Project allocation NGEN03 2014 Long-term Holocene increases in - PowerPoint PPT Presentation

Project allocation NGEN03 2014

Long-term Holocene increases in atmospheric CO2 and CH4 concentrations: natural or anthropogenic? (Mats Rundgren) • In 2003 William Ruddiman, a respected palaeoclimatologist, published a paper in which he argued that the increasing atmospheric CO2 and CH4 concentrations recorded over the past 8000 and 5000 years, respectively, were caused by human land use. The rise in carbon dioxide was suggested to result from early agriculture and deforestation in Eurasia, and the methane increase was attributed to rice irrigation. According to Ruddiman, the high greenhouse gas concentrations in the late Holocene relative to earlier interglacials has prevented ice accumulation in northeastern Canada and postponed the transition into the next glacial period. This ‘outrageous’ hypothesis has become highly debated within the scientific community. This project should present and discuss the evidence and arguments put forward by Ruddiman and the contra-evidence and arguments that challenge his hypothesis. References to start with: • Ruddiman, W.F. 2003. The anthropogenic greenhouse era began thousands of years ago. Climatic Change 61, 261-293. • Claussen, M. et al. 2005. Did humankind prevent a Holocene glaciation? Climatic Change 69, 409-417. • Olofsson, J. & Hickler, T. 2008. Effects of human land-use on the global carbon cycle during the last 6,000 years. Vegetation and Archaeobotany 17, 605-615. • Vavrus, S. et al. 2008. Climate model tests of the anthropogenic influence on greenhouse-induced climate change: the role of early human agriculture, industrialization, and vegetation feedbacks. Quaternary Science Reviews 27, 1410-1425. • Elsig, J. et al. 2009. Stable isotope constraints on Holocene carbon cycle changes from an Antarctic ice core. Nature 461, 507-510. • Kutzbach, J.E. et al. 2010. Climate model simulation of anthropogenic influence on greenhouse-induced climate change (early agriculture to modern): the role of ocean feedbacks. Climatic Change 99, 351-381. • Stocker, B.D. et al. 2011. Sensitivity of Holocene atmospheric CO2 and the modern carbon budget to early human land use: analyses with a process-based model. Biogeosciences 8, 69-88. I

Stable isotope composition of CH4 in ice cores spanning the last glacial and the Holocene: what does it reveal about the relative importance of different, natural and anthropogenic, methane sources? (Mats Rundgren) • Ice core records spanning several glacial-interglacial cycles show that atmospheric CH4 levels are tightly coupled to orbitally-controlled insolation variations. A strong climatic influence on atmospheric methane concentrations is also indicated on centennial timescales for the last glacial-interglacial transition. In contrast, the Holocene methane record is more difficult to directly relate to climate-related processes and, at least during recent centuries, anthropogenic processes are likely to have been important. One way to better understand the relative importance of different, natural and anthropogenic, processes for the observed CH4 changes is to analyse the stable carbon (δ13C of CH4) and hydrogen (δD of CH4) isotope compositions of methane preserved in ice cores. Because the isotopic composition of different methane sources, e.g. wetlands, soils, lakes, biomass burning, fossil fuels and marine clathrates, is relatively well known, CH4 isotope and concentration records can be used as input in model calculations to estimate the relative contribution of these processes. A number of recent studies adopting this approach have provided interesting information about carbon cycle dynamics during the last glacial, the last glacial-interglacial transition and the Holocene (both before and during the recent period of strong anthropogenic influence). • References to start with: • Ferretti, D.F. et al. 2005. Unexpected changes to the global methane budget over the past 2000 years. Science 309, 1714-1717. • Schaefer, H. et al. 2006. Ice record of δ13C for atmospheric CH4 across the Younger Dryas -Preboreal transition. Science 313, 1109-1112. • Sowers, T. 2006. Late Quaternary atmospheric CH4 isotope record suggests marine clathrates are stable. Science 311, 838-840. • Fischer, H. et al. 2008. Changing boreal methane sources and constant biomass burning during the last termination. Nature 452, 864-867. • Mischler, J.A. et al. 2009. Carbon and hydrogen isotopic composition of methane over the last 1000 years. Global Biogeochemical Cycles 23, GB4024, doi:10.1029/2009GB003460. • Sowers, T. 2010 Atmospheric methane isotope records covering the Holocene period. Quaternary Science Reviews 29, 213-221. II

