Climate change: evolving evidence and implications Michael Raupach 1,2

1. Climate change: evolving evidence and implications Michael Raupach1,2 1Centre for Australian Weather and Climate Research, CSIRO Marine and Atmospheric Research, Canberra, Australia 2ESSP Global Carbon Project Thanks: • Pep Canadell, Corinne Le Quéré, many other GCP colleagues • Vanessa Haverd, Peter Briggs, many other CSIRO colleagues • Colleagues in PMSEIC “Energy-water-carbon intersections” • Colleagues in “Negotiating our future: Living Scenarios for Australia to 2050” Fenner Conference “Population, resources and climate change: implications for Australia’s future” (AAS, Canberra, 10-11 October 2013)

2. Outline • Context • The climate system is a touchy beast • We are poking it with a stick • IPCC Fifth Assessment (AR5) • What the evidence says (past century, coming century) • The false debate • The “carbon budget” for avoiding dangerous climate change • How and why it works • Implications for mitigation rates

3. The Anthropocene:an epoch of growth • Since 1800, global per-capita wealth and resource use have doubled every 45 years • Growth rates (1860-2010) • Population: 1.3 %/y • GWP: 2.8 %/y • GWP/Pop: 1.5 %/y Year AD Angus Maddison(http://www.ggdc.net/maddison/)

4. We believe that western technological society has ignored two vital facts: • The resources of planet earth are finite. • The capacity of the environment to renew resources that are used up and to repair the damage caused by the exploitation of these resources is limited and decreasing. • The Australian, May 21 1971

5. Earth system: forcing and responses Approximately exponential forcing Response 1: atmospheric GHG concentrations Response 2: climate change • CO2emissions (fossil fuels + land use change) • CO2 concentrations(composite record) • Global temperature(land + ocean, HadCRUT3)

6. The climate system Volcanoes GHGs(CO2, …) Aerosols Biosphere Solar radiation Human activities Orbital variations Climate (temperature) Heat radiation Water vapour, clouds Oceans Ice sheets Adapted from: Australian Academy of Science (2010) The science of climate change: questions and answers

7. Climate in the distant past (800,000 years) Present