Shifting Baselines in the Anthropocene

By Angela Cruz

Species loss, arctic ice loss, sea level rise: measuring any difference over time requires a starting point for reference. This reference point is typically referred to as a baseline. Baseline data measure things such as the population size of a fishery, sea level, or average size of harvested fish, at a specific moment in time. Using a baseline from a certain year affects how we perceive–or fail to perceive–change in real time and in our everyday lives. When we keep resetting and using different baselines, this phenomenon is called a shifting baseline. We are currently living in a time period frequently referred to as the “anthropocene,” which is characterized by large scale environmental change as a result of human activities. Given that we are experiencing rapid change, how can we avoid falling into a problem with shifting baselines? 

Old nautical charts, like the one above from 1853 in Key Biscayne, Florida, can inform historical ecologists on the extent of coral cover before human activities led to their decline. Credit: Wikimedia Commons and the United States Coast Survey.

Daniel Pauly was the first person to coin the phrase “shifting baseline” in 1995. Though initially it was used in reference to the fisheries field, the concept of shifting baselines can be applied to a range of environments and day-to-day situations. For example, I grew up in Chicago and used to not get cold until it was below 20˚F. Now, after spending a few years on the West Coast, I get cold once it’s below 50˚F. My baseline for “cold” has shifted based of my recent experiences. Another example is in 2006, when the first invasive emerald ash borer was found in Illinois. In the following years, the huge majority of native ash trees were removed and cut down due to the beetle infestation. I still remember ash trees lining the suburban streets, but someone slightly younger than me would never know they are missing as they lie in their sunny front yard. Their baseline for what trees are abundant to Illinois is different from mine. The difference in whether I’m cold or not is fairly insignificant, but when we talk about shifting baselines in the environment and oceans, it’s anything but.

Shifting baselines in the ocean can be an entire species being lost, or the average size of harvested tuna reducing over time. The perceptions of a changing ocean are compounded by the inability to see under the water at all times. A key part of the issue with shifting baselines is that humans tend to think on a human timescale. If I go diving at a site for the first time and see one hammerhead shark, that’s great! I will probably believe that was a pretty successful dive. But as Bryan Walsh describes, you may not even realize at that moment that hammerheads were once very abundant. Meanwhile, practitioners were doing something similar. Pauly discusses how fisheries scientists had a habit of using whatever baseline data was available at the beginning of their career and measuring change from this point of reference. This led to slowly reduced optimal population estimates over time.

Diving of the coast of Maui for the first time in 2019, you would hardly be concerned about the health of the reefs when, in fact, Maui lost 25% of its coral cover between 1994 and 2006. Credit: Kelly Martin

How much of an impact can this really have on estimates of loss in things like coral cover beyond a few decades? Well, that is difficult to assess. Luckily, there are a group of scholars looking at that. A recently named Pew Fellow, Dr. Loren McClenachan, and her colleagues used 250 year old nautical maps that described coral cover to see how reef coverage has changed near the Florida coast since before the American Revolution. Unsurprisingly, they determined that the amount of coral cover that has been lost due to human activity is seriously underestimated when you use a more recent baseline. We may have lost significantly more than we previously thought.

There are considerable issues that can be created from shifting baselines that can impact conservation efforts. One study looked at participants’ willingness to pay for conservation based on their perception of declining reef habitat. Those participants who had baselines going further back in time had a higher willingness to pay for conservation, whereas those who were unaware of the long-term changes that have been taking place had lower willingness to pay. If individuals are unaware of how much biodiversity used to be in the oceans before their own lifetime, they may perceive the absence (or at least a watered-down perception) of a problem. An individual may believe the ocean they knew as a child was “pristine,” when it was, in fact, in worse shape than it was just a hundred years prior. It is important for conservationists, science communicators, and practitioners to consider how their baseline is impacting perceptions of change to support conservation and action moving forward. I would also argue that shifting baselines can greatly affect our vision for the future. In a perfect world, do we seek to return levels of ocean biodiversity to what we observed in the 1980s or to levels pre-anthropocene? I, for one, would prefer to have a vision of the latter.