Arctic climate Valérie Masson-Delmotte LSCE (CEA-CNRS-UVSQ/IPSL), Gif-sur-Yvette, France Helge Drange Univ. of Bergen and the Bjerknes Centre, Norway V Possible title page. Drawing from In Northern Mists by Fridtjof Nansen (1911) In Northern Mists, by Fridtjof Nansen (1911)

Observed temperature (1880-2014) and Arctic sea ice (1953-2014) V

Temperature animation here H Animation of GISS annual mean surface temperature for 1880-2014 relative to 1951-1980 (3 yr averages)

H Mean temperature anomaly for the decade 1905-1914.

Polar amplification H Mean temperature anomaly for the last decade (2005-2014): Polar amplification

Extent of Arctic sea ice, September Reduced with more than ⅓ since 1978, halved since the 1950s Satellite 2014 Reconstructed Extent (106 km2) H The standard figure … Sep sea ice extent in the Arctic: 36% reduction over the time span of satellite obs http://nsidc.org/data and http://www.metoffice.gov.uk/hadobs

Extent of Arctic sea ice, September Reduced with more than ⅓ since 1978, halved since the 1950s Satellite 2014 Reconstructed Extent (106 km2) H …Increasing to about 50 % reduction if reconstructed sea ice is included http://nsidc.org/data and http://www.metoffice.gov.uk/hadobs

Mean ice cover, September 2012 H How things looked like in Sep 2012

Modelled change in Arctic surface temperature (1979-2012) Global temperature: +0.6 °C −1.0 1.0 1.7 2.4 3.0 V “Another view of the polar amplification…”. Surface temperature change between 1979 – 2012 from renalaysis; highlighting the polar amplification Bader (2014), Ding et al. (2014)

Central questions: How unusual? Naturally occurring variations? Degree of human influence? What about the future? −1.0 1.0 1.7 2.4 3.0 V Bader (2014), Ding et al. (2014)

From a paleoclimatologist’s point of view… V

(i) How unusual are these recent changes? Toolbox: proxy records from natural archives V

(ii) How unusual are these recent changes? Temperature change (°C) Year V Arctic warming, and sea ice retreat unprecedented in more than 1400 years Similar conclusions for sea level rise and global warming PAGES2k, 2013

(iii) How unusual are these recent changes? 1800 ppb 400 ppm Atmospheric composition V EPICA and Vostok ice core data

(iv) How unusual are these recent changes? Past sustained polar warming over thousands of years has led to deglaciation of ice sheets and sea level rise by several meters Threshold for Greenland ice sheet deglaciation between 1 and 4°C global warming above pre-industrial level V IPCC AR5, Climatechange2013.org

From a climate modellers' point of view… H

Conservation water vapour motion and growth/melting sea ice + Human-made greenhouse gases and aerosol particles Equation of motion Conservation water vapour Conservation heat Radiation/clouds/ Particles/etc. Atmosphere Surface friction Exchange of heat of water Water budget Snow and ice budget Heat Land Runoff H Schematic of a climate model Conservation of salt Equations for motion and growth/melting sea ice Conservation of heat Equation of motion Ocean & sea ice After Manabe & Stouffer (2000)

Conservation water vapour motion and growth/melting sea ice Equation of motion Conservation water vapour Conservation heat Radiation/clouds/ Particles/etc. Atmosphere Surface friction Exchange of heat of water Water budget Snow and ice budget Heat Land Runoff H Schematic of a climate model, highlighting the interaction between atm and the ocean Conservation of salt Equations for motion and growth/melting sea ice Conservation of heat Equation of motion Ocean & sea ice After Manabe & Stouffer (2000)

uncertainty ≠ no certainty Possible future uncertainty ≠ no certainty H

Global population (billion) Global CO2-emissions (Gt-C/yr) 2006 Global population (billion) Global CO2-emissions (Gt-C/yr) V. Blue colour: Global population 1960-2100 (actual until 2014, estimated thereafter). Black line: Total CO2-emissions to atmosphere (human+natural) up to 2006, the starting point for the AR5-scenarios

Global population (billion) Global CO2-emissions (Gt-C/yr) 2006 Global population (billion) Global CO2-emissions (Gt-C/yr) V. Business-as-usual scenario (high-end scenario; almost tripling of global co2-emissions)

Global population (billion) Global CO2-emissions (Gt-C/yr) 2006 Global population (billion) Global CO2-emissions (Gt-C/yr) V. Two intermediate scenarios, one with max emissions in 2080, another with max emissions in 2040

Global population (billion) Global CO2-emissions (Gt-C/yr) RCP8.5 RCP6.0 RCP4.5 RCP2.6 2006 Global population (billion) Global CO2-emissions (Gt-C/yr) V. A scenario constructed to be consistent with 2C warming (note possibility for negative emissions towards 2100)

Global population (billion) Global CO2-emissions (Gt-C/yr) RCP8.5 RCP6.0 RCP4.5 RCP2.6 2006 2014 Global population (billion) Global CO2-emissions (Gt-C/yr) V. What about the actual co2-emissions between 2006 and 2014?

Global population (billion) Global CO2-emissions (Gt-C/yr) RCP8.5 RCP6.0 RCP4.5 RCP2.6 2006 2014 Global population (billion) Global CO2-emissions (Gt-C/yr) V. …they have been increasing, closely following RCP8.5. In the following, results from RCP8.5 and RCP2.6 will be shown

Modelled change in annual mean temperature, Arctic (2081-2100 relative to 1986-2005) RCP8.5 RCP2.6 +9 to +11 °C +2 to +3 °C Arctic amplification occurred during the past and is expected in the future Climate models are tested against past climate data Global warming by more than 2°C would be outside of the range of variations of the past million years For comparison, modern woman and man has been on Earth for some 200.000 years H

Modelled change in annual mean precipitation, Arctic (2081-2100 relative to 1986-2005) RCP8.5 RCP2.6 ~ 50 % ~ 10 % H

Modelled change in heavy (>97,5 %) precipitation (2081-2100 relative to 1986-2005) RCP8.5 RCP2.6 > 50 % 30-50 % Approaching unknown territory for ecosystems and societies H

Arctic sea ice in September, 1900-2100 Observed 1953-2014 | Model simulations 1900-2100 Extent (106 km2) Large differences between the scenarios (solid lines) Large model uncertainty (shadings) H (or V) Virtually no sea ice Stroeve et al. (2012), updated

NB: Poorly modelled sea ice thickness (Sep) Observed (ICESat) Defference Models – Obs Multi-model mean H (or V) Stroeve, NSIDC

Future sea level change For the next decades, dominant role of ocean warming and glacier retreat For the long term, key uncertainty associated with the response of the Greenland and Antarctic ice sheet Large warming would lead to up to 1 m sea level rise in 2100, 3 m by 2300 V

Concluding remarks For the Arctic, amplifying mechanisms acting at the regional scale but also at the global scale Arctic climate change leads to a complex mixture of opportunities and vulnerabilities Risks of irreversible loss: biodiversity, cultural heritages Thawing of the vast permafrost regions in the Arctic is ongoing, with poorly known climate implications Based on current understanding, rapidly reduced greenhouse gas emissions will strongly limit climate changes in the Arctic V