Tipping positive change to avoid climate tipping points

Tipping positive change to avoid climate tipping points Tim Lenton Director, Global Systems Institute, University of Exeter t. m. lenton@exeter. ac. uk

Generic example of passing a tipping point

Temperature in Greenland m

Schellnhuber et al. (2016) Nature Climate Change 6: 649 -653

Climate tipping elements Lenton et al. (2008) PNAS 105: 1786 -1793

Changing risk assessment of tipping points 2001 IPCC 2007 Assessment Reports and Special Reports 2013 Undetectable Low High Very high 2019 0 Past 1 2 1. 1°C (2020) 3 Future Global average temperature above pre-industrial 4 5 °C

Greenland ice sheet Ice loss accelerating Arctic sea ice Massive reduction in area Permafrost Thawing underway Boreal forest Fire regime changing Atlantic circulation 15% slowdown since 1950 s Coral reefs Massive die offs Amazon rainforest Unprecedented droughts in last 15 years West Antarctic Ice Sheet Ice loss accelerating Wilkes basin, East Antarctica Ice loss accelerating

Coupling between tipping events Steffen et al. (2018) PNAS 115: 8252 -9

A global tipping point? Steffen et al. (2018) PNAS 115: 8252 -9

What should we do about tipping point risks? Price Cost of mitigation Cost of climate damages But what if there are uncertain tipping points? Optimum (? ) Global temperature change

Key Nordhaus’ DICE model updated risk preferences with climate tipping points Cai, Lenton, Lontzek (2016) Nature Climate Change 6(5): 520– 525

Global CO 2 emissions to meet Paris goals Committee on Climate Change (2019) Net Zero: The UK’s Contribution to Stopping Global Warming

Tipping positive change Otto, Donges et al. (2020) PNAS 117(5): 2354 -2365

Tipping public opinion

Tipping collective action • Uncertainty about the location of a damaging climate 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

Tipping social-technical change Easter Parade, 5 th Avenue, New York City 1900: Spot the automobile 1913: Spot the horse

Tipping the energy system new vs vs new existing Lenton, Pichler, Weisz (2016) Earth System Dynamics

Conclusions • We cannot rule out that ice sheet tipping points have already been passed and if we continue burning known fossil fuel reserves then other climate tipping points will become high impact high probability events • This is an existential threat! – we should be doing everything in our power to avoid irreversible, damaging tipping points, including governments setting a carbon price today of >$100/t. CO 2 • We need to tip the narrative – to find ways to tip transformative change in societies to secure collective human wellbeing