On the Climate During the Holocene - Elisa Ideat · On the Climate During the Holocene With special...

Climate Seminar, Gothenburg 2nd May 2006

Boris Winterhalter, 2006

On the Climate During the Holocene

With special emphasis on the variable climate thatfollowed the retreat and final melting of the continental

ice sheet that had covered all of northern Europe.

Climate from 10,000 years ago to the present.

byBoris Winterhalter



Continental Ice Sheet

Extent of the continental icesheet that covered northernEurope 20,000 years ago, andsummer sea-surfacetemperatures.

Central Europe had a climatecomparable to northernSiberia, and forests as we seethem today in Norden couldbe found in southern Europe.

About 10000 years ago the icemelted and the Holocene, aperiod of pleasant climate,began.



The current paradigm of Holocene climate accepts significant natural variabilityat annual, decadal, centennial, and millennial scales and with considerablespatial variation.

The Paradigm of Holocene Climate

Ideas by H.J.B. Birks ([email protected]) to be presented at HOLIVAR2006 Open ScienceMeeting -Natural Climate Variability and Global Warming, London 12-15 June, 2006

Global summaries are thus of limited relevance, whereas changes at differentlatitudes are more relevant and are of considerable significanceenvironmentally, ecologically, and socially.

The major questions in Holocene climate research continue to be problems inabsolute chronology and hence in reliable correlation between differentproxies and between different geographical areas.

Further problems include evaluating the reliability of quantitative palaeoclimaticreconstructions and realistically estimating their uncertainties, understandingwhat aspects of the environment different proxies reflect and respond to, andinterpreting observed changes in terms of different forcing functions.



How do we study past climate?

" Long sediment cores from peat bogs, from the bottom of small ponds to thedeep oceans have been used extensively to decipher past climates.

" Chemical, physical, and above all, microfossil analysis of the sediment providesproxy information on the conditions that prevailed during deposition.

" Diatoms, foraminifera, corals, etc. provide information on water conditions, e.g.salinity, nutrients, temperature.

" Pollen analysis will tell about the vegetational history of nearby land areas.

" Also sea level variations can be deduced from on and offshore cores.

" Trees record information about past environments and climate in their annualgrowth rings.

" Variations in ring thickness and density (end of growth sequence) provideinformation on growth conditions, drought, precipitation, temperature, etc. and isused by dendroclimatologists to reconstruct past climates.

" The information is, however, limited to the immediate growth site and also to thegrowing season, i.e. in higher latitudes to summer time.



Continued

P The size of the stomata, gas-exchange openings on the underside offossilized leaves from peat deposits provide information on carbon dioxideconcentration in the atmosphere during their growth.

P The growth rings (layers) of corals and especially their isotopic analysis canprovide information on nutrient conditions, salinity and also on temperatureof the surrounding water.

P Ice cores from glaciers and ice sheets exhibit accumulation layers that canbe used for dating. The deposition rate can be established also by isotopicdating. Gas disolved or trapped in bubbles in the ice provides information onthe atmospheric composition that prevailed during the compaction of thesnow to ice.

P Stalagmites and stalactites (in caves) often exhibit annual growth bands. The isotopic composition of the carbonate can give clues on the conditionsthat prevailed during deposition.

P Archeological and especially historical archives can provide valuableinformation on past climates.



Tree ring example fromFinnish Lapland

Ref. Eljas Pohtila, 1979. Climatic fluctuations and forestry in Lapland. Holarctic Ecology 3: 91-98, Copenhagen 1980.

Pohtila (1979) observed a clearcorrelation between tree ringgrowth (index) and sunspots. Henoted also a strong correlationbetween ring growth and theatmospheric zonal circulationindex, which in turn stronglyinfluences regional temperature(Slonosky et al. 2001).

Temperature has a very clearregional and seasonal signature.

Pohtila also noted that the correlation between tree rings and temperature asdegree days was quite low. It seems that solar activity does have a direct influenceon ring growth although the actual mechanisms are still being debated.



Sediment studies in the Baltic Sea

A long sediment core wasanalyzed for chlorofyll a, derivedmainly from marine blue greenalgae (cyanobacteria).

