In working on Pembina's recent Facing
the Climate Challenge fact
sheet on climate science, I had a chance to wade into the literature on sea
level rise (no pun intended). It's a rapidly-evolving area of research as
scientists' understanding of how ice sheets melt and move ("ice sheet dynamics")
is growing every day.
Here's why that matters. Scientists thought they had already
understood the relationships between warming and sea level rise fairly well.
Climate models generally attribute most of the sea level rise to thermal
expansion (water getting "bigger" as it warms), with the remainder coming from
glaciers melting in the linear fashion they were understood to do.
But these models have been unable to account for the fact that in
recent decades, observed sea level rise has been about 50 per cent greater
than predicted.
The difference lies in the murky world of ice sheet dynamics. We are
only just beginning to understand how the processes of melting work in real
life, but it is already clear that the Greenland, West Antarctic and even East
Antarctic ice sheets are losing mass much more quickly than anticipated.
Because this is very new science, the glaciers' increasing contributions to sea
level rise were not well enough understood to be included in the Intergovernmental Panel on Climate
Change (IPCC)'s most recent
report , which was published in 2007. The IPCC's projections were thus
relatively modest (if you can call a half-metre of sea level rise modest). By attributing
the majority of sea level rise to thermal expansion, those projections excluded
a large amount of the melting that we see today. New methods of estimating the
likely contribution from all sources (including ice sheets) now project
roughly triple the amount of sea level rise that the IPCC estimated.
