One of the things that has always struck me as being problematic with CAGW is part of its reported origins. There have been individuals who suggested hydrocarbons could cause a problem with warming the planet very early in the 1900s and some in the late 1800s. Warming was not necessarily viewed as a bad outcome. Some people thought the warming could be beneficial.
So where did the catastrophic warming idea come from? NASA had a scientist, James Hansen, studying the planet Venus. He came up with a theory, borrowed in part from Carl Sagan, that Venus had fallen victim to a runaway greenhouse effect. This caused “the oceans to boil” (a fate Hansen has also publicly predicted for earth if we did not stop burning fossil fuels and increasing the CO2 in the atmosphere. Hansen modified his research on the runaway greenhouse effect and applied it to Earth. His research lead him to conclude the same thing could happen here.)
Unfortunately, there appears to be NO evidence that Venus ever had oceans, let alone looked like Earth. Everything we know about Venus we learned from looking through a telescope and from probes sent to penetrate the atmosphere and land on the surface. Venus is so inhospitable the probes burn up shortly after landing. The surface has been mapped from above. The composition of the atmosphere was determined. Beyond this, we have no clue as to whether or not Venus ever had an atmosphere that was Earth-like or if there were any type of lifeforms present. It’s all conjecture.
Mars was also looked as a possible way to learn more about our planet. Again, there is the belief that Mars may have been like Earth at one time. The surface of Mars does allow for exploration with a rover. Dust storms have been observed that lower the temperature rapidly, leading to speculation that similar forces are at work on Earth. Of course, Mars has very little atmosphere which makes such speculation questionable. It did seem to provide much excitement among climate scientists who claim this validates some of the climate change theory. Again, it is unclear how the behaviour of dust on Mars in any way explains the behaviour of dust on Earth. While physical laws are the same on all planets, that is where the similarity ends. Atmospheres are very different, as are surface temperatures, and so forth.
IF Venus was like Earth and fell victim to runaway greenhouse warming and Venus is governed by the same physical laws as Earth, Earth could fall victim to runaway greenhouse warming. Looking at Venus may help us avoid this fate if we study the forces contributing to this effect on Venus. Does this mean we could be subjected to the same fate as Venus? NO—there is no way to know unless there is definitive proof that Venus was once like Earth. Which there is not. Thus, the conclusion runaway greenhouse warming could occur on Earth does NOT follow. First, we must prove the phenomena actually occurred on Venus or Mars and then that we understand the mechanism by which this occurred. Lastly, we must prove the mechanisms that caused the runaway greenhouse warming on other planets can be modified to work for predicting such an outcome on Earth. Currently, we have no evidence to support any of these suppositions.
If we remove the concept of runaway greenhouse warming due to lack of evidence that such a thing has actually happened on other planets, there does still exist CO2 and it’s role in warming Earth. How much of the predictions concerning CAGW depend on Venus and Mars being role models? It’s difficult to say, but without an example of CAGW occurring anywhere in the past, predicting it will happen in the future is pretty much a toss of the dice.
Is the earth warming? Yes. Does that mean we are headed for a Venetian or Martian runaway greenhouse warming and destruction of Earth as we know it? It’s impossible to say. The evidence is just not there.