It's worth noting that the 9/11 U.S. insolation study showed a human-created mitigating factor, not a causal factor. That is, it showed that high-altitude contr

It's worth noting that the 9/11 U.S. insolation study showed a human-created mitigating factor, not a causal factor. That is, it showed that high-altitude contrails create clouds high enough to raise the average albedo and reflect solar energy that otherwise would reach the surface. This is, to some extent, "hiding" a portion of the true warming one would expect from the current mix of the atmosphere and solar activity. That doesn't offer evidence either way for a hypothesis that there are natural processes yet undescribed that could surprise us with their contribution to warming. Discovering one new thing about a complex phenomenon doesn't make it more likely that another new thing is out there to be discovered. If anything, it makes it less likely, on the theory that there are a finite number of factors contributing to a result of given significance in a deterministic system--in this case, global average temperature trend. And anyway, what we're really worried about is long-term warming, and this paper is not about that. It's about factors that contribute to temperature variance on shorter time scales during the known long-term warming. From the article: > However, the relative influences of natural drivers of climate change – such as volcanic eruptions, ocean cycles, and the sun – on warmer and cooler phases superimposed on the long-term warming trend is still an area of active research. There are two levels to the question of global warming. One is the overall, global question--are we making the surface of the Earth warmer by burning fossil fuels? This is a relatively simple question to answer, so simple that it was first proposed over a century ago, basically when thermodynamics was being invented. Very little contemporary research goes toward answering this question; it has basically been answered. The other level is: can we predict the consequences of this warming at time scales and resolutions relevant to human society? This is an incredibly complex endeavor and where the bulk of contemporary time and resources are spent (including this paper).