Tag Archives: Canada

On 25th April 2019, the Arctic sea ice extent was 1.2 million km² below the 1981-2010 mean.

Sea ice in the Arctic currently ~1.2 million km² below the 1981-2010 mean. 25 April 2019.

If we compare the sea ice extent today, with the mean sea ice extent for the period 1989-93, the red colours show where there is currently relatively low sea ice.

The Arctic sea ice extent on 25 April 2019 (LHS), with the mean extent 25 April 1989-93. On the RHS blues = more sea ice than 89-93 mean, reds less sea ice.

As we expect the sea ice edge around virtually the whole Arctic has moved poleward compared with 1989-93, and there has been a lot written about the incredibly low sea ice extent in the Bering Sea over the last year year. For example this from twitter:

And of course this year follows on from the historic lows highlighted in spring 2018 by NASA.

Zooming in on Hudson Bay shows the current conditions there.

The Hudson Bay sea ice extent on 25 April 2019 (LHS), with the mean extent 25 April 1989-93. On the RHS blues = more sea ice than 89-93 mean, reds less sea ice.

On the west of Hudson Bay the sea ice is clearly 10-20% lower now than 1989-93 mean.  With a quick comparison of two MODIS satellite images just 1 day apart, you can see that the sea ice is mobile.

MODIS images from 21 and 22 April 2019 showing the heavily fractured sea ice in Hudson Bay.

What I think is happening is that the spring break up is coming earlier. If you look at the science literature you can see that the cycle of sea ice in Hudson Bay. This is from de la Guardia et al. (2017). I have added the shaded yellow box to show the time period we are looking at. When spring comes earlier that drop off as the sea ice decreases in concentration moves to the left, so the result is the sea ice is low compared with the 1989-93 mean.

Sea ice concentration (SIC) climatology in Hudson Bay from 1979 to 2000 (mean 1 SD). Estimated with Canadian Ice Service monthly SIC data (CIS; solid line with open triangles), passive microwave satellite SIC data from Comiso (1999) (PMW-BS; dashed line with open circles) and Cavalieri et al. (1996) (PMW-NT; solid line with open squares), and model run using realistic atmospheric forcing fields (NCEP; dashed line with dots), and using atmospheric output from the CGCM 3.1 (T64) – 20C3M run (solid line with open circles). Figure 2 From de la Guardia et al. (2017)

The early break up is on trend with the literature as well. For example, all of the blue dots in the grid below (From Kowal et a; 2017) show a trend for earlier sea ice breakup over the time period 1971-2011. In that paper they also show a trend to later freeze up as well, meaning the sea ice season is getting shorter in Hudson Bay.

Fig. 9 Significance of points according to the Mann-Kendall trend analysis for current analysis using ice-free dates. *p<0.10 (yellow); **p<0.05 (red); ***p<0.01 (blue); p>0.10 (green; NS). Note in the counts of significant points, NS (green) and * (yellow) are considered not to be statistically significant. Thus, 31 points (red, blue) have statistically significant trends. From
Kowal et al (2017).

Actually Kowal et al (2017) was pretty clear about the data:

[there is] evidence of an accelerated change in sea ice metrics
temporal trends.

A recent paper by (Mudryk et al 2018) displays the Hudson Bay trend over time: It is 10.8% decrease in sea ice concentration per decade.

More than 10%!

Time series of summer total sea ice area for the (d) Hudson Bay regions from 1968 to 2016. From Mudryk et al (2018) Figure 7.

Hudson Bay is a well known for polar bears, and those bears rely on sea ice for significant components of their prey. de la Guardia et al. (2017) stated:

the links between sea ice decline and the future fate of polar bears have long been recognized.

Those authors looked at three possible CO₂ emissions pathways and they concluded that for:

two scenarios, predicted advances in breakup also threaten to decrease polar bear reproductive rate after 2060. If, however, we significantly reduce our GHG emissions and follow the low emission path of B1, polar bears may persist in WH [West Hudson Bay].

We expect to lose the summer sea ice in the high Arctic in the next couple of decades, we could expect an impact on the West Hudson Bay polar bears not long after.

References

Castro de la Guardia, L., Derocher, A. E., Myers, P. G., Terwisscha van Scheltinga, A. D., & Lunn, N. J. (2013). Future sea ice conditions in Western Hudson Bay and consequences for polar bears in the 21st century. Global Change Biology, 19, 2675–2687. WEBLINK

Kowal, S., Gough, W. A., & Butler, K. (2017). Temporal evolution of Hudson Bay Sea Ice (1971–2011). Theoretical and Applied Climatology, 127(3), 753–760. WEBLINK

Mudryk, L. R., Derksen, C., Howell, S., Laliberté, F., Thackeray, C., Sospedra-Alfonso, R., et al. (2018). Canadian snow and sea ice: historical trends and projections. The Cryosphere, 12(4), 1157–1176. WEBLINK