Saturday 24 August 2013

Seeking Understanding vs Spouting Empty Rhetoric

There will be talk of this year representing a reversal of fortune for the sea ice, and an imminent recovery, or that conditions now are the same as in decades before the turn of this century. I don't take this seriously. And I use it as a measure of the complete lack of grasp those expressing such views have on the situation in the Arctic.

Hat tip to Neven, link, for directing me to WTFWT and consequently getting my hackles up. The result is probably better than just the series of images I was about to post, which can be found by scrolling down to the underlined heading.

The best guide to what is really going on in the Arctic remains PIOMAS, the Pan Arctic Ice/Ocean Modelling and Assimilating System, link. It is our best proxy of long term changes in volume and volume is the driving force behind the changes we are seeing in sea ice. However as I have previously blogged; Cryosat 2 supports the picture painted by PIOMAS, link.

And the picture painted is one of a massive long term decline in volume.

This decline however has been of what might seem a rather peculiar type: The decline has come from the older thicker ice, which is shown by comparison of submarine and satellite data, as discussed in an early post, link, and shown in this graphic from a paper by Nghiem (which I can't put my hands on right now, Doh!).

In line with that observational (Satellite and Submarine) data, PIOMAS shows that the decline of volume has come from thicker (multi year ice) over the longer term.

The above graphic shows the volume contributions from ice over and under 2m thick in April, plotted with the decline in Cryosphere Today Area (CT Area) at September minimum, calculated from gridded data (see link at end). The decline in thicker, older (multi-year) ice accounts for all of the volume loss, with thinner first year ice actually increasing to replace this. The agreement between the plot of volume over 2m thick and CT Area is not a coincidence it is due to increasing 'open water formation efficiency'. As the ice thins it becomes easier for a given thinning during the melt season to open up stretches of open water.

I was going to just post the images that follow, but perhaps it is best that I was distracted before posting reading Neven's post (and WTFWT). Which led to the digression and has provided some context. What follows are January images from QuikScat and PIOMAS (the latter my own rendering from PIOMAS gridded data), source data linked to at the end of the post. January is used because the ice under 2m thick is likely to be mainly first year ice in the process of thickening over the winter, the ice over 2m thick is very likely to be multi-year ice that has been thickened over many years. This is because 2m is the typical maximum thickness ice can grow from open water in September to the end of the freeze season in April. The PIOMAS gridded data is the monthly average, I have chosen the 15 January for the QuikScat images to be representative of average monthly conditions.

The PIOMAS plots are coloured, blue is over 2m thick, red is under 2m thick. In the greyscale QuikScat images the satellite sensor is able to discern the first year ice and presents this as darker grey, while the multi-year ice appears as white. The only change to the QuikScat images is a rotation (45degrees) to match the PIOMAS plot orientation. So the following represent a comparison of observation and model.

PIOMAS and QuikScat comparison for January of the stated years.











This series of images shows what a good job PIOMAS is doing in terms of the spatial positioning of the thicker older ice. But they also show the decline of older thicker multi-year ice in the first part of this century, and this is shown not just by a model, but by satellite data from a system originally designed to monitor winds. For a more recent comparison see this post.

Any discussion claiming that the ice is recovering that does not address the clear decline in multi-year ice should be treated with great scepticism. This is a problem for those in denial of the reality of human caused climate change, for them the long term decline of multi-year ice is a rather inconvenient truth. So they resort to insinuations and showing pictures of submarines in small ponds of water in 1987.

I'm in no way being so arrogant as to say that I fully understand, but I'm driven by a desire for understanding, so questions such as whether the transition to a seasonally sea ice free state will be fast (this decade) or slow (in the 2030's or 40s) are a source of fascination for me, not a problem. But the fact remains that, whether fast or slow, we are on a path to that transition, and no amount of empty rhetoric from those who've lost the scientific argument will change that.

PIOMAS plots compiled from PIOMAS gridded data available here.
QuikScat images available from here.

1 comment:

Chris Reynolds said...

I give a further explanation of why I consider the use of PIOMAS thickness above and below 2m as a reasonable proxy for FYI/MYI here.