David Roberts (Vox) on Why Zero is Way More Than 2 or 350


Much of the debate on how to frame the climate change challenge is between the generally agreed-upon goal of limiting temperature rise to 2°C (3.6°F) or even 1.5°C or less over pre-industrial levels, or keeping levels of carbon dioxide (CO2) in the atmosphere to 350 parts per million. In both cases people are being asked to avoid something: a 2 degree rise or more than 350 ppm CO2.

The 2 degree or lower avoidance test was formally adopted by parties to the U.N. Framework Convention on Climate Change (UNFCCC) in a 2010 meeting in Cancun, Mexico, and reaffirmed at the climate talks in Paris in December 2015. It was a remarkable achievement that 195 nations agreed to it, and it has been widely adopted by the scientific community.

The 350 ppm test is advocated by the organization, 350.org, founded by Bill McKibben, the American environmentalist/activist/writer, with strong support from Dr. James Hansen, an early champion of climate change action. The test is simply a way of measuring the ratio of carbon dioxide molecules to all of the other molecules in the atmosphere. For much of life on earth, the level of CO2 in the atmosphere was at 275 ppm and only with industrial growth and the burning of fossil fuels did the level begin to rise, slowly at first and faster and faster in the 20th century. We now have 400 ppm in the atmosphere and the scientific consensus is that we need to reduce levels to 350 ppm if we are to avoid the catastrophic impacts from a runaway global warming.

As an alternative way of talking about what we need to do to survive, some used the concept of a carbon budget where we estimate the additional amount of carbon that can be released into the atmosphere before we run out of room for more carbon and avoid the worst impacts. In the Summary for Policymakers for the 5th Report on climate change, the Intergovernmental Panel on Climate Change (IPCC) indicated that in order to have a 66% chance of avoiding catastrophic climate change in excess of 2°C, the planet is limited to a total of one trillion tons total carbon emissions since the dawn of the industrial revolution. In effect, this sets a budget for how much carbon can be emitted. Unfortunately, we have already burned half of that amount and we will exceed the budget by 2040.

A natural outgrowth of the carbon budget talk was the concept of Zero carbon. Since we have loaded the atmosphere with so much carbon that will last for decades, we have to get to the point of eliminating all carbon emissions to save the planet for future generations. No more carbon. None. Zero.

2-1-16 Zero copy








Roberts in Vox

Roberts points out that the zero-carbon budget was adopted by the parties in the Paris climate talks. Quoting from Article 4 of the Paris Agreement:

In order to achieve the long-term temperature goal set out in Article 2 [the 2°C or less test], Parties aim to reach global peaking of greenhouse gas emissions as soon as possible, recognizing that peaking will take longer for developing country Parties, and to undertake rapid reductions thereafter in accordance with best available science, so as to achieve a balance between anthropogenic emissions by sources and removals by sinks of greenhouse gases in the second half of this century, on the basis of equity, and in the context of sustainable development and efforts to eradicate poverty. (Emphasis added). Article 4

In effect, the parties have agreed that by between 2050 and 2100, there will be a balance between GHG emissions and carbon sinks. In other words, after accounting for carbon sinks there will be no net carbon emissions, which constitutes (net) Zero carbon emissions. Or, one will be allowed to emit any carbon only if it is offset by a carbon sink or carbon capture and storage.

Roberts explicates the paragraph above for all the legalese and diplomatese, and argues that despite the equivocations shooting for zero carbon emissions is so much clearer as a way to frame the debate, and he’s right. The 2°C temperature rise and cap on 350 ppm of CO2 are science-based, but they require complicated assumptions and scenarios to fully understand. Moreover, a 2°C temperature rise does not sound very threatening and so much more explanation has to be added. And 350 parts per million of something that is invisible does not seem scary.

It is simply easier for people to understand that we have to shoot for a concrete target of no more carbon in the atmosphere. Zero. The message is clear: we will get to a point when people/businesses/governments will not be allowed to emit ANY carbons.

The concept has what Roberts calls “a bracing clarity of vision.”

2-1-16 riding the burning zero copy







The distinction between Zero carbons and the other tests is parallel to the distinction between a cap-and-trade system of reducing GHG and a carbon tax. The carbon tax is simply easier for most people to understand and it is so much easier to administer than a cap-and-trade regime.

It must be noted that the provision of the Paris agreement on which Robert focuses does not in fact use the word “zero,” presumably because it would raise tremors among the regulated community (that’s all of us). Just like the term carbon tax raises the ire of regressive forces in certain communities.

But the critical point, as Roberts argues, is that the meta-message is out there. Like it or not, we are headed toward a world where there will be no tolerance for more carbon emissions. None. Zero.

Of course we do not know when we will get to this world and even necessarily how we will get there. But we have started down that road and there is no turning back. As Roberts says: “We’re headed for carbon zero. It sends a clear signal to investors that each new long-term fossil fuel investment, each new mine, well, pipeline, coal plant, or export terminal, is riskier than the last.”

2-1-16 zero-people copy




The fact that not many, if any, of the commitments of the Paris Agreement are legally binding is not a deterrent. The die has been cast, the headline set in bold type: “We are heading for zero…That’s a clearer goal, and a more hopeful and inspiring vision of the future, than avoiding 2 degrees [or 350 ppm]”



A caveat. Speaking of zero “carbon” emissions does gloss over the critical contribution of other GHGs to the global warming problem. For instance, in Ireland methane remains a significant component (about 30%) of the country’s total GHGs and methane has a more global potential warming effect than CO2. Going to zero methane would provide short term relief to global warming until zero carbon took effect.



David Roberts, “Why zero is a better climate target than 2 degrees,” Vox (21 December 2015).  www.vox.com/2015/12/21/10629172/climate-change-target-zero

350.org, The Science. 350.org/about/science/

Conference of the Parties Twenty-first session Paris, 30 November to 11 December 2015, ADOPTION OF THE PARIS AGREEMENT  www.cop21.gouv.fr/wp-content/uploads/2015/12/l09r01.pdf

“Carbon Budget” in the iePEDIA section of irish environment magazine (1 October 2013).  www.irishenvironment.com/iepedia/carbon-budget/

“Global Potential Warming” in the iePEDIA section of irish environment magazine (1 December 2011).  www.irishenvironment.com/iepedia/global-warming-potential/





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