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"Based on the best historical data that we have available CO2 is probably increasing at a rate at of least 100 times faster than at any time in the last 800,000 years." Pieter Tans lead scientist of NOAA's Global Greenhouse Gas Reference Network.

Peter Tans approved the above verbatim quote to be directly attributed to him. I contacted him by email today on the basis of this material:

“The rate of CO2 growth over the last decade is 100 to 200 times faster than what the Earth experienced during the transition from the last Ice Age,” Pieter Tans, lead scientist of NOAA’s Global Greenhouse Gas Reference Network, said in a statement. “This is a real shock to the atmosphere.”

The annual rate of increase in atmospheric carbon dioxide over the past 60 years is about 100 times faster than previous natural increases, such as those that occurred at the end of the last ice age 11,000-17,000 years ago.

https://e360.yale.edu/digest/co2-levels-continue-to-increase-at-record-rate https://www.climate.gov/news-features/understanding-climate/climate-change-atmospheric-carbon-dioxide

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  • $\begingroup$ What makes you think the rise is due to natural causes instead of human activities? For that type of increase to be caused naturally, extreme volcanic activity, which the Earth hasn't had over the past 70 years, would be a most likely cause. $\endgroup$
    – Fred
    Commented Oct 5, 2019 at 5:35
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    $\begingroup$ @Fred I do think it was caused by human activities. I just want to make sure that there are no other loopholes. $\endgroup$
    – polcott
    Commented Oct 5, 2019 at 12:41
  • $\begingroup$ I think a major meteor impact could cause such a spike. $\endgroup$
    – Erik
    Commented Oct 7, 2019 at 7:33

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There are things that could do it, but they would be very noticeable.

  1. A whole string of thousands of the largest volcanic eruptions to ever occur on Earth. Volcanoes can briefly match human output, but they only erupt for minutes, hours, or days. You would need the equivalent of Mount St Helens erupting continuously for 70 years.

  2. The burning of every forest on the planet. I'm sure humans would notice such a firestorm, and I'm not even sure if that would be enough.

  3. The slow extinction of photosynthetic algae. Without the bulk of photosynthesis to convert $\ce{CO2}$ back into oxygen, it could build up. Of course we monitor this so it would not go unnoticed. More importantly, oxygen levels would also drop dramatically which hasn't happened. (See: https://scied.ucar.edu/imagecontent/carbon-cycle-diagram-ipcc)

  4. The ignition and continuous burning of millions of miles of exposed coal beds. You would need to burn approximately ~3 teratons of coal. Coal beds can be ignited by natural causes but we would notice a coal fire larger than a continent.

  5. A drop in sea level by hundreds of feet would do it. A large sea level drop would cause outgassing of methane and $\ce{CO2}$ from wetlands and sea muds. But again New York would notice if Long Island stopped being an island.

Some of these have actually happened in Earth's geologic history, just none recently, and not as generally not as consistently as needed (at least not since life evolved). Really scientists have spent a lot of time and money looking for other causes, and no one has found any. Scientists concluded it was human activity by eliminating every other conceivable cause.

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    $\begingroup$ I could not find any ice-core or geological data that indicated nearly the same vertical spike that we have had in the last 70 years. I found the next closest spike in this ice-core data: cdiac.ess-dive.lbl.gov/ftp/trends/co2/vostok.icecore.co2 244,863 years ago. The current spike is 11,400% faster than this next fastest spike. $\endgroup$
    – polcott
    Commented Oct 6, 2019 at 18:47
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    $\begingroup$ You won't find them in ice cores, you need to go back to the deccan traps eruption, or the KT impactor. And even then they will not happen as fast, possibly the PT impactor, but just possibly. which is kinda scary all on its own. $\endgroup$
    – John
    Commented Oct 6, 2019 at 21:19
  • $\begingroup$ We are currently at 2 PPM per year. This seems to be at least 100-fold faster than ever before. I want to verify that of all the climate change data that exists is what is the next fastest rate of CO2 increase? $\endgroup$
    – polcott
    Commented Oct 6, 2019 at 23:57
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    $\begingroup$ That is what I intended by my original question. You did a much better job of answering my question than I expected. You really covered a lot of different scenarios. To paraphrase your answer it seems like you are saying that there is no natural process (in the last 600 million years) that could reasonably cause a rate nearly as fast as the current 2.11 PPM per year rate. Is that accurate? $\endgroup$
    – polcott
    Commented Oct 7, 2019 at 3:00
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    $\begingroup$ @jamesqf there is decent evidence for an impactor, but the mistake is assuming it has to be one or the other, an impactor can induce flood basalts on the other side of the planet, thanks to shockwave coalescence. Your not going to find a lot of direct evidence of an impactor that old if it hits oceanic crust, we don't have any sizable pieces of oceanic crust that old. $\endgroup$
    – John
    Commented Oct 7, 2019 at 13:33

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