ZEC is a crucial component for calculating the remaining carbon budget
Simulations to quantify it are missing from CMIP6
We request just ONE tier-1 simulation from ESMs. EMICs and ESMs may perform additional simulations too
Participating model groups will be offered co-authorship on a manuscript to be submitted this year (by Dec 2019)
The Zero Emissions Commitment (ZEC) is a key component of calculating the remaining carbon budget to stay within climate targets. Much effort is put into measuring and constraining TCRE - the Transient Climate Response to cumulative carbon Emissions - but also required is parallel information on the ZEC which quantifies the subsequent temperature change following cessation of emissions. Both are required to relate carbon emissions to the eventual warming.
Lack of literature on near-term ZEC led IPCC Special Report on 1.5 degrees to assume for the estimation of carbon budgets that ZEC was zero. But evidence exists that ZEC can be (a) non-zero; (b) both state and rate dependent. When we consider very low climate targets, such as 1.5 or 2 degrees a small uncertainty in ZEC (of even just 0±0.1oC) leads to a very substantial fractional uncertainty in the remaining carbon budget.
It has therefore emerged that quantitative information on ZEC is a key gap in our knowledge, and one which is not filled by currently planned CMIP6 simulations.
ZEC-MIP aims to fill this gap as efficiently as possible: it has been designed to address this vital question with only ONE tier-1 simulation (A1, see document link below).
A paper is planned for submission before the end of December 2019 to quantify ZEC from ZEC-MIP simulations. Any participating group will be invited for co-authorship. Beyond this it is anticipated that IPCC AR6 WG1 report will draw on ZEC-MIP simulations in their assessment of remaining carbon budgets. Data available in the ESGF by the data submission cutoff of circa Sept. 2020 will be eligible to contribute to that assessment even if it was not included in the submitted paper.
The document linked here lays out the ZEC-MIP simulations.
B.1 emissions data for 1000 PgC "bell curve"
B.2 emissions data for 750 PgC "bell curve"
B.3 emissions data for 2000 PgC "bell curve"