Towards Peak Impact

The Evidence for Decoupling

In the past few years, decoupling – breaking the link between economic growth and environmental impacts – has become the new catchword in environmental debates. The OECD has declared it a top priority, and UNEP’s International Resource Panel launched a report series on the topic in 2011. And last year, interest in the idea shot up after the publication of An Ecomodernist Manifesto which declared decoupling a central objective of ecomodernism.

Some observers, though, have questioned whether decoupling has occurred, and whether it is even possible. The Guardian columnist George Monbiot declared that humanity can’t consume more and conserve more at the same time. Responding to An Ecomodernist Manifesto, Jeremy Caradonna and seventeen co-authors described decoupling as a “myth” and a “fantasy.” In this essay, I’m going to review the evidence for relative decoupling (impacts growing more slowly than the economy) and absolute decoupling (impacts being stable or declining in absolute terms). I’ll look at what trends are positive, what challenges remain, and what the future might look like with the right policies and technologies.

Trends in consumption of materials are often used as an indicator of whether or not decoupling is happening. By this measure, a landmark analysis by Thomas Wiedmann and others found that “achievements in decoupling in advanced economies are smaller than reported or even nonexistent.” By allocating all raw material extraction to the places where the final consumption of goods occur, they were able to account for the fact that most developed countries increasingly buy their goods from abroad rather than producing them domestically. Wiedmann et al. concluded that the total per-capita consumption of material resources (including fossil fuels, metal ores and industrial minerals, construction minerals, and biomass) had kept pace with or even exceeded growth in GDP in most developed countries between 1990 and 2008.

However, the study’s findings are not quite as discouraging as they first appear. As Chris Goodall has pointed out, most of the rise in developed economies’ resource consumption was in the form of indirect use of construction materials, especially in China. A big part of these construction materials went into built structures that will last for decades; linking these on a year-to-year basis to consumption in developed economies likely exaggerates their material footprint.

More importantly, trends in material consumption are not necessarily good indicators of trends in environmental impacts. Decoupling, as Ester van der Voet, an industrial ecologist at the University of Leiden, observes, “is not just a matter of weight.” Wiedmann et al. are clear on this too, acknowledging that the material footprint ”does not provide information on actual environmental impacts of resource use but only on the potential for impacts.” Without factoring in the technologies that are used to extract raw materials and turn them into goods, we know very little about trends in environmental impacts like greenhouse gas emissions, land-use change, water depletion, or pollution.

There is no better illustration of this fact than the case of mined resources like metal ores, industrial minerals, and construction materials. These make up the lion’s share of the material throughput of most countries, yet do not rank high in terms of global environmental threats, especially in terms of biodiversity loss.

Mining of iron, bauxite, copper, gold, and silver – which together account for the vast majority of metals used globally – occupies about 0.007% of earth’s ice-free surface, according to a recent study. Metals and minerals make up more than half of the raw materials consumed in the EU, but account for less than 10% of global warming potential and land-use competition (although they are estimated to represent about one third of human toxicity).

In terms of overall human impacts on the environment, the burning of fossil fuels and consumption of biomass loom much larger than mining for minerals and ores. Biomass consumption, in the form of crops, meat, and wood, is the world’s major source of habitat and biodiversity loss, as well as a big contributor to greenhouse gas emissions and pollution of air and waters. Yet despite increasing per-capita demand for crops and animal products, the total amount of biomass harvested per capita worldwide has remained nearly constant over the last century according to a 2013 study by Fridolin Krausmann of the Institute of Social Ecology in Vienna.

The total biomass harvest has remained constant because while food demand has risen, the use of biomass for energy has declined dramatically. Starting in the 19th century, coal replaced wood as the leading source of primary energy globally. Around the same time, tractors, trolleys, trains, and automobiles began to displace draft animals for motive power, reducing demand for animal feed. And a variety of technological improvements raised the efficiency with which biomass is converted into final goods.

Looking more closely at wood, total global consumption has been stable since the late 1980s, suggesting absolute decoupling in this regard. The actual impacts of wood production – especially land-use change – are harder to measure, both because declining wood harvesting from natural forests has been partly offset by expanding tree plantations and because it is entangled with cropland expansion and other drivers. Nevertheless, the plateauing demand for wood combined with a larger share of plantations – which tend to have far higher yields – suggests that the total area impacted by wood harvesting may have declined in absolute terms.


With declining demand for biomass for energy and more efficient wood production, the environmental impacts of biomass consumption have shifted toward food production. Consumption of crops and meat, the main driver behind farmland expansion, has increased dramatically in the last half century, with global food calorie consumption roughly tripling and per-capita consumption going up by about one-third since 1960. But that doesn’t mean that the land footprint of agriculture has risen proportionally.

The total area of cropland and pasture grew by about 10% between 1960 and the mid-1990s. But since then, FAO data indicate little further growth. (For the last five to ten years, the aggregate trend reported by FAO may not be reliable, as there has been an uptick in harvested cropland area, and the decline of pasture in the same period may be an artifact of reporting.) Meanwhile, the amount of farmland used in food production per capita has declined by about half since 1960, in spite of much richer diets, thanks to higher yields and cropping frequencies as well as improved efficiency in the conversion of feed to meat.


