ICE CORES AND CLIMATE

Transcription

1 ICE CORES AND CLIMATE Media Either Hype Complex, Slow Events. Introduction to Glaciology Þröstur Þorsteinsson CLIMATE RECORDS Throstur Thorsteinsson Environment and Natural Resources & Institute of Earth Sciences, University of Iceland Tree rings Ice cores Speleothems GISP2 at 1837 m depth. 18 O LAST 542 Ma Records way back in time 1

2 TEMPERATURE, T (65 Ma) T PAST 5 Ma, SEDIMENTS (Top) Mean temperature change between 1950 s and 2000 s (Bottom) Global average temperature change from 1850 RECENT TEMPERATURE CHANGE Last 2000 years LATITUTE TIME SECTIONS GLOBAL MEAN T 2

3 IPCC 2007 Global mean surface T risen by 0.74 C ± 0.18 C over the last 100 years ( ). The rate over the last 50 years is 0.13 C ± 0.03 C vs C ± 0.02 C per decade. PUBLISHED RECORDS Average arctic temperatures increased at almost twice the global average rate in the past 100 years Observed Antarctic Warming Trend ( C/decade) from Ocean surface T SURFACE ELEVATION CHANGE Arctic air T -1.5 m/y 0.5 m/y Pritchard et al. (2009) 3

4 MELTING IN GREENLAND DATING ICE CORES Layer counting Isotopes Known layers eruptions, bomb tests,... Modeling 19 cm long section of GISP 2 ice core from 1855 m ISOTOPE RATIOS Define R as the ratio of heavy to light isotope R 0 as the standard reference value Standard Mean Ocean Water (SMOW) Then, R R 1000 R 0 0 OCEAN ISOTOPES Nearly uniform composition Ratios are: H 16 2 O : HD 16 O : H 18 2 O : : Where is in parts per thousand, and always negative 18 O 18 O AS A TEMPERATURE PROXY Then R = O 18 /O 16 Given as 18 O For Greenland, an approximate relation is 18 O = 0.67 T 13.7 Note, will depend on distance from source also Not very precise (closer inspection revealed) Heavy isotopes evaporate less easily Condense more readily 4

5 PROBLEMS WITH -VALUES PROBLEMS WITH -VALUES (II) With increasing depth in an ice core, the ice comes from further inland (higher elevation) Not a problem at an divide, IF the divide hasn t moved in the past Past ice sheet thickness changes Total gas content can give information about this Ice flow changes Seasonality of precipitation changes Atmospheric circulation changes Changes in the ocean Water locked up in ice sheets, higher 18 O in ocean, but sea level lower (longer path) partly offsets Noise Flow disturbances GREENLAND ICE CORES Ice cores extracted from the 3 km thick Greenland ice sheet preserve records of ancient air temperatures. The records show several times when climate shifted in time spans as short as a decade. THE LITTLE ICE AGE The Norse abandoned their Greenland settlements when the climate turned abruptly colder 700 years ago. Between 1300 and 1850, severe winters had profound agricultural, economic, and political impacts in Europe. ARTWORK SHOWS THE EFFECT Myndin sem fylgir sýnir hve kaldir veturnir voru á þessum tíma; mynd frá A Scene On the Ice eftir Hendrick Avercamp ( ), frá Hollandi. THE MEDIEVAL PERIOD An abrupt warming took place about 1,000 years ago. It was not nearly so dramatic as past events, but it nevertheless allowed the Norse to establish settlements in Greenland. 5

6 THE 8,200-YEAR EVENT THE YOUNGER DRYAS A similar abrupt cooling occurred 8,200 years ago. It was not so severe and lasted only about a century. But if a similar cooling event occurred today, it would be catastrophic. About 12,700 years ago, average temperatures in the North Atlantic region abruptly plummeted nearly 5 C and remained that way for 1,300 years before rapidly warming again. D18O PAST 1200 YEARS Medieval Period D18O PAST 12 KA Beginning of Little Ice Age 8,200 Younger Dryas VOSTOK D ICE CORE T, PAST 450 ka 6

7 VOSTOK, 420 ka CO 2 AND ICE AGES EPICA ICE CORE RETREATING GLACIERS European Project for Ice Coring in Antarctica (EPICA) 1858 Great Aletsch Glacier (Switzerland) 2001 Pictures provided by Hanspeter Holzhauser and Wilfried Häberli, University of Zürich, Switzerland Lower Grindelwald Glacier Retreat of the d'argentière Glacier (Mont Blanc area, French Alps) between 1896 (old postcard) and

8 RHONE GLACIER 1870 Wurtenkees Glacier in the Austrian Alps CO 2 CONCENTRATION PAST/FUTURE Sea level SEA LEVEL GLACIATION 18 ka AGO 8

9 ICE AGE LOWER SEA LEVEL CLIMATE MODELS EFFECT ON EXTREME TEMPERATURES Throstur Thorsteinsson MODEL IMPROVEMENTS ICE

10 SOLAR VS. HUMAN INFLUENCE CONTRIBUTION OF GLACIERS AND ICE-CAPS TO GLOBAL SEA-LEVEL SEA ICE GLOBAL T SCENARIOS Emissions pathways to give 67% chance of limiting global warming to 2ºC GLOBAL AND CONTINENTAL T Comparison of observed continental- and globalscale changes in surface temperature Decadal averages of observations are shown for the period (black line). Lines are dashed where spatial coverage is less than 50%. Blue shaded bands show the 5 95% range for 19 simulations from 5 climate models using only the natural forcings due to solar activity and volcanoes. Red shaded bands show the 5 95% range for 58 simulations from 14 climate models using both natural and anthropogenic forcings. 10

11 GLOBAL AND CONTINENTAL T PROJECTED SURFACE T PROJECTED PRECIP CHANGE 11