@SWMtweet #suswm2018. Keynote address. Myles Allen. University of Oxford Lead contributing author of IPCC Special Report

Transcription

1 @SWMtweet #suswm2018 Keynote address Myles Allen University of Oxford Lead contributing author of IPCC Special Report

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3 Global Warming of 1.5 C Key findings from an IPCC special report on the impacts of global warming of 1.5 C above pre-industrial levels and related global greenhouse gas emission pathways, in the context of strengthening the global response to the threat of climate change, sustainable development, and efforts to eradicate poverty. Myles Allen, Coordinating Lead Author, Chapter 1, Framing and Context

4 Where are we now? Since pre-industrial times, human activities have caused approximately 1 C of global warming, increasing at 0.2 C per decade. Already seeing consequences for people, nature and livelihoods At the current rate of warming, temperatures would reach 1.5 C around 2040 Past emissions alone do not commit the world to 1.5 C Ashley Cooper / Aurora Photos

5 SPM.1: Cumulative emissions of CO 2 and future non-co 2 radiative forcing determine the probability of limiting warming to 1.5 C Informal presentation by Myles Allen & Mikiko Kainuma. Kirsten Zickfeld, Richard Millar & Natalie Mahowald, key Chapter 1 authors Panmao Zhai, WG1 co-chair Angela Morelli & Tom Johansen, Infodesignlab

6 Observed monthly global mean surface temperature from four available published and peer-reviewed datasets Global warming relative to ( C) Global warming relative to ( C)

7 Changes in the global energy balance determines the timing of human-induced and natural changes in global temperatures Global warming relative to ( C) Global warming relative to ( C) Solar variability Greenhouse gases and aerosols Explosive volcanoes

8 Observed warming is used to estimate the magnitude of human-induced and natural changes in global temperatures Global warming relative to ( C) Global warming relative to ( C)

9 Anthropogenic global warming has reached 1 C, with a likely range of 0.8 to 1.2 C, and is increasing at 0.2 C per decade Global warming relative to ( C) 1.0 C

10 Placing 0.5 C of warming in context: significant changes in weather extremes already observed between and C

11 Placing 0.5 C of warming in context: significant changes in weather extremes already observed between and Fraction of global land area that has experienced a change in extreme event frequency for 0.5 C warming between and Internal variability estimated by statistical resampling of 20yr sets from Figures S3.6 & S3.7, main report Schleussner et al., 2017

12 20-40% of the world s population live in regions that have already warmed by more than 1.5 C in at least one season Figure 1.1, main report

13 Global warming is likely to reach 1.5 C between 2030 and 2052 if it continues to increase at the current rate 1.5 C

14 Impact: Countries in the tropics and Southern Hemisphere subtropics are projected to experience the largest impacts on economic growth due to climate change should global warming increase from 1.5 C to 2 C 1.5 C 2 C relative to no additional warming 1.5 C relative to 2 C 2018 The Authors. Felix Pretis et al. Phil. Trans. R. Soc. A 2018;376:

15 Impact: Countries in the tropics and Southern Hemisphere subtropics are projected to experience the largest impacts on economic growth due to climate change should global warming increase from 1.5 C to 2 C 2018 The Authors. Felix Pretis et al. Phil. Trans. R. Soc. A 2018;376:

16 Impact: Countries in the tropics and Southern Hemisphere subtropics are projected to experience the largest impacts on economic growth due to climate change should global warming increase from 1.5 C to 2 C

17 Anthropogenic emissions from the pre-industrial period to the present alone are unlikely to cause global warming of 1.5 C. Aerosol rebound Methane decline Centennial adjustment to constant non-co 2 forcing Figure 1.5, Chapter 1, & Smith et al, 2018

18 1.5 C greenhouse gas emissions pathways Limiting warming to 1.5 C would require changes on an unprecedented scale Deep emissions cuts in all sectors A range of technologies Behavioural changes Increased investment in low carbon options Neil Emmerson / Aurora Photos 18

19 SPM.3a: Global emissions pathway characteristics: Limiting warming to 1.5 C with no or limited overshoot Limiting warming to 1.5 C with high overshoot

20 SPM.3b: Characteristics of four illustrative model pathways CO 2 emission reductions are mainly achieved by P1: social, business and technological innovations result in lower energy demand up to 2050 P2: a broad focus on sustainability with limited societal acceptability for BECCS. P3: changing the way in which energy and products are produced, and [some] reductions in demand. P4: technological means, making strong use of CDR through the deployment of BECCS.

21 Achieving 1.5 C in 2100 means a simple choice: faster emission reductions before 2030 versus CO 2 removal after 2030

22 Achieving 1.5 C in 2100 means a simple choice: faster emission reductions before 2030 versus CO 2 removal after 2030

23 Achieving 1.5 C in 2100 means a simple choice: faster emission reductions before 2030 versus CO 2 removal after 2030

24 Achieving 1.5 C in 2100 means a simple choice: faster emission reductions before 2030 versus CO 2 removal after 2030

25 All scenarios show similar maximum absolute reduction rates so

26 All scenarios show similar maximum absolute reduction rates so every tonne of carbon dumped in the atmosphere before reductions begin has to be scrubbed out again before 2100

27 Pathways with no emission reductions before 2030 imply CO 2 removal exceeding 20 GtCO 2 per year by 2100 (1980 emissions in reverse) and temperatures overshooting 1.5 C by 2050 So what would it cost to avoid overshoot and reliance on CO 2 removal?

28 Annual average energy-related investments over the period in 4 scenario categories (Fig 2.27 underlying report) Approx. 2.8% global GDP $830 bn = +37% 4 C 3 C 2 C 1.5 C Explanation courtesy of Elmar Kriegler

29 Spending on energy Context: annual average energy-related investments relative to energy-related expenditure (assuming this follows GDP) Additional energy-related investment for 1.5 C is <1% of GDP, and <10% of current annual spending on energy *

30 So what can cities do? Adapt: Urban heat islands often amplify the impacts of heatwaves in cities. Engage: Strengthening the capacities for climate action of national and sub-national authorities, civil society, the private sector, indigenous peoples and local communities can support the implementation of ambitious actions implied by limiting global warming to 1.5 C. Lead: Reaching and sustaining net zero global anthropogenic CO 2 emissions and declining net non-co 2 radiative forcing would halt anthropogenic global warming on multi-decadal time scales.

31 Implications To reach net zero before global temperatures exceed 2 C, carbon dioxide emissions must fall, on average, by 10% of their current level for every tenth of a degree warming from now on. To reach net zero before global temperatures exceed 1.5 C, carbon dioxide emissions must fall, on average, by 20% of their current level for every tenth of a degree warming from now on. Right now, a warming of 0.1 C takes 5-7 years. Cities and companies are increasingly making net zero by 2050 pledges but what if we get to 1.5 C in 2040, or 2070? Why not pledge net zero by 1.5 C and use annual announcements of the level of humaninduced warming to track your progress?

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