| Climate configurations09-02-2011 00:23 | |
| micheelsen☆☆☆☆☆ (3) |
There's something that's been nagging me for quite sometime and I'm wondering if there's anyone out there who can help answer a question I have: What do we do with the fact that we could very well have passed a climate tipping point and our computer models of coupled climate systems cannot work at a level of complexity that allows to tell us weather that is the case or not. The first thing is that the climate models are worked out from a point of view of continuous progression. In other words, the models work with the climate as if it has a direction. The models do not allow for discrete rapid and irreversible transitions. Even worse, we keep looking to temperatures as the tell-tale of the state of the climate. Quite obviously, the temperature will always lag behind any climate tipping point. If we already have passed a Dangerous Bifurcation then forget any idea of lowering CO2 emissions to diminish climate change: The climate will have changed configurations and a whole new climate is playing it self out. We'll just have to see what that is but one thing is for sure; it will be majorly different than what we know. The second thing is in terms of computer modeling. It seems that the complexity of the coupled climate models are ever increasing. That has its consequences when it comes to programming these models meaning "building the (earth/climate) systems right". The programs to the best of my knowledge are built modular, which is great. However, you still end up with the system complexity being crunched into the couplings. So system dynamics in one module have to interface with system dynamics of a very different description in another module. As I see it, as long as we don't ask for too much from the computer models, we can work out some predictions. Imagine sitting in a car as one of several passengers and the car accelerates. But you are blindfolded and have ear plugs and experiencing everything at "bulit-time". Now it could be that it's the driver that hit the accelerator. That's fine, the driver can let go of the accelerator and even hit the breaks and the speed will go back to what it was a moment ago. It could also be a 50 Ton truck that just slammed your car from the back. Now, one of the passengers reads the speed increase and predicts the speed in a moment based upon a model (remember its bulit-time). However, the model does not allow for discrete rapid and irreversible transitions. Now which is it? Is the speed increase due to driver or the truck? There is no way that they can foretell the climate tipping points that are so well known and so present in pre-historic data. So what do we do with this? Erik Micheelsen Astrophysicist |
| 14-02-2011 21:09 | |
| alej☆☆☆☆☆ (2) |
Erik I'm unaware of "climate tipping points that are so well known and so present in pre-historic data". At least to the extent of my understanding of the phrase "tipping points". Perhaps you could enlighten me. Alej Retired Environmental Regulator |
| 19-02-2011 17:40 | |
| micheelsen☆☆☆☆☆ (3) |
Well, I don't know about the enlightenment thing ;-) The climate tipping point is simply when the climate makes a sudden and irreversible change. The interesting thing about the climate tipping point is that the linear level feed back effects cancel just before the tipping point. This means that the system slows down before tipping. Think of a spring that has been pulled beyond a critical length and can then no longer go back to its original state of rest (as one consequence). To provide a few examples: Look at the end of the Younger Dryas when the arctic warmed +7 degrees Celsius in 50 years. There is also the desertification of North Africa 5000 years ago or the end of the last glaciation, and the ends of three earlier glaciations. Once you reach the tipping point - that's it! The old climate configuration no longer exists. The thing to look for is not how high or how low the temperature is. It's not the temperature that marks the tipping point. We're looking for the cancellation of feedbacks that are part of a current steady-state. So for instance, the area covered by ice in the arctic has a strong positive feedback. Less area covered by ice leads to less sun (energy) reflected and resulting in temperature increase etc. The question in this case is - what and where is the threshold and have we passed it!?! But take your pick - this is just one tipping point option. There's probably also a threshold for the Greenland ice sheet, the Atlantic thermohaline circulation is without doubt a candidate but there are many others. My worry is that everybody thinks that changing the temperature "back" first of all, is a possibility. Secondly, that temperature is THE parameter of the state of the climate. Politicians are looking in the wrong direction and not by a long shot preparing our societies (infrastructure wise) with the kind of flexibility needed. Keep in mind: NOBODY can predict life on the other side of a climate tipping point. Edited on 19-02-2011 17:43 |
| 21-02-2011 19:49 | |
| alej☆☆☆☆☆ (2) |
My comments are in bold following some of your comments. The interesting thing about the climate tipping point is that the linear level feed back effects cancel just before the tipping point. This means that the system slows down before tipping. Yes it is interesting but I can't picture exactly how its supposed to work. Perhaps you can give me a real world example with the forcings and feedbacks and how the feedbacks cancel just before the mode change. Think of a spring that has been pulled beyond a critical length and can then no longer go back to its original state of rest (as one consequence). To provide a few examples: Look at the end of the Younger Dryas when the arctic warmed +7 degrees Celsius in 50 years. There is also the desertification of North Africa 5000 years ago or the end of the last glaciation, and the ends of three earlier glaciations. I don't see anything in the paleo-record that demonstrates an irreversible tipping point. Sure, a mode of climate might change, on various time scales and intensities, such as those caused by Milankovich