Klimat i förändring. Deliang Chen. August Röhss Professur i Naturgeografi Professor i fysikaliska meteorologi Institutionen för Geovetenskaper

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1 Klimat i förändring Deliang Chen August Röhss Professur i Naturgeografi Professor i fysikaliska meteorologi Institutionen för Geovetenskaper Tack till IPCC, Erik Kjellström, Jessica Andersson, Markku.Rummukainen Miljöimpuls!, 24 november 2008

2 Vad ska jag prata om? Varför ändras klimat? Sammanfattning av IPCCs senaste rapporten (AR4, 2007) Vad har hänt efter 2006 (AR4)? Framtid: vad ska vi tänka på (säkerhet eller osäkerhet)?

3 Varför varierar jordens klimat? Variationer i solstrålningen Variationer i jordbanan Ändringar i atmosfärens sammansättning (gaser) Variationer i naturliga och antropogena aerosoler (partiklar) Ändringar i markanvändning Interna variationer i klimatsystemet

4 Human factors Greenhouse gases Volcanic activity Natural factors Atmospheric aerosols The earth s s climate can change because of anthropogenic or natural factors Variations of Solar radiatios Land-use change Natural variability (ENSO, NAO)

5 Socio-ekonomisk världsutveckling Utsläpp Hur räcknar man framtids klimat szenario/påverkan? Atmosfärens sammansättning Ofta bara det! Globalt klimat Regionala klimat Effekter

6 Klimat- och sårbarhetsutredningen Sverige blir varmare och blötare Risken för översvämningar, erosion, ras och skred ökar i stora delar av landet Infrastruktur hotas kostnadskrävande insatser Skogstillväxten ökar och förutsättningarna för jordbruk förbättras anpassningsåtgärder krävs för att t ex minska skadeangrepp Östersjön hotas marina arter hotas att slå ut Vattenkvaliteten försämras vattenreningen måste förbättras Fjällen förbuskas vinterturismen drabbas, markkonkurrens drabbar rennäringen Värmeböljor och smittspridning ökar nya smittbärare och ökad dödlighet Mer gynnsam energibalans ökat kylbehov, minskat uppvärmningsbehov, mer vattenkraft

7 Fundamental Climate Change Questions

8 Main aspects of IPCC AR4 (2007) Consistent and strong message. Less uncertainty, better observations, methods, models and understanding Earth is getting warmer Many aspects of warming are increasing in recent decades Most of recent warming attributable to human influences. Future changes will be larger than those experienced until now Major reductions in greenhgouse gas emissions are required to avoid large scale changes The report is a challenge to world leaders: - We are facing major climate change challenges - Decisions in the next decades will be key to the outcome

9 Atmospheric CO2-content is 30% higher than ever measured covering the past years

10 Greenhous gas forcing over the past years

11 Anthropogenic and natural forcings from 1750 to 2005

12 Observed change in global surface temperature Warmest 12 years: 1998,2005,2003,2002,2004,2006, 2001,1997,1995,1999,1990,2000 Period Rate ± ±0.018 Years /decade

13 lobal T: 0.76 o C 1 of the 12 armest years ccurred in the ast 12 years ea level crease: 17cm ow: 3mm/år) snow cover: 0% : Sea ice area d thickness o reduced

14 Bergen: distribution of winter precipitation /500 1/ Grønås og Kvamstø (2005)

15 Fingerprinting of the anthropogenic effects other GHGs aerosols volcanic solar natural internal Climate models

16 dentificaton of the anthropogenic signature on global and continental warming olid line= Observed ink = With GHG lue = Without GHG

17 It is very likely that the last 50 years in the NH are the warmest in the past 500 years (90% confidence based on expert judgement)... and: likely that they are the warmest in the past 1300 years (66% confidence)

18 It is very likely (90%) that most of the climate changes during the past 50 years originates from human activities

19 Future scenarios: NB: Scenarios are conservative in the sense that the main uncertainties are on the warming side, e.g. Carbon Cycle Feedbacks which most likely will exacerbate warming

20 SRES emission scenarios: Pathways of future greenhouse gas emissions, derived from selfconsistent sets of assumptions about energy use, population growth economic development, and other factors. A variety of possible "world-views", Explicitly exclude any global policy to reduce emissions Six illustrative SRES "marker" scenarios were selected for use in the climate projections. Scenario descriptions Economic emphasis: A1B balanced energy A2 and A1FI Fossil-fuel Intensive A1T high-tech renewable Environmental emphasis: B1, B2

