In the last century, humans have so dramatically transformed the environment in which they live that the Earth has entered a new geological epoch: the Anthropocene. The magnitude, extent, and rate of change in the environment is so great that it is often hard to comprehend.

The difficulty people have to realize how much ecosystems have been transformed partly comes from an environmental generational amnesia 1, caused by shifting baselines between generations 2:  children of each generation perceiving the environment into which they are born as normal, accepting new degraded states as the norm.

Shifting baselines have been associated with a wide range of global environmental issues faced today, such as overfishing 3, defaunation 4, loss of natural habitats and processes 5, and increased levels of pollution 6.

How have ecosystems changed over the past century?

Quantifying changes between baselines can be a difficult task as it relies on not-always-objective human memory. Old photographs remain as witnesses of past situations, showcasing drastic changes in the composition of ecosystems such as the size and amount of fish that used to be taken out of the sea.

There is evidence from shifting baselines occurring all over the world: studies show that in Eastern Indonesia, younger fishers perceived less the decline in the wildlife population, compared to older fishers  7. In the Bolivian Amazonia, younger generations perceived a lower number of locally-extinct tree and fish species compared to older generations 8. In Alaska, younger generations identified less overall change in climate (e.g., increased temperatures, decreased snow cover)  than older ones 9. In Tanzania, younger fishermen were less likely to perceive that the current size of the fish catch has declined and that fish stocks were overexploited, compared to older ones 10. Likewise in the UK, the older generation’s perception about the abundance of ten local bird species overtime was more accurate than the younger one, showing that younger, less experienced people were less aware of historical ecological conditions 11.

The rate of change between baselines of two succeeding generations is likely to have increased in the past two centuries, following technological innovations leading to modified interactions with surrounding ecosystems, increased consumption of goods, biodiversity loss, population growth, etc., to an extent that baselines can now be drastically different for generations living at the same time.

Few places have long enough biodiversity monitoring data to be able to measure the extent of change, and a “recent” baseline from an older generation may not be representative of historical reality. For instance, the number of salmons in the Columbia River today is twice what it was in the 1930s. But at this time, salmon in the Columbia River represented only 10% of what they were in the 1880s 12.

One needs to go to truly remote places to see what historical natural baselines could be like. In some very remote islands in the Pacific where no human being ever lived, Pr. Nancy Knowlton describes coral reefs where 80% of the living biomass were top predators, an ecosystem structure never found in reefs where humans have been living close by 13.

Why does it matter? Consequences of shifting baselines

Shifting baselines lead to three major consequences 14:
(1) an increased societal tolerance for progressive environmental degradation, such as the decline in wildlife populations, loss of natural habitats, and increasing pollution;
(2) a change in people’s expectations as to what is a desirable state (i.e., worth protecting) of the natural environment;
(3) inappropriate targets (i.e. based on what people know of a place at present) for environmental conservation, restoration, and management programs. For example, North Sea fisheries are managed using a baseline from 1970, but by 1970 there had been over a hundred years of mechanized fishing, which had been devastating for stocks 15.

As Callum Roberts writes in The Unnatural History of the Sea

“Shifting environmental baselines cause a collective societal amnesia in which gradual deterioration of the environment and depletion of wildlife populations pass almost unnoticed. Our expectations diminish with time, and with them goes our will to do something about the losses.”

How to limit shifting baselines?

Soga & Gaston (2018) proposed four recommendations to prevent shifting baselines.

  1. Restoring the natural environment, since environmental degradation is triggering shifting baselines in the first place. This could happen through rewilding and ecosystem restoration. Marine Protected Areas with fishing excluded have successfully demonstrated how ecosystems can recover to forgotten baselines, “recreating the past people cannot conceive” (Daniel Pauly)16.
  2. Monitoring and collecting data, to allow future generations to have a solid objective baseline about past environments. The rise in citizen sciences is one approach to scale up data collection. Collecting data also enables the reconstruction of past environments to help present-day managers take decisions on what is a desirable state of the environment.
  3. Reducing the extinction of experience by promoting people’s interactions with natural environments.
  4. Education, to reinforce people’s familiarity with their environment and its past and current conditions.

It may seem hard to understand how humans can deem normal an extensively exploited field in Europe or a defaunated forest in the Brazilian Atlantic forest. Part of the why probably lies in the fact that the currently living generations never experienced anything else, or their experiences may soon be forgotten.  Acknowledging the fact that what people consider a “healthy” environment is biased toward what they experience as being the natural world and that their experience is not complete, and objective, is the first step towards being able to see the bigger picture and limiting shifting baselines.

Daniel Pauly said that “humans transform the world, but they don’t remember”. Now that we know we are forgetting, there is a chance to manage ecosystems in a better way, by learning from the past.

Photo credit: ©Peat Bakke, flickr.


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