Arctic sea ice still appears to be trending downwards.
This chart is a little different over last year's, as TPTB have re-evaluated some past years' extent of sea ice, and found the previous estimates wanting. Almost every value has declined somewhat. The updated values have been added into the analyses below. I have no comment on the updates or the methodology, which is available here.
The question at issue is whether the change we are observing is a secular trend towards zero (in-line with global warming arguments) or part of a larger cycle, in which sea ice extent may eventually return to the heights of the late 1970s.
Many natural systems (and some unnatural ones) are characterized by multistability, whereby there are more than one equilibrium within a system for a given set of boundary conditions. Multistable systems show long periods of relative stability about an area of phase space, punctuated by brief, rapid shifts to alternative long-term behaviours.
The phase space portrait projected above into two dimensions has been interpreted as representing a system that has "switched" from one metastable mode of operation to another. The existence of different modes of operation is tied to the presence of both negative and positive feedbacks within the system. The interpretation is based on empirical data, not on models.
Unfortunately we don't have enough data to be confident of the interpretation. If we had a longer record, we might be able to infer multistability--but ice extent records prior to the advent of continuous satellite monitoring are difficult to compare with more recent records. Unless some proxy record is discovered, we will just have to wait.
This chart is a little different over last year's, as TPTB have re-evaluated some past years' extent of sea ice, and found the previous estimates wanting. Almost every value has declined somewhat. The updated values have been added into the analyses below. I have no comment on the updates or the methodology, which is available here.
The question at issue is whether the change we are observing is a secular trend towards zero (in-line with global warming arguments) or part of a larger cycle, in which sea ice extent may eventually return to the heights of the late 1970s.
Many natural systems (and some unnatural ones) are characterized by multistability, whereby there are more than one equilibrium within a system for a given set of boundary conditions. Multistable systems show long periods of relative stability about an area of phase space, punctuated by brief, rapid shifts to alternative long-term behaviours.
The phase space portrait projected above into two dimensions has been interpreted as representing a system that has "switched" from one metastable mode of operation to another. The existence of different modes of operation is tied to the presence of both negative and positive feedbacks within the system. The interpretation is based on empirical data, not on models.
Unfortunately we don't have enough data to be confident of the interpretation. If we had a longer record, we might be able to infer multistability--but ice extent records prior to the advent of continuous satellite monitoring are difficult to compare with more recent records. Unless some proxy record is discovered, we will just have to wait.
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