7 ms·

Causal feedbacks in climate change

64 points by gtt 10y ago

cryptoz 10y ago
Here is some additional information about this paper: "Direct evidence for a positive feedback in climate change: Global warming itself will likely accelerate warming": http://phys.org/news/2015-03-evidence-positive-feedback-climate.html http://phys.org/news/2015-03-evidence-positive-feedback-clim...
- xyzzy4 10y ago
  Then why would an ice age ever happen?
  - eximius 10y ago
    Presumably global cooling accelerates cooling. I think the point is that deviation from some 'normal' global temperature catalyzes or inhibits greenhouse gas proliferation. (At least in the positive direction, I haven't read it so I don't know if their proposal supports this.)
  - arcadius 10y ago
    A very interesting topic is how the details of Earth's orbit at any one time affect the change in global temperature. You can read more about it here: https://en.wikipedia.org/wiki/Milankovitch_cycles https://en.wikipedia.org/wiki/Milankovitch_cycles
    - cossatot 10y ago
      Milankovitch cycles are thought to be a major factor, by everyone from climate scientists to oil companies (who have refined the history of these cycles exquisitely to help identify petroleum in particular rock units deposited during rising or falling sea levels). Another, much longer term factor (tens to hundreds of millions of years) has to do with the positions of the continents on earth, which affects how well ice can be stored. If there is considerable landmass near the poles and it's cold, then ice sheets can form, which increase the amount of reflected solar radiation (albedo) and decrease the amount of heat stored in the oceans (which have less volume due to ice sheet storage, and because sea level falls, the warm shallow seas that hold a lot of heat are much smaller). This can help cooling feedbacks. When the continents are arranged such that there is little polar landmass, these situations are reversed which leads to heating.
    - JshWright 10y ago
      PBS Space Time did a great video on this topic. https://www.youtube.com/watch?v=ztninkgZ0ws https://www.youtube.com/watch?v=ztninkgZ0ws
  - ChuckMcM 10y ago
    And that is a really good question. The interesting thing about this paper is it points out that prior to a glacial period there is a rise in temperature. The onset of ice ages appears to be much more rapid than the onset of warming. This was one of the ideas used in the "Day After Tomorrow" movie, although soundly criticized for presenting a very short time frame change into an ice age, that an overly warm earth can trigger a transition into an ice age is not unheard of. Lots of time questions about time frame and mechanism. I lost the paper I read that was suggesting the mechanism was water vapor (a pretty important green house gas) which as the planet warmed the air carried more vapor which hits critical mass, turns into a nearly permanent covering layer of clouds in the upper atmosphere, which then causes water at lower altitudes to precipitate out as snow. Sort of a self induced nuclear winter type scenario. The key conclusion of the paper is that the system responds in a non-linear way. That makes predicting its behavior with models like the one IPCC uses very challenging.
  - milesvp 10y ago
    The best models that predict surface temperatures that I've seen have to do with the deep sea ocean conveyors (https://en.wikipedia.org/wiki/Thermohaline_circulation https://en.wikipedia.org/wiki/Thermohaline_circulation). There's something like 3 major currents with periods measured in years, and their phase greatly influences global temperatures. One of the current theories that I find very convincing is that ice ages happen when one or more of these currents gets disrupted. If the heat from the equator stopped making it to the poles, you could start seeing massive glaciation start to happen. http://science.nasa.gov/science-news/science-at-nasa/2004/05mar_arctic/ http://science.nasa.gov/science-news/science-at-nasa/2004/05...
  - snowwrestler 10y ago
    Feedbacks still need a forcing. Other comments below name a couple of forcings: orbital variations and continental distribution. These are forcings because nothing in the Earth's climate causes them--they are essentially external inputs that change the fundamental limit of energy available the climate: insolation. If the amount of solar energy available to the climate changes, then the temperature equilibrium of the climate must change. As things change, the changes can themselves cause further changes, producing nonlinear effects. That's what this paper is addressing: the idea that warming itself can cause additional warming. But it all starts with a forcing. If the forcing is removed or reversed, then the equilbrium must shift back. Regardless of how strong a feedback might be, it can't overcome a forcing. (That's the essential distinction between the two.) So: regardless of how much the temperature is run up by various feedbacks when the Earth gets closer to the sun, once the Earth moves away from the sun again, the temperature must go down again. And another ice age begins.
eximius 10y ago
I would be interested to know if they are claiming that 1) it will be harder to undo the changes we caused or 2) greenhouse gas changes occurred as a result of temperature change or some other combination of things.
- neltnerb 10y ago
  It claimed by time series analysis for different variables that temperature rises release greenhouses slowly while greenhouse gas concentration rises increase temperature nearly instantaneously (geologically speaking). i.e. positive feedback loop, but with drastically different time scales.
