Wherever ecologists look, from tropical forests to tundra, ecosystems are being transformed by human land use and climate change. A hallmark of human impacts is that the rates of change in ecosystems are accelerating worldwide.
Surprisingly, a new study, published today in Science, found that these rates of ecological change began to speed up many thousands of years ago. "What we see today is just the tip of the iceberg" noted co-lead author Ondrej Mottl from the University of Bergen (UiB). "The accelerations we see during the industrial revolution and modern periods have a deep-rooted history stretching back in time."
Using a global network of over 1,000 fossil pollen records, the team found - and expected to find - a first peak of high ecosystem changes around 11,000 years ago, when the Earth was coming out of a global ice age. "We expected rates of ecological change to be globally high during this transition because the world was changing fast as glaciers retreated and the world warmed" explains co-lead author Suzette Flantua. However, the timing of peak changes varied among regions, suggesting a fairly complex suite of climate and ecosystem changes during the end of the last ice age.
More surprisingly, the team found a second period of accelerating change that began between 4.6 and 2.8 thousand years ago and has continued to present. Remarkably, these recent rates of change are now as fast or faster as the massive ecosystem transformations that accompanied the end of the last ice age.
To achieve this global analysis, the team developed new statistical tools that allowed them to calculate rates of change in stratigraphic sequences. "We found a way to compare the many records across different continents and smaller regions" explains Alistair Seddon at UiB and Bjerknes Centre for Climate Research. "That was a major breakthrough as it allowed us to demonstrate that different regions experienced peak rates of change at different times".