The Impact of Climate Change and Feedback Processes on the Ocean Carbon Cycle
We have been aware of the concept of global climate change since the advent of modern science in the 17th Century and the emergence of disciplines such as geology. However, it is only in the last century that a putative link, termed the ‘the Greenhouse Ef
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7.1
Introduction
7.1.1 Climate and Change – Present Status We have been aware of the concept of global climate change since the advent of modern science in the 17th Century and the emergence of disciplines such as geology. However, it is only in the last century that a putative link, termed the ‘the Greenhouse Effect’ (Wood 1909), has been suggested between the atmospheric concentrations of particular gases and climate. The composition of the atmosphere has been studied routinely since the late fifties/early sixties with the establishment of monitoring sites for atmospheric CO2 (such as Mauna Loa) where the 40-year dataset clearly demonstrates the rise of atmospheric CO2 (Keeling et al. 1995). Similar anthropogenically-mediated increases in the atmospheric concentrations of other gases such as nitrous oxide and methane have also been recorded in the last 40 years (Bigg 1996; IPCC 2001). Such increases in the concentrations of these gases in the atmosphere alter the radiative forcing globally by decreasing the longwave radiative flux leaving the trophosphere (Houghton et al. 1990) which is thought to lead to climatic effects. Alongside the global monitoring of atmospheric concentrations and distributions of greenhouse gases, there have been concerted efforts to use mathematical models to better understand the nature of the relationship between the observed changes in gas concentrations, subsequent alteration of radiative forcing and climate. While it is now well established that anthropogenic activities are responsible for observed increases in atmospheric gas concentrations such as CO2 (IPCC 2001), the relationship between altered atmospheric composition and climate change is less well established. Nevertheless “there is new and stronger evidence that most of the warming observed over the last fifty years is attributable to human activities” (IPCC 2001), and that “emissions of greenhouse gases and aerosols due to human activites continue to alter the atmosphere in ways that are expected to affect climate” (IPCC 2001). Recently, a synthesis of many observational studies indicates that the global average surface temperature has
M. J. R. Fasham (ed.), Ocean Biogeochemistry © Springer-Verlag Berlin Heidelberg 2003
increased by ca. 0.6 °C in the 20th Century (IPCC 2001), and there is also strong evidence that the oceans are exhibiting a warming trend (Levitus et al. 2000). Indeed, the present rate of change in atmospheric CO2 is without precedent, necessitating the development of a mechanistic understanding of the processes controlling climate change (IPCC 2001). In addition to contemporary changes in atmospheric CO2, there is evidence of substantial climate change from the geological past with, for example, glacial core records showing large variations in temperature and greenhouse gas concentrations associated with glacial/interglacial oscillations over the last 400 000 years (the Vostok core record; Petit et al. 1999). Throughout this period, there are consistent trends of lower atmospheric CO 2 levels during the
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