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That's not true according to the latest IPCC report, which estimates "equilibrium climate sensitivity" to a doubling of CO2 (which hasn't happened so far) to be

That's not true according to the latest IPCC report, which estimates "equilibrium climate sensitivity" to a doubling of CO2 (which hasn't happened so far) to be between 1.5 and 4.5 degrees C. Incidentally, the 1.5 to 4.5 degree C uncertainty range is unchanged for decades, illustrating the lack of progress in this field of science.

pier25 7y ago
Not only the IPCC is extremely cautious and conservative but since it works by committee it takes years to reach an agreement. Their reports are always full of outdated data. One example, the IPCC has ignored feedbacks in its latest reports something which has been frequently criticized. > Mario Molina, who shared the Nobel prize in chemistry in 1995 for his work on depletion of the ozone layer, said: “The IPCC report demonstrates that it is still possible to keep the climate relatively safe, provided we muster an unprecedented level of cooperation, extraordinary speed and heroic scale of action. But even with its description of the increasing impacts that lie ahead, the IPCC understates a key risk: that self-reinforcing feedback loops could push the climate system into chaos before we have time to tame our energy system, and the other sources of climate pollution.” https://www.theguardian.com/environment/2018/oct/09/tipping-points-could-exacerbate-climate-crisis-scientists-fear https://www.theguardian.com/environment/2018/oct/09/tipping-... Edit: "ignored" was probably a too strong word. "Understated" would have been closer to reality. Edit 2: Here's what the founder of 350.org said about the last report: > This is the scariest thing about the IPCC Report — it’s the watered down, consensus version. The latest science is much, much, much more terrifying. https://twitter.com/Agent350/status/1049717120697753601 https://twitter.com/Agent350/status/1049717120697753601
- radford-neal 7y ago
  It's only by accounting for possible positive feedbacks that the IPCC gets up to the 1.5 to 4.5 degrees C range. It's widely accepted that if there were no positive feedbacks, the increase from doubling CO2 would be about 1 degree C. So you're saying that after decades of not being able to decide how big the net feedback is, scientists have suddenly established that it's "safe to say" that for even less than a doubling of CO2, an increase of at least 2 degrees C is "a given"?
  - pier25 7y ago
    It's a fact the IPCC has not considered feedbacks seriously. I have no qualifications to declare this, but many high profile scientists have stated it. Also, the new models which will be presented in the 2021 report will show how warming is occurring much faster than previously stated. > In earlier models, doubling atmospheric carbon dioxide (CO2) over preindustrial levels led models to predict somewhere between 2°C and 4.5°C of warming once the planet came into balance. But in at least eight of the next-generation models, produced by leading centers in the United States, the United Kingdom, Canada, and France, that “equilibrium climate sensitivity” has come in at 5°C or warmer. Modelers are struggling to identify which of their refinements explain this heightened sensitivity before the next assessment from the United Nations’s Intergovernmental Panel on Climate Change (IPCC). But the trend “is definitely real. There’s no question,” says Reto Knutti, a climate scientist at ETH Zurich in Switzerland. “Is that realistic or not? At this point, we don’t know.” https://www.sciencemag.org/news/2019/04/new-climate-models-predict-warming-surge https://www.sciencemag.org/news/2019/04/new-climate-models-p... Also, I've said from my first comment that there is more to it than feedbacks. For example NASA said in 2010: > Scientists believe the cooling from sulfates and other reflective aerosols overwhelms the warming effect of black carbon and other absorbing aerosols over the planet. Models estimate that aerosols have had a cooling effect that has counteracted about half of the warming caused by the build-up of greenhouse gases since the 1880s. https://earthobservatory.nasa.gov/features/Aerosols/page3.php https://earthobservatory.nasa.gov/features/Aerosols/page3.ph... A more recent paper from 2019 used a new method to determine how much cooling is happening from aerosols and determined it to be about double over previous estimations. https://www.sciencedaily.com/releases/2019/01/190122104611.htm https://www.sciencedaily.com/releases/2019/01/190122104611.h... https://science.sciencemag.org/content/363/6427/eaav0566 https://science.sciencemag.org/content/363/6427/eaav0566 So this means that while the official observations indicate we are at 1ºC above baseline, we may very well be actually much closer to 2ºC even ignoring feedbacks and climate lag. And then there is this whole business of how the IPCC defined what preindustrial baseline is. So even the official 1ºC of current warming might be wrong and we could be close to 1.2ºC. See this twitter thread: https://twitter.com/MichaelEMann/status/1049702520984141824 https://twitter.com/MichaelEMann/status/1049702520984141824 And finally you have to consider climate lag. Current warming has not yet been affected by GHG emissions from the past 3-4 decades, and we have emitted more GHG during that time than the previous 150 years.