Uppermost 460 cm consist ofsoft clayey mud, frequentlylaminated, and deposited in theLitorina Sea, beginning about8000 years ago.

The high chlorofyll contentbetween 60-110 cm coincideswith the Roman and MedievalWarm Periods.

Modified from: Kowalewska G. 2001. Algal pigments as markers. Clim Res 18: 89–96, 2001



Example of historical data

Grazyna Kowalewska, 2001. Algal pigments in Baltic sediments as markers of ecosystem and climate changes. Clim Res 18: 89–96, 2001.

Meteorological phenomena, which could promote primary production in theBaltic Sea and favour preservation of pigments in sediments, such as floods,river overflows (Odra and Vistula), rains, severe winters etc., based onhistoricalc hronicles( Girgu s& S trupczewski1 965)o fe xceptionalmeteorological events along the SE Baltic Sea coasts. Vertical scale showsintesity of the events.



Our politicians and the general public were confronted with the “Hockey stick” bythe IPCC in 2001 as proof that the escalating use of fossil fuels is changing ourglobal climate.

The Hockey Stick

Note! The curve showsneither the well-documented MedievalWarm Period nor theLittle Ice Age!

THE SCARE:

A catastrophic climatefuture is ahead of usunless we drasticallylower global emissions ofgreenhouse gases.



Hockey Stick debate

From the moment the “Hockey Stick” became the “logo” of the IPCC TAR 2001report, it has been heavily critisized. In 2003 Steven McIntyre and Ross McKitrick(M&M) came out with a study, based on the same data as was used by Mann,Bradley and Hughes (MBH), but with a drastically different message.

Mann et al. insisted that therewas a continuous slow drop intemperature from 1000 yearsago till 1900, when a rapidincrease began due toincreasing CO2 emissions.

M&M showed that thetemperature rise during the20th century was in no wayunprecedented, and infactshowed that MBH had madeserious errors in calculatingtheir curve.



Millennial temperature curve?

The latest word in the debate is shown in the above graph. The neweststudy by Moberg et al. (2005) shows a warmer than present “MedievalWarm Period”, a very cold “Little Ice Age” and the recent warming.



A schematic visualisation of the variability of clim atebased on various temperature proxies from the end ofthe last glacial to modern time.



Greenland Ice Core Project Two



Holocene Temperature Recordsfrom High Northern Latitudes

Bradley, R. S. (2000). Past global changes and their significancefor the future. Quaternary Science Reviews 19: 391-402.

Record of summer melting on the Agassiz Ice Cap,northern Ellesmere Island. Melt indicates the fractionof each core section containing evidence of melting. (Koerner Fisher 1990). Note! The present warming

Summer temperature anomalies estimated from thealtitude where sub-fossil pine wood samples werecollected (black bars) relative to temperatures at themodern pine limit, adjusted for isostatic rebound. Upper limit of pine growth (dashed orange line). (Dahl& Nesje 1966)

Paleotemperature reconstruction from oxygenisotopes in calcite sampled along the growth axis of astalagmite from a cave in Mo i Rana, northernNorway. (From Lauritzen 1996, 1998 with Lundberg).Note that Lauritzen and Lundberg (1999) re-studiedthe data and the steep cooling trend from 6 degC to 3is no longer obvious.

Graph from http://www.pages.unibe.ch/



Cont.Does the summer melting on the Agassiz Ice Capindicate actual decrease in the extent of the ice cap? The question: is this data representative of annualHolocene temperatures ???

The germination of pine seeds is a function of earlysummer temperature and suitable humidity. Thequestion: is the upper limit of pine growth (dashedorange line) indicative of Holocene climate ???

Obviously Bradley wanted to give animpression of the temperature trendsdropping from a high Holocene warm periodto the sub-recent low followed by 20thcentury unprecedented warming?

Corrected curve from Lauritzen and Lundberg,1999



Holocene temperature record fromcave in northern Norway

Comparison of temperatures based onoxygen-18 isotope studies of stalagmitecalcite from the Søylegrotta, cave in Mo iRana to the GISP2 data.

Comparison of the curves reveals a generalcorrelation in timing, duration, and direction althoughperhaps not in magnitude of events for the main part of the record.

