Climate-change impacts on ecological systems: introduction to a US assessment

www.frontiersinecology.org © The Ecological Society of America G environmental change has moved our world into a new geological era sometimes called the Anthropocene (Crutzen 2002). Ecosystems and life on Earth are subjected to multiple global-change stressors resulting from human activities, including habitat loss and degradation, water resource demands, toxic contaminants, and invasive species. Human activities also contribute to rising atmospheric concentrations of greenhouse gases, which drive climate change, a globalchange stressor of increasing importance. Ecosystems, and the biodiversity and services they support, depend intrinsically on climate. During the 20th century, climate change had documented impacts on species and ecosystems, and such impacts are expected to increase in frequency and severity as climate change continues and perhaps accelerates. This paper introduces a series of thematic papers, developed from a technical input report on biodiversity, ecosystems, and ecosystem services (BEES) prepared for the US National Climate Assessment (NCA; Staudinger et al. 2012; hereafter referred to as the BEES report). With a focus on the US, the BEES report was written by a diverse group of experts who evaluated how climate change is affecting alterations in ecosystem structure or function (Grimm et al. 2013) that, in turn, alter the viability of species and communities (Staudinger et al. 2013) and the delivery of ecosystem services (defined as benefits that people derive from ecosystems; Nelson et al. 2013). The team also examined the interactions among climate change and many other stressors (Staudt et al. 2013), as well as the current status of climate adaptation research and practice (Stein et al. 2013). Articles in this Special Issue synthesize current knowledge within each of these subject areas; here, we provide an overview of the BEES assessment process and highlight findings from those more detailed treatments that exemplify the complex interactions among them.