This is the point. There is not "near-unanimous consensus of climatologists." Certainly there are areas where that is true, but not in general. One of the articles references a WSJ article. Note the bullet points in the middle.
http://online.wsj.com/articles/climate-science-is-not-settled-1411143565
Credentials: Dr. Koonin was undersecretary for science in the Energy Department during President Barack Obama's first term.
You can get near unanimous consensus that there is climate change. You can get nearly as much consensus that there is a human element. After that the consensus starts to fray. There would also be near unanimous agreement that natural factors play a role. There is disagreement how to divide the pie between natural and man dependent causes.
When you get to the position of, say, Al Gore, how much scientific support is there? Would the majority agree in substance or would the majority believe he has exceeded reasonable conclusions? If the latter, by how much?
J
I don't disagree with some of the assessments made here, such as (brackets mine):
These [cloud feedbacks, changes in ocean and atmospheric circulation, and the fact that climate sensitivity is only known to be in the range 1.5-4.5 C/doubling of CO2] are fundamental challenges to our understanding of human impacts on the climate, and they should not be dismissed with the mantra that "climate science is settled."
That's why climatology is a fascinating field right now - there are a tremendous number of uncertainties related to the extreme complexity of the ocean-atmosphere-land system.
Clouds and aerosols, for instance, are still very poorly understood. If you look at the IPCC's summary of anthropogenic impacts, GHGs by themselves are comparatively well understood: the error bars are not insignificant but fairly small relative to the error bars around the impacts from clouds and aerosols. Each cloud droplet condenses around (and then dissolves, if the particle is soluble) an aerosol particle such as dust, pollen, sea salt, or smoke emitted from automobiles, factories, natural and artificial forest fires, and so on. We don't know very well to what extent this is offsetting our global warming from GHGs (or enhancing it, in the case of sooty 'black carbon' particles).
Whether a cloud reflects more heat than it traps heat or vice versa depends on particular characteristics of the cloud. Typically lower-altitude clouds and thicker clouds reflect more than they trap, and vice versa for thin and higher-level clouds (e.g. cirrus) but it's not very tidy in practice. Additionally, some aerosols, such as sulfate-based particles (mostly ammonium sulfate) reflect light on their own and are contributing to some sort of global dimming effect. Its magnitude is hard to measure, however, despite all our satellites, aircraft, and surface stations. Sulfate particles precipitate out in a few weeks, on average; contrast CO2 where a large proportion of the molecules will exist in the atmosphere for centuries to millennia, and most of the rest (a majority in sum) end up in the ocean which acidifies in response.
I've started a graduate program in atmospheric science this fall (with some preliminary stuff this summer) at Illinois, and the group I'm working with is working intensively on small-scale, particle-resolved models of aerosols and cloud formation. Ultimately we want to bridge up to the large-scale models to come up with a model of large-scale , but it takes an insane amount of computational power to bridge from models that can simulate the evolution of individual particles to models that work on a global-scale.
In summary, there's a tremendous amount of uncertainty as to what exactly will happen. My own best guess is that humans hit some combination of improving technological innovation and increasing fossil fuel cost that ultimately limit CO2 emissions to a ballpark peak CO2 concentration of ~550-600 ppm.
But there are a lot of unknown-probability, high-impact events such as rapid and non-linear melting of large portions of the Greenland and West Antarctic ice caps and unexpectedly high methane releases from Arctic permafrost and continental shelf methane clathrates, that we just can't quantify at the moment. Nobody knows where exactly the thresholds are before these become significant, and the IPCC report largely omits them because they're so poorly understood. The paleoclimate record doesn't give us much for the last several million years with CO2>400 ppm (present level) and average global temperature >2 C above today (brief spike at the Eemian interglacial, for instance).
Among actual scientists (not just Gore-style activist types) it's these unquantifiable risks that cause a large proportion of the long-term fear over climate change. Even without them, we'd have difficult-to-predict changes in precipitation and other sea level rise over the next century.
Gore's documentary is as good as it gets from politician types, but that's not saying much: obviously there are a bunch of polar bears clinging to small pieces of ice (which they do for fun) and so on. But the science isn't out of line with his main conclusions.
I still dislike that he took a scientific issue and helped make it a political one, and that he proceeded to continue flying in his private jet to climate conferences and so on. None of this means Al Gore is wrong in the main points of his documentary, it just means he's a rich hypocrite. But as Gore the politician should know, that's a huge loss in the PR scene.
