Was Wally Right?

As the end of this blog approaches, I would like to draw a rather interesting paper for my last discussion on ocean circulation. Alley (2007) provides a substantial literature review on the evidence to support Wally Broecker’s ‘conveyor belt’ hypothesis which has advanced the study of abrupt climate change, particularly in relation to millennial-scale events.  Earlier posts in this blog have explored the scientific basis (see post 3) in addition to evidence used to support Broecker’s hypothesis (e.g. The 8.2 ka event and The Younger Dryas), these are not of the main concern here.

Rather, I would like to focus on what Alley (2007: 242)  describes as the ‘predictive power’ of Broecker’s hypothesis.  Alley (2007) argues that Broecker’s hypothesis can allow us to make certain predictions about the impact of anthropogenic climate change in relation to abrupt climate change. These predictions are particularly of relevance to the last few blog posts on the notion of “surprises”.

 This is that shutdown of the meridional overturning circulation (MOC) although unlikely, is still a crucial issue. This argument can be related to the last post on the a potential collapse of the thermohaline circulation, and that typical global warming “runs” over the next century appear to produce a slowing down of the MOC without it shutting down.  Secondly, Alley (2007) notes that meltwater inputs from the melting of the Greenland Ice Sheet could be sufficient to trigger a slowdown or shutdown. The findings from the Antarctic blog post, to highlight demonstrated a bipolar seesaw effect whereby melting from the Antarctic Ice Sheet seemed to have a stabilization effect on the MOC.  The key observation from that blog is the notion that a shutdown of the MOC will not be sufficient to trigger an ice age (As the Day after Tomorrow had us believe!). This reason will be explained in a forthcoming blog post.

Predicting the impacts of future anthropogenic climate change on ocean circulation is complex. As demonstrated, through the examples of the Antarctic, Greenland and thermohaline circulation; providing definitive and quantifiable answers are difficult. This uncertainty can be attributed to the fact that these questions seem to test our understanding of ocean circulation in using the analogue of the past. Thus, Broecker’s analogy of the conveyor belt can used as a sensible analogy to fill this void to conceptualise future impacts of global warming on ocean circulation. However, the non-zero possibility and potential large of abrupt climate change sows the seed for warrant research which is likely to in the long-term provide crucial knowledge to policy makers.