pier25 7y ago

Not only the IPCC is extremely cautious and conservative but since it works by committee it takes years to reach an agreement. Their reports are always full of outdated data. One example, the IPCC has ignored feedbacks in its latest reports something which has been frequently criticized. > Mario Molina, who shared the Nobel prize in chemistry in 1995 for his work on depletion of the ozone layer, said: “The IPCC report demonstrates that it is still possible to keep the climate relatively safe, provided we muster an unprecedented level of cooperation, extraordinary speed and heroic scale of action. But even with its description of the increasing impacts that lie ahead, the IPCC understates a key risk: that self-reinforcing feedback loops could push the climate system into chaos before we have time to tame our energy system, and the other sources of climate pollution.” https://www.theguardian.com/environment/2018/oct/09/tipping-points-could-exacerbate-climate-crisis-scientists-fear https://www.theguardian.com/environment/2018/oct/09/tipping-... Edit: "ignored" was probably a too strong word. "Understated" would have been closer to reality. Edit 2: Here's what the founder of 350.org said about the last report: > This is the scariest thing about the IPCC Report — it’s the watered down, consensus version. The latest science is much, much, much more terrifying. https://twitter.com/Agent350/status/1049717120697753601 https://twitter.com/Agent350/status/1049717120697753601

radford-neal 7y ago
It's only by accounting for possible positive feedbacks that the IPCC gets up to the 1.5 to 4.5 degrees C range. It's widely accepted that if there were no positive feedbacks, the increase from doubling CO2 would be about 1 degree C. So you're saying that after decades of not being able to decide how big the net feedback is, scientists have suddenly established that it's "safe to say" that for even less than a doubling of CO2, an increase of at least 2 degrees C is "a given"?
- pier25 7y ago
  It's a fact the IPCC has not considered feedbacks seriously. I have no qualifications to declare this, but many high profile scientists have stated it. Also, the new models which will be presented in the 2021 report will show how warming is occurring much faster than previously stated. > In earlier models, doubling atmospheric carbon dioxide (CO2) over preindustrial levels led models to predict somewhere between 2°C and 4.5°C of warming once the planet came into balance. But in at least eight of the next-generation models, produced by leading centers in the United States, the United Kingdom, Canada, and France, that “equilibrium climate sensitivity” has come in at 5°C or warmer. Modelers are struggling to identify which of their refinements explain this heightened sensitivity before the next assessment from the United Nations’s Intergovernmental Panel on Climate Change (IPCC). But the trend “is definitely real. There’s no question,” says Reto Knutti, a climate scientist at ETH Zurich in Switzerland. “Is that realistic or not? At this point, we don’t know.” https://www.sciencemag.org/news/2019/04/new-climate-models-predict-warming-surge https://www.sciencemag.org/news/2019/04/new-climate-models-p... Also, I've said from my first comment that there is more to it than feedbacks. For example NASA said in 2010: > Scientists believe the cooling from sulfates and other reflective aerosols overwhelms the warming effect of black carbon and other absorbing aerosols over the planet. Models estimate that aerosols have had a cooling effect that has counteracted about half of the warming caused by the build-up of greenhouse gases since the 1880s. https://earthobservatory.nasa.gov/features/Aerosols/page3.php https://earthobservatory.nasa.gov/features/Aerosols/page3.ph... A more recent paper from 2019 used a new method to determine how much cooling is happening from aerosols and determined it to be about double over previous estimations. https://www.sciencedaily.com/releases/2019/01/190122104611.htm https://www.sciencedaily.com/releases/2019/01/190122104611.h... https://science.sciencemag.org/content/363/6427/eaav0566 https://science.sciencemag.org/content/363/6427/eaav0566 So this means that while the official observations indicate we are at 1ºC above baseline, we may very well be actually much closer to 2ºC even ignoring feedbacks and climate lag. And then there is this whole business of how the IPCC defined what preindustrial baseline is. So even the official 1ºC of current warming might be wrong and we could be close to 1.2ºC. See this twitter thread: https://twitter.com/MichaelEMann/status/1049702520984141824 https://twitter.com/MichaelEMann/status/1049702520984141824 And finally you have to consider climate lag. Current warming has not yet been affected by GHG emissions from the past 3-4 decades, and we have emitted more GHG during that time than the previous 150 years.