Seminar University of Brno, Dept of Geography, October 2013 From proxy data to large-scale paleo reconstructions; new insights on past and present European summer temperature over the past 2500 years Prof. Jürg Luterbacher, PhD Department of Geography Justus Liebig University of Giessen Department of Geography Justus Liebig University of Giessen > University established 1607, one of the oldest in Germany > Approx. 70 km north of Frankfurt > > 23000 students > Department of Geography was funded in 1864 > Currently 1000 students (Bachelor, Master, PhD and teachers) > 6 Professorships - Geomorphology/soil sciences (physical Geography) - Climatology (physical Geography) - Economy Geography - Anthropo Geography - Regional Planning - Geography didactics and pedagogics Leading research questions addressed in this seminar > How can we reconstruct climate before the instrumental period? > How did European summer temperature vary over the past two millennia and how reliable are those reconstructions? > What are the natural variations of European summer temperature back to Roman times? > Is the current warmth and warming trend exceptional in the context of the past two millennia? > What is the influence of human and natural forcing on past European summer temperature? > The exceptional warm summers of 2003 and 2010; is there evidence for similar past extremes?  Importance of Palaeoscience for global change research Importance of Palaeoscience for Global Change Research > Palaeoscience is the study of climate and environmental processes in the past prior to the existence of instrumental records > In order to better understand current climate changes and to project future scenarios, knowledge of the past is imperative > The palaeorecord evidence in concert with modelling of past scenarios provides a quantitative understanding of past Earth System variability and the underlying processes > The past does not provide a prescriptive guide to the future but can form the basis for an evaluation of present day trends, future probabilities, uncertainties and likely human consequences (PAGES 2009) 5 AR5 IPCC 2013: Northern Hemisphere temperature variations back to AD 1 IPCC AR5 2013, chapter 5  NH mean reconstructions do not provide information about seasonal and spatial variations 6 Global summer temperature anomalies 2012 NCEP/NCAR 7 Arctic Sea Ice Extent The 2007 minimum record of sea ice extent was broken on 24, August, 2012 8 Summer temperature change within the instrumental period GISS NASA CRU 2003/2010 ???? Continental temperature change 19th and 20th century ??? IPCC AR5 2013, chapter 10 PAGES Initiative, 2000 years of high resolution continental climate reconstructions Tree rings Varved  sediments Speleothems Historical  documents sedimentary flood records Proxies used for climate reconstructions Bradley 1999 Corals Marine &         lacustrine cores Pfister 1999 Types of climatic proxies Early instrumental measurements Nordli et al. 1997 Documentary evidence, different sources • narrative sources (annals, chronicles, memories) • visual daily weather records • personal correspondence • newspapers • scientific papers • epigraphic records • economic records (books of accounts, correspondence, about natural disasters) Brazdil et al. 2005 ff; Dobrovolny et al. 2010ff; Pfister et al 2008 Central European summer temperature reconstruction 1500-2000 using documentary & instrumental information Dobrovolny et al. 2010 Documentary evidence, Grape harvest data  past summer temperature (France, Switzerland, Austria) Chuine et al. 2004 2003 1540 Types of climate proxies Pfister 1999 Natural archives, Glacier Nigardsbreen (western Norway) Nesje et al. 2002; Steiner et al. 2008 RR-Win TT-Aut RR-Spr Natural archives, Tree rings Climate information from: tree ring width; wood morphological changes throughout the growing season (early and late wood; tree density); isotopic components Tree rings can provide information on summer temperature (Scandinavia/Alps) or precipitation (Mediterranean, UK) Maximum Late Wood Density derived from northern Scandinavian Pinus sylvestris trees  summer temperature reconstruction Esper, Luterbacher et al. 2012, Nature C C Summer temperature and precipitation in central Europe BC 500 to today Büntgen et al. 2011 Schematic diagram of the methodology used to reconstruct past climate NRC 2006 23 Neukom 2010 24 Detection and attribution of past and present European summer temperature > …is the European temperature variability prior to the 20th century really ‘fundamentally