Stockholm Seminar 8th June 2010 KVA Prof. Johan Rockström Stockholm Resilience Centre Stockholm Environment Institute Anthropogenic global environmental change – risks and uncertainties

PNAS Special Feature: Tipping elements in the Earth System, Jan 2010, vol 106 (49) Tipping elements in the Earth system – PNAS Special Feature released December 2009

IPCC AR4 2007

Global Mean Temperature Trend

TAR cm (9-88 cm) ”high uncertainty” AR cm (18-79 cm) ”larger cannot be excluded”

”Our understanding of these processes is limited. As a result, they are not included in current ice sheet models and there is no consensus as to how quickly they could cause sea level to rise. Note that these uncertainties are essentially one sided. That is, they could lead to substantially more rapid rate of sea-level rise but they could not lead to a significantly slower rate.....” Church et al., Sea-level rise A post IPCC

Thermal Expansion Greenland Artic Antarctica SOURCESESTIMATESSOURCEASSUMPTIONS Thermal Expansion in 300 yrsIPCC TAR (2X ppm)) Weakening of thermohaline circulation Mountain Glaciers0.4 m (80 % loss)0.5 m sea level rise held (IPCC TAR) Greenland0.9 m – 1.8 m in 300 yrs IPCC TAR 0.9 m (local warming 5.5 C) Rapid melting not included in IPCC estimate AntarcticaWAIS 1-2 m(estimate including disintegration) Stable ice sheet models inadquate EAIS stable Total2.7 – 5.1 m m/centuryNow 3 cm/decade for 0.6 C warming. 3 C warming = 1.4 m/century S. Rahmstorf and C. Jäger, 2007

11 Uncertain uncertainty ref: Baer and Mastrandrea (2006) 3 ºC 6 ºC

IPCC AR4 Scenarios

2 º C warming corresponds to a barrier of 2.5 Wm -2 of radient energy added by humans. This corresponds to 441 ppm CO 2 eq (range ~ ppm) We have already added 3 Wm -2 of radiant energy. CO 2 (1.65 Wm -2 ) and non-CO 2 GHGs (1.35 Wm -2 ) (non-CO 2 GHGs are methane (CH 4 ); nitrous oxide (N 2 O); halocarbons (HCs) which include CFCs, HCFCs, and HFCs; and tropospheric ozone (O 3 ). What does a 2 º C limit mean?

Why have we only seen ~0.7 º C warming so far? ~0.5 C stored in oceans (20 %) ~ 1.2 C masked by cooling aerosols (50 %) possibly combined with a climate sensitivity at the lower end of the climate science analyses (but, even if climate sensitivity is 50 % lower than the median sensitivity, the added energy corresponds to ~1.2 º C)

Ramanathan and Xu, PNAS, 107 (18) : Masking and avenues to fast track mitigation

Climate Change < 350 ppm CO 2 < 1W m 2 (350 – 500 ppm CO 2 ; W m 2 ) Ocean acidification Aragonite saturation ratio > 80 % above pre- industrial levels (> 80% - > 70 %) Ozone depletion < 5 % of Pre-Industrial 290 DU (5 - 10%) Global Freshwater Use <4000 km 3 /yr (4000 – 6000 km 3 /yr) Rate of Biodiversity Loss < 10 E/MSY (< 10 - < 1000 E/MSY) Biogeochemical loading: Global N & P Cycles Limit industrial fixation of N 2 to 35 Tg N yr -1 (25 % of natural fixation) (25%-35%) P < 10× natural weathering inflow to Oceans (10× – 100×) Atmospheric Aerosol Loading To be determined Land System Change ≤15 % of land under crops (15-20%) Chemical Pollution Plastics, Endocrine Desruptors, Nuclear Waste Emitted globally To be determined Planetary Boundaries

Adapted from Canadell et al., 2007 atmosphere Terrestrial and Marine Carbon sinks Gt Carbon/yr ocean land Fossil CO 2 Land CO 2 Agric/waste/energy CH 4 Agric/others N 2 O CFCs/Tropospheric O 3

Ocean acidification Challenge to marine biodiversity and ability of oceans to function as sink of CO 2 Southern Ocean and Arctic ocean projected to become corrosive to aragonite by Turley et al 2006

From R. Buddemeier, based on Kleypas et al. 1999

Global emission pathways in compliance with a 2 ºC guardrail (WBGU 2009)