21 CO 2 (GHG) emission scenarios A2 A1B B1

22 EU-target (Anomalies relative to )

23 CO 2 emissions per habitant (based ontreut) Pays Inde Cuba Mexique Chili Venezuela Afrique du Sud Corée du Sud Chine Emission de CO 2 par habitant Ukraine France Italie Royaume Uni Japon Allemagne Belgique Australie Canada USA 0,00 5,00 10,00 15,00 20,00 25,00 tonne par habitant

24 nsemble mean from two emission scenarios: B1: major emission reductions Moderate Current trend continues Some reduction in the Gulf Stream System

25 Precipitation Consistent patterns Continuation of present trends

26 Extreme events: Ongoing trends will continue: Larger and more frequent heat waves More of the precipitation will come as extreme events in many places More intense tropical storms (Atlantic Ocean) AND: Continued reduction in snow and sea ice cover By the end of the 21st century it is likely that the Arctic is blue during summer

27 Main remaining uncertainties Regional changes and natural variability Feedbacks not accounted for interactively in model projections (e.g. C-cycle feedbacks) Ocean circulation and sea ice distribution Aerosoles-cloud albedo Dynamical changes in ice-sheets

28 Cryospheric vs ocean contribution? Address scientific uncertainties: sea-level rise Larger values cannot be excluded Current sealevel rise nea the upper end of the IPCC projections and accelerating why? IPCC 2001; IPCC 2007; Rahmstorf et al. 2007

29 Address scientific uncertainties: global carbon cycle nderstandin the role of marine and terrestrial cosystems in global arbon cycle nd climate system.

30 Develop and test next generation climate models, confront them with observations and build confidence At various scales: time (seasonal to decadal prediction and attribution), space (global to regional prediction) Refine model intercomparison techniques Advance full Earth system model development

31 Fundamental :oupled climate mode run including the oceans. Develop and test next generation climate models: First decadal climate prediction Smith et al., Science

32 Grid points in climate models

33 Why downscaling of GCM output? (3) Global climate models often do not provide what is needed in impact studies!

34 Temperatur och nederbörd i Sverige sedan 1860 Källa: SMHI

35 Medelvärde i trenden över alla stationer R 2 =0.2 slope=0.11 R 2 =0.2 y=0.11*x R 2 = d/100år (R 2 =0.03) R 2 =0.1 slope=0.04 y=0.04*x 54 y=0.003*x nrain smoothed linear trend Antal nederbördsdagar years rain per rain day (mm) Nederb./nederbördsdag pint smoothed linear trend years 99th percentile (mm) percentil pq99 smoothed linear trend years px5d smoothed linear trend 2 =0.3 R 2 =0.3 slope=0.1 y = 0.19*x pxcwd smoothed linear trend 2 =0.12 y = 0.04*x 68 R 2 =0.12 slope= max. 5 day amount (mm) max. no of consecutive wet days största 5-dygns nb years 9 max. antal sammanh. blöta dagar years

36 Trender i olika årstider Röd: sig. 95%

37 Ändring i 2m-temperatur (A2) jämfört med (SMHI) DJF JJA ÅR Göteborg University Regional Climate Group 37

38 Ändring i nederbörd jämfört med (B2) (SMHI) ÅR JJA DJF

39 Förändring i årsmedelvärden: SRES A2 ( ) minus kontroll ( )

40 Hantering av osäkerheter i klimatfrågan Det finns naturliga variationer i klimatet. Gör många klimatsimuleringar. Emissionsscenarierna bygger på en rad antaganden. Använder flera scenarier. Förbättrar scenarierna. Klimatmodellerna innehåller svagheter. Använder flera olika modeller. Förbättrar modellerna. Det kan finnas överraskningar i klimatsystemet. Försöker förstå systemet bättre.

41 Summary of key messages Global warming is unequivocal Warming since the mid of the 20 century is mostly due to human activities (90-95% likelihood) Climate change projections generally in line with previous assessments and observations so far Dependent on emission scenarios Regional patterns emerging Abrupt changes are not projected to occur in the 21 st century, but they could occur at longer time scales under sustained warming