Email interview: Dr. Christopher Shuman, Research Scientist, June 8-13, 2017

Dr. Christopher Shuman (bio)

Question 1

In a recent Forbes article, you stated that the Larsen C rift differs from the rifts of Larsen A and B, because this one has been growing during a period of cooling relative to previous decades. It is my understanding that the annual mean temperature of the Antarctic Peninsula has decreased at a statistically significant rate since the late 1990s, but that this decrease is not reflective of the continent as a whole, and furthermore, that “decadal temperature changes in this region are not primarily associated with the drivers of global temperature change but, rather, reflect the extreme natural internal variability of the regional atmospheric circulation” [Turner et al, 2016]. Is this understanding correct, and is there anything you would add to clarify/expand?

Response 1

Even though the temperature data is not perfect, the northern Antarctic Peninsula is fairly well known in terms of its temperature history going back to the mid-1940s, especially compared to other parts of the polar regions. The signal is fairly clear relative to the noise as a result, showing both long-term warming (multi-decadal), some 'no change', and a recent slight cooling (~decadal) depending on where you pick the inflection.

However, although Turner et al and Oliva et al (2017) believe that the cooling initiated in the late 1990s, it is spatially variable (from Oliva paper abstract):

Our results also indicate that the cooling initiated in 1998/1999 has been most significant in the N and NE of the AP and the South Shetland Islands (> 0.5 °C between the two last decades), modest in the Orkney Islands, and absent in the SW of the AP.[1]

...

So, the point I'm really trying to make is that even recent 'decades' of little change or slight cooling have not prevented the Larsen C from responding to much longer-acting forces including the generally warming atmosphere and especially ocean temperatures.

After the LGM, as ice mass water was returned to the global ocean, a combination of sea level rise (especially early on) and both atmospheric and oceanic warming (especially in the past ~century) has caused losses or major retreat of multiple glacier/shelf systems that had been stable for thousands of years (e.g. Cook et al 2016 [2] and Lambeck et al 2014 [3]).

Question 2

In this larger context, is the coming event illustrative of any larger trends that may be driven by climate change, or is this really a mechanism of ice shelf loss that climate change doesn’t affect at all?

Response 2

Your last question is the hardest to answer right now as even the USGS 2600-B map only gives us a sense of the ebb and flow of the Larsen C's extent over the whole period. What we can say now is that this will be the furthest inland that the Larsen C has retreated during the period where humans have been mapping the area. 

Although the Larsen C could advance, especially if conditions continue to 'cool' in the region, my best guess is that the overall area will return to warming and this 'initial loss' of shelf area will be followed in the years to come by much more retreat of the ice in the Larsen C area just as happened after the initial losses in the Larsen A (late 1980s) and Larsen B (mid 1990s).