Atmospheric temperature trends under increasing CO2: contrasting CMIP5 and CMIP6 models

Atmospheric temperature trends under increasing CO2: contrasting CMIP5 and CMIP6 models

Scientific motivation

it has been widely reported that the CMIP6 models have much higher climate sensitivity that the CMIP5 models. going beyond global mean surface temperature, it would be interesting to document the entire vertical structure of temperature changes caused by increasing CO2, notably polar amplification, the warming of the tropical upper troposphere and the cooling of the stratosphere. one would like, for instance, to answer the following questions: since CMIP6 models have larger climate sensitivity, do they also have a larger polar amplification than the CMIP5 models? does the stratosphere cool more in the CMIP6 than in the CMIP5 models?

Proposed Hacking

make latitude/height plots of temperature trends, as well as time series plots, grouping the CMIP5 and CMIP6 models, and contrast: 1/ global mean surface temperature, 2/ Arctic temperature and polar amplification, 3/ upper tropospheric tropical temperature and 4/ stratospheric temperatures under A/ 4xCO2 forcing, B/ 1% forcing, C/ historical forcing and D/ SSP585 forcing.

Anticipated Data Needs

monthly surface temperature and atmospheric temperature fields

1 Like

@polvani - I’m also interested in this project. I was curious about this a couple weeks ago and plotted the global mean tas trends. With my set of models (13; trying to compare across generations, e.g., CAM5-CAM6) it appears that the multimodel mean historical trend went down in CMIP6 in the subset of models I looked at (historical / rcp8.5 in CMIP5; historical in CMIP6). This is pretty interesting, right?

Note there is a connection to Sample Model Like Observations project (I was interested in sampling surface trends like observations; this could be extended to other fields, too (as noted in that thread).

edit to note that “it went down” might be better described as it is basically the same, despite the widespread attention over ECS trends going up in CMIP6.

delighted to hear you are interested in this… can you share with us a version of the Figure you have already made? it might serve as a starting point to get us thinking.

CMIP5 Models — CMIP6 Models
CanESM2 — CanESM5
bcc-csm1-1-m — BCC-CSM2-MR
bcc-csm1-1-m — BCC-CSM2-MR

Maybe not significantly different or a result of the subset of models used, but generally not in the direction you’d expect given the increase in ECS in CMIP6.

The trends (in parenthesis) are in units of K/decade.

thanks. i guess we need more models…

I am interested in contributing to this project. I have been working on similar analysis in old models (e.g. IPCC First Assessment Report models) but would be keen to look at the CMIP6/CMIP5 models.

Getting excited for this! Looking forward to it!

Hi all,

I am part of the UW cmip6hackthon. After spending an entire morning on trying to get “Hello_world” run on Cheyenne, I realized that it is more convenient for me to work in a project with local people at UW, although this project sounds very interesting to me.

Good luck with the project!