Climate Negotiators Wrestle with Dangers of Half a Degree

The striking shift to 1.5 degrees is an acknowledgment that a mere half degree of extra warming could mean profound changes for the planet.

After years of debate over whether it is adequate or even possible to limit global warming to 2 degrees Celsius, negotiators in Paris are suddenly nodding more in the direction of 1.5 degrees.  Why?

Mostly, it's a matter of climate science—not of backroom deal-making, green ideology or cold-blooded calculations about how fast the world's nations are willing to change.

The latest science shows that a mere half degree of extra warming between now and the end of the century could mean profound changes for the planet and many of its inhabitants.

An expert review published by the UN several months ago offered several sobering examples of the difference between the 1.5 degree and 2 degree pathways.

"Most terrestrial and marine species would be able to follow the speed of climate change," it said of the 1.5 degree track.  "Up to half of coral reefs may remain; sea level rise may remain below 1 meter; some Arctic sea ice may remain; ocean acidification impacts would stay at moderate levels; and more scope for adaptation would exist, especially in the agricultural sector."

So the striking shift toward the 1.5 degree goal that seems to be emerging in Paris shouldn't be dismissed as crassly political.  It's not just bait to draw more nations into embracing the treaty.  Rather, it is an acknowledgement that an extra half degree of warming would indeed hit many of them harder than others.

Nor is it blithely ideological. If the most vociferous campaigners like Greenpeace, Oxfam and Friends of the Earth have rallied around the 1.5 degree mark as an article of faith, that was not just to make bolder headlines, but because they saw the writing on the wall earlier than some political leaders did.

And it’s not a Pollyannish prescription that refuses to acknowledge how difficult it would be to hit the 1.5 target.  Rather, this is a decision not  to shrug off the very science that is the at the heart and soul of the treaty process.

Judging by an update issued late Tuesday night by a Paris subcommittee hashing out the different perspectives, the main question now seems to be how much weight to give the 1.5 degree goal.

Most parties, the subcommittee reported, want "to somehow reflect the 1.5 degree C temperature limit" in the section of the pact that describes its ultimate purpose.

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