What is climate change? Tim Lenton University of Exeter

Transcription

1 What is climate change? Tim Lenton University of Exeter

2 Outline A (geo)physiological view of the Earth The diagnosis: Dangerous tipping points ahead What to do about it? Medicate or tackle the underlying causes?

3 Atmospheric compositions Mixing Ratio Hydrogen Methane Nitrogen Nitrous Oxide Carbon Monoxide Carbon Dioxide Oxygen Earth Mars Venus

4 Environment Origin Oxygen Revolution Complexity Revolution Ages in Ga (10 9 yr BP) Life T. M. Lenton et al. (Working Group 1) 91 st Dahlem Workshop on Earth System Analysis for Sustainability (2003)

5 Generic example of a tipping point (System state) (System state) Thanks to Chris Boulton for the animation

6 Tipping points in Earth history PAL = Present Atmospheric Level Lenton (2016) Earth System Science: A Very Short Introduction (OUP)

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8 Projected Concentration After 50 More Years of Unrestricted Fossil Fuel Burning Recent ice age cycles 400 Today s CO2 Concentration 300 CO 2 [ppmv] Temperature proxy 600, , , ,000 Age (yr BP) 200, ,000 0

9 600 After 40 More Years of current energy use patterns Today s CO2 Concentration 300 CO 2 [ppmv] Temperature proxy 600, , , ,000 Age (yr BP) 200, ,000 0

10 Ice age abrupt climate changes Temperature in Greenland Monsoon in Amazon Monsoon in India Age (thousands of years ago = ka) Time Deplazes et al. (2013) Nature Geoscience 6:

11 Smooth projections of future change IPCC (2013) Working Group 1

12 IPCC AR5, WG1 SPM, 2013

13 Knutti et al. (2016) Nature Geoscience 9: Future worlds

14 Lenton et al. (2008) PNAS 105(6): Climate tipping elements

15 How close are tipping points? Lenton & Schellnhuber (2007) Nature Reports Climate Change

16 Atlantic overturning circulation

17 Expert elicitation of probabilities Three different warming scenarios: Example: collapse of Atlantic meridional overturning circulation Kriegler et al. (2009) PNAS 106(13):

18 Likelihood of tipping points 2-4 C warming: >16% probability of passing at least one tipping point >4 C warming: >56% probability of passing at least one tipping point Atlantic Greenland Antarctica Amazon El Niño Kriegler et al. (2009) PNAS 106(13):

19 Abrupt changes in climate models Drijfhout et al. (2015) PNAS 112(43): E5777-E5786

20 Tipping points of tropical tree cover Hirota et al. (2011) Science 334: 232-5; Staver et al. (2011) Science 334: 230-2

21 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 From expert elicitation: Kriegler et al. (2009) PNAS 106(13):

22 Thanks to Jonathan Donges and Ricarda Winkelmann, PIK, for the image

23 Early warning prospects System being forced past a tipping point Held & Kleinen (2004) GRL 31: L23207; Lenton et al. (2008) PNAS 105(6):

24 Thanks to Chris Boulton for the animation Early warning indicator

25 Abrupt climate change early warning Ice-core temperature proxy Detrended data Early warning indicator Lenton, Livina, Dakos, Scheffer (2012) Climate of the Past 8:

26 Early warning of a modelled tipping point Atlantic Meridional overturning circulation (AMOC) is currently monitored at 26 o N In the FAMOUS model we can collapse the AMOC and see early warning signals at 26 o N Early warning indicator Boulton, Allison, Lenton (2014) Nature Comms. 5: 5752

27 Where are the best early warning signals? How early are they? Autocorrelation AR(1) Variance Red areas indicate early warning signals that are significant at p<0.05 Boulton, Allison, Lenton (2014) Nature Comms. 5: 5752

28 Trends in sea surface temperature fluctuations Boulton & Lenton (2015) PNAS 112(37): Red = slowing down Blue = speeding up

29 Pacific decadal oscillation (PDO) Autocorrelation Variance Boulton & Lenton (2015) PNAS 112(37):

30 Implications for marine ecosystems Ecosystem correlation with ocean Ecosystem standard deviation AR(1) of ocean variability AR(1) of ocean variability Autocorrelation (AR(1)) of ocean variability Boulton & Lenton (2015) PNAS 112: , adapting the model of Di Lorenzo & Ohman (2013) PNAS 110:

31 What should we do about tipping point risks? Collapse of West African Monsoon Increase in El Nino amplitude Disintegration of West Antarctic ice sheet Irreversible meltdown of Greenland ice sheet Highest risk Relative impact Collapse of Atlantic thermohaline circulation Dieback of boreal forest Dieback of Amazon rainforest Loss of Arctic summer sea-ice Lowest risk Relative likelihood Lenton (2011) Nature Climate Change 1:

32 Conventional cost-benefit analysis Cost of mitigation Cost of climate damages Price But what if there are uncertain tipping points? Optimum (?) Global temperature change

33 Adding uncertain tipping points to a widely-used integrated assessment model Lontzek, Cai, Judd, Lenton (2015) Nature Climate Change 5(4):

34 Representation of tipping points Tipping element Hazard rate (%/yr/k) Transition time (years) Final damages (% world GDP) Atlantic overturning (AMOC) Greenland ice sheet (GIS) West Antarctic ice sheet (WAIS) Amazon rainforest (AMAZ) El Nino (ENSO) Lontzek, Cai, Judd, Lenton (2015) Nature Climate Change 5: ; Cai, Lenton, Lontzek (2016) Nature Climate Change

35 Cai, Lenton, Lontzek (2016) Nature Climate Change 6(5):

36 Tipping collective action Uncertainty about the location of a tipping point can lead to failure to coordinate to avoid it If uncertainty can be reduced below a critical level, social dynamics are tipped from free riding to coordinating to avoid catastrophe Barrett & Dannenberg (2014) Nature Climate Change 4: 36-39

37 Tipping the energy system Source: Michael Liebreich, Bloomberg New Energy Finance

38 Conclusions If business-as-usual continues then climate tipping points are expected to become high impact high probability events Tipping point early warning systems have been successfully tested and could be developed as an aid to adaptation to forewarn societies and trigger pre-emptive action The threat of multiple, interacting, uncertain climate tipping points should be triggering much stronger action to tackle climate change now, with a carbon price today of >$100/tCO 2

39 Want to learn more? 4 new Massive Open Online Courses (MOOCs) Climate Change: The Science Climate Change: Solutions Tipping Points Valuing Nature FutureLearn Early 2018 Climate Change: Your Stories (