DennisP 10y ago
As far as I can tell from reading the abstract, this process was described in Hansen's book Storms of My Grandchildren. Sometimes, he wrote, we do get temperature increases in the geological record right before we see the CO2 go up. Historically, that's happened on a regular basis due to orbital variations. The fact that CO2 goes up afterwards is not reassuring, it's a positive feedback that drives the temperature even further. That's why climate change is so worrisome; it's not just the direct heating effect of our emissions we have to worry about, but the additional heating from the extra CO2 released by the planet.
- danieltillett 10y ago
  Yes our ignorance about how the climate will respond to all the GHG release is a cause for worry. The only area I can agree with the deniers is our climate models are not very good and the error bars quite high - this is not a cause for compliancy, but great concern.
  - adrianN 10y ago
    Exactly. There more we move away from "0° warming" the more likely we are to encounter some nonlinearity that our current models completely miss.
nonbel 10y ago
As far as I know it remains controversial whether causality is a topic for philosophy or science (ie do any of our most successful physical laws require the concept of causality, I think not). It irks me to see that term mixed into scientific discussions, because I am sure it will just be assumed that everyone knows what they mean by "casual" and accepts it as a useful scientific concept.
- nerdponx 10y ago
  It sounds to me like you're arguing that we should never try to prove that anything causes anything because we don't have a good definition of causality. I hope that's not what you're saying, because it's absurd.
  - nonbel 10y ago
    >"we should never try to prove that anything causes anything" I don't know about never, but the "c-word" gets thrown around way too freely in my opinion. But yea, I am saying that the most successful science has had little to nothing to do with causality. You see the focus on causality is more common in the less successful endeavors such as the social sciences, perhaps it is time to consider that the causality concept is a red herring (at least when it comes to science). To be sure, I am far from the first to entertain such thoughts: "Causality in physics has had bad press in philosophy at least since Russell’s famous 1913 remark: “The law of causality, I believe, like much that passes muster among philosophers, is a relic of a bygone age, surviving, like the monarchy, only because it is erroneously supposed to do no harm” (Russell 1913, p. 1). Recently Norton (2003 and 2006) has launched what would seem to be the definite burial of causality in physics. Norton argues that causation is merely a useful folk concept, and that it fails to hold for some simple systems even in the supposed paradigm case of a causal physical theory – namely Newtonian mechanics." http://philsci-archive.pitt.edu/4690/1/CausalFundam.pdf http://philsci-archive.pitt.edu/4690/1/CausalFundam.pdf
    - tlarkworthy 10y ago
      Causality is central to hard science. Its why we have concepts like dependent and independent observations. We split observable dimensions into these groups so we can change the independent variable and find out their causal effect on the dependent variables. The whole reason we have "experiments" is so an experimenter can deliberately change the system in a focused way, outside of its normal dynamics, to reveal the causal structure of the system under observation. You can't do this by passively observing the system. This is why we have experiments. This is core to the scientific method.
TrainedMonkey 10y ago
Here is PDF link to the paper: http://deepeco.ucsd.edu/~george/Publications/15_causal_feedbacks_climate.pdf http://deepeco.ucsd.edu/~george/Publications/15_causal_feedb... edit: article -> paper
- danieltillett 10y ago
  Here is the link to reference 8 which is the key method used in this analysis. http://www.uvm.edu/~cdanfort/csc-reading-group/sugihara-causality-science-2012.pdf http://www.uvm.edu/~cdanfort/csc-reading-group/sugihara-caus...
mirimir 10y ago
tl;dr > In conclusion, our analysis provides direct confirmation that internal Earth system mechanisms rather than orbital forcing have controlled climate dynamics over the Pleistocene cycles. Moreover, they demonstrate the existence and importance of a feedback effect of temperature variability on GHGs in driving the dynamics (Fig. 1b). This confirms the existence of a positive feedback operating in climate change whereby warming itself may amplify a rise in GHG concentrations. As CCM infers causality directly from the time series, the consistency of our results with elaborate mechanistic analysis represents remarkable empirical confirmation and, moreover, provides a clock for the response times involved. We suggest that this new and powerful approach may also help to assess causality behind the numerous other time series we have for the Earth system.
- semi-extrinsic 10y ago
  So, we all know that correlation does not imply causation. Yet it sounds like this paper does some fancy dynamical systems theory stuff to prove causation based on correlation. Can anyone shed some light on how this works?
  - mirimir 10y ago
    Well, it's explained in Methods, but over my head. I gather that instead of just looking at correlation between X and Y, they first map X to a ‘shadow attractor manifold’. Then they fit a relationship between this transformed X and Y. They cite Sugihara, G. et al. Detecting causality in complex ecosystems. Science 338, 496–500 (2012) for this.

