Il ghiaccio e i cambiamenti climatici

Transcription

1 Associazione Galileo 2001 Convegno Clima, Energia, Società Roma, 13 e 14, ottobre 2009 Il ghiaccio e i cambiamenti climatici Massimo Frezzotti massimo.frezzotti@enea.it ENEA, Roma, Italy Programma Nazionale di Ricerche in Antartide

2 Sommario 1. I ghiacci polari come archivio naturale della storia del clima nell ultimo milione di anni. 2. I ghiacci continentali ed il livello dei mari 3. Il ghiaccio marino componente fondamentale nell'equilibrio climatico/ambientale

3 Paleoclimatology: Natural Archives PCM PEG Moberg et al. (2005)

4 PALEO-GLACIOLOGY: ICE, CO 2 & TEMPERATURE >35 Myr CO ±250 ppm Sea level +73 m Pre-industraila Era CO ppm Sea level 0 m around 32 Myr CO 2 500±150 ppm Sea level +45±5 m LGM 21 kyr CO ppm Sea level -130±10 m t Alley et al., 2005 Relation between estimated atmospheric CO 2 and the ice contribution to eustatic sea level indicated by geological archives and referenced to modern (pre-industrial Era) conditions.

5 Greenhouse gases the long-term perspective Jouzel et al., 2007, Petit et al., 1999, Lüthi et al., 2008, Loulergue et al., 2008, Schilt et al., 2009 Dome C, Vostok Higher greenhouse gas concentrations during warm climate periods. Seasonal and latitudinal variations in insolation due to changes in Earth's orbit. Strength of major warming implies amplification through albedo and greenhouse gas changes t

6 CO 2, CH 4 & TEMPERATURE!D CO 2 CH 4 CO 2 concentrations lagged Antarctic warming from 800±200 to 600±400 years No doubt on the strong coupling of CO 2 and temperature CO 2 and albedo key amplification factor of the large temperature variations of glacial-interglacial cycles Monin et al., 2001; Fisher et al., 2005; Siegenthaler et al., 2005 t

7 CO 2, CH 4 & TEMPERATURE MBE!"#$%&'()*&$ +(,-(. 300!"#$%&'()*&$ !"#$%&'()*&$ 350 No analog of present-day values during the last 800 kyr CO 2 (and CH 4, except MIS 19) show lower interglacial concentrations before 400 kyr BP CO 2 dominated by Southern Ocean (mixing, iron fertilization) t Siegenthaler et al, 2005 ; Spahni et al., 2005 ; Lüthi et al., 2008 ; Loulergue et al., 2008

8 CH ppbv +135%!CO ppmv ( ) +37% +(,-(. CO 2, CH 4 & TEMPERATURE 300 MBE!"#$%&'()*&$!"#$%&'()*&$!T T ~ 12 C!CO ppmv !"#$%&'()*&$!CH ppbv 350 No analog of present-day values during the last 800 kyr CO 2 (and CH 4, except MIS 19) show lower interglacial concentrations before 400 kyr BP CO 2 dominated by Southern Ocean (mixing, iron fertilization) t Siegenthaler et al, 2005 ; Spahni et al., 2005 ; Lüthi et al., 2008 ; Loulergue et al., 2008

9 CO 2 Amplitude and period variability in natural and anthropogenic condition Greatest CO 2 preindustrial rate is 3.6 ppm/century from 14.6 kyr BP to 14.3 kyr BP 20 times smaller than the average rate of 71 ppm/century during 20th century. Joos & Spahni, 2008

10 RAPID EVENT IN GREENLAND t HO YD YD B/A B/A t HE1 Sequence of rapid events during last deglaciation (Greenland ice core) Low latitude trigger, (dust changes first) ; deuterium excess transition in 1-3 years Steffensen et al, 2008

