Renewable resources reach their limits

The term peak in the context of resource use is not new as it was popularized in the discussion about peak oil initiated in the mid-1970s. The peak oil analysis of the mid 1970s alleged that the crude oil extraction rate would significantly decline after a given year. Whether such a decline will happen and what would be the ultimate cause has been hotly debated among scientists. Though oil production has actually continued to expand, other resources have followed such a pattern. UFZ researchers used a dataset of more than 25 resources and made limited assumptions, relying on computer power to extract pattern from the database. "For many resources, but not oil, we indeed observed a peak pattern," states Dr. Seppelt.

Surprisingly, they discovered not only that 20 resources had a peak-year but also that for 16 of the 20 resources with a peak-year, the peak-year lay between 1988 and 2008 -- a very narrow range in the history of humanity! "The key commodities that a person needs for food and must harvest are limited," summarizes Dr. Seppelt, Head of the Landscape Ecology Department at the UFZ. Renewable resources become scarcer. The authors were able to illustrate this using a various examples: The maximum global growth rate in crop yields for soya beans was in 2009, for milk it was 2004, for eggs it was 1993 and for the fish caught it was 1988. Data from other studies confirm these results. For example, the crop yield per area with maize, wheat, soya and rice on more than a quarter of the farming area around the world is stagnating or decreasing according to the US scientists.

Dr. Seppelt gives explanations for why many of the peak-year are synchronized -- they occur at about the same time. The global population growth is a major driver. Due to the rising population and change in diet in some regions of the world over the past few decades, such as India and China, the demand for renewable resources increased and thus the pressure to produce as much food as possible. These findings can also be illustrated in other aspects of resource use: the team found the highest rate of increase in the cultivation of arable land to be in the 1950s; the peak for human-made irrigation areas then followed in the 1970s, and the peak for nitrogen fertilisers was subsequently in the 1980s. "This shows that the land available for agriculture was used more intensively for growing food," conclude Dr. Klotz, Head of the Department of Community Ecology. However, they can no longer see major opportunities for the intensification of farming. "Experts see opportunities for further increases in agricultural yield of about one to two percent per year due to better breeding techniques and genetically modified organisms," states Dr. Seppelt. But then it will be tight: "The global community needs to accept that renewable raw materials are also reaching their yield limits worldwide."

Not all resources have passed their peak-year. For example fish obtained from aquaculture (not caught fish from the wild) is an expanding resource. However, "the environmental cost of aquaculture is hotly debated ," mentions Dr. Seppelt.

Conclusions of global relevance can be drawn from the study "We are facing enormous challenges that affect the majority of the resources that we use," states Dr. Seppelt. Indeed, the synchrony of peak-years casts doubts on the notion that as resources become scarcer or less accessible, they can be replaced by other resources ad infinitum. As the foundation of humanity's current standard of living is eroding, it becomes essential to take action by using fertilizer and water more efficiently for example. "At the individual level, we can start by preferring a vegetarian diet, or eating chicken instead of beef," opines Dr. Seppelt.