Wednesday, 1 February 2017

Do you want ice with that?

A popular pastime amongst those of us who have an interest in what's going on with the climate is to try to guess how much Arctic sea ice there will be each season when the annual minimum is reached.

For anyone reading who thinks this might interest them, there is an almost endless ongoing source of information, graphs and analysis at the excellent Arctic Sea Ice Blog/ Forum/Graphs.


There is also a science program which collects various predictions, from the technical (model-based) to the amateur (heuristic), called SIPN (used to be ARCUS).


Part of the fun of this is to try to work out the different factors which may or may not affect future sea ice level down the line. On a long time scale, this is easy enough, if you simply reference the climate data since 1979 and look at the history of decline in Summer sea ice levels. It is quite possible to do a 'rough fit' with historic data and come up with a prediction which is not far off the mark, though this is going to be more by chance than reason.


One of the most popular sources of data and information is the NSIDC dedicated sea ice and cryosphere pages. These focus on the measured data rather than prediction, but contain a wealth of useful graphics and links.


On the recent page you will notice a reference to a recent piece of research conducted by some of the members of the team, Serreze M. C. et. al., JGR (2016).


This paper demonstrates a connection which has an effect on the annual minimum:


"...They found that 68 percent of the variance in the date that ice retreats from the continental shelf break in the Chukchi Sea in spring can be explained by fluctuations in the April through June Bering Strait oceanic heat inflow..."


So, one way in which we can now make a more reliable prediction in relation to one part of the Arctic is in place.


Then, I noticed (not reported widely elsewhere yet) that others of the team have been involved in a different piece of research at the opposite side: Fram Strait sea ice export variability and September Arctic sea ice extent over the last 80 Years. (Smedrud et.al.). Here we find the useful:


"...Increased ice export during winter will generally result in new ice growth and contributes to thinning inside the Arctic Basin. Increased ice export during summer or spring will, in contrast, contribute directly to open water further north and a reduced summer sea ice extent through the ice–albedo feedback..."


and: "...We find a general moderate influence between export anomalies and the following September sea ice extent, explaining 18 % of the variance between 1935 and 2014, but with higher values since 2004...".



These two useful recent pieces of work add to our understanding of two of the mechanisms which contribute to Arctic Summer minima. They don't give the whole picture; the number and range of the variables are such that we don't have a full picture of all of the teleconnections or causes.


What we can do, though, is look at these two parameters and add some inferences to our other observations. If Fram export has been relatively high recently, then the September minimum is likely to be lower than the long term average. If Bering Sea heat input is higher than usual during the Spring, then the September
minimum is likely to be lower. 


If both cases occur simultaneously, it is reasonable to infer that there is a high likelihood of a reduced minimum, if the other other known variables (such as the Arctic oscillation - AO) do not contradict this, and if the historic patterns of weather and overall seasonal temperature anomalies are also in alignment.


This is an example of how ongoing scientific research and information collecting adds to our understanding of the ways in which the climate can vary, and the trends which show how the climate is changing relative to the past.