Jy blaai in die argief vir historical.

Climate Change: The debate in Geobulletin (continued)

30/01/2013 in Uncategorized

Climate change – The Short Story (William McClenney) (continued)

The climb out from the Last Glacial Maximum of the Wisconsin ice age (called Termination 1with sea level bottoming out about 121 meters below present) into the Holocene is studded with the Younger Dryas, a 1,300 year near instantaneous return to ice age conditions. “Briefly, the data indicate that cooling into the Younger Dryas occurred in a few prominent decade(s)-long steps, whereas warming at the end of it occurred primarily in one especially large step of about 8 degrees C in about 10 years and was accompanied by a doubling of snow accumulation in 3 years; most of the accumulation-rate change occurred in 1 year (National Research Council,2002)”. Far more suddenly we came out of it: “Taylor et al (1997) found that most of the change in most indicators occurred in one step over about 5 years at the end of the Younger Dryas, although additional steps of similar length but much smaller magnitude preceded and followed the main step, spanning a total of about 50 years (NRC,2002)”.

Termination 1 went into top-fuel, carbon-free overdrive with what is referred to as melt water pulse 1a (mwp-1a) centered at about 14,680 years ago which resulted in a 24 meter rise in sea level believed to have occurred at the rate of 4.5 cm a year. It was followed around 12,260 years ago by mwp–1b with a 28 meter rise nearer 5cm a year. Recent model results predict that sea level is currently rising at 32cm/100 years. If we take the low-end of the natural ‘noise’ clocked at 4.5 cm/yr (or 450 cm/century) we will have to kick in some serious turbos (carbos?) to net one and a half orders of magnitude boost if we hope to trump mother nature’s bottom bracket.

Another variable worth devoting some cpu time to is just how astonishingly well the fourth cycle of eccentricity matches up with hominid evolution.

“An examination of the fossil record indicates that the key junctures in hominid evolution reported nowadays at 2.6, 1.8 and 1 Ma coincide with 400 kyr eccentricity maxima, which suggests that periods with enhanced speciation and extinction events coincided with periods of maximum climate variability on high moisture levels.” state Trauth et al (2009) in Quaternary Science Reviews. There is just nothing quite like having such a natural fly land in your climate change soup. As it turns out, periods of wet maximum climate variability (in modern lingo, global warming/global cooling correctly re-branded as climate change), cook-up the larger braincases. We went from 500-550 cc braincases 2.8 mya to the average of about 2,500 cc today in the most rapid encephalization of any mammal in the fossil record.