If you’re a regular reader of my blog, you will have heard me refer to the climate “Hard stop”. See e.g. “Can variations in lapse rate & cloud cover explain ice-age temperature changes and the inter-glacial “hard stop”?”
To explain this very simply, each time the planet warms from an interglacial, it comes to a stop within a very narrow band of temperatures:
Simplified features of the ice-age cycle
What this means to anyone who understand feedback mechanisms (which is extremely important in analogue electronics), is that there is a non-linearity in the feedback mechanisms at this “level” (temperature), such that there’s a “hard stop” in the signal so that (within normal limits) it cannot warm further.
In other words, whilst the warming from the interglacial seems extremely likely to be the result of the dreaded positive feedbacks so beloved by climate snowflakes, if we didn’t have the “hard stop”, the climate would just keep warming and warming and warming (in the vicious cycle of “non stop warming” so beloved by Climate Snowflakes) and following the very first such warming, the earth would have turned into a fiery ball of flame!
So, the positive feedbacks that are almost certainly present when we come out of an ice-age, either disappear to come to nought at our interglacial temperature, or some strong negative feedback appears OR BOTH!
By chance I came across a recent article on WUWT:
Claim: climate feedback is low due to clouds “impeding global warming”
In response to increased carbon dioxide, climate models predict a nearly uniform warming of the planet that favors reductions in highly reflective low clouds and a positive feedback. In contrast, over the last 30 years, tropical surface temperatures have increased in regions where air ascends and decreased where air descends. “This particular pattern of warming is nearly optimal for enhancing low cloud coverage because it increases low-level atmospheric stability that keeps the lower atmosphere moist and cloudy”, said Stephen Klein, the third co-author.
This research is important, not because I am particularly interested in the “planetary hard stop” – because I’ve known for many years that it existed and that further warming was extremely unlikely.
However, what is important is knowing that it relates to low level clouds, rather than to the sudden disappearance of positive feedbacks. This means I don’t need to find a positive feedback with some “kink” in the feedback curve so that the positive feedback suddenly disappear by some mechanism at the interglacial temperature. Instead the evidence points to the appearance of negative feedbacks in the cloud.
In other words, I can treat the “hard stop” as being distinct from the “warming” and “cooling” phases of the ice-age cycle.
Furture Plans
Trump’s election, further movement towards common sense of climate is far more likely to come from what Trump’s administration do, than anything I can achieve in the science.
So, my current plan is to leave further work on the ice-age cycle until after the development of the La Nina (if any). That’s for two reasons: first, with the huge instrumentation and earth coverage we now have, this strong El Nino – La Nina cycle should provide tons of data (if not necessarily answers). And secondly, if you’re going to write about ice-ages, the best time to do it is when the earth appears to be cooling.
No guarantees but this might be relevant to the “hard stop”:
‘Because a substantial part of the Sun’s heat is used up in evaporation and rain formation, temperatures in the tropics rarely exceed 35°C; a daytime maximum of 32°C is more common. At night the abundant cloud cover restricts heat loss, and minimum temperatures fall no lower than about 22°C. This high level of temperature is maintained with little variation throughout the year.’
http://www.ecoca.ro/meteo/tutorial/climate/older/tropical_climate.html
So the theory might be that once these temperature levels are reached (after a global cooling cycle has ended) the Earth has no option but to get rid of the ‘excess’ heat.
Thanks, that’s really got me thinking. The key thing as you highlight is that it somehow relates to a temperature. When I say “hard stop”, in real terms it’s more likely to be like a “bouncy castle” – so that we see a rapidly changing scale of “something” even if we aren’t at the hard stop temperature. So, between the El Nino peak temperature and the La Nina minimum, we have maximum chance of seeing the “something”.
However, one thing that gets me is how there can be a temperature with a “hard stop” is that that kind thing only tends to happen as a result of phase changes (liquid-solid) and there is nothing close to 35C. So it it were a phase change, it’d either be related to something higher in the atmosphere – like the Stratopause, or something in higher latitudes like the ice-caps.
So, my guess is that it is something complex in the way clouds behave that starts happening at a temperature of about the interglacials in the tropics.
Of course the other one is that it’s something biological!
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Strictly as a non-expert I suggest that when ocean temperatures reach a certain level, evaporation starts to take precedence over further heating of the water, which then puts a brake on the rate of incoming heat by means of greater cloud formation shielding more of the sun’s rays.
Other things would be going on but that would be an important part of the picture. Maybe this is all obvious but still worth putting into words IMO.
The Irony is that that’s as good a suggestion as any of the experts.
The most obvious place to look is the hottest part of the globe on the equator, and the effect ought to be highest in the hottest years (El Nino).
In Africa: ‘As distance from the equator increases, the duration, amount and reliability of precipitation all decrease.’
http://courseware.e-education.psu.edu/courses/earth105new/content/lesson07/03.html
Until the subtropical deserts appear in two strips, well to the north/south of the equator.
http://upload.wikimedia.org/wikipedia/commons/thumb/2/2a/Subtropical.png/640px-Subtropical.png