Peter Harris provided us with a challenging debate here on this blog where the similarity between the current situation and the 400 kya glacial transition was discussed. I sought more information from Jan Hollan – but some background here first.
So if the present time was really analogous to 400,000 years ago (kya) transition, the advice to the IPCC that no ice age was due for many 10,000s of years would be incorrect and a major concern to humanity.
Augustin et al in Nature 429, 623-628 (10 June 2004) | doi:10.1038/nature02599 discuss 8 glacial cycles from Antarctic ice cores. The transition from glacial to interglacial conditions about 430,000 years ago (Termination V) resembles the transition into the present interglacial period in terms of the magnitude of change in temperatures and greenhouse gases, but there are significant differences in the patterns of change. The interglacial stage following Termination V was exceptionally long—28,000 years compared to, for example, the 12,000 years recorded so far in the present interglacial period. Given the similarities between this earlier warm period and today, our results may imply that without human intervention, a climate similar to the present one would extend well into the future.
Jan Hollan reported here that the first ever pronounced fall of summer insolation happens some 130 thousands years from now, but it is not at all so deep as those ones that started the last two Ice Ages. So, we can say there is no conceivable cause for another glaciation for at least those 130,000 years. Quite probably, another glaciation cannot come sooner that 620 thousand years from now.
Berger and Loutre argue in their Science paper that with or without human perturbations, the current warm climate may last another 50,000 years. The reason is a minimum in the eccentricity of Earth’s orbit around the Sun.
There are three interacting aspects of the Earth’s orbit that need to be accounted for in making the Milankovitch radiation calculations – discussed here. The mechanisms are orbit eccentricity (roundness to elliptical); obliquity (axial tilt) and precession (wobble around the axis).
The calculations of solar radiation at 65 degree North from Milankovitch mechanisms are based on a derivative of Laskar et al.
Jan Hollan now provided an additional graph from 500,000 years ago to 200,000 years from present.
Made for a rather low 1366.3 W/m2 solar constant again. -400 ka summer insolation minimum was some 10 W/m2 lower than that one we have almost reached already. No pronounced decline of solar orbital summer forcing at 65° N is ahead of us next 50,000 years. Jan Hollan suggests we should not extrapolate past trends (like decline in summer insolation, or the shape of the past glaciation cycles). We should look at reliably computed past, current and future forcings instead (see Laskar et al for the mathematics involved). Hollan states that it is evident we have almost reached the near-future insolation minimum already. Before the atmosphere returns to normal (thousands of years), we will be on the increasing part of the insolation curve again.
Which all means – no Milankovitch based ice age predicted for 50,000 years and more likely 130,000 or 620,000 years hence according to Jan Hollan.
Jennifer Marohasy BSc PhD is a critical thinker with expertise in the scientific method.
*crickets chirping*
Luke,
I have been very patient in my attempts to get you to understand my simple thesis “NO TO AN EXTENDED HOLOCENE” but you seem to want to blindly accept the interpretation by Hollan without any attempt at critical analysis and without adressing my simple argument.
I have used no theoretical model projections, only the mathematics which has been on the public record for over 15 years, and validated geology.
I do not dispute the mathematics by Hollan, Berger and Loutre or by Laskar.
I have used the work by Quinn , Levine and Raymo which is in close agreement with Laskar.
I dispute the findings that have been projected from the work of Berger,Paillard and Hollan and now amplified by the IPCC.
As we seem to be going over the same ground repeatedly I will explain it only one more time Luke.
The IPCC has made a “robust finding” that “it is very unlikely that Earth would naturally enter another ice age for at least 30000 years” This finding is based on the work by Berger & Loutre who reported on the similarity between the 400KY orbital geometry and now, and by Paillard that “the interglacial (lasted) an additional precessional cycle, yielding a total duration of 28000 years”
INSOLATION NOW HAS NO ADDITIONAL PRECESSIONAL CYCLE THEREFORE THERE IS NO SUCH CASE FOR THE ADDITIONAL 28000 YEARS HOLOCENE.
Hollan used the math by Laskar as well as the outdated TAR modeling for CO2 radiative forcing and made the finding that because insolation now will not cycle as low as the 400KY precedent there will be no transition for 130000 years.
THE 400 KY TRANSITION OCCURRED AT THE SAME INSOLATION LEVEL AS TODAY AND NOT AT THE LOWEST CYCLE VALUE, SO DID THE TRANSITIONS AT 320,240,190,AND 120 KY THERE IS NO CASE FOR THE 130 KY HOLOCENE ON THIS BASIS
The transitions occur when insolation is in rapid decline and with a frequency of 80-100KY but are not linear with insolation.Small insolation like 400KY led to large glaciation like the other cycles.
Given that the case for an extended Holocene is UNSAFE then we should reexamine the probability of a transition to the coming ice age.
1.Insolation is in rapid decline similar to the 400KY precedent and all of the other transitions.
2.We are past the end of the regular 100KY glacial cycle
3.The present interglacial is near the average age for termination.
4.The transitions occur when insolation is in rapid decline as it is today
5.The Southern Hemisphere is cooling since 1998 and is expected to lead the transition.
6.Solar activity is expected to a 100 year low in 2022.
I have nothing more to say Luke. I would be happy to answer any questions from others, but I suspect they are long gone.
1-4 are irrelevant if the formal calculation of insolation is that we’re 10 watts short.
You have consistently shied away from a formal calculation.
The average age for a termination in not relevant if you wish to use 400 kya as an example. Indeed averages are not that helpful with 3 overlaid periodic phenomena.
Cooling since 1998?
If the southern hemisphere is cooling then it appears that Australia is warming – wonder why that is – see mean temperature here
http://www.bom.gov.au/cgi-bin/silo/reg/cli_chg/timeseries.cgi
Rapid ocean warming around Australia?
No trend in solar insolation