The Limits of Limits

Scientists Debate Planetary Boundaries at New York Academy of Sciences


Intense debate among scientists over how local and global tipping points are interconnected have spurred trenchant questions about the science behind the planetary boundaries thesis. While some scientists maintain we are fast approaching a point of no return, others challenge if this framework serves to achieve environmental goals or to breed complacency and hopelessness.

March 26, 2013 | Robert Lalasz,

Does Earth have limits — limits to how far we can push its natural systems and deplete its resources, beyond which we will incur major blowback?

Almost every environmentalist would answer “yes” — and have pugnaciously strong opinions about what we should do (or stop doing) to avoid crossing such lines. But what does science tell us about Earth’s limits? Which are really science-based? Can innovation stretch any of them? Are they even useful for motivating policymaking and behavior change?

A world-class panel of scientists grappled with these questions last Thursday’s during “The Limits of the Planet: A Debate” — the final forum in this year’s “Nature and Our Future” discussion series, sponsored by The Nature Conservancy and held at The New York Academy of Sciences headquarters in lower Manhattan.

The major disagreements of the evening came over 1) whether outlining global limits for the stable functioning of nature (as opposed to tipping points for individual ecosystems) is good science — and 2) whether “limits” are the correct approach to achieving environmental goals. On both points, not everyone was in the Bill McKibben/ camp.

“The evidence is incontrovertible that there are local tipping points — for coral reefs, for instance — but not so for global ones,” said Erle Ellis, a panelist and associate professor of geography and environmental systems at the University of Baltimore, Maryland County. “It’s not a runaway train. Ecosystems change, but it’s not a domino effect. You can change all the systems on the planet. But does that constitute a global tipping point?”

Howarth, Liverman and Galaz: This Is Not Your Father’s Population Control, Limits-on-Growth Debate

Moderator David Biello, an associate editor at Scientific American, framed the discussion by introducing the seminal 2009 paper by Rockstrom et al. in Nature (“A safe operating space for humanity“) that first broached numerical thresholds for nine “planetary boundaries” — categories of human-nature interaction ranging from climate change to land system change, rate of biodiversity loss to ozone depletion.

The planetary boundaries thesis maintains that crossing these thresholds amounts to passing tipping points, beyond which regional or even global ecological systems could be destabilized. For example, boundary advocates warn that increasing global atmospheric carbon dioxide concentration above 350 parts per million could accelerate the effects of climate change into a nightmarish scenario of extended heat waves, killer storms, droughts, crop failures, species extinctions and mass environmental refugee movements.

“These might be the limits that determine the length or the brevity of the Anthropocene,” said Biello.

Bob Howarth, professor of ecology and environmental biology at Cornell and a proponent of the planetary boundaries thesis, agreed — and added that the paper even omitted or underestimated factors such as methane from cattle and nitrogen pollution, which are emerging as critical threats to the planet’s environmental health.

Methane is the unseen driver in climate change,” Howarth said. “The climate system is much more responsive to methane than to carbon dioxide, and even if we control carbon, we’ll still have warmed the planet by 2 degrees in 35 years because of methane pollution alone. But this is low-hanging fruit — with shifts in diet to less meat consumption, we could make a big difference.”

And nitrogen pollution, he added, is degrading two-thirds of our coastal bays and estuaries as well as 20% of US annual agricultural production — not to mention contributing to ozone pollution that causes 30,000 premature deaths in the United States every year. “We are already over the global tipping point for nitrogen,” Howarth said.

Diana Liverman, co-director of the Institute of the Environment at the University of Arizona and a coauthor of the Nature paper, said it’s crucial to add meeting basic social needs — like freedom from hunger and poverty and access to safe drinking water — to the call for staying within planetary boundaries. (This is known in policy circles as “the doughnut.”) Combining these social and ecological goals into one paradigm might seem daunting — but doing so would often require just small percentage shifts in resources, she argued.

“To meet the food needs of everyone on the planet, we would need to increase or reallocate food supply by 3 percent,” Liverman said. “To provide electricity to everyone would only increase CO2 emissions by 1 percent. 80 percent of the world’s nitrogen production goes to meat production — small decreases in that would really help. Limits don’t necessarily mean less consumption, but redistribution and innovation.”

Victor Galaz, associate professor and senior lecturer at the Stockholm Resilience Centre, added that the planetary boundaries concept has made a deep contribution to environmental policy and science by recasting Earth as a set of very complex systems. “This is a very very different discussion that the limits-to-growth debates of the 70s,” he said, in which simple reductions in the growth of population, consumption and GDP were considered to be the answers.

