Sunday, April 12, 2020

Twas the best of times for proxy reconstructions . .

An interesting thing about proxy reconstructions is that it was only with the end of the last century that they could be done, some trivial, some not much talked about.

Why well take a look at the latest, Pages 2K

and the first multi-proxy reconstruction, MBH 98

The first trivial reason is that it was only after 1850 or so that there were enough weather stations with reliable instrumentation and procedures to create globally reliable instrumental temperature records.  BEST tried to push the global instrumental temperature records back in time

They attribute the large negative deviations to volcanoes, which from left to right before 1900 would be Grimsvötn(1785), Tambora (1815), Cosiqüina(1835), Krakatoa (1883) with the 1808 mystery eruption. 

The second trivial reason is obviously the availability of proxy records which overlap the instrumental ones.  Even tho they can be chained there were not so many early on.

The third reason which is the one that interests Eli (and maybe some bunnies) is that it has only been in the 20th century that there was a large enough change in global temperatures to allow a useful calibration.  The changes before 1800 were just too damn small to allow a useful calibration of the changes in the proxys.


Canman said...

In the first one, it looks like industrialization headed off a severe downtrend.

Barton Paul Levenson said...

C: In the first one, it looks like industrialization headed off a severe downtrend.

BPL: Warmer is better! We stopped an ice age! CO2 is plant food! Ein Volk, Ein Reich, Ayn Rand!

Old_salt said...

That is why the science says the actual warming by humans is greater than 100% of the signal. The milankovitch forcing is toward cooler temperatures.

Canman said...

Any theories on the 1000 year downward elbow?

Unknown said...

Sure, go look up

Canman said...

Thanks for the link. Initial summary/abstract says a CO2 decrease was half pandemic, a quarter deforestation and a quarter feedback.

John Mashey said...

Minor nits:

1) MBH98 didn't to back to 1000CE, that was extension in MBH99.

2) Bradley&Jones(1993) combined multiple proxies in each region.
Fig 8 has the curve IPCC(1995) used, to which they added the modern temperature measurements.

I mentioned it in

BBD said...

Ein Volk, Ein Reich, Ayn Rand!

:-0 Good one BPL.

Canman said...

Certainly better than his usual bile, but his stuff never stings.