Scientists Are Gearing Up for a Fight Over How Much to Limit Global Warming

Speaking in London on Monday, UN climate chief Christiana Figueres confirmed her commitment to limiting global temperature rise to below 1.5°C. To achieve this, she noted that total emissions would have to fall by almost double what would be required to achieve a 2.0°C limit, a goal that some already say is unrealistic.

She called the new target a "moonshot."

Now, the UN's Intergovernmental Panel on Climate Change is preparing to study it. On Thursday, the IPCC announced that it will produce a report on keeping global temperature rise below 1.5°C, as requested by governments attending the COP21 conference in Paris in December. There, they agreed to the goal of holding warming "well below 2.0°C" and to "pursue efforts to limit the temperature increase to 1.5°C." For many countries faced with the threat of drought and sea level rise, the half-degree target is a major victory.

The report will task scientists with determining the exact carbon emission cuts necessary for countries to meet that extremely ambitious goal.

Many scientists have been critical of such aspirational targets, arguing that countries aren't likely to agree on the needed emission reductions—current emissions targets are already insufficient for even a 2.0°C limit—and the plans rely on the use advanced carbon capture and storage technology to remove existing carbon from the atmosphere.

In other words, technology that, as yet, doesn't exist at a useable scale.

Writing this week in the journal Nature Climate Change, Glen Peters, a senior researcher at the Center for International Climate and Environmental Research in Oslo, Norway, argues that any special report must avoid "unachievable mitigation pathways." He points out that the last IPCC report assessed 116 scenarios for keeping temperatures below 2°C by 2100.

Of those, 93 percent relied on the future use of large carbon removal technology, much of which is currently unproven.

"A few years ago, these exotic Dr Strangelove options were discussed only as last-ditch contingencies. Now they are Plan A," writes Kevin Anderson, deputy director of the Tyndall Centre for Climate Change Research in Manchester, in a column for the journal Nature.

Michael Hulme, a professor of climate and culture at King's College London, has questioned why scientists are being asked how to limit warming to 1.5°C by the same countries whose current emissions commitments "fall well short" of that goal.

In a commentary for Nature Climate Change earlier this year, he notes that climate research shouldn't serve a "political agenda, " and that the IPCC should pursue more "pragmatic and decision-centred applications of climate research."

But the 1.5°C limit is largely the result of political pressure from a group of nations on the front lines of climate change. The Alliance of Small Island States has been pushing for its inclusion in official agreements since the UN's Copenhagen Climate Change Conference in 2009, and commissioning scientific reports to support their case.

For them, the issue is existential. A recent UN report suggested that the lower limit might keep sea level rise below 1 meter, and limit ocean acidification and damage to marine life. For many people, that could be the difference between staying, or abandoning their country. Several African nations, who may see far worse drought in that half-degree range, also pushed for the lower limit.

The report, which is expected in 2018, will have to address both the scientific feasibility of holding warming to 1.5°C—and the consequences if those efforts fail.