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.
1.1.1 Scope and goals of the chapter
The aim of this chapter is to assess studies of observed changes in natural and managed systems related to recent regional climate change, particularly temperature rise in recent decades, and to assess the aggregate changes in regard to potential influence by anthropogenic increase in greenhouse gas concentrations. Temperature rise is selected as the major climate variable because it has a strong and widespread documented signal in recent decades, demonstrates an anthropogenic signal, and has an important influence on many physical and biological processes. Effects of changes in other climate variables related to temperature rise, such as sea-level rise and changes in runoff due to earlier snow melt, are also considered.
The chapter first reviews data sources and methods of detection of observed changes, investigating the roles of climate (including climate extremes and large-scale natural climate variability systems) and non-climate drivers of change (Section 1.2). Evidence of no change, i.e., regions with documented warming trends but with little or no documentation of change in natural and managed systems, is analysed as well.
In Section 1.3, evidence is assessed regarding recent observed changes in natural and managed systems related to regional climate changes: cryosphere (snow, ice and frozen ground – including permafrost), hydrology and water resources, coastal processes and zones, marine and freshwater biological systems, terrestrial biological systems, agriculture and forestry, human health, and disasters and hazards. Evidence regarding other socio-economic effects, including energy use and tourism, is also assessed. The term ‘response’ is used to denote processes by which natural and managed systems react to the stimuli of changing climate conditions.
In Section 1.4, studies are surveyed that use techniques of larger-scale aggregation (i.e., synthesising studies across systems and regions), including meta-analyses and studies that relate observed changes in natural and managed systems to anthropogenic climate change. From the studies assessed in individual systems in Section 1.3, a subset is selected that fits criteria in regard to length of study and statistically significant changes in a system related to recent changes in temperature or related climate variables, in order to assess the potential influence of anthropogenic climate forcing on observed changes in natural and managed systems.
We consider what observed changes are contributing to the study of adaptation and vulnerability (where there are relevant studies), and address data needs in Section 1.5. There is a notable lack of geographical balance in the data and literature on observed changes in natural and managed systems, with a marked scarcity in many regions. The Supplementary Material (SM) contains additional literature citations and explanatory data relevant to the chapter.