Sunday, September 06, 2015

Arctic Sea Ice Extent, in Standard Deviations


For the entire year, 2012's record low minimum was -3.66 standard deviations from the mean.

2015's low (at least so far) was -3.10 sd's from the mean, on March 9th.

The linear fit to the data, which is pretty good, has the ice extent losing 0.09 standard deviations a year.

5 comments:

Unknown said...

Yes, Arctic ice has been shrinking. What's your point? You surely aren't basing a global warming prediction on a cherry-picked subset of the globe.
David in Cal

Ned said...

I can't speak for David Appell, but it seems to me that "David in Cal" is a bit confused.

A reasonable person would not "base a global warming prediction" on whether Arctic sea ice is shrinking or growing. Instead, that expectation of global warming would be based on the following more or less obvious facts:

(1) Humans are burning a lot of fossil carbon
(2) When burned in oxygen, those fuels produce CO2
(3) About half of the added CO2 remains in the atmosphere
(4) In the atmosphere, CO2 absorbs outgoing longwave radiation
(5) Absorbing more outgoing longwave radiation warms the planet

None of that is controversial. Predicting the magnitude of warming is less certain, because it depends on both unknown future consumption of fossil fuels plus only moderately well understood feedbacks and natural variability in the climate.

The downward trend in Arctic sea ice is interesting as an effect of warming, not as a reason to predict warming.

Unknown said...

Ned, I agree with you as to the science. However, IMHO the Arctic chart was selected as way to exaggerate the certainty and the magnitude of global warming. I deduce this motivation, because Mr. Appell did not show the chart of Antarctic sea ice. It has had an increasing trend and recently reached a record high level. Isn't that equally interesting?

The contraction of Arctic sea ice is only partially due to global warming. There seems to be process that has caused Arctic sea ice to contract while Antarctic sea ice expands. This may be due to changes in wind or water currents.

BTW I think your point about feedbacks being only moderately well understood is an understatement. The impact of feedbacks is measured by "climate sensitivity" (the warming caused by a doubling of CO2.) It's believed to be an constant, but the true value is unknown. The latest IPCC report gave a very wide range for climate sensitivity of 1.5 to 4.5 deg. C. Furthermore, the IPCC admitted that they're not even sure that the true value lies within this range.
David in Cal

Steve said...

David in Cal
David Appell did not mention the significant declines in Greenland, West Antarctica, the Antarctic Peninsular and in mountain glaciers. Using your line of argument,our host could be accused of down playing the importance of global warming.

With regard to Climate Sensitivity (CS), both you and Ned are correct in seeing this as the major current issue, as the value of CS is not as well understood as the five points outlined by Ned. There are serious problems, though, in using the uncertainty of CS as a means of downplaying the problems we face.

As you point out, according to the IPCC CS could be as low as 1.5C or as high as 4.5C. The dangers of mid range and high values are clear, but low values cannot be used as an argument that Global Warming is not a problem. If we do not take action we are heading for more than a doubling of CO2, probably more than a tripling. Even if CS is as low, (1.7C), as Nic Lewis (the most respectable of the "CS is low" people) claims, a tripling of CO2 would result in an eventual increase of about 2.5C which is dangerously high. Most experts think CS is in the range of 2.5 to 3 deg C, which is clearly dangerous. The final part of the puzzle to be put into place is the cloud feedback (CF), which is why Richard Lindzen is trying (unsuccessfully) to show that the cloud feedback is strongly negative. Andrew Dessler claims that the CF is positive and his value for CF results in a value of 2.7C for CS which is close to the value agreed by most experts.

The value of CS will likely be tied down during the next decade. I will be very surprised if the final value agreed by experts is far from 3 C.

Here is an interesting lecture from Dessler. The Climate Sensitivity part begins at about 16 minutes:
https://youtu.be/7ImRv58XJO8

David Appell said...

Unknown wrote:
"However, IMHO the Arctic chart was selected as way to exaggerate the certainty and the magnitude of global warming. I deduce this motivation, because Mr. Appell did not show the chart of Antarctic sea ice. It has had an increasing trend and recently reached a record high level."

Wrong David. And you should admit you're wrong.

First of all, the increase in Antarctic sea ice does not in any way disprove AGW. (Winds.)

Secondly, as of yesterday, Antarctic sea ice extent is -610,000 km2 below last year value on this date.