Current and future impacts of climate and global change on biodiversity and the structure and functioning of ecosystems

Background/Question/Methods  

Climate fundamentally controls Earth’s distribution of ecosystems, species ranges, and process rates. Yet the impacts of climate change can be difficult to assess against a background of other globally prevalent and mainly anthropogenic changes, as well as natural variability. An assessment was conducted of the state of knowledge on how climate change has affected and will affect biodiversity, ecosystems, and ecosystem functioning. Emphasis in the evaluation of biodiversity changes was on how rapidly distribution and phenology are shifting in space, how composition of species assemblages and their interactions are changing, and individualistic species responses. For impacts on ecosystems, the focus was on the fluxes of matter and energy and the biotic and abiotic elements of structure that contribute most to those fluxes. Together with assessment of the impacts of climate change on ecosystem services, the process involved the bringing together of over sixty experts from academic, governmental, and non-governmental organizations.

Results/Conclusions

Changes in species ranges, distributions, and phenologies are occurring more rapidly than previously thought, although the velocities of species change are highly individualistic. Although entire biomes may appear to shift to higher latitudes, in reality new assemblages are likely to be formed, producing novel interactions with the potential for surprises. Collective attributes of ecosystems, such as their rate of primary productivity, respond in complex ways to climate change because of multiple controlling factors. For example, whether a forest is a carbon source or sink depends on the balance of primary production and ecosystem respiration, which respond to different drivers. Physical changes in ecosystems—for example, changes in thermal stratification patterns in lakes and oceans, flood and drying regimes in streams and rivers, or intensification of the hydrologic cycle across large basins—lead to changes in ecosystem structure and functioning. But it is often the changes in timing or extremes, rather than mean conditions, which have the greatest impact. Recognizing these issues, climate-change action plans and management strategies have begun to incorporate forecasting of extremes or seasonality.