As a physicist, I often feel compelled to do my best to engage in discussions with people who deny or minimise the effect of CO2 as a drive for the current climate change. Most arguments that are brought up by these "sceptics" are rather easy to refute, but there are two that I tend to struggle with. I am hoping you can provide me with some additional ammunition.
1) There are physicists and mathematicians who argue against trusting climate models, because the models are highly non-linear. Obviously, looking at averaged quantities like a global mean surface temperatures averages out fluctuations, such that you could argue that these quantities are more robust, but still your models are ultimately unstable. I personally do not find this argument convincing, since it is kind of an asymptotic claim. In other words, models will become unstable at some point in time, but this does not imply that you cannot make predictions on transient time scales. I believe that for quantities such as global mean surface temperature you generally estimate stability by using various models, and running them with many slightly different initial conditions. Scientifically literate sceptics usually counter this argument by saying that it implicitly assumes that your fluctuations are not too "wild", which is not completely evident for non-linear models. All of the above would essentially be applicable to any non-linear dynamical system, so my question is whether there are some climatological arguments to estimate the time scales over which climate models should be stable (or stable enough to make useful predictions)?
2) Some people also argue that the warming we see now could just be a natural fluctuation (a bit like a rogue wave at the see). The counter argument is that, when you look at the historic record, the presently observed warming trend (and in particular the time scale over which it takes place) is unprecedented in the last ~100000 years (?). My question is two-fold: Do we really have enough temporal resolution in historical data to see a sharp rise and fall in temperatures that only lasts ~100 years? If so, how far in time can we go back and still have enough resolution to see such an event?
I am sorry for the long questions, in particular since the answers are probably available in the scientific literature. Still, I hope you could help me understand these aspects a bit better (even if it were by just directing me to some references). Thank you!
awesomattia2 karma
Dear Dr. Hayhoe,
Thank you for doing an AMA!
As a physicist, I often feel compelled to do my best to engage in discussions with people who deny or minimise the effect of CO2 as a drive for the current climate change. Most arguments that are brought up by these "sceptics" are rather easy to refute, but there are two that I tend to struggle with. I am hoping you can provide me with some additional ammunition.
1) There are physicists and mathematicians who argue against trusting climate models, because the models are highly non-linear. Obviously, looking at averaged quantities like a global mean surface temperatures averages out fluctuations, such that you could argue that these quantities are more robust, but still your models are ultimately unstable. I personally do not find this argument convincing, since it is kind of an asymptotic claim. In other words, models will become unstable at some point in time, but this does not imply that you cannot make predictions on transient time scales. I believe that for quantities such as global mean surface temperature you generally estimate stability by using various models, and running them with many slightly different initial conditions. Scientifically literate sceptics usually counter this argument by saying that it implicitly assumes that your fluctuations are not too "wild", which is not completely evident for non-linear models. All of the above would essentially be applicable to any non-linear dynamical system, so my question is whether there are some climatological arguments to estimate the time scales over which climate models should be stable (or stable enough to make useful predictions)?
2) Some people also argue that the warming we see now could just be a natural fluctuation (a bit like a rogue wave at the see). The counter argument is that, when you look at the historic record, the presently observed warming trend (and in particular the time scale over which it takes place) is unprecedented in the last ~100000 years (?). My question is two-fold: Do we really have enough temporal resolution in historical data to see a sharp rise and fall in temperatures that only lasts ~100 years? If so, how far in time can we go back and still have enough resolution to see such an event?
I am sorry for the long questions, in particular since the answers are probably available in the scientific literature. Still, I hope you could help me understand these aspects a bit better (even if it were by just directing me to some references). Thank you!
View HistoryShare Link