oscillations and other natural forcings, but nothing permanent such as the "sprung" spring. Yes it did warm up at the end of the Younger Dryas but it also warmed up several thousand years before that up to the Bolling-Allerod whose temperatures were almost equal to those of today. Then the temperatures began to decrease almost immediately down into the Younger Dryas for a period of about two thousand years. Before the B-A temperatures had been relatively constant for six thousand years (See GISP2 temperature data) even though the ice sheets had been melting at almost a constant rate and continued to do so right up to around 6500 BP. So I agree that a distinct mode of climate had changed around 20KBP but it had nothing to do with temperature and nothing to do with ice. There have been several studies that show that the Arctic had been ice free during the middle Holocene from around 8.5 KBP to 6.0 KBP (at least in the summer) but obviously this condition was not irreversible. Also at the peak of last Interglacial (Eemian) the temperatures were at least 1 degree more than today with a Sea Level at least 5 meters higher than so one could speculate that there was no summer ice remaining in the Arctic. And of course that condition quickly reversed. A recent computer model study of the effects of an ice-free Arctic Ocean in the summer demonstrated that the ice would recover within two years and therefore cannot be a candidate for an irreversible mode. Once you reach the tipping point - that's it! The old climate configuration no longer exists. The thing to look for is not how high or how low the temperature is. It's not the temperature that marks the tipping point. We're looking for the cancellation of feedbacks that are part of a current steady-state. I don't think the climate is ever in a "steady-state". One only has to look at the temperature record of the past to see that climate oscillates. One might make the case that a mode change occurred sometime in the 19th century that ended the Little Ice Age and we're still on the upward swing of that change. How would you distinguish between a feedback and an initial forcing? So for instance, the area covered by ice in the arctic has a strong positive feedback. Less area covered by ice leads to less sun (energy) reflected and resulting in temperature increase etc. A few years ago I read a study that showed that as Arctic Ice is reduced evaporation is increased and therefore more low clouds are produced which overall maintains the same albedo of the region as was there before the ice reduction. The question in this case is - what and where is the threshold and have we passed it!?! I doubt if there is one...an irreversible one that is. But take your pick - this is just one tipping point option. There's probably also a threshold for the Greenland ice sheet, the Atlantic thermohaline circulation is without doubt a candidate but there are many others. Yes I've seen the list. The Greenland Ice Sheet has been smaller in the past as evidenced by a much higher Sea Level during the Eemian and arguably during the mid-Holocene as well but later "recovered". There is no evidence that its demise has been accelerating. It seems that about every other year one reads a study that suggests the THC is either speeding up or slowing down or some new revelation regarding its power source. Currently I hold favor with Carl Wunsch's theory that the THC is driven by wind primarily and secondarily by tides because results of the past few years suggest that such a convectively driven mass flux, as proposed by many, is impossible. My worry is that everybody thinks that changing the temperature "back" first of all, is a possibility. Secondly, that temperature is THE parameter of the state of the climate. I agree that temperature is only an indicator of the state of the climate that is effected by many different things. My favorite indicator is Ocean Heat Content (OHC). By observing the change in this metric one can determine immediately if the climate system is retaining or losing energy as 85% of the climate energy is retained within the oceans of the world. Over the past eight or nine years OHC has remained relatively static. Politicians are looking in the wrong direction and not by a long shot preparing our societies (infrastructure wise) with the kind of flexibility needed. Keep in mind: NOBODY can predict life on the other side of a climate tipping point. There may be big changes either from anthropomorphic or natural sources that might cause a mode change but I really don't see any indicators that the change would be irreversible. |
| 22-02-2011 13:30 | |
| micheelsen☆☆☆☆☆ (3) |
You're missing the point. Let's forget the whole idea of temperature for a moment. It no longer exists. Now look at the climate and everything else that's dynamically going on. The way the dynamics play out has boundary conditions. The steady-state (not any class of equilibrium!!) has to do with how the dynamics play out within those boundary conditions. If those dynamics suddenly begins to work in a very different way and/or the boundary conditions change then we have a new steady state. Once you have this transition, it does not go back to the "old" steady state. The temperature (as one of a number of parameters) helps the system keep to the steady state you're in. The rise or fall of temperature says only something of the climate "flexing", not if it's about to change. However you'll most likely see a strong response once the climate HAS changed (adoptiation). Just a sec - I'll explain it a bit differently as soon as I have a bit more time. |
| 11-05-2011 23:08 | |
| hotair☆☆☆☆☆ (11) |
The only known 'tipping point' is the melting of the permafrost which will allow organic material to decay and turn into methane. Right now, the permafrost prevents this methane from escaping. However, there has been some work in trying to locate and identifying this effect, like so; http://ine.uaf.edu/werc/people/katey-walter-anthony/videos/ Permafrost thaw is a irreversible change. That is to say, you can't put it back. Or in engineering terms, if you want to fix the mess, you'll have to do it by some other means. |