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Everyone is saying we are in a global warming, an unnatural one at that because of CO2.

Has there ever been a 'global warming' in Earth's history? I know that global cooling is cyclical and 'looks' like global warming at the beginning of the cycle and luckily it is cyclical. There was a good explanation that the 'great dying' was because of global warming. If there is such a thing what would make global warming cyclical.

Venus is global warming for sure but what could have stopped the cycle of warming to go to cooler therms and stop the 'Venus' effect that can not be changed? There is a negative feedback for global cooling thus keeping that in check. Is there a negative feedback for global warming?

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    $\begingroup$ I might give this one a shot, but if anyone else wants to, feel free. I feel I should point out that what's happened with Venus is a runaway greenhouse effect, essentially a permanent effect. The only thing that could cool Venus down would be to knock it out somewhere close to or past Mars' orbit. Venus is a tough example, also, because we don't know enough of it's geological history. That lack of knowledge of it's history and it's very different "runaway" situation makes Venus largely irrelevant. Good question regarding Earth though. $\endgroup$
    – userLTK
    Mar 25, 2016 at 2:53
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    $\begingroup$ For prehistoric examples, look up the Paleocene-Eocene Thermal Maximum (PETM) and the Permian-Triassic Extinction event. Also note that Venus receives approximately twice as much solar energy per unit area as Earth does. $\endgroup$
    – jamesqf
    Mar 25, 2016 at 6:04
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    $\begingroup$ I'm trying to work out this question, but as I read it, I'm not sure what you're asking, when you say this "I know that global cooling is cyclical and 'looks' like global warming at the beginning of the cycle and luckily it is cyclical" and this "If there is such a thing what would make global warming cyclical." I don't quite see what you're asking. Very loosely speaking, negative feed-backs aren't that important, it's positive feedbacks that drive the pretty significant temperature changes. $\endgroup$
    – userLTK
    Mar 25, 2016 at 8:34
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    $\begingroup$ @stormy Glaciers work as a feedback mechanism in both directions. As Ice forms over land, Albedo drops, more light is directly reflected back into space, Earth cools. Oceans are a feedback as they hold more CO2 as they cool. Methane which forms, trapped under glaciers and tundra, as the ice thaws, Methane is released and that warms the Earth. Water is a greenhouse gas and warmer air holds more water vapor (not clouds, just humidity), colder air holds less. Feedbacks are anything that amplify a temperature change. They're significant factors. $\endgroup$
    – userLTK
    Sep 4, 2016 at 9:10
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    $\begingroup$ @stormy They don't like conversation here, so perhaps it should be turned into a new question, but my understanding a negative fedback doesn't turn warmer to colder, per say, it turns warmer to less warmer. Think of a positive feedback as a slippery slope where one step forward you slide forward 2 more and a negative feedback as drag where 1 step is against resistance so you take half a step. The poles (glaciers) gaining ice may be true, but it's just one glacier, the biggest one, the East Antarctic, which isn't evidence against climate change. On Chem trails - no idea but I smell bunk $\endgroup$
    – userLTK
    Jan 6, 2017 at 2:05

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Has Earth's climate ever changed? Sure.

paleoclimate record [1]

There are many feedbacks within the climate system, some negative as you mention but some also positive. A well-known positive feedback is the greenhouse gas effect, which in the present age is caused by anthropogenic fossil fuel emissions. Increasing greenhouse gases (GHG) causes the atmosphere to trap more longwave radiation and increase the temperature. Negative feedbacks can occur in the climate, such as the "Planck" feedback which describes the T$^4$ dependence of radiation emission--so as the planet warms it emits an even larger amount of radiation.

Climate models already take into account many of these feedbacks, but one of the largest unknowns is the effects of clouds and aerosols on the climate. The distribution of phase of clouds may change as the climate changes, which could possibly counteract the warming (as made popular in the hotly-contested Iris hypothesis [2]) or further enhance the warming.

A forcing related to clouds that further complicates their feedback is the aerosols that they form on. Let's say the climate warms a lot and the planet goes into a major drought. That will cause more deserts which will increase the amount of dust in the air. That dust (for a given amount of water) could potentially suppress precipitation in the clouds, thereby extending their lifetime and increasing the amount of sunlight reflected. Without fully knowing the distribution and effects of aerosols (and their respective impacts on clouds), an accurate estimate of cloud feedbacks is difficult.

A runaway effect on Earth could technically be possible. You talk about feedbacks as a mechanism to prevent that, but some mechanisms are not easily reversible. Thinking about the ice coverage in Earth's polar regions, if all of that ice melts for a given increase in T, decreasing T does not necessarily allow that ice to grow back to the same coverage...and especially not at the same rate.

So a changing climate is a complex system with many different interrelated components that cannot simply be predicted by a $dT/dt = dGHG/dt$ relationship. There are numerous feedbacks that are all dependent not only on each other but also sometimes-irreversible processes.

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  • $\begingroup$ What do you know about Grand Solar Minimums that happen every 206 years? We have plenty of history to know what happens and it ain't pretty and we should be getting prepared. Global warming is a done deal, over, totally put to bed with all the other lies. youtube.com/watch?v=ZTJCY6M-3fY&t=500s Check this guy out, John Casey who has been systematically barred from the internet, news, speaking events because he is trying to warn us about the Eddy Minimum we have been in since 2004...should last at least 20 to 30 years could last hundreds. Associated with earthquakes; New Madrid $\endgroup$
    – stormy
    Nov 8, 2017 at 8:13
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    $\begingroup$ @stormy lol..... $\endgroup$
    – user253751
    Jan 15, 2020 at 13:35
  • $\begingroup$ principia-scientific.org/evidence-co2-is-not-a-greenhouse-gas $\endgroup$
    – stormy
    Jan 29, 2020 at 5:46

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