the latest round of corrections, you can see in this plot that the satellite temperatures although very spiky are also consistent with the land and sea surface temperature records and that they showed this warming in the last few decades. That will turn out to be a smoking gun for the human impact on Earths climate. [MUSIC]