Monday, July 29, 2013

Variability Makes Stuff Tuff

Steinacher, Joos and Stocker write in Nature about how "Allowable Carbon Emissions Lowered by Multiple Climate Targets", that hitting a single target, for example 2 C requires a lot less effort than limiting harm from multiple limits.  Essentially the same tautology as given natural variability on top of a rising base, then the hotter extremes are going to get hotter and you don't need a degree in meteorology or statistics to figure that out.  The authors selected a number of global metrics, mean sea level rise, steric sea level rise, Aragonite undersaturation in the Southern Ocean, global loss of aragonite saturated waters, cropland loss and soil carbon loss. 

Meeting the multi-target 1 is very unlikely (<10 360="" eff="" exceed="" if="" u="">+
40 GtC mean and maximum-minimum range from RFNC scenario uncertainty), although it becomes likely to meet the 1.5 C target (which is a part of set 1) at this range of emissions (Fig. 4).  Similarly it is unlikely that multi-target 2 can be met if Eff exceed 470 + 80 GtC while it is still likely to meet the 2 C target if they stay below.
Now certainly bunnies can argue about the choice of metrics, the emission scenarios and the models used to play what if, but the central point remain, it is easy to mislead policy makers if one focuses on a single metric. 

Worse, fitting a single globally and temporally averaged metric, such as temperature anomaly is an exercise in making von Neumann's elephant wiggle his trunk without a dose of physics and chemistry.  Further, anyone who uses global metrics fall into the trap one anonymouse saw with another study
It's the creeping statistical hints between the lines of this paper that really bother me. Long before or even if we never see broad areas permanently enter a existentially threatening torrid regime, what about excursions? For instance, Pakistan this year has seen record temperatures approaching 54 degrees C in places where many people live, fortunately with lower humidity and only for handful of days but what about when/if such aberrations extend to a handful of weeks and are accompanied by inexorably increasing humidity? The resulting disaster would cause migrations. The worst-case scenario in Sherwood and Huber would not have to happen before we effectively lose major swathes of territory for year-round habitability.
Eli is an optimist of course.


EFS_Junior said...

Google is your friend;

Three hits, first hit is Nature version.

Or here;

Nature copy + SI + N&V

Now I'd rather read the Nature formatted copy than a copy with no explicit abstract, conclusion and discussion sections.

Oops, the Nature copy has no C&D sections. Oh my. :(

Now as to meeting six apparently arbitrary and capricious targets versus one target, all in a row column format, which of those six targets is the limiting target for their four scenarios?

Also the six targets are;

DSAT Global mean SAT increase since 1800 1.5 2 3 4 uC
SSLR Steric sea level rise since 1800 20 40 60 80 cm
ASO Aragonite undersaturation of Southern Ocean surface 5 10 25 50 Percentage of area south of 50uS
Global loss of surface waters with Varag.3 60 75 90 100 Percentage of area in 1800
NPP.10% Cropland area with NPP losses .10% 5 10 20 30 Percentage of crop area in 2005
Ccarbon loss Global soil carbon loss on croplands 5 10 20 30 Percentage of soil carbon in 2005

(sorry for the formatting (its a simple C&P from the PDF).

No SLR per se, just the STERIC component of SLR.

And why just six targets and only four scenarios?

Heck if we are going to go there, how about the full matrix of permutations, say with a few dozen constraints and a few dozen levels.

At that point I'm quite sure that we won't meet one cell of that matrix even if we stop all GHG emissions three days before the day after tomorrow.

Now that's what I would call tautology.


Russell Seitz said...

54 C during ramadan in Pakistan ?

No wonder the Taliban are getting testy

Jeffrey Davis said...

That has to be 45C. 54C is close to Death Valley all time record. 45C (114F) is bad enough. A lot of crops die at that temp. Rice has problems over 97F.

BBD said...

Jeffrey Davis

An albeit quick furtle round google didn't corroborate the 54C claim.

I did find out that there was a 53.5C station reading reported in May 2010 but I don't know if this was subsequently verified.

Anonymous said...

Eli's anonymouse quote is from 2010, and "approaching 54 degrees C" is not a typo. In the May 2010 heatwave, 50+ (122F) was reported from a dozen different cities, most of which had 3 to 5 days at or above this. The highest was 53.5C (128.3F) in Mohejo-daro. Only Death Valley and a slighly doubtful reading of 53.9 from Israel have higher temps.

I can't say whether those verified readings, but they were widely reported at the time, and are used in some scientific papers hosted on the website of the Pakistan Meteorological Department (the official government Met agency).

Frank D. Mouse

Russell Seitz said...

This may refer to Jacobabad, a railway cantonment way down south near Quetta that set Victorian records in the 50's

Lars Karlsson said...

Brian, I suspect that HTML has played a trick on you in the second paragraph (you probably entered something with an < in it).

Gaz said...

Meanwhile, down here in sunny Sydney Australia, we just finished the hottest July on record.

People are complaining we don't have winters any more.

Jeffrey Davis said...

Late to the thread.

I looked it up and, yes, the temperature was 54C. The site, Mohenjo-daro, is an arid one, but just east of an agricultural one. The Indus River floods the site so I wonder if the dew points there are as low as in Death Valley.

According to Wikipedia, the site was an ancient city, which had such amenities as waste water drains and heated baths. The modern name means -- apt for our thread -- Mound of the Dead. (The ancient name of the city itself is lost.)

2010 -- the year of this temp -- eclipsed 1998 as, world-wide, the hottest ever recorded. Soon, we'll have years where either drought or flood threatens all the major agricultural regions in the world.