"The extent of land at risk of ecosystem changes approximately doubles between 2 and 3 degrees of warming above present-day conditions," Lila Warszawski of the Potsdam Institute for Climate Impact Research, Germany told environmentalresearchweb. "The large uncertainty across the models confirms that we are not yet in a position to rule out discontinuous changes to natural ecosystems, putting unique plant and animal communities at risk of extinction, and endangering the ecosystem services on which many human communities rely."

Together with colleagues from Germany, the UK, France, Japan and the US, Warszawski assessed the risk parameter – a measure of the changes in biogeochemical properties such as biomass, carbon turnover, water flows and species composition – projected by seven different global vegetation models driven by future climate scenarios. The team assumed that the changes in these properties can act as a proxy for the risk of ecosystem shift.

"We argue that such shifts in the fundamental biogeochemistry are likely to imply transformations in the underlying system characteristics, such as species composition, and relationships between plants, herbivores and pollinators," they write in Environmental Research Letters (ERL). "For example, if the productivity of a land area increases or decreases, the composition of species it carries will be affected; similarly, prolonged drought or increased rainfall in an area will cause changes to trophic chains."

For a warming of 2°C above 1980–2010 levels, the models showed that 5–19% of the naturally vegetated land surface is at risk of severe ecosystem change. For a temperature rise of 4°C, that figure would become a median 27% of naturally vegetated land surface.

"We have put a special focus on quantifying risk of shift in ecosystem state as a function of global mean temperature change," said Warszawski. "We consider this to be particularly relevant to the international decision-making process regarding mitigation targets, which are usually expressed in terms of a maximum global mean temperature rise."

The models – JeDi, SGVM, VISIT, JULES, Hybrid4, LPJmL and ORCHIDEE – did not agree well, however, about which regions face the highest risk. Areas likely to be affected first include the tundra and shrublands of the Tibetan Plateau, the grasslands of eastern India, the boreal forests of northern Canada and Russia, the savanna region in the Horn of Africa and the Amazon rainforest. The increased risk was largely due to carbon fluxes, apart from in the Amazon, where water flux changes were involved as well.

Warszawski believes that the uncertainty in the extent of land at risk produced by the different models points "to the need for extensive investment in model improvement, development and comparison, to understand which processes are still missing from the models, and from where the disagreement between models comes".

Previous studies have used global vegetation models to assess changes in biogeochemical variables like net primary product or vegetation carbon without looking at the impacts on the whole ecosystem, or have looked at individual species or habitats.

Now the team is working on the next phase of ISI-MIP, which Warszawski says will include additional impact sectors, more models in each sector, and regional as well as global models, and improving the sensitivity of the impact models to extreme climatic events. "There will also be a particular focus on understanding the interactions of the different sectors," she added. "For example, how expansions of agricultural land impact on natural ecosystems, or how changes in available water impact agricultural yields."

Related links

Related stories