Scientists hopeful but cautious on Paris climate deal

While global leaders hailed Saturday’s Paris agreement as historic some scientists have warned that the cap on warming, and the deal’s timetable for phasing in greenhouse gas reductions, may yet fail to avert catastrophic climate change.

US President Barack Obama said the Paris deal is ‘the best chance we have to help save the planet’.

"We came together around the strong agreement the world needed. We met the moment," he said.

One of the crucial points of the accord was to place a cap on warming to ‘well below’ two degrees Celsius (3.6 degrees Fahrenheit) above pre-industrial levels, and to "pursue efforts" to limit the increase to 1.5°C.

But findings from the UN's own climate science body, the Intergovernmental Panel on Climate Change (IPCC) conclude that to have a two-thirds chance of limiting warming to two degrees, emissions would have to fall by 40-70 percent by mid-century.

And to reach the 1.5°C target also embraced in the new pact, those mid-century cuts would have to be even deeper: 70 to 95 percent.

"This is an historic agreement," said Steffen Kallbekken, director of the Centre for International Climate and Energy Policy.

"But this ambitious temperature goal is not matched by an equally ambitious mitigation goal," he said, using the scientific term for the drawing-down of heat-trapping gases.

Without these hard numbers -- dropped from an earlier draft -- the climate pact "does not send a clear signal about the level and timing of emissions cuts," Kallbekken cautioned.

Some scientists also voiced concern about the fact the new deal allows several years to pass before ramping up emissions reduction efforts.

"For all that is encouraging in the agreement, the time scales -- or the lack thereof -- are worrying," said Ilan Kelman of University College London. "Little substantive will happen until 2020 whilst clear deadlines for specific targets are generally absent."

Jean Jouzel, a leading French climate scientist and contributor to the UN's Nobel-winning climate panel, questioned the feasibility of hitting at 1.5°C target, saying it could only be achieved by overshooting the mark and then pulling back, which could take decades or longer.

Doom fossil fuel industry
However, some environmentalists said the Paris agreement was a turning point, predicting the 1.5°C goal would help to doom the fossil-fuel industry.

"That single number, and the new goal of net zero emissions by the second half of this century, will cause consternation in the boardrooms of coal companies and the palaces of oil-exporting states," Greenpeace International chief Kumi Naidoo said.

On the crucial financing issue, developed countries agreed to muster at least $100 billion (92 billion euros) a year from 2020 to help developing nations.

However, following US objections, it was not included in the legally binding section of the deal.

While nations most vulnerable to climate change lobbied hard for the wording to limit warming to 1.5°C, big polluters, such as China, India and oil-producing giant Saudi Arabia, preferred a ceiling of 2°C, which would have enabled them to burn fossil fuels for longer.

China's chief negotiator Xie Zhenhua said the pact was not perfect.

"However, this does not prevent us from marching historical steps forward," he said.

The crux of the climate change deal is the elimination of fossils fuels such as coal, oil and gas, to be replaced with renewable energy options and the creation of carbon markets to enable countries to trade emissions.

In an effort to get countries to scale up their commitments, the agreement will have five-yearly reviews of their pledges starting from 2023.

But scientists say that, even if the pledges were fully honoured, the Earth will still be on track for warming far above safe limits.

"This agreement is a turning point for a world transformation within a 1.5-2°C safe operating space on Earth," said Johan Rockstrom, director of the Stockholm Resilience Center.

"But now we need action consistent with science to reach decarbonisation by 2050," he said.