“There’s obviously still lots of disagreement about how the tipping points are connected, especially among regional systems — that’s the frontier of the science,” Galaz said. “But there isn’t an opposition between innovation and boundaries. Planetary boundaries and earth systems can inform a focus on innovation that’s less focused on technology and more on economic and social innovation. They can be quite powerful political constructions that mobilize political action — it just depends very much on the nature of the threshold, what the scale is, and the nature of the collaboration.”

Blomqvist and Ellis: Almost All Limits Are Local

But Linus Blomqvist, director of the Conservation and Development Program at the Breakthrough Institute, countered that global limits have limited utility in shaping policy — becauseissues such as land-use and nitrogen are essentially local.

“It makes sense to use global indicators for CO2, because it doesn’t matter where a carbon molecule comes from for it to have an effect on climate,” Blomqvist said. “But taking a gallon of water from the Amazon River is very different from taking one from the Colorado River. You’re adding apples, oranges, tomatoes and bananas — it’s risky and misleading to build policy on global indicators for these activities.”

He also argued that a global boundary for nitrogen masks that nitrogen is unevenly distributed globally. “The problem is not total nitrogen, it’s that nitrogen ends up in the wrong places,” he said. “To treat it as a global issue is bad science and could lead to bad policy. We need to think about these issues at the right scale to get to the goals we all want to reach.” (Howarth later disagreed, saying that global policies and techniques that segregate crop production from the animals those crops feed — and then don’t return the animal waste back to the field — have made nitrogen pollution a planetary-scale issue.)

Ellis went further than Blomqvist, deriding the very utility of limits and the catastrophic tipping points they imply. “The original planetary boundaries paper had ‘The Road to Copenhagen’ in its subtitle,” he said. “In other words: ‘Paved with good intentions, but doomed.’”

“Climate science does give us evidence for tipping points regarding climate change,” Ellis continued. “Butthe theory and evidence is weak that there are planetary tipping points that will shift a global biospheric process into a very negative state. Our ecosystems are amazingly distinct; they can be transformed, and you can still save some. And while climate change will push all the systems in the same way, they behave very differently in response.”

Ellis also criticized some of the planetary boundaries as having no basis in science. “In many parts of the world, land use has been sustained at or above the planetary boundary of 15 percent for many centuries — there’s no evidence for the 15 percent number used in the paper,” he said. “And we shouldn’t be using a quota system for species loss. Instead, we should be focusing on incentives and opportunities, not targets and quotas. Things people can get on board with make a lot more sense.”

What Good is Setting A Line if Only to Cross It?

The advocates for the planetary boundaries thesis countered by arguing that transgressing boundaries will have severe costs for the Earth – from wars over water access to more droughts to continued coastal degradation and abrupt and irreversible changes in climate, said Howarth.

“There are likely to be thresholds for a lot of these, with a lot of non-linearities when we breach them,” Howarth added. “And not all the difficulties will be abrupt — some will be chronic, like ocean acidification.”

Is there any reason for optimism? Ellis maintained that some major trends such as agricultural intensification and urbanization are already improving the state of the biosphere by reducing human footprints. “We can feed more people with less land if we manage it with policy,” he said. “We could already have a reduction in extinction rates without focusing on extinction.”

“That’s going to require shifts in biofuel policy,” countered Howarth. “The trends we have today show that we someday could be using 30-100% more land on biofuels than food.”

Galaz said that there are “huge opportunities” in genetic technologies, synthetic biology, and information technology — but that the Anthropocene had put a premium on shifting to systems thinking and getting institutions aligned with that paradigm.

“We need to be thinking about the Earth as a very complex system,” he said. “We’re going to continue to have debates about things such as geoengineering and invasives, and we have to get used to them. There are no more isolated problems. Planetary boundaries teaches us that systems mesh and have to be dealt with together.”

But is “limits” thinking the best motivator for facing these challenges? 

“If we do pass some limit, like 350 [parts per million CO2] — what do we do?” asked Ellis. “Setting a line and crossing it — what advantage does that give us? It doesn’t seem an effective strategy. We shouldn’t fear a boundary, but ask: What are we doing, and how can we do it better? We’re costing our children money.”

“Targets are inherently artificial, and yeah, you’re going to go over them, but they are an effective way to communicate to policymakers and the public,” countered Howarth. “We can all agree that we should be less than we are now. So I view planetary boundaries as a pretty powerful synthesis and communications tool.”

“Getting people to the basic social foundations doesn’t take much,” added Liverman, who said that rapidly growing nations such as Brazil and China are learning how to grow with less environmental impact. “It’s very possible for us to reduce our resource use back to acceptable levels. I think that’s possible. If I didn’t, I wouldn’t have been working on this for 30 years.”


Photo Credit: Flickr user solobasssteve

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