Observation-based early-warning signals for a collapse of the Gulf Stream

But the key here is that in this discussion 'heat' here is a measure of energy not specifically temperature.

Climate change is the response of the current system when it has more latent energy versus without that latent energy. Those changes are varied, from changing thermoclines in the ocean to the changing ice levels at the poles.

A graduate student at Berkeley observed that the reason we talk about "glacial" cycles is because they leave durable marks in the landscape. But what sort of markers would a "hot cycle" leave? That was the fundamental question he was trying to answer. I believe his advisor had done his PhD on glacial cycles and there was a question of why weren't we in one given the periodicity of the geologic record.

So he was exploring the question of whether or not a "hot cycle" would somehow lead to a "cold cycle". The working hypothesis was was investigating cloud formation. I'm presuming that you've read the IPCC report and a number of papers on the models that are used so that you are familiar with the way in which they handle clouds. There are two kinds, clouds in the ionosphere and clouds in the troposphere. Their effect on surface temperature are exactly opposite.

From Chen Zhou in correspondence about his model work on climate, "It is worth noting that different cloud types have different climate radiative effects to the earth: high thin cirrus clouds warm the earth, while the marine boundary low clouds cool the earth significantly. To set a 90% cloud cover, you have to determine whether cirrus clouds or low clouds should be added: if you add cirrus clouds, the earth will warm significantly; if you add low clouds, the earth will cool."

And of course there were a number of papers that discussed "nuclear winter" which was a disruption of weather patterns by the particulates in the air from a general nuclear exchange. And papers that studied the weather effects of volcanic eruptions like Pinatubo in 1991.

So what this grad student was looking at was this; When you increase the mean temperature of the atmosphere, the ability for the air to hold moisture increases. When you increase the mean temperature of the oceans, evaporation rates increase. So more energy in the air means more moisture. There was another paper that discussed 'wet bulb' temperatures and how those would become more common as more moisture was being held in the air as well.

So what does that moisture do? Well it eventually condenses out of the air, first into clouds and then into precipitation. Because the difference in temperature between the surface and the ionosphere is greater, when rapid temperature changes occur (as they do when water condenses out of the air) you get huge upwellings. Basically much stronger storms, stronger tornadoes, and stronger hurricanes Etc. So what if there is enough heat in the air so that it keeps the moisture from condensing into drops and stays as clouds? Well if they appear at low altitude the surface gets really cold, if they appear at high altitude the surface gets hotter. Which we get isn't in the models because nobody knows yet how that will play out.

What that meant is that it is worth considering the effect of tropospheric clouds. If things got really cold, it could blanket the northern latitudes with 100% of snow cover that did not melt all year round. The 'year without a summer' which occurred when Krakatoa erupted is believed (but not proven) to have been this sort of effect. Snow cover increases the planets albedo and that increases the radiation of heat into space. If the northern lattitudes were covered in cloud and snow 365 days of the year you create a new model where water is evaporating in an over heated equatorial region flowing north and south and then contributing to the continuing cloud cover and precipitation. And THAT could lead to glaciation.

Is that going to happen? I don't think anyone knows. Can you tweak the current climate models and make it happen? Sure, just add a lot of low continuous cloud cover being resupplied with moisture from the equator.

But it is equally important to understand that this is climate change which is just as much human induced as baking in a dry desert. It isn't denying the science, it is looking at the science and the models and asking "Okay, given what we know what changes in the model cause what changes in the habitability of the planet?" And perhaps more importantly, how can we identify, as early as possible, how the model needs to incorporate what we're seeing in order to continue to help us understand what the future may hold.

We have evidence of wide scale changes made by humans long before written records existed. We also now have better records, so it’s easier to point to this one here done by this person, instead of only picking up what is visible in the fossil record (which is by it’s nature spotty and incomplete). But that doesn’t mean it didn’t happen.

When I see these flat assertions stated as foregone conclusions IRL by friends, I am prompted to ask, “What mitigations did you already implement against this conclusion?”

Revealed preferences demonstrate that overwhelmingly their assertions are far stronger than their mitigations. This is worrisome, as it shows even “true believers” are not taking commensurate action. The dislocation when it arrives, if as large a magnitude as claimed by IPCC, will be large even for that cohort.