Sharjah24 – AFP: UN projections of how much current climate policies and national pledges to cut carbon pollution will slow global warming are more uncertain than widely assumed, researchers reported Monday.

Leading into this month's COP26 summit, the UN said existing policies would see Earth's average surface temperature rise a "catastrophic" 2.7 degrees Celsius above preindustrial levels by 2100.

Renewed pledges from large emitters such as India would have a negligible effect on warming this century, the UN said during COP26, and were still worlds away from the Paris Agreement temperature goal of 1.5C of warming.

But the apparent precision of these estimates is misleading, according to a new study, written by several contributors to the UN reports it calls into question.

"The false precision to climate outcomes given during COP26 may lead countries to believe they are making good progress, when the opposite may be true," said first author Ida Sognnaes, a senior scientist at the CICERO climate research centre in Olso.

At issue is the standard method used to connect the dots between a set of climate policies and the end-of-century temperature increases they might lead to.

Most climate projections are based on models that start with the desired temperature outcome –- a cap on global warming of 1.5C or 2C, for example -– and then work backwards to see what policy levers need to be pulled in order to get there.

In this "backcasting" approach, experts adjust variables such as coal use, renewables and afforestation to hit the end-of-century target.

Seven different climate modelling groups used this technique to assess how voluntary pledges under the Paris treaty running to 2030 -- known as nationally determined contributions -- would play out by 2100.