64 points by gtt 10y ago

Here is some additional information about this paper: "Direct evidence for a positive feedback in climate change: Global warming itself will likely accelerate warming": http://phys.org/news/2015-03-evidence-positive-feedback-climate.html http://phys.org/news/2015-03-evidence-positive-feedback-clim...

xyzzy4 10y ago
Then why would an ice age ever happen?
- eximius 10y ago
  Presumably global cooling accelerates cooling. I think the point is that deviation from some 'normal' global temperature catalyzes or inhibits greenhouse gas proliferation. (At least in the positive direction, I haven't read it so I don't know if their proposal supports this.)
- arcadius 10y ago
  A very interesting topic is how the details of Earth's orbit at any one time affect the change in global temperature. You can read more about it here: https://en.wikipedia.org/wiki/Milankovitch_cycles https://en.wikipedia.org/wiki/Milankovitch_cycles
  - cossatot 10y ago
    Milankovitch cycles are thought to be a major factor, by everyone from climate scientists to oil companies (who have refined the history of these cycles exquisitely to help identify petroleum in particular rock units deposited during rising or falling sea levels). Another, much longer term factor (tens to hundreds of millions of years) has to do with the positions of the continents on earth, which affects how well ice can be stored. If there is considerable landmass near the poles and it's cold, then ice sheets can form, which increase the amount of reflected solar radiation (albedo) and decrease the amount of heat stored in the oceans (which have less volume due to ice sheet storage, and because sea level falls, the warm shallow seas that hold a lot of heat are much smaller). This can help cooling feedbacks. When the continents are arranged such that there is little polar landmass, these situations are reversed which leads to heating.
  - JshWright 10y ago
    PBS Space Time did a great video on this topic. https://www.youtube.com/watch?v=ztninkgZ0ws https://www.youtube.com/watch?v=ztninkgZ0ws
- ChuckMcM 10y ago
  And that is a really good question. The interesting thing about this paper is it points out that prior to a glacial period there is a rise in temperature. The onset of ice ages appears to be much more rapid than the onset of warming. This was one of the ideas used in the "Day After Tomorrow" movie, although soundly criticized for presenting a very short time frame change into an ice age, that an overly warm earth can trigger a transition into an ice age is not unheard of. Lots of time questions about time frame and mechanism. I lost the paper I read that was suggesting the mechanism was water vapor (a pretty important green house gas) which as the planet warmed the air carried more vapor which hits critical mass, turns into a nearly permanent covering layer of clouds in the upper atmosphere, which then causes water at lower altitudes to precipitate out as snow. Sort of a self induced nuclear winter type scenario. The key conclusion of the paper is that the system responds in a non-linear way. That makes predicting its behavior with models like the one IPCC uses very challenging.
- milesvp 10y ago
  The best models that predict surface temperatures that I've seen have to do with the deep sea ocean conveyors (https://en.wikipedia.org/wiki/Thermohaline_circulation https://en.wikipedia.org/wiki/Thermohaline_circulation). There's something like 3 major currents with periods measured in years, and their phase greatly influences global temperatures. One of the current theories that I find very convincing is that ice ages happen when one or more of these currents gets disrupted. If the heat from the equator stopped making it to the poles, you could start seeing massive glaciation start to happen. http://science.nasa.gov/science-news/science-at-nasa/2004/05mar_arctic/ http://science.nasa.gov/science-news/science-at-nasa/2004/05...
- snowwrestler 10y ago
  Feedbacks still need a forcing. Other comments below name a couple of forcings: orbital variations and continental distribution. These are forcings because nothing in the Earth's climate causes them--they are essentially external inputs that change the fundamental limit of energy available the climate: insolation. If the amount of solar energy available to the climate changes, then the temperature equilibrium of the climate must change. As things change, the changes can themselves cause further changes, producing nonlinear effects. That's what this paper is addressing: the idea that warming itself can cause additional warming. But it all starts with a forcing. If the forcing is removed or reversed, then the equilbrium must shift back. Regardless of how strong a feedback might be, it can't overcome a forcing. (That's the essential distinction between the two.) So: regardless of how much the temperature is run up by various feedbacks when the Earth gets closer to the sun, once the Earth moves away from the sun again, the temperature must go down again. And another ice age begins.

eximius 10y ago

I would be interested to know if they are claiming that 1) it will be harder to undo the changes we caused or 2) greenhouse gas changes occurred as a result of temperature change or some other combination of things.

neltnerb 10y ago
It claimed by time series analysis for different variables that temperature rises release greenhouses slowly while greenhouse gas concentration rises increase temperature nearly instantaneously (geologically speaking). i.e. positive feedback loop, but with drastically different time scales.