Thomas Kastner and others have shown how this pattern holds for every world region, where the amount of cropland needed for final consumption – including crops grown for livestock feed – has declined over time, on a per capita basis.*

Source: Kastner et al., 2012

In large parts of Europe, this decline has been so significant as to offset even growth in population, meaning that the amount of cropland needed to meet food demand in these regions has fallen in absolute terms. What’s even more interesting is that the cropland requirement is not necessarily higher in rich countries than it is in poor countries. For instance, the per-capita cropland requirement is about the same in Western Europe as it is in West Africa. This is explained by the combination of low yields and meager diets in West Africa, and high yields and rich diets in Western Europe.

Much of the improvement in farming efficiency has been put to richer diets rather than farming less land. In particular, the larger share of meat in diets as countries get richer has further increased the amount of crops required for the average diet. Yet with further economic growth, pressures tend to ease somewhat. Food calorie consumption stabilizes by the time countries reach high-income status, and while meat consumption continues to grow, per-capita demand for resource-intensive beef has declined markedly in developed countries.

While many of the trends are promising, it’s too early to declare “peak farmland.” Forecasts suggest the world will need to produce 70-100% more crops by 2050. Doing so without expanding cropland area will require a rate of crop yield improvement on a par with that seen during the second half of the 20th century, if not larger. Maintaining historical yield trends may not be enough to stop farmland area from growing in the next few decades. Accelerating the pace of crop yield gains is therefore among the chief environmental and conservation challenges of this century. (The extent of pasture, on the other hand, might continue to fall as it is intensified and beef production systems become increasingly grain-based.) And it’s important to remember that even peak farmland might not stop deforestation in the tropics, since agricultural production is gradually shifting from temperate to tropical countries.

The agricultural intensification that has enabled the yield improvements to date has been associated with other environmental impacts, like greenhouse gas emissions and nutrient pollution. But here too, there are encouraging trends. While intensive agriculture uses more energy and other inputs, which generate carbon emissions, this is more than offset by the lesser amount of deforestation that results from higher yields. Jennifer Burney et al. estimate that agricultural intensification over the past several decades has substantially reduced emissions compared to a counterfactual scenario without intensification. Astonishingly, a study published in January 2016 finds that total greenhouse gas emissions from farming – from operations as well as land-use change – peaked in the early 1990s. If these results hold up to further scrutiny, they constitute the most important and underreported instance of absolute decoupling to my knowledge.

Another recent study by Xin Zhang et al., published in Nature, suggests cause for optimism also when it comes to nitrogen pollution on farmland. They analyzed trends in nitrogen surplus – the fraction of applied nitrogen that is not taken up by crops and thus contributes to runoff and eutrophication – in 113 countries over five decades. In 56 of these countries – representing 87% of global nitrogen fertilizer consumption – the rate of increase in nitrogen surplus has slowed or leveled off, and in half of these 56 it has even started to decline, following the classical Environmental Kuznets Curve pattern. The remaining countries, mostly in the developing world, are yet to reach the peak, but are likely to do so as technology and regulation catches up.

Source: Zhang et al., 2015 Adapted by permission from Macmillan Publishers Ltd: Nature 528.7580 (2015): 51-59, copyright 2015

Trends are not as encouraging in other areas. While relative decoupling of carbon emissions from economic growth has been the norm in developed economies, and some countries have dramatically decarbonized their power sectors, absolute decoupling has not occurred on a broad, sustained basis. A study by Glen Peters and colleagues, in which emissions embodied in imported goods are accounted for, greenhouse gas emissions continued their upward trajectory in developed countries between 1990 and 2008. A similar analysis for the United Kingdom showed that emissions associated with domestic consumption kept rising until the recession.

Source: BP. Historical Data Workbook. Stat. Rev. World Energy, 2014

There are, of course, many other important types of environmental impacts, such as overexploitation of wild animals, other forms of pollution, as well as water extraction. Including these only makes it clearer that that there is no single metric that can tell us whether decoupling overall is happening now, or whether it could ever happen. Trends differ greatly between types of environmental impact, and their interpretation depends on what timeframe you look at, and the the phase of economic development in the country or region in question. Still, among the most important forms of environmental pressure, relative decoupling is the norm. Absolute decoupling is happening in some, but far from all, cases. (For more detailed discussion of decoupling trends and drivers, see Breakthrough’s publication Nature Unbound: Decoupling for Conservation.)

What about the future? The fact that many impacts have continued to grow in absolute terms over the last few decades does not necessarily mean that they will continue to grow forever. Population growth is slowing down and we may (or may not) reach peak population in the second half of this century. As countries become wealthier, demand begins to saturate for at least some categories of good, like food and construction materials. And while continued technological advances should not be taken for granted, there is every reason to think they could continue, given large gaps in global crop yields, the carbon intensity of energy, and so on. Taken together, these trends suggest that relative decoupling has a good chance to turn into absolute decoupling this century. How soon and at what level peak impact occurs will depend greatly on policies, investments, and other choices made by governments, corporations, and civil society. Decoupling is possible, and for now, I remain cautiously optimistic that human development and a flourishing natural world can coexist.

*Kastner et al. use the same consumption-based accounting as Wiedmann et al.