The Story of the Trillion Tons of Carbon


Here is an axiom that bears repeating: Measure what matters. The classic case of faulty measurement remains Gross Domestic Product, whose counterproductive calculations were pilloried in a 1968 speech by Robert Kennedy and detailed in a 1996 essay, “If GDP is up, why is America down?

Yet even solid measures may offer narrow views. And so, a corollary: What matters may have multiple measures. Take the example of the three targets for action on human-induced climate change. Two may be familiar: 2ºC and 350 (or 450) parts per million. An additional figure, a trillion tons (metric tons), appeared only this spring. Each is distinct, and each has a story to tell.

Three Measures, Three Stories

Most intuitive and visceral among the measures is temperature change. We know what a 2ºC difference feels like. At least we think we do. In reality, projected and potential effects of a 2ºC warming on precipitation patterns, crop viability and human health are often greater than one might imagine. Seeking to keep these impacts to a minimum, many scientists have urged efforts to restrict temperatures rises to within 2ºC of pre-industrial levels, and the European Union has taken 2ºC as its warming target.

Human-caused temperature changes are the result of rising concentrations of CO2 and other greenhouse gases in the atmosphere. It is often said that limiting temperature increases to 2ºC requires stabilizing CO2 concentrations at 450 parts per million (ppm), but some studies suggest a lower figure. Climate scientist James Hansen and others have recommended 350 as the best target for minimizing planetary feedback like ocean acidification and ice sheet melting. Atmospheric targets can inform the design of emission caps in any cap-and-trade system, as Paul Krugman wrote in a recent column.

A fresh perspective is offered by the measure of total carbon emissions, tallied from the beginning of the industrial era and into the future. The authors of a recent paper published in Nature find that roughly a trillion tonnes (i.e. metric tons, each roughly equivalent to 1.1 tons) represents the total human carbon emissions budget, the amount that can be released with a fair probability of holding to the 2ºC margin of relative climate stability. And they find that we are about halfway there. A little more than half a trillion tons have been released since the beginning of the industrial era. (More on the Nature paper here.)

Progress by the Ton

Let’s continue the budget metaphor. Say that all of humanity – past, present and foreseeable future – has a dollar to spend on carbon-fueled economic growth. Those of us that have reaped the industrial world’s benefits doled out two [four] bits or so from 1750 to 2008, and some of those investments paid off handsomely. Standards of health, education and material living rose. And the global digital network emerged.

Fair to say, these expenditures largely preceded any broad realization that the carbon go-go days might be a passing phase. But that is no longer the case. The total bank – set, not by resource limits, but by the planet’s capacity for waste absorption – has been counted. One need not embrace central planning to wonder how a pragmatic and just CFO might eye the remaining balance. Future carbon-miserly development will depend on investments in renewable energy and energy-efficient infrastructure, as well as on institutions and norms that foster disruptive innovation. What other considerations arise?

The Global and the Multi-Generational
At last month’s Three Degrees Conference on Climate Change and Human Rights, philosopher Henry Shue stated directly: “Carbon emissions are zero-sum. … We are in direct competition for a scarce resource with future generations. … What portion of the remaining half trillion tons will be needed for global development to subsistence levels?”

Back in 1993, Shue advanced the idea (originally articulated by India’sCenter for Science and the Environment) of allocating carbon emissions based on developmental needs. Shue distinguished subsistence emissions – those required for the satisfaction of basic rights to food, water and so on – from luxury emissions. It is a view that informs the more recent Greenhouse Development Rightsframework, a climate stabilization program that allows for continued development among the world’s poorest.

Bending toward Justice, Slowly

The difficulties of reaching an international rights-based agreement are clear. It has been said that, with broad consensus on the physical science-based understandings of climate change, the discussion now turns to social science-based explorations of human systems, responses and values.

Under the anonymity of Chatham House Rules at the Three Degrees conference, one speaker lamented the “path dependency” of international human rights and climate change conversations, with officials from the two areas barely consulting each other. Other speakers pointed to recent instances in which the two paths have begun to merge. In January, the Office of the UN High Commissioner for Human Rights issued a report on the relationship between climate change and human rights, and last month the Global Humanitarian Forum published a comprehensive look at the topic.

Measures and the Unmeasurable

The trillion tons serves to frame a historical narrative, an index with which to measure how far humanity has come, where we stand and where we might go. Still, I am reminded of the words of Donella Meadows. “No one can precisely define or measure justice, democracy, security, freedom, truth, or love,” she cautioned. “Pay attention to what is important, not just what is quantifiable.”

As so, while not misconstruing carbon-driven development for justice, let’s reflect on the lopsided consumption of the first half trillion. And consider that climate-friendly progress along the arc of history may depend on a more just agreement for the next half.