Quote from: AbruptSLR on October 22, 2015, 05:02:12 PM While this thread is focused on pointing at recent measurements indicating that the responses of key feedbacks (most prominently now due to wildfires) have now (2015) reached bifurcation points (not tipping points) where their rates of responses have abruptly accelerated (possibly triggered by our current Super El Nino event). While looking at satellite measurements is reassuring because their uncertainties are relatively low, what is most important is that Earth System Models, ESMs, not only capture such non-linear accelerations, but also the synergistic interactions between the various feedbacks (given that: "All models are wrong, but some models are useful), as this synergistic interaction will give us all a better idea where climate change is going in the next few decades. In this regards, in addition to they El Nino triggering of droughts and associated tropical rainforest wildfires, I list some other feedback synergies that it will be important for state-of-the-art ESMs like ACME to accurately model, if policy makers are going to have reasonable model forecasts of what is coming (assuming that 2015 is a turning point):



A) Permafrost degradation is not only accelerated by wildfires (currently not modeled, & especially not the burning of the peat & forest litter) but also by the polarward migration of burrowing animals and forest killing invasive insects.

B) Not only do droughts (including that induced by our Super El Nino) promote tropical forest wildfires (with high CO2 emissions), but subsequent flooding leads to submergence of the dead vegetation that leads to accelerated CH4 emission in subsequent years. Also, tropical rainforests generate atmospheric conditions that promote rainfall, so the current high rates of deforestation & tropical wildfires will result in less future rainfall, and more droughts (even without El Ninos). Also, I note that run-off from tropical rainforests contains high levels of CO2, so we can expect the next round of floodwater to carry unusually are amounts of CO2 into the oceans, thus accelerating ocean acidification.

C) Both paleo-evidence and Hansen et al. (2015) point both to the synergy between the bipolar seesaw and both Arctic Amplification and also to planetary energy imbalance, via changes with both polar sea ice and the MOC.

D) I note that both increasing ocean heat content and ocean acidification contribute to a trend indicating a reduction in the size of plankton which synergistically results in less CO2 absorption, less dimethyl sulfide (DMS) emissions, and less CO2 sequestration into deep ocean waters.

F) Accelerating global deforestation (due to droughts, insect damage, wildfires, etc.) result in reduced VOC emissions, which means less negative feedback.

G) The increase in tropical atmospheric deep convection works synergistically to promote stronger El Nino events, more positive cloud feedback and poleward telecommunication of atmospheric energy thus promoting Polar Amplification.



Such synergies between non-linear feedback mechanisms could lead to future tipping points that will be extremely difficult to reverse such as:

A) A possible atmospheric flip to an equable climate (possibly by the end of this century).

B) Abrupt collapse of the marine portions of ice sheet (possibly starting in a couple of decades time).

C) A possible MOC collapse (if the marine portions of the ice sheets collapse).

D) A possible abrupt transition to a Canfield ocean (with high sulfide producing bacteria).



Out of all the feedbacks, that last one is the most important because an abrupt transition to a carnfield ocean seals the deal on a great extinction event, thus the chances of this feedback occurring are terrifying, especially with the (not sure how abrupt) abruptness of the feedback.



It was not my intention in my post to focus on the tipping points, but rather on the synergies of the numerous positive feedbacks (that seem to be currently accelerating) that could lead to such tipping points (all of which are discussed in other threads). But speaking about importance, I note that the three top priorities (to avoid unexpected/unpleasant surprises) for the ACME program are to more accurately model: (a) ice mass loss from ice sheets; (b) mechanisms that lead to more positive cloud feedbacks (such as deep equatorial atmospheric convection); and (c) mechanisms associated with acceleration of the water cycle.While there is a fair amount of discussion in this forum on both ice sheet mass loss and positive cloud feedback mechanism; I feel that there is insufficient discussion about mechanisms associated with acceleration of the water cycle. Therefore, I re-post the following information about the linked reference, which provides evidence that the equation most commonly used in current climate models to predict evaporation flux is most likely in error. As water vapor is most abundant GHG in the atmosphere, it is critical that current climate change models be up dated to reflex these new findings (which indicate that evaporation flux can be significantly greater than currently assumed, and can be significantly affected by the speed of the wind above bodies of water [and I note that wind velocities increase with continued climate change]):Robert Hołyst, Marek Litniewski and Daniel Jakubczyk (2015), "A molecular dynamics test of the Hertz–Knudsen equation for evaporating liquids", Soft Matter, DOI: 10.1039/C5SM01508A http://pubs.rsc.org/en/Content/ArticleLanding/2015/SM/c5sm01508a# !divAbstractAbstract: "The precise determination of evaporation flux from liquid surfaces gives control over evaporation-driven self-assembly in soft matter systems. The Hertz–Knudsen (HK) equation is commonly used to predict evaporation flux. This equation states that the flux is proportional to the difference between the pressure in the system and the equilibrium pressure for liquid/vapor coexistence. We applied molecular dynamics (MD) simulations of one component Lennard-Jones (LJ) fluid to test the HK equation for a wide range of thermodynamic parameters covering more than one order of magnitude in the values of flux. The flux determined in the simulations was 3.6 times larger than that computed from the HK equation. However, the flux was constant over time while the pressures in the HK equation exhibited strong fluctuations during simulations. This observation suggests that the HK equation may not appropriately grasp the physical mechanism of evaporation. We discuss this issue in the context of momentum flux during evaporation and mechanical equilibrium in this process. Most probably the process of evaporation is driven by a tiny difference between the liquid pressure and the gas pressure. This difference is equal to the momentum flux i.e. momentum carried by the molecules leaving the surface of the liquid during evaporation. The average velocity in the evaporation flux is very small (two to three orders of magnitude smaller than the typical velocity of LJ atoms). Therefore the distribution of velocities of LJ atoms does not deviate from the Maxwell–Boltzmann distribution, even in the interfacial region."See also:Extract: "The hitherto model of evaporation was based on the principle of conservation of mass: the mass of molecules released from the surface of a liquid had to respectively increase the mass of the gas in its surroundings. Physicists from the IPC PAS noticed, however, that since the particles released from the surface have a certain velocity, in order to describe this phenomenon what should be applied is the principle of conservation of momentum.The discovery of the IPC PAS researchers is of the utmost importance for, among others, the understanding of the real mechanisms responsible for global warming. Contrary to common belief, the most abundant greenhouse gas in the atmosphere of our planet is not carbon dioxide but water vapour. At the same time, it is known that the speed of flow of air masses over the oceans can significantly exceed one hundred kilometres per hour and therefore they will certainly affect the rate of evaporation. The hitherto evaluation of the rate of evaporation of the oceans must therefore be subject to error, which will certainly affect the accuracy of the predictions of contemporary models of the Earth's climate."