IPCC AR6 WG1 Physical Science Basis Report Released

[bdgwx]

The long awaited Assessment Report 6 from the IPCC Working Group 1 regarding the Physical Science Basis Report has been released.

https://www.ipcc.ch/report/ar6/wg1/

[bdgwx]

This will take months to read, but the headline topic of equilibrium climate sensitivity comes as a surprise to me. I was not expecting the big jump from 1.5 to 2.5C on the lower bound.

A.4.4 The equilibrium climate sensitivity is an important quantity used to estimate how the climate responds to radiative forcing. Based on multiple lines of evidence, the very likely range of equilibrium climate sensitivity is between 2°C (high confidence) and 5°C (medium confidence). The AR6 assessed best estimate is 3°C with a likely range of 2.5°C to 4°C (high confidence), compared to 1.5°C to 4.5°C in AR5, which did not provide a best estimate. SPM pg. 14

[LibertyBell]

3 hours ago, bdgwx said:

This will take months to read, but the headline topic of equilibrium climate sensitivity comes as a surprise to me. I was not expecting the big jump from 1.5 to 2.5C on the lower bound.

A.4.4 The equilibrium climate sensitivity is an important quantity used to estimate how the climate responds to radiative forcing. Based on multiple lines of evidence, the very likely range of equilibrium climate sensitivity is between 2°C (high confidence) and 5°C (medium confidence). The AR6 assessed best estimate is 3°C with a likely range of 2.5°C to 4°C (high confidence), compared to 1.5°C to 4.5°C in AR5, which did not provide a best estimate. SPM pg. 14

Okay so I was reading the graphs correctly.  From the report I got that a 3C rise was the most likely outcome, do you concur?  4C is considered the likely ceiling, but who knows at this rate.

What's this new report that's supposed to come out in March 2022?  I heard that one will be important too.

 

[bdgwx]

54 minutes ago, LibertyBell said:

Okay so I was reading the graphs correctly.  From the report I got that a 3C rise was the most likely outcome, do you concur?  4C is considered the likely ceiling, but who knows at this rate.

What's this new report that's supposed to come out in March 2022?  I heard that one will be important too.

 

Correct. Note that "likely" means 66% likelihood and "very likely" means 90% likelihood.

The "very likely" range is 2.0-5.0C.

The "likely" range is 2.5-4.0C.

This is the first report that provides a best guess...3C.

The IPPC divides the assessment reports into 3 parts called working groups. WG1 is the Physical Science Basis, WG2 is Impacts, Adaptation, and Vulnerability, and WG3 is Mitigation of Climate Change. It may be the WG2 report that is expected to be released in March '22.

[bdgwx]

Here is a great post by Gavin Schmidt on the ECS.

https://www.realclimate.org/index.php/archives/2021/08/notallmodels/

[bdgwx]

The report has been finalized and is now officially available. There is a lot of information here. As I get time I'll try to post some of the most pertinent facts and figures.

How much does net anthropogenic forcing contribute to net total forcing. 96% 

How much does CO2 contribute to the net anthropogenic forcing. 79%

How much does CO2 contribute to the net total forcing. 76%

This is table AIII.3 which summarizes the effective radiative forcing (ERF) in W/m2 of various contributing factors.