Humans are having a huge impact on the ecosystems of our planet, either directly – by land-use change – or indirectly, through climate change. Researchers in Germany have found that the area of Earth's ecosystems exposed to at least moderate climate-change impacts in just one century is comparable in size to all of the land transformed by human societies for cropping and pastures.

This finding, made by Sebastian Ostberg and colleagues from the Potsdam Institute for Climate Impact Research, is surprising because land-use change is a high-impact local phenomenon, whereas climate change is global and its effects are often perceived less strongly than local land-use change. To make the two comparable, the researchers looked at landscapes at a common spatial scale: mosaics of managed lands and natural ecosystems that jointly experience climate change.

"There are still many areas across the globe that are free of agriculture, but we were expecting to find that land-use change has had the greatest impact on our planet, even at the scale of landscapes," said Ostberg. "We were surprised to discover the magnitude of the effect of 20th century climate change and that, when averaged out over the globe, in 100 years it is almost equal to the effect 300 years of land-use change has had on our planet's landscapes."

To quantify changes in the biosphere, Ostberg and his colleagues used Γ, a metric of biogeochemical and vegetation-structural change. This metric brings together quantitative changes in a high number of parameters that were previously only studied separately. It enables the relative strengths of the two pressures – climate change and land-use change – to be compared, despite considerable differences in their mechanisms, affected processes and spatial patterns.

"This is the first time that this indicator of change has been applied to study the effects of land use," Ostberg told environmentalresearchweb. "We used observation-based climate data and historical reconstructions of cropland and pasture together with the LPJmL Dynamic Global Vegetation Model (DGVM) that is capable of simulating vegetation–soil dynamics of both natural vegetation and agricultural ecosystems to describe ecosystem states with and without the effects of land use and climate change."

The researchers found that in their interaction at the landscape scale, both land-use change and climate change have jointly exposed 55% of the global land surface to at least moderate biogeochemical and vegetation-structural changes of a magnitude comparable to the difference between distinct biomes.

Ostberg and colleagues believe their work will help to inform future policy, and underlines the need to consider both land-use change and climate change as equally important drivers for changes in the global biosphere. "For example, large-scale biomass plantations are often considered as climate-change-mitigation strategies, but our work shows that it is important to make sure that these projects are not just substituting climate impacts for land-use impacts," said Ostberg.

The researchers are now planning to extend their work to look into the future. "We plan to investigate the relative effects of different future land-use-change scenarios, and different climate-change scenarios on the Earth's ecosystems," said Ostberg.

The team reported the findings in Environmental Research Letters (ERL).

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