Sunday, 16 December 2012

Permafrost - the bottom line

In a recent post UNEP Report - Policy Implications of Warming Permafrost I identified a major contradiction therein, and debunked claimed "increases" in CO2 and methane over permafrost areas. I've been digesting parts of the leaked IPCC AR5 draft report, and found this in WG1 chapter 6: Emissions 
Over the past decades, however, there is no evidence for significant emission of CH4 from permafrost and hydrates (Dlugokencky et al., 2009). 
.... from the horse's mouth.

And a little further on this section: Permafrost Carbon
Current estimates of permafrost soil carbon stocks are 1670 PgC (Tarnocai et al., 2009), the single largest component of the terrestrial carbon pool and higher than previously thought. Terrestrial carbon models show a land CO2 sink with warming at high northern latitudes, however none of the models participating in C4MIP or CMIP5 included explicit representation of permafrost soil carbon decomposition, which at a minimum requires sufficient vertical resolution in modelled soil carbon distribution and processes to separate surface pools from very old (Pleistocene) permafrost carbon pools. Including permafrost carbon processes into an ESM can change the sign of this C response to warming from a sink to a source in northern high latitudes (Koven et al., 2011). The magnitude of this source of CO2 to the atmosphere from decomposition of permafrost carbon varies widely by 2100 according to different model estimates: process-model estimates include 7–17 Pg (Zhuang et al., 2006), 55–69 Pg (Koven et al., 2011), and 126–254 Pg (Schaefer et al., 2011); estimates of uncertainty ranges suggest the source could range from 33 to 114 Pg C (68% range) under RCP8.5 warming (von Deimling et al., 2012), or 50–270 PgC (5th–95th percentile range; Burke et al., subm.). Combining observed vertical soil C profiles with modelled thaw rates estimate that the total quantity of newly-thawed soil C by 2100 will be 246 Pg for RCP4.5 and 436 Pg for RCP8.5 (Harden et al., 2012 in press). Sources of uncertainty for the permafrost C feedback include the physical thawing rates, the fraction of C that is release after being thawed and the timescales of release, possible mitigating nutrient feedbacks, and the role of fine-scale processes in determining the terrestrial response. 
Note the model results for emissions from permafrost to 2100: 7–17 Pg (petagrams), 55–69 Pg, 126–254 Pg, and the consequent estimated uncertainty range of 33 to 114 Pg C or 50–270 Pg C at the 5th–95th percentile range. What does this all mean?

They don't know.

No comments:

Post a Comment