The IPCC Working Group II Third Assessment Report (WGII TAR) found evidence that recent regional climate changes, particularly temperature increases, have already affected many physical and biological systems, and also preliminary evidence for effects in human systems (IPCC, 2001a). This chapter focuses on studies since the TAR that analyse significant changes in physical, biological and human systems related to observed regional climate change. The studies are assessed with regard to current functional understanding of responses to climate change and to factors that may confound such relationships, such as land-use change, urbanisation and pollution. The chapter considers larger-scale aggregation of observed changes (across systems and geographical regions) and whether the observed changes may be related to anthropogenic climate forcing. Cases where there is evidence of climate change without evidence of accompanying changes in natural and managed systems are evaluated for insight into time-lag effects, resilience and vulnerability. Managed systems are defined as systems with substantial human inputs, such as agriculture and human health. The chapter assesses whether responses to recent warming are present in a broad range of systems and across varied geographical regions.

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