As we cover the current record Arctic melt season and its potential to break the record low set in 2007, it is important to put this event and the events of the past five years into context. In short: no one expected the melt to happen so rapidly. The scientists, who relied on model systems for guidance, found that the models they were using were entirely too conservative and that they consistently under-predicted the great volumes of sea ice melt that kept coming up again and again in observation.
Models, in general, are only as good as the information you feed into them. In this case, the rule of garbage-in, garbage-out reigns. If a model is fed false assumptions or incomplete information, it is more likely to put out an erroneous conclusion. And, in general, researchers have been having a beast of a time getting the sea ice melt prediction models right.
This image shows both past and current model runs (red and blue lines and shades) predicting loss of sea ice extent due to global warming compared with observations (black line):
The blue line represents the average combination of model runs used in the IPCC’s 4th assessment report in 2007 (CMIP3). The information fed into the models was based on the assumed forcing effects caused by business as usual greenhouse gas emissions (business as usual assumes all the fossil fuels will be burned). The blue and purple shaded areas reflect the standard deviation for these model runs. As you can see, the black line representing current Arctic sea ice melt is well outside even the lowest standard deviation range for these first model runs.
Recently, a second set of model runs was made in an attempt to more accurately predict Arctic sea ice melt. The average for these model runs is shown by the red line. And the standard deviation for these runs is shown by the pink and purple shaded areas. As you can see, the second set of runs (CMIP5), though more accurate, just barely manages to catch current Arctic Melt within its lower standard deviation.
Getting into the data a little, it seems likely that the models are missing a number of feedbacks that are currently impacting the Arctic. Another issue is that models tend to be very bad at managing tipping point events. In short, models tend to make smooth curves, but a tipping point is a jagged turn. Needless to say, climate researchers should be applauded for their efforts as current policy regarding climate change is in dire need of a clear predictive capacity and current efforts to refine these models are likely to increase understanding of how the Arctic is most likely to respond to human-caused global warming.
Meanwhile, this year’s current Arctic sea ice melt remains on track the break the record set in 2007…