Ina dditiont ot hel owert emperatures( mean- 34 C),GISP2 shows a greater range of temperature changesthanS G93( 1 Cc hangei nS G93c orrespondst oaround1 .6 CinG ISP2).

Cont.

Reference: Lauritzen, S.E. and Lundberg, J. 1999. Calibration of the speleothem deltafunction: an absolute temperature record for the Holocene in northern Norway. TheHolocene 9,6 (1999) pp. 659–669



Absolute Holocene tempera ture ..... continued.

The correlation is remarkable for the last 1000 years including the‘Little Ice Age’, when stalagmite SG93 stopped growing.

The correlation between the two curves is weakest for the very slowfirst 1000 years of SG93’s growth.

Between 8000 and 4000 cal. BP the correlation is remarkably high.

SG93 shows greater variations between 4000 and 3500 cal. BP.

The correlation is less clear from 3500 to 2500 cal. BP, breaking downat 2500 cal. BP. However, it is of interest that GISP2, at this point,does not correlate with the other Greenland Summit ice core, GRIP.

SG93 correlates better with the historic record (next slide) than itdoes with GISP2 for the period 2000–1000 cal. BP. The highertemperatures of the Roman Empire times are apparent only in SG93.



Speleothem temperature history inferred for the last2000 years compared with known ‘historic’ events.

Speleothem temperature history inferred for the last 2000 years comparedwith known ‘historic’ events. Purple line - 5 point running mean.

Reference: Lauritzen, S.E. and Lundberg, J. 1999. Calibration of the speleothem delta function: an absolute temperature record forthe Holocene in northern Norway. The Holocene 9,6 (1999) pp. 659–669



Vegetation in Nordenduring the Late Preboreal

The continental ice sheet has retreatedto central Scandinavia. A cool dryclimate prevails in Norden. Birch is thedominant tree species beyond theimmediate influence of the glacier. Stone-age man left traces in Askolasoutheastern Finland. Slowamelioration of the climate continued.

Modified from Berglund 1968

Yoldia Sea around 10,000 years ago



Boreal climate in Norden

The continental ice sheet has vanishedand a warmer dry climate developed. Birch and pine dominated in Norden. Spruce was found in the easternmostparts and hazel was spreading northand reached southern Sweden andsouthernmost Finland.


(10 - 8.5 kyr)



Atlantic climate in Norden

During the Atlantic warm period pinewas abundant even in the northernmostparts of Lapland; in areas wherecurrently only birch grows and whichwas barren tundra prior to the present.

Deciduous trees were found even in thenorthernmost parts of central Finland.

Climatic optimum 8000-4000 BP,2-3 deg C warmer than today6800-5500 yrs ago.



Vegetation during theSub-Atlantic

The present forest vegetation zones (modified Ahtiet al. 1968)- T = temperate, H.B. = Hemiboreal,S.B. = Southern Boreal, M.B. = Middle Boreal, N.B. = Northern Boreal, O.H.A = Orohemiarctic.

A cooler climate has moved the treelineto lower altitudes and deciduous treeshad retreated southward to southernFinland and Sweden.




Spruce migration

The natural migration of spruce intoFinland. The first occurrences wereobserved before 5500 BP and by2000 BP spruce was found all overthe country with suitable soilmoisture and climate as aprerequisite. (Tolonen 1983)



To what extent is the Sun to be blamed?

The Sun is frequented by sunspotsduring 11 year cycles. Between 1645and 1715 ("Maunder Minimum")sunspots did not appear. At the sametime Europe was hit by a very coldspell: the Thames River in Londonfroze, glaciers advanced in the Alps,and northern sea ice increased. An earlier centuries-long active Sunhad the opposite effect: Vikings wereable to settle coastal Greenland in the980s, and even grow enough wheat toexport the surplus to Scandinavia.

Inferred variations in solar intensity (red and green lines) over the last 900 years appears tohave influenced the severity of winters in London and Paris. The red line is deduced from theabundance of carbon-14 in tree rings. This "isotope" is formed in the upper atmosphere whenincoming cosmic rays smash into carbon dioxide molecules.