11 ! Dcorr [ / ] ! 18 Ocorr [ / ] CH4 [ppbv] Greenland ACR AIM 1 DO1 H1 AIM 2 AIM AIM DO8 DO H2 H3 H4 H5 4.1 EDML NGRIP age [yr BP] AIM 12 EDC NorthGRIP Greenland CH 4 composite EDML Tsurf [ C]! 18 O [ / ] NGRIP stadial duration [yr] Every rapid warming in Greenland (D/O) has a counterpart in Antarctica (AIM) Antarctica warms up when Greenland is cold and vice versa Antarctica (AIM) temperature amplitude linearly related to duration of subsequent D/O event EPICA Community Members, 2006 Antarctica t EDML! Tsurf [ C] BIPOLAR SEESAW 4 8

12 outgoing longwave radiation BIPOLAR SEESAW net radiation Sud Nord outgoing longwave radiation!"##$%&$' ($)&"*)+*& Stocker, 2003 t

13 McCarty Glacier, Alaska

14 Gurglerferner (Austria, Oetztal) Similaun Glacier, Ozti mummy, 5350 yr BP

15 Kilimangiaro, Africa

16 Upsala Glacier, Argentina, Patagonia

17 CLIMATE SIGNAL FROM 169 GLACIER RECORDS t Oerlemans, 2005

18 ca 4000 km

19 ICE DISCHARGE 110±70 Gt/yr in 1960s near balance in 1970s 1980s 97±47 Gt/yr in ±38 Gt/yr in E E E+07 GREENLAND 1987 Total Melt Area April - October E E t 5.00E Year Area of summer melting is increasing Melt water rapidly migrates to the ice sheet base and enhances basal sliding and accelerating ice discharge Increasing summer temperatures, more melt water, and greater ice acceleration. Zwally et al., 2002; Rignot et al., 2008

20 Temperature over the Antarctic Peninsula has risen 2.5 C in the past 50 yr (Turner et al., 2005). Many glaciers of Peninsula and Amundsen Sea are accelerating (doubling) and thinning (up to 9 m yr- 1 ) ANTARCTICA Rapid disintegration or collapse of Antarctic Peninsula and Amundsen Sea ice shelves due to atmospheric and ocean warming. Larsen B ice shelf collapsed in 3 weeks after 10,000 years of existence. Larsen B Feb 2002 (de Angelis & Skvarca, 2003; Domack et al., 2005; Prichard et al., 2009)

21 ICE SHEET MASS BALANCE AND SEA LEVEL RISE GREENLAND ANTARCTICA Allison et al., 2009

22 19th AND 20th CENTURY SEA LEVEL RISE Satellite altimetry Bindoff et al., ± 0.3 mm yr -1 Holgate and Woodworth, ± 0.3 mm yr -1 Church et al., 2004, 2006 Current sea level rise has occurred at a mean rate of 1.8 ± 0.3 mm per year for the past century, and more recently at rates estimated to 3.2 ± 0.3 mm per year. Sea level acceleration up to the present appears to have started at the end of the 18th century (Jevrejeva et al., 2008).

23 SEA LEVEL RISE SINCE LAST GLACIAL MAXIMUM from roman time to pre-industrial SLR >0.1 mm yr -1 last century SLR 1.8 mm yr -1 Today SLR 3.2 mm yr times current rate MWP1A SLR 0 mm yr -1 t Last Glacial Maximum eustatic sea level -125±5 m, twice the present volume of Greenland and Antarctic Ice Sheets. Sea level rise about 20 m in 500 yr (40 mm yr -1 ) during MWP1A caused by ice-sheet instability Sea level rise slowly (0.13±0.09 m or 0.06 mm yr -1 ) from 2000 years ago until 19th century (Lambeck et al., 2004; Clarke et al., 2009).

24 max min North Pole Sea ice extent: max 12 M km 2 min 4 M km 2 Ice sheet: Greenland min max South Pole Sea ice extent: max 20 M km 2 min 4 M km 2 Ice sheet: Antarctica

25 Arctic Antarctica

26 ARCTIC SEA ICE EXTENSION: IPCC simulation vs observations (modified from Stroeve et al., 2007)

27 Grazie per la vostra attenzione