New Delhi, Dec. 8: No scientific assessment has clearly justified a key target of climate-change negotiations: to limit the rise in average global temperatures to less than 2°C, a team of scientists said yesterday.

It said that while the 2°C target had helped anchor discussions, including the UN climate-change talks now under way in Paris, it had been ineffective in triggering emission reductions.

The scientists, from the Institute of Atmospheric and Climate Science in Zurich, Switzerland, said negotiators and countries should stop wrangling over temperature targets and focus instead on just starting serious actions to reduce their Earth-warming greenhouse gas emissions.

Their critique of the 2°C climate change target, published yesterday in the journal Nature, comes at a time negotiators from 196 countries are trying to finalise a global pact that seeks to achieve this limit through emission reduction.

Several scientists had earlier suggested the Earth was likely to experience severe impacts of climate change if the average temperature rise exceeded 2°C by 2100.

"It is foolish to think that we set ourselves a goal with the idea to maintain it for nearly a century - we don't do that for any other problem in life," said Reto Knutti, the head of the climate physics group and lead author of the paper in Nature.

The UN Framework Convention on Climate Change formally decided in 2012 to pursue actions in line with a 2°C target.

Knutti and his colleagues say this target was a political decision only loosely informed by science.

No scientific assessment has ever defended or recommended a particular target, the researchers said, adding it was "high time" for a scientific assessment to determine whether the global average temperature was even a meaningful quantity.

"The discussion (on a target temperature) is like debating whether to take the escalator or the stairs when there are flames all over the house, and at the same time not getting up from the coffee table," Knutti told The Telegraph. "You don't need full certainty to act when the house is on fire."

Ahead of the Paris talks, over 180 countries, including India, had pledged action plans - from expanding renewable energy and increasing energy efficiency to adding forests - as part of their individual effort to reduce emissions. But an analysis of these pledges suggests they are not sufficient to cap the temperature rise at 2°C.

"No matter what target we pick, the same things need to happen, sooner or later. Countries should focus on where to start mitigation and not where to end," Knutti said.

The researchers have also called for scientific studies to quantitatively determine the local impacts of a 2°C increase in temperature: that is, how a temperature rise will impact different sectors such as agriculture, health, water resources and sea levels.

An independent study by US scientists released in November had suggested that the pledges made by countries for emission-reduction action up to 2030 had the potential to reduce the probability of the highest levels of warming.

"It is not just about the 2 degrees," Gokul Iyer, the study's lead scientist at the University of Maryland in the US, had said in a media release.

"It is also important to understand what the (pledged actions) imply for the worst levels of climate change."

In their study, published in the US journal Science, Iyer and his colleagues had found that if countries did nothing to reduce emissions, it was likely that the temperature increase would exceed 4°C.

"Long-term temperature outcomes would hinge on emission-reduction efforts beyond 2030," Iyer said. "If countries implement their pledges to 2030 and ramp up efforts beyond 2030, we'll have a much better chance of avoiding extreme warming."