When the Sun's activity is low, its weakened magnetic field lets more cosmic rays into the solarsystem, so carbon-14 abundances go up. (Notice on the graph that the scale for carbon-14 isupside down.) This image by John Eddy is based on an earlier one that appeared in Science,192, 1189 (1976). http://science.nasa.gov/headlines/y2003/17jan_solcon.htm



P Tree-ring-based temperature reconstructions show cooling effects of largeexplosive volcanic eruptions.

P Freshwater outbursts from proglacial lakes due to final steps of deglaciationcaused stagnation of the thermohaline circulation and cooling phases in theNorth Atlantic. (BW ?)

P Variations in solar activity - as reflected by 14C and 10Be cosmogenicisotopes - were a major driving factor behind Holocene climate oscillations.

P The classical transition from the dry and warm Sub-Boreal to the cool, moistSub-Atlantic around 850 calendar years BC appeared to be linked to atemporary decline of solar activity.

P The hypersensitivity of the climate system to relatively small changes in solaractivity points to the existence of amplification mechanisms. The lack ofaccurate knowledge about such mechanisms still hampers balancedevaluation and modelling of present and future climate.

At HOLIVAR2006 Bas van Geel will give a talk on Holocene climatechange on decadal to centennial time scales and the potential role

of solar variability and other forcing factors.

HOLIVAR2006 Open Science Meeting - Natural Climate Variability and Global Warming, London 12-15 June, 2006



P1. Nigel Calder and Henrik Svensmark have collaborated toproduce a new book and are now looking for an appropriatepublisher. It describes Henrik's work on solar-magnetic effectson cloud formation.

P2. Henrik's laboratory work on solar-magnetic interactions withcloud formation (conducted in his 'basement') using realcosmic rays is completed.

P3. Henrik's long-desired laboratory work on solar-magneticinteractions with cloud formation using the Berne particleaccelerator is to be conducted in September.

– Continued

Newest on clouds and solar activity

Richard S. Courtney sent the following news a few weeks ago:



- continued

Svensmark hopes to repeat his "basement experiments” kilometersbelow the Earth's surface (where few muons penetrate) followingthe particle accelerator experiments.

Therefore, the hypothetical relationship of solar-magneticinteractions with climate may now be about to be elevated to thestatus of a theory on the basis of empirical data.

So, by the end of this year it may no longer be possible to make avalid scientific claim that atmospheric CO2 concentrationdominates global temperature. However, also at the end of thisyear, the next IPCC Report is expected to repeat that claim.



Climate actors

CLIMATE ACTORS OF TODAY AND TOMORROW

Although some outflow glaciers areretreating in Greenland, it seemsthat the net accumulation of snowcounteracts this loss in ice andthere is no iminent danger of sealevel rise.

In northern Europe we enjoy atemperate climate thanks to theprevailing south-westerlies and thereare no indications of a change inpattern.

Influence of the Gulf Stream onEuropean climate has obviouslybeen considerably exaggerated(Seagar et al. 2002).

The Sun, the Cosmos, natural dynamics and changes in landuse



P Past climates, with no anecdotal history, can only be inferredfrom proxies.

P Most proxies exhibit spatial and temporal limitations.

P Some proxies are representative of air temperature orprecipitation while others may mirror water temperature ornutrient availability.

P The choice of suitable proxies and their proper analysis is seldomstraight forward and may lead to questionable interpretationespecially when employing complex statistical manipulation.

P Cross-correlation of various proxies, across the globe, forreconstruction of GLOBAL Holocene temperatures and/or climateis difficult, in fact almost impossible at this stage. This isbecause local or even regional climates can not be properlynormalized (compared), one of many reasons being thedifficulties in reliable and accurate dating.

Reconstruction of past climates -Conclusions



No Global Warming, Because There’s No Global Climate!

“There is not one “global” climate, but a large variety of climates,depending on latitude, geographic conditions, and atmosphericdynamics.”

Statement by Marcel Leroux, professor in climatology at Jean MoulinUniversity in France and director of the Laboratory of Climatology, Risk, andEnvironment. 21st Century Research Communications, Fall 2005.

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