Present and future impacts of anthropogenic CO2 increase on ocean chemistry and marine ecosystems (Mats Rundgren) • Ocean CO2 uptake in response to the anthropogenic increase in atmospheric CO2 concentrations over the past decades has been larger than the ocean buffering capacity, resulting in an ocean pH decrease. Since 1800 A.D., ocean pH has decreased from 8.16 to 8.05. A further drop to around 7.8 is estimated by the end of the century ( Feely et al. 2009), and within a few hundred years ocean pH may reach levels not experienced in the last 20 million years or more. Because many marine organisms, both planktonic and benthic, are known to be sensitive to changes in pH, human CO2 emissions are likely to have important consequences for marine ecosystems. For example, experiments in artificially acidified waters show that organisms with carbonate shells have difficulties maintaining their shells at lower than present pH. In addition to this pH effect, ocean CO2 uptake results in changes in the chemistry of the oceans that reduce their ability to absorb additional atmospheric CO2. This project should describe and discuss the likely effects of the anthropogenic CO2 increase on ocean chemistry and marine ecosystems, both at present and in the future. • C aldeira, K. & Wickett, M.E. 2003. Anthropogenic carbon and ocean pH. Nature 245, 365. • Feeley, R.A. 2004. Impact of anthropogenic CO2 on the CaCO3 system in the oceans. Science 305, 362-366. • Feely, R.A., Doney, S.C., and Cooley, S.R. 2009. Ocean acidification: present conditions and future changes in a high CO2 world. Oceanography 22, 36-47. • Kerr, R.A. 2010. Ocean acidification unprecedented, unsettling. Nature 328, 1500-1501. • U. Riebesell, K. G. Schulz, R. G. J. Bellerby, M. Botros, P. Fritsche, M. Meyerhöfer, C. Neill, G. Nondal, A. Oschlies, J. Wohlers & E. Zöllner. 2007 Enhanced biological carbon consumption in a high CO2 ocean. Nature 450, 545-548. • Ridgwell, A. & Zeebe, R.E. 2005. The role of the global carbonate cycle in the regulation and evolution of the Earth system. Earth and Planetary Science Letters 234, 299-315. • Orr, J.C. et al., 2005. Anthropogenic acidification over the twenty-first century and its impact on calcifying organisms. Nature 437, 681-686. • Sunda, W.G. 2010. Iron and the carbon pump. Science 327, 654-655. • Ruttimann, J. 2006. Sick seas. Nature 442, 978-980 . • Ruttimann, J. 2006. Sick seas. Nature 442, 978-980 . III

Has ancient DNA helped understanding of animal ecology during the Quaternary? (Richard Bradshaw) • Recovery and sequencing of ancient DNA from extinct and surviving fauna have altered understanding of the combined effect of climate change and human impact on population dynamics and ecology. In this project you will assess the strengths and limitations of this new analytical technique, including the issues of contamination. You will review selected studies to highlight how they have contributed to our knowledge of past community dynamics and extinction. • Willerslev, E. et al. (2014) Fifty thousand years of Arctic vegetation and megafaunal diet. NATURE 506, 47-51. • Haile, J. et al. (2009) Ancient DNA reveals late survival of mammoth and horse in interior Alaska. PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA Volume: 106 Issue: 52 Pages: 22352-22357 • Hofreiter, M. et. (2012) Ancient biomolecules in Quaternary palaeoecology. QUATERNARY SCIENCE REVIEWS 33, 1-13. IV

The Holocene spread of spruce and beech in Europe. Climatic control, human influence or migration biology? (Richard Bradshaw) • The establishment of large populations of spruce and beech in northern Europe occurred during the late Holocene, long after the establishment of pine, oak, elm alder and other tree species. Why was this the case? In this project you will review the evidence for climatic control, migration biology and disturbance processes on the dynamics and distribution of spruce and beech in Europe during the Holocene. • Magri, D. (2008) Patterns of post-glacial spread and the extent of glacial refugia of European beech (Fagus sylvatica). JOURNAL OF BIOGEOGRAPHY 35, 450-463. • Lehsten, D. et al. (2014) Modelling the Holocene migrational dynamics of Fagus sylvatica L. and Picea abies (L.) H. Karst. GLOBAL ECOLOGY AND BIOGEOGRAPHY 23, 658-668. • Bialozyt, R. et al. (2012) Modelling the spread of Fagus sylvatica and Picea abies in southern Scandinavia during the late Holocene. JOURNAL OF BIOGEOGRAPHY 39, 665-675. • Bradshaw, R.H.W. & Lindbladh, M. (2008) Regional spread and stand- scale establishment of Fagus sylvatica and Picea abies in Scandinavia. ECOLOGY 86, 1679-1686. V