Global Cooling
 

Last week, PBS NOVA aired, 'DINOSAUR APOCALYPSE', which had to do with the mass extinction event, 66-million years ago, which took out 75% of all species on Earth, including all, non-avian dinosaurs.
Something which stood out had to do with 'Impact-Winter,' created by 3-trillion tonnes of sulfur-based rock, from the Yucatan Peninsula being vaporized, and ejected into space.
Earth's gravity pulled the vaporized rock back into the atmosphere, where it gave its heat up, allowing the vapor to cool into glass spheroids, which rained down, while turning the air into a hot-air broiler, incinerating most terrestrial and oceanic life forms.
Earth was dark for about a decade, all food systems collapsed.
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The interesting part was that, the sulfate aerosols created by the asteroid impact, remained in the stratosphere long enough to cool the whole planet by 48-degrees-F. This phenomena was first discussed by Benjamin Franklin, who coined the term ,'parasol effect', which is used in today's general circulation climate models.
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Today's 'cooling' is associated with coal-fired power plant emissions, which are keeping the troposphere about 1-C cooler than it would be without the aerosols. In effect, the Earth has already warmed 2.1-C, we just won't 'feel' it, until all these plants are taken offline, and the aerosols have a couple months to precipitate out.
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If you haven't seen the show, it's worth a look. The paleontologists have reasonably demonstrated that dinosaurs were present right at the time the 'Mount Everest'- sized asteroid came in at 45,000-mph.
None, except the 'chickens' existed afterwards.

A more recent example was the week or more in 2011. DDG's top result

https://weathermodificationhistory.com › september-11-2001-airline-groundings-contrails-affect-daily-temperature-range
September 11, 2001 Airline Groundings: Contrails Affect Daily ...
During the 11-14 September 2001 grounding period natural clouds and contrails were noticeably absent on high-resolution satellite imagery across the regions that typically receive abundant contrail coverage. A previous analysis of temperature data for the grounding period reported an anomalous increase in the U.S.-averaged, 3-day DTR value.

Is the 12,000-year cycle more likely to be asteroids or vulcanism?

Proving the point that even asteroids are a more concerning existential threat than the outdoor thermostat going up a couple degrees?

Seems to me Gretta should be pulling her hair out that we've not sufficiently guarded ourselves against that inevitable event. "How dare us".

12,000-year cycle
 

1) I don't have anything with me for a 12,000-year cycle.
2) The asteroids large enough to be detected are continuously monitored around the clock.
3) 'Vulcanism' or 'Volcanism?' I don't know anything about 'vulcanism'.
4) Volcanism is not periodic in nature. There are no 'cycles' associated with it that I've experienced in the literature. It is associated with tidal forces, plate tectonics, lithospheric isostatic rebound as ice sheets melt, and seismic activity.
5) The Milankovich 'wobble' has a periodicity of 23,000-years.
6) The 'tilt' cycle is 41,000-years.
7) The 'ellipticity' cycle is 96,000-years.
8) The solar sunspot cycle is eleven years, with a delta-irradiance of 0.50%.

sufficiently guarded
 

NASA'a doing what they can, to monitor asteroids. Next year, one will pass between the Moon and Earth.
Global warming's a sure thing. It's accelerating, non-linearly, as I type.
It will ultimately be the 6th mass extinction. It's what the people who control information want, and they're going to get it. A great success story!

You say po-tah-to, I say to-ma-to? :)

DDG says:

what would yellowstones eruption do to the planet? at least we can stop an astroid. cant stop yellowstone...

Dansgaard..................
 

I'm not as organized as I'd like.
Willi Dansgaard of Denmark is the namesake for the 'Dansgaard' half of the adjective.
'Heinrich' refers to 'so-called' Heinrich ice-rafting and iceberg discharge events ( boulders and everything to make glacier moraines ), transported for vast distances; associated with Ice Age terminations and Younger Dryas, which introduced freshwater pulses to the oceans surface water, affecting cessation of deepwater convection and circulation because of thermohaline/ density issues.
At 12,000-years ago there was a 'Allerod warming' where a vigorous deep convection returned.

Yellowstone super-volcano
 

All I remember was that, all, as far as Texas, would be killed.
Same for all living around the caldera at Carson City, Nevada.

well yeah but how would it affect the planets overall air quality or temperature?