Climate Change
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Abstract
Global climate change is signifi cantly altering the structure and functioning of many ecosystems and, consequently, temporal and spatial patterns of population and species abundance (e.g. Stenseth et al ., 2005 ; Rosenzweig et al ., 2008 ). Signifi cant advances in the scientifi c understanding of climate change now make it clear that there has been a change in climate that goes beyond the range of natural variability. As stated in the Fourth Assessment Report (AR4) of the Intergovernmental Panel on Climate Change (IPCC), the warming of the climate system is ‘unequivocal’ and it is ‘very likely due to human activities’. The culprit is the astonishing rate at which greenhouse gas (GHG) concentrations are increasing in the atmosphere, mostly through the burning of fossil fuels and changes in land use, such as those associated with agriculture and deforestation. GHGs are relatively transparent to incoming solar radiation while they absorb and reemit outgoing infrared radiation. The result is that more energy stays in the global climate system, not only raising temperature but also producing many other direct and indirect changes in the climate system. The indisputable evidence of anthropogenic climate change, and the knowledge that global climate change will continue well into the future under any plausible emission scenario, is now a factor in the planning of many organizations and governments. Global warming does not imply, however, that future changes in weather and climate will be uniform around the globe. The land, for instance, is warming faster than the oceans, consistent with its smaller heat capacity. Moreover, uncertainties remain regarding how climate will change at regional and local scales where the signal of natural variability is large, especially over the next several decades ( Hawkins and Sutton, 2009 ). Regional differences in land and ocean temperatures arise, for instance, from natural variability such as El Niño Southern Oscillation (ENSO) events. Natural variability can result from purely internal atmospheric processes as well as from interactions among the different components of the climate system, such as those between the atmosphere and ocean, or the atmosphere and land. El Niño events produce very strong warming of the central and eastern tropical Pacifi c Ocean, while the ocean cools over portions of the subtropics and the tropical western Pacifi c. Over the Atlantic, average basin-wide warming is imposed on top of strong, natural variability on multi-decadal time scales, called the Atlantic multi-decadal oscillation (AMO). The level of natural variability, in contrast, is relatively small over the tropical Indian Ocean, where surface warming has been steady and large over recent decades. Importantly, these differences in regional rates of sea surface CHAPTER 2