Monday, January 28, 2013

New paper finds worst-case scenario is ice-free Arctic by year 2400

A paper published today in Geophysical Research Letters finds that even under the most exaggerated "strongest" forcing scenario simulated by climate models, the Arctic "becomes summer ice-free by the end of the 21st century and year-round ice-free by the end of the 23rd century." Leaving aside that climate models offer little more than simulating a random walk, many alarmist climate scientists have had no shame from incorrectly predicting a year-round ice-free Arctic many times in the past or within the next two years.

Implications of Arctic sea ice changes for North Atlantic deep convection and the meridional overturning circulation in CCSM4-CMIP5 simulations

A. Jahn,
M. M. Holland

Abstract: Using CCSM4 climate simulations for 1850–2300 with four different future forcing scenarios, we show that the maximum strength of the Atlantic meridional overturning circulation (MOC) decreases proportionally to the applied CO2 forcing. This weakening of the overturning is caused by a reduction or shut down of North Atlantic (NA) deep convection due to a surface freshening. In the Labrador Sea, the surface freshening is caused by strongly increased liquid freshwater exports from the Arctic, which are largely due to the decrease in the Arctic sea ice cover. In the strongest forcing scenario (RCP8.5), the Arctic becomes summer ice-free by the end of the 21st century and year-round ice-free by the end of the 23rd century. As a result of the associated freshening, all NA deep convection ceases by 2145, which leads to a 72% (18 Sv) decrease of the MOC strength by the end of the simulation in 2300.

4 comments:

  1. Man's dream for 500 years: a northwest passage. Shipping the great circle route from Europe to Asia. Too bad it can't happen sooner.

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    1. Surely, this wasn't just "man's dream" -- it must have been "man's only dream." But it has never been my dream -- am I missing the "greatest story ever told," or something. Or, maybe, "a northwest passage" has never really been all that high on the world's list of critical problems to be solved, even if it was high on the list of a handful of people.

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  2. Unfortunately, there's much more complexity involved here that doesn't lend itself to linear approximations. The Arctic ice coverage has been translating (mathematical term) downwards, both upper and lower parts of the sinusoidal curve. Eventually, just the September portion will "hit bottom" and be totally ice free, followed by August & October, and then July - November.

    This downward translation will have dips and recoveries, but the general trend will be downward, and the trend will be log accelerating for reasons that I don't have time to go into, but salinity increase is one of them. The meteorological implications are stunning and reading up on Ewing and Donn will get you off in the right direction!!!

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    1. Uh, this is not a linear approximation. It is based on [albeit highly flawed] nonlinear climate models with the highest CO2 forcing assumptions.

      You seem to know it all, so please do explain exactly how melting ice causes an increase in salinity, which leads to a runaway positive-feedback tipping point not captured by these state-of-the-art climate models.

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