This morning's must-read scientific paper comes from Science, where a team from the University of Insbruck led by Ben Marzeion has been looking at glacier recession. The results seem to have pleased the green fraternity, and a glance at the abstract shows why:
The ongoing global glacier retreat is affecting human societies by causing sea-level rise, changing seasonal water availability, and increasing geohazards. Melting glaciers are an icon of anthropogenic climate change. However, glacier response times are typically decades or longer, which implies that the present-day glacier retreat is a mixed response to past and current natural climate variability and current anthropogenic forcing. Here we show that only 25 ± 35% of the global glacier mass loss during the period from 1851 to 2010 is attributable to anthropogenic causes. Nevertheless, the anthropogenic signal is detectable with high confidence in glacier mass balance observations during 1991 to 2010, and the anthropogenic fraction of global glacier mass loss during that period has increased to 69 ± 24%.
An abstract written with headlines in mind, I'm sure you will agree.
The results are currently being trumpeted by, among others, the Carbon Brief:
69±24% of glacier loss since 1991 was caused by humans - Science
Chris Hope:
Man-made warming becomes main cause of glacier retreat, study says
and Bob Ward:
New study concludes about two-thirds of glacier mass loss worldwide in last 20 years is due to human activities
There are many others too.
So. let's take a look at how this startling conclusion was reached.
...we quantify the evidence for a causal link between anthropogenic climate forcing and observed glacier surface MBs [mass balance], not of individual glaciers but of all the world's glaciers outside of Antarctica combined. We then attribute the global glacier retreat since 1851 to natural and anthropogenic causes. We use a model of global glacier evolution that treats the MB of each of the world's glaciers contained in the Randolph Glacier Inventory (RGI)... individually, including a simple parametrization of ice dynamics leading to glacier hypsometry change... Forced by observed climate... the glacier model has been independently validated against both annual surface MB observations (fig. S1) and observed, temporally accumulated volume changes of hundreds of glaciers...
For each of 12 reconstructions of the global climate between 1851 and 2010, produced by general circulation models (GCMs) from the CMIP5 ensemble... we reconstructed the area and volume of each glacier in 1851... From this reconstructed glacier state, we modeled the evolution of each glacier forward in time. This forward model was run twice for each GCM: once subject to all known forcings (i.e., solar variability, volcanic eruptions, land-use change, anthropogenic aerosols, and greenhouse gas emissions; we call these model runs the FULL runs below), and once subject to only natural forcings (i.e., solar variability and volcanic eruptions; we call these model runs the NAT runs below).
So if I understand this correctly, we take the CMIP5 models - the ones that failed to predict the recent hiatus in global surface temperature rise and which, by mainstream climatologists' own admission don't include an important part of the climate system, namely heat transport to the deep oceans. Then, despite the fact these models have no known ability to reproduce regional climate either we use their output to feed glacier simulations, which include their own parametrisations. And from this conclusions are drawn.
It's models upon models upon models. And models, moreover, that are known to be unsuitable.
And from this our green friends expect us to accept their entirely uncaveated statements about glacier retreat.
Amazing.