DennisP 10y ago

As far as I can tell from reading the abstract, this process was described in Hansen's book Storms of My Grandchildren. Sometimes, he wrote, we do get temperature increases in the geological record right before we see the CO2 go up. Historically, that's happened on a regular basis due to orbital variations. The fact that CO2 goes up afterwards is not reassuring, it's a positive feedback that drives the temperature even further. That's why climate change is so worrisome; it's not just the direct heating effect of our emissions we have to worry about, but the additional heating from the extra CO2 released by the planet.

danieltillett 10y ago
Yes our ignorance about how the climate will respond to all the GHG release is a cause for worry. The only area I can agree with the deniers is our climate models are not very good and the error bars quite high - this is not a cause for compliancy, but great concern.
- adrianN 10y ago
  Exactly. There more we move away from "0° warming" the more likely we are to encounter some nonlinearity that our current models completely miss.

nonbel 10y ago

As far as I know it remains controversial whether causality is a topic for philosophy or science (ie do any of our most successful physical laws require the concept of causality, I think not). It irks me to see that term mixed into scientific discussions, because I am sure it will just be assumed that everyone knows what they mean by "casual" and accepts it as a useful scientific concept.

nerdponx 10y ago
It sounds to me like you're arguing that we should never try to prove that anything causes anything because we don't have a good definition of causality. I hope that's not what you're saying, because it's absurd.
- nonbel 10y ago
  >"we should never try to prove that anything causes anything" I don't know about never, but the "c-word" gets thrown around way too freely in my opinion. But yea, I am saying that the most successful science has had little to nothing to do with causality. You see the focus on causality is more common in the less successful endeavors such as the social sciences, perhaps it is time to consider that the causality concept is a red herring (at least when it comes to science). To be sure, I am far from the first to entertain such thoughts: "Causality in physics has had bad press in philosophy at least since Russell’s famous 1913 remark: “The law of causality, I believe, like much that passes muster among philosophers, is a relic of a bygone age, surviving, like the monarchy, only because it is erroneously supposed to do no harm” (Russell 1913, p. 1). Recently Norton (2003 and 2006) has launched what would seem to be the definite burial of causality in physics. Norton argues that causation is merely a useful folk concept, and that it fails to hold for some simple systems even in the supposed paradigm case of a causal physical theory – namely Newtonian mechanics." http://philsci-archive.pitt.edu/4690/1/CausalFundam.pdf http://philsci-archive.pitt.edu/4690/1/CausalFundam.pdf
  - tlarkworthy 10y ago
    Causality is central to hard science. Its why we have concepts like dependent and independent observations. We split observable dimensions into these groups so we can change the independent variable and find out their causal effect on the dependent variables. The whole reason we have "experiments" is so an experimenter can deliberately change the system in a focused way, outside of its normal dynamics, to reveal the causal structure of the system under observation. You can't do this by passively observing the system. This is why we have experiments. This is core to the scientific method.

TrainedMonkey 10y ago

Here is PDF link to the paper: http://deepeco.ucsd.edu/~george/Publications/15_causal_feedbacks_climate.pdf http://deepeco.ucsd.edu/~george/Publications/15_causal_feedb... edit: article -> paper

danieltillett 10y ago
Here is the link to reference 8 which is the key method used in this analysis. http://www.uvm.edu/~cdanfort/csc-reading-group/sugihara-causality-science-2012.pdf http://www.uvm.edu/~cdanfort/csc-reading-group/sugihara-caus...

mirimir 10y ago

tl;dr > In conclusion, our analysis provides direct confirmation that internal Earth system mechanisms rather than orbital forcing have controlled climate dynamics over the Pleistocene cycles. Moreover, they demonstrate the existence and importance of a feedback effect of temperature variability on GHGs in driving the dynamics (Fig. 1b). This confirms the existence of a positive feedback operating in climate change whereby warming itself may amplify a rise in GHG concentrations. As CCM infers causality directly from the time series, the consistency of our results with elaborate mechanistic analysis represents remarkable empirical confirmation and, moreover, provides a clock for the response times involved. We suggest that this new and powerful approach may also help to assess causality behind the numerous other time series we have for the Earth system.

semi-extrinsic 10y ago
So, we all know that correlation does not imply causation. Yet it sounds like this paper does some fancy dynamical systems theory stuff to prove causation based on correlation. Can anyone shed some light on how this works?
- mirimir 10y ago
  Well, it's explained in Methods, but over my head. I gather that instead of just looking at correlation between X and Y, they first map X to a ‘shadow attractor manifold’. Then they fit a relationship between this transformed X and Y. They cite Sugihara, G. et al. Detecting causality in complex ecosystems. Science 338, 496–500 (2012) for this.