UK IGBP - Paleo and modern perspectives on global change: A personal summary
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The need to understand the mechanisms and processes of climate and environmental change is a fundamental scientific challenge with profound practical implications. The components of the Earth System respond to perturbations on very different timescales: the atmosphere reacts in hours to years, natural ecosystems over years to centuries, the ocean over centuries to millenia, and the cryosphere over millennia and longer. Thus, it is important to examine climate and environmental changes in the perspective offered by the geological record of the past million years or so, as well as in the recent or historical period, in order to assess (and potentially improve) our ability to quantify anthropogenic effects. Questions that arise from the paleorecord are modeling foci in several of the IGBP core projects. Explaining the tightly controlled upper and lower limits on atmospheric trace gas concentrations through glacial-interglacial cycles as shown by the ice core record is a focus in IGAC, iLEAPS and SOLAS. Understanding how ecosystem structure and function are affected by changes in atmospheric composition, biogeochemical cycles and climate is a focus in GLP and IMBER. However, paleodata gathering and analysis activities (necessary to compare with modeling results) fall within the domain of PAGES. This structure, combined with the generally limited communication between modelers and observationalists and between scientists working on modern and paleo timescales, may limit progress towards an integrated understanding of global change. It was with these concerns in mind that the UK IGBP Committee organized a oneday meeting at the Royal Society in June this year to explore commonalities between modern and paleo-perspectives on global change. Speakers from each of the core projects, and members of the PAGES community, were invited to address the common themes of: biodiversity, ecosystem structure and functioning; the regulation of ocean productivity; ocean fertilization and the biological pump; fluxes to the coastal ocean—changing land-surface conditions and human interactions; and natural regulation of atmospheric oxidizing capacity. One theme that emerged is the scarcity of high-quality data on key processes. In the ocean, for example, there are large uncertainties in estimates of primary production and vanishingly few measurements of respiration outside the Atlantic. Estimates of iron solubility in the ocean range over several orders of magnitude; different measures of export production sometimes yield opposite signals of change between glacial and interglacial states. On land, assessments of contemporary rates of biodiversity loss are heavily biased by sampling of charismatic species, while natural migration rates are poorly constrained. There are few experiments quantifying CO 2 fertilization outside the temperate forest zone; there is very limited understanding of the differential resilience of plants, insects and mammals to environmental change. However, the lack of data to address key questions may sometimes be more apparent than real: a major limitation is the availability of data in appropriate formats and centralized facilities. Networking and synthesis activities sponsored by PAGES and the Paleoclimate Modeling Intercomparison Project (PMIP) have shown that there are many hundreds more individual paleo records than are generally known to the paleo-modeling community. Similarly, GLOPNET (Wright et al., 2004) and the IGBP Fast-Track Initiative on Plant Functional Classification are demonstrating that there is an untapped wealth of measurements that could be used to analyze plant and ecosystem processes when brought together in a global database. A second emerging theme was that multiple data sources can offer valuable complementary perspectives but that this synergy is often not exploited. The existence of multiple paleo proxies for a given process or variable has often been interpreted as increased “uncertainty” in paleoclimate reconstructions, largely because of the focus on statistical rather than process-based interpretation of the records. Paleo-observations can challenge our understanding of modern processes in surprising ways: the record of past changes in vegetation patterns, for example, indicates that migration rates can be fast, and that plant species have been extremely resilient in the face of large and rapid climate changes such as occurred in the North Atlantic region during the deglaciation. Sedimentary records from estuarine environments indicate much fisheries, and the potential role of upwelling in the drawdown of atmospheric CO2, further understanding of climate feedbacks in upwelling regions and the ecological and socioeconomic repercussions is imperative. This study also demonstrates that marine sediment cores do provide levels of information comparable to more traditional high-resolution proxies. Future studies focused on decadal-resolution marine sediment cores have the very real potential to contribute invaluable data on ocean and climate processes. Note The data are archived at the Publishing Network for Geoscientific and Environmental Data public digital library (www.pangaea.de/).
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