"Limiting overshoot" is a wonderful phrase for describing failure. It is the title UNEP gave its latest report, which concedes in effect that the world will exceed the 1.5°C limit set at the Paris COP.
The headline finding is that the world is now set to cross the 1.5°C threshold, relative to pre-industrial levels, within the next few years, earlier than previously expected. That is an admission of defeat, even as the report tries to put it in context. The question has shifted from "can we avoid it?" to "how do we limit how far above it we go, and for how long?"
The report is disappointing but probably inevitable. The global unity of purpose that produced the Paris targets began to fade once the scale of the task became hard numbers at national level. The Trump administration's attitude weakened the resolve further, and for some countries the consequences are already large and growing.
Three figures from the report will probably anchor the revised targets, and together they form one spectrum:
• If national pledges are fully met: peak warming of around 1.8°C.
• If current policies continue unchanged: roughly 2.6°C of warming by 2100.
• Without stronger action: many scenarios peak well above 2°C.
Even the best case overshoots 1.5°C by about 0.3°C.
The report also sets out the larger risks. We already see extreme weather around the world but what this assessment envisages goes well beyond anything we have observed. The longer and higher temperatures overshoot 1.5°C, the more likely the world is to trigger irreversible tipping points, including destabilisation of major ice sheets, degradation of the Amazon rainforest and disruption of Atlantic Ocean circulation. Each additional fraction of a degree intensifies the impacts.
My default position is optimistic as I have always looked for the upside. But the pace of progress, the lack of urgency and the competence of the leadership tasked with addressing climate change are pushing me towards realism.
Two terms in national climate reporting explain why. "With existing measures" (WEM) projects emissions on the policies already in force. "With additional measures" (WAM) adds the measures governments have planned but not yet adopted. In business terms, WEM is the probable outcome and WAM is the possible one.
It is tempting to read the report's "pledges fully met" case as leaving room for upside. As Ireland's figures below show, even the WAM ceiling falls short of the legal target. The gap has to be closed with policies that do not yet exist.
Only the EU and Ireland report WEM and WAM formally. For the UK the bars show the Climate Change Committee's credible plans and the government's full plan. For the USA, current policies and for the world, current policies against fully implemented NDCs. The US has no additional-measures case because it has withdrawn its pledge.
UN Secretary-General António Guterres says the world must make the overshoot above 1.5°C "as small and short as possible". The report puts the cost of delay plainly: "Every year of delay and every fraction of a degree above 1.5°C increases risks and makes recovery harder."
