Future risk of tipping points

Transcription

1 Future risk of tipping points Tim Lenton Thanks to Chris Boulton, Valerie Livina, Vasilis Dakos, Marten Scheffer, John Schellnhuber

2 Outline Tipping points Early warning Taster of applications

3 Little things can make a big difference Tipping element A component of the Earth system, at least subcontinental in scale (~1000km), that can be switched under certain circumstances into a qualitatively different state by a small perturbation. Tipping point The corresponding critical point in forcing and a feature of the system at which the future state of the system is qualitatively altered. Lenton et al. (2008) PNAS 105(6):

4 Bifurcation tipping point Irreversible point of no return

5 Bifurcation tipping point Reversible tipping point Irreversible point of no return Reversible transition

6 Tipping elements in the climate system Updated from Lenton et al. (2008) PNAS 105(6):

7 Estimates of proximity Lenton & Schellnhuber (2007) Nature Reports Climate Change

8 Likelihood Imprecise probability statements from experts formally combined. Under 2-4 C warming: >16% probability of passing at least one of five tipping points Under >4 C warming: >56% probability of passing at least one of five tipping points Atlantic Greenland Antarctica Amazon El Niño Kriegler et al. (2009) PNAS 106(13):

9 Tipping point early warning System being forced past a bifurcation point Held & Kleinen (2004) GRL 31: L23207; Lenton et al. (2008) PNAS 105(6):

10 Example of bifurcation-tipping Thanks to Chris Boulton for the animation

11 Thanks to Chris Boulton for the animation Example of an indicator

12 MOC (Sv) MOC (Sv) Model tests of early warning: Collapse of the thermohaline circulation GENIE-1 intermediate complexity model GENIE-2 atmosphere-ocean GCM Lenton (2011) Nature Climate Change 1:

13 MOC (Sv) MOC (Sv) Model tests of early warning: Collapse of the thermohaline circulation GENIE-1 intermediate complexity model GENIE-2 atmosphere-ocean GCM Lenton (2011) Nature Climate Change 1:

14 The end of the ice age in Greenland GRIP ice-core δ 18 O proxy temperature Detrended data Early warning indicator Lenton, Livina, Dakos, Scheffer (2012) Climate of the Past 8:

15 Pacific decadal oscillation (PDO)

16 Mantua PDO index n = 1343 No de-trending in this example Boulton & Lenton (nearly submitted!)

17 Testing against a null model 10,000 realisations of x t+1 = x t + t with fixed = 0.95, n = 1342 points = has p < Boulton & Lenton (nearly submitted!)

18 Testing against a null model 10,000 realisations of x t+1 = x t + t with fixed = 0.95, n = 1342 points 10,000 realisations of x t+1 = x t + t with linear increase = = has p < Boulton & Lenton (nearly submitted!)

19 Inter-annual temperature variability ERA-40 reanalysis 2m temperature data Comparing the periods before and after 1980 Percentage change in standard deviation Huntingford, Jones, Livina, Lenton, Cox (2013) Nature 500:

20 Relative impact Risk matrix? Collapse of West African Monsoon Increase in El Nino amplitude Collapse of Atlantic thermohaline circulation Disintegration of West Antarctic ice sheet Dieback of Amazon rainforest Irreversible meltdown of Greenland ice sheet Highest risk Dieback of boreal forest Loss of Arctic summer sea-ice Lowest risk Relative likelihood Lenton (2011) Nature Climate Change 1:

21 Early warning systems Common elements: Risk knowledge Warning service Communication Response capability Basher (2006) Phil Trans A 364: ; Lenton (2012) Env Sci & Policy 27: S60-S75

22 Conclusion Several tipping elements in the climate system could be triggered this century by anthropogenic forcing Some could be high impact high probability events but we need improved information on their likelihood and their impacts Early warning methods exist for bifurcation-tipping points and these have been successfully tested in models and paleo-data The same methods find remarkable slowing down signals in some observational data e.g. North Pacific sea surface temperature fluctuations Tipping point early warning systems could be developed as an aid to adaptation (and a trigger for avoidance activity)

23 Publications Lenton, T. M., and H. J. Schellnhuber (2007), Tipping the scales, Nature Reports Climate Change, 1, Lenton, T. M., et al. (2008), Tipping Elements in the Earth's Climate System, PNAS, 105, Lenton, T. M. (2011), Beyond 2 C: Redefining dangerous climate change for physical systems, WIRes: Climate Change, 2, Lenton, T. M. (2011), Early warning of climate tipping points, Nature Climate Change, 1, Lenton, T. M. (2011), 2 C or not 2 C? That is the climate question, Nature, 473, 7. Lenton, T. M. (2012), Arctic climate tipping points, AMBIO, 41, Lenton, T. M., et al. (2012), Climate bifurcation during the last deglaciation?, Climate of the Past, 8, Lenton, T. M., et al. (2012), Early warning of climate tipping points from critical slowing down, Phil Trans A, 370, Lenton, T. M. (2012), What early warning systems are there for environmental shocks?, Environmental Science and Policy, 27, S60-S75 Lenton, T. M., and J. C. Ciscar (2013), Integrating tipping points into climate impact assessments, Climatic Change, 117, Livina, V. N., and T. M. Lenton (2007), A modified method for detecting incipient bifurcations in a dynamical system, GRL, 34, L Livina, V. N., et al. (2010), Potential analysis reveals changing number of climate states during the last 60 kyr, Climate of the Past, 6, Livina, V. N., et al. (2011), Changing climate states and stability: from Pliocene to present, Climate Dynamics, 37, Livina, V. N., et al. (2012), An independent test of methods of detecting and anticipating bifurcations in time-series data, Physica A, 391, Livina, V. N., and T. M. Lenton (2013), A recent bifurcation in Arctic sea-ice cover, The Cryosphere, 7,

24 Interactions between tipping events Reduced warming of Greenland Cooling of NE tropical Pacific, thermocline shoaling, weakening of annual cycle in EEP + Shift to a (more) persistent El Nino regime + + +/- Warming of Ross and Amundsen seas Enhanced water vapour export from Atlantic Tropical moisture supply changes - Drying over Amazonia - Dieback of Amazon rainforest Heat accumulation in Southern Ocean Collapse of Atlantic thermohaline circulation Disintegration of West Antarctic Ice Sheet Melt of Greenland Ice Sheet Freshwater input +/- + + Southward shift of Intertropical Convergence Zone Fast advection of salinity anomaly to North Atlantic +/- Increase in meridional salinity gradient Tipping events are connected A B if at least 5 experts judged that triggering A had a direct effect on the probability of triggering B thereafter Sea level rise causing grounding line retreat /- Increase in probability Decrease in probability Uncertain direction of change Kriegler et al. (2009) PNAS 106(13):