a consequence of unforced variability’? (Bengtsson et al., 2006)  their argument is based on the consistent variability for short timescales in an unforced AOGCM control simulation and continental reconstruction > We apply D&A methods to seasonally reconstructed European land areas back to AD 1500  separate externally driven variability from internal fluctuations  Quantify the role of external forcing 25 Fingerprint method : estimates contribution of forced fingerprint (multimodel mean) to reconstructions - The uncertainty of the fit is estimated by superimposing samples of internal climate variability from the climate model and unexplained variance from the reconstruction - Estimate of climate variability: from model runs after subtracting a scaled all forcings EBM run; compared to residual in reconstructions Multiple regression: Fingerprint fi: 1-signal: multimodel mean response (tls estimate, ie variability noise in fingerprint and reconstruction considered) [3 signal (GHG + aerosol; volcanic; solar): Energy Balance Model simulation in response to forcing i] noisenoisetfatT ii forcings proxy   ))(()( Hegerl, Luterbacher et al. 2011, Nat. Geosci. 26  Role of solar forcing not detectable for whole record, not robust over time  Post 1970 acceleration of summer warming is unusual and likely caused by anthropogenic influences (Christidis et al. 2011)  Solar influence on European summer temperatures remains speculative Contribution of external forcing to reconstructed European summer temperature Response to volcanic eruptions in summer temperature for 17 past eruptions Fischer, Luterbacher et al. 2007; Hegerl, Luterbacher et al. 2011  Spatial pattern of multi-model volcanic fingerprint can be detected in the first 2 summers  Similar temperature anomalies as for reconstructions  Significant summer cooling after volcanoes, strongly expressed 1816 after Tambora 28 European summer mean temperature distribution Barriopedro, Luterbacher et al. 2011 1540 1816 29 Summer temperature anomalies 2003 and 2010 (wrt 1961-1990) and ‘preconditions’ GISS/NASA; Barriopedro et al. 2011  Extremly dry in spring and early snow melting period in the Arctic  strong and fast drying of the soil  persistent Omega-situations, subsidence, weak winds and/or warm air advection, strong insolation and reduced latent heat flow (no moisture); downstream floodings in Pakistan 30 Balance after the hot summers of 2003 and 2010 > >70000 heat related death > Actual total loss: 1300 Mio USD > Large crop yield loss and shortage of animal feed in widespread Europe > Widespread forest fires > High fish mortality in central Europe > Heat, drought, ozone and fine dust pollution led to health problems > Problems with energy supply > Record melting of Alpine glaciers Volume loss of 10 % > >55000 heat related death > Actual total loss: 3600 Mio USD > 25% less crop yield in W Russia > Widespread forest fires in western Russia > 2500 destroyed houses > Heat, drought, ozone and fine dust pollution led to health problems > Problems with energy supply (Münchener Re Insurance, 2011; Emergency Control Ministry of Russia) 2003 2010 31 Possible explanations for the exceptional heat summers of 2003 and 2010 > Controversial discussions > Stott et al. (2004, Nature)  ‘human influence on climate has doubled the risk of such an event’ > Dole et al. (2011, GRL): 2010 Heatwave was “mainly natural in origin” > Rahmstorf und Coumou (2011, PNAS): 2010 heatwave: “with a probability of 80% “the 2010 July heat record would not have occurred” without the large-scale climate warming since 1980, most of which has been attributed to the anthropogenic increase in greenhouse gas concentrations > Otto et al. (2012, GRL): based on ensemble experiments, both is possible, depending on the research question Conclusions > Europe offers a broad spectrum of different proxy information to reconstruct past climate > European summers were warm during Roman & Medieval times. Cooler summers were experienced 14th-19th centuries > The current warmth and warming trend are unusual, but not unprecedented in the context of natural climate variability over the past two millennia > 2003 & 2010 are unusual, but not unprecedented (± 1K uncertainties)  1540, a disaster beyond all expectations > Good agreement between reconstructions and palaeo models  Evidence for a better agreement with the palaeo model ensemble using strong total solar irradiance > Tropical volcanism trigger changes in dynamics, summer cooling 1 and 2 years after the eruption (‘year without a summer’)