Clotilde Dubois

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“Two ice shelves that existed before Canada was settled by Europeans diminished significantly this summer, one nearly disappearing altogether, Canadian scientists say in new research,” reports an Associated Press (AP) article in the San Francisco Chronicle.

“The impact is significant and yet only a piece of the ongoing and accelerating response to warming of the Arctic,” Dr. Robert Bindschadler, emeritus scientist at NASA’s Goddard Space Center, told the AP.

The Canadian team’s research confirms MIT scientists‘ recent finding that the Arctic is shedding ice much faster than forecast by the UN Intergovernmental Panel on Climate Change’s (IPCC) Fourth Assessment Report (AR4), published just four years ago (2007). Which of course is taken to mean that global warming ‘is even worse than scientists previously believed.’

Not so fast, say climatologists Patrick Michaels and Chip Knappenberger, editors of World Climate Report (WCR). Paradoxically, more-rapid-than-projected Arctic ice loss is additional evidence that IPCC climate models are too “hot” — that is, overestimate climate sensitivity and forecast too much warming.

In IPCC climate models, decline of Arctic sea ice is treated as both a consequence of rising greenhouse gas (GHG) concentrations and as an important “positive feedback” that amplifies the direct GHG warming effect. Al Gore popularized this idea in An Inconvenient Truth, noting that as Arctic ice melts, less solar energy is reflected back to space and more absorbed by the oceans.

But, as WCR points out, if the IPCC models’ climate sensitivity estimates were correct, then the greater-than-expected positive feedback from greater-than-expected Arctic ice loss should be producing greater-than-expected global warming. Yet, despite the extra unanticipated warming influence from accelerating ice loss, the world is warming more slowly than IPCC models project.

Far from being a portent of doom, greater-than-projected ice loss, coinciding as it does with smaller-than-projected warming, indicates that actual climate sensitivity is less than model-estimated sensitivity.

Similarly, argues WCR in a related post, had IPCC models properly accounted for the planet’s recovery from the cooling effect of aerosols blown into the stratosphere by the Mount Pinatubo volcano eruption, they would be projecting even more warming than they do now. Yet model current projections already exceed the observed warming of the past 10-15 years.

The relevance to the survival of civilization and the habitability of the Earth? WCR explains:

The reason that all of this is important is that climate models which produce too much warming quite possibility are doing so because they are missing important processes which act to counteract the warming pressure exerted by increasing greenhouse gas concentrations—in other words, the climate sensitivity produced by the climate models is quite possibly too high.

If this proves to be the case, it means that there will be less future warming (and consequently less “climate disruption”) as greenhouse gas emissions continue to increase as a result of our use of fossil fuels.

Evidence continues to mount that this is indeed the case.