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Friday, February 01, 2013

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Fairfax Climate Watch

A substantial volume remains unsaid in this article, and the rise in SST raises many concerns in many areas.

For instance: hurricane/cyclone strength increased? Antarctic ice sheet disintegration?

The projected warming around the Antarctic ice sheet should be interpreted carefully. The model used, GISS II, has a fixed ice sheet. The amount of water heating shown in the model might not be possible until after the Antarctic ice shelves are gone, because as they collapse, icebergs will float north and cool adjacent water. Eventually, or quickly (geologically speaking, rapidly) the West Antarctic and parts of the East Antarctic ice shelf will go, raising sea levels by about 3 to 4 meters. So, if you imagine 3 to 4 meters of ice spread over top the world's oceans, let's say spread over 10 years, that comes to 30 to 40 cm of ice, enough to cool the ocean surface layer by several degrees. The ice won't make it to all areas of the oceans though, but instead stay mostly in the S. Atlantic and S. Pacific. The loss of ice from Greenland however, is another story, and should a large volume of that make it out at once, the N. Atlantic could also find itself awash in icebergs. This raises another interesting question: what will the effect of a whole lot of ice have on ocean circulation in conjunction with the increased radiative forcing? We know that in the past, when icebergs sloughed off and out like this, there were major changes, but the background scenario was fundamentally different because radiative forcing wasn't also streaking upwards at the same time.

It could be, unlike the past, that as the ice discharges, it will temporarily cool the Antarctic water and rapidly slow Antarctic ice loss, but that once the discharged ice melts, SST will quickly rise back and above previous levels because of the persistent elevated imbalance in radiative forcing.

And if this is the case, then once the ice shelves are gone, the Antarctic mainland ice will be melting at a pretty fast rate. A lot of icebergs will calve off the mainland ice sheet and start to cool the water again, but these new icebergs from the mainland will be smaller than the ones that came from the breakup of the shelves. This means they'll melt faster, before they make it far north. That means that the inhibition (negative feedback) of Antarctic ice loss will initiate faster, but also possibly end sooner. Although, it is not clear to me yet if an icy cold surface layer around Antarctica at such a point would inhibit or accelerate atmospheric transfers of energy to the mainland ice sheet. It's also unclear what a thick surface layer of freshwater would do to ocean circulation patterns which have a direct significance to methane hydrate deposits.

Perhaps most of all, it's not known how much methane resides beneath the ice shelves of Antarctica, or how much will be released if the ice shelves go. And for another unknown, the actual breakup of the ice shelves...the timing of that event is still speculative. People who casually say it won't happen for another hundred or two hundred years ...ask them how they know that...

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Convert carbon dioxide (CO2) weight to carbon (C) weight

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CO2/3.67 = C 

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ex: 40 GtCO2 ≈ 10.9 GtC

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1 Gt (Gigatonne) = 1 billion tonnes

1 tonne = 1,000 kg

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Also: 1 Pg = 1 Gt

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1 Pg (Petagram) = 1 quadrillion grams

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Soil specialists tend to use Pg, as they are used to working with gram units per square meter of soil area. Atmospheric specialists tend to use Gt. 


Convert carbon emissions to ppm atmospheric CO2

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GtC/2.12 = ppm

To convert emissions of carbon to atmospheric ppm CO2, carbon sinks must be taken into account. 

So far, terrestrial and oceanic sinks have taken up about 50% of CO2.

source

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ex: 40 GtCO2 emissions ≈ 10.9 GtC

10.9 GtC/2.12 ≈ 5.14 ppm CO2 before accounting for sinks

5.14 ppm CO2 x 0.5 ≈ 2.57 ppm CO2 after accounting for sinks

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