From Cancun to Katowice: a remarkable journey: Jo Tyndall reflects on her experience as New Zealand's climate change ambassador.

• Author: Tyndall, Jo

I have had the privilege of working on climate change over a critical period for the multilateral system of international rules. The WTO Doha negotiating round hit stormy waters, from which it has not yet recovered.

For its part, the United Nation's overarching climate treaty (United Nations Framework Convention on Climate Change, or UNFCCC) was dealt a near-mortal blow in Copenhagen (2009) when world leaders failed to get a new global climate change treaty across the line. The international rules-based system was, therefore, looking a little shaky when I was appointed New Zealand's climate change ambassador six months later.

For those who (not unreasonably) think multilateral negotiations move at a glacial pace and achieve little, it is salutary to think back to the lead-up to the Cancun climate meeting in 2010. At that time, the UNFCCC process was characterised by a stark North-South divide, with the pressure to take action on climate change exerted solely on developed countries. This was encapsulated in

* a near-exclusive developing country focus on securing commitments from the developed world via a second Kyoto Protocol commitment period, CP2 (which was ultimately achieved, but with Japan, Russia and New Zealand deciding not to join CP2 and Canada withdrawing entirely from the protocol).

* A near total breakdown in trust within the UNFCCC process.

* A severely weakened secretariat with little room for manoeuvre.

* Minimal political will to advance a new agreement, with world leaders still smarting from their Copenhagen experience.

By the time my tour of duty ended after the ministerial conference (the 24th conference of the parties, or COP 24) in Katowice, the UNFCCC had secured the Paris Agreement, and landed the essential 'rulebook' (transparency and accountability) to enable the agreement to function. This sets a clear but flexible basis for all member countries to take climate action and gives the globe a fighting chance of avoiding dangerous temperature rise (albeit with a narrow window within which to do so).

How did all that happen? It is self-evident that, if the United States is not engaged, then securing a global agreement is pushing the proverbial water uphill. Conversely, it is absolutely the case that the biggest single reason we have the Paris Agreement is because post-Copenhagen the United States made a sustained, determined effort to work with China as the first critical step. The companion announcements by Presidents...