Climate variability and human impact on the environment in South America during the last 2000 years: synthesis and perspectives

Abstract

Abstract. An improved understanding of present-day climate variability and change relies on high-quality data sets from the past two millennia. Global efforts to reconstruct regional climate modes are in the process of validating and integrating paleo-proxies. For South America, however, the full potential of vegetation records for evaluating and improving climate models has hitherto not been sufficiently acknowledged due to its unknown spatial and temporal coverage. This paper therefore serves as a guide to high-quality pollen records that capture environmental variability during the last two millennia. We identify the pollen records with the required temporal characteristics for PAGES-2 ka climate modelling and we discuss their sensitivity to the spatial signature of climate modes throughout the continent. Diverse patterns of vegetation response to climate change are observed, with more similar patterns of change in the lowlands and varying intensity and direction of responses in the highlands. Pollen records display local scale responses to climate modes, thus it is necessary to understand how vegetation-climate interactions might diverge under variable settings. Additionally, pollen is an excellent indicator of human impact through time. Evidence for human land use in pollen records is useful for archaeological hypothesis testing and important in distinguishing natural from anthropogenically driven vegetation change. We stress the need for the palynological community to be more familiar with climate variability patterns to correctly attribute the potential causes of observed vegetation dynamics. The LOTRED-SA-2 k initiative provides the ideal framework for the integration of the various paleoclimatic sub-disciplines and paleo-science, thereby jumpstarting and fostering multi-disciplinary research into environmental change on centennial and millennial time scales.

Out of Amazonia: Late-Holocene climate change and the Tupi–Guarani trans-continental expansion

“…yr BP (Figures 4-6b, Movie S1, available online). This is exemplified by (1) the expansion of the southern Amazon rainforest margin (Carson et al, 2014;Flantua et al, 2015;Mayle et al, 2000); (2) expansion of seasonally dry tropical forest margins in the Chiquitanía region of lowland Bolivia and at the southern margin of the Cerrado (savanna) biome (Ledru, 1993;Oliveira-Filho and Ratter, 1995), the expansion of gallery forests in the central Brazilian savannas (Silva et al, 2008); (3) the development of dry forest in the Misiones region of southern Brazil (Zech et al, 2009); and (4) the development and expansion of Araucaria forests in the southern Brazilian highlands (Behling and Pillar, 2007). This temporal pattern of forest expansion follows the trend of increasing rainfall through the mid-late-Holocene, pointing to a causal relationship (Figures 4 and 5).…”

Long-Term Vegetation Dynamics in a Megadiverse Hotspot: The Ice-Age Record of a Pre-montane Forest of Central Ecuador

“…The assumption of glacial tolerance range would imply a higher sensitivity to climate change of the forest during interglacials such as the present one. Holocene palaeoecological studies have manifested a high dynamism of plant communities through the entire Amazon basin (e.g., Flantua et al, 2016 ). Given the current projections on climate change, it is expected that cloud coverage of the eastern Andean flank will continue moving upwards and narrowing as the temperature rises ( Bush, 2002 ; IPCC, 2013 ).…”

The South American Monsoon Variability over the Last Millennium in CMIP5/PMIP3 simulations

“…On the proxy side, a stronger effort to not only reconstruct surface climate at individual locations, but also focus on reconstructions of modes of variability or entire climate components such as the SAMS, which implicitly include circulation changes, are needed. Proxies such as pollen or stable hydrogen and oxygen isotopes from lakes, speleothems and ice cores have shown potential to record larger-scale climate signals and changes in the tropical hydrological cycle over South America (Vuille and Werner, 2005;Vimeux et al, 2009;Bird et al, 2011;Vuille et al, 2012;Ledru et al, 2013;Flantua et al, 2015;Hurley et al, 2015). Multi-proxy reconstructions from such networks, which implicitly incorporate remote and large-scale circulation aspects, may therefore provide a better tool to assess the performance of climate models than reconstructions that are based solely on local precipitation estimates.…”