The idea that Earth’s climate has changed, or is changing, is relatively new.

Back in the 1800s, scientists began to suspect that coal smog clogging the air over London and Paris might be more than just pollution.

Because airborne carbon lets solar radiation pass, but reflects back to Earth many wavelengths of terrestrial radiation, there could be a buildup of heat in the lower atmosphere. So we started measuring, and we’ve found that atmospheric CO2 has been increasing, and at an increasing rate. And it matches pretty well with the graph of increasing Earth temperature.

Then, in June of 1988, climatologist James Hanson of NASA testified before Congress that he was 99% sure that the warming observed in the 1980s was caused in part by greenhouse gasses. Sen. Al Gore, later the Vice President, was on that sub-committee, and was eventually inspired to make the film “An Inconvenient Truth.” Climate Change became a mainstream topic. Research accelerated. But it also became political.

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To dig through the politics and propaganda on this topic is not easy. But let’s try.

Point one: it’s the lower atmosphere that’s warming. The stratosphere is not warming up at all. This is exactly what you would expect of a process that traps heat in the lower atmosphere.

Another factor: Increasing the temperature of the lower atmosphere also increases evaporation on a global scale, causing higher humidity. This helps explain why more of the measured warming has occurred at night. That 2 degree rise here in the valley? Average daytime highs have risen only about 1 degree while nightly lows have risen more than three.

And then there’s the climate models. At the time of James Hanson’s Congressional testimony, climate models weren’t very sophisticated. But modeling has improved immensely. A verification process called hindcasting has contemporary models accurately recreating today’s climate from the past. But the models show the Earth having cooled … unless the increasing CO2 is included. Looking ahead, that the 2 degree rise in the last hundred years is forecast to become at least 4 to 5 degrees, and maybe twice that, by 2100.

To read more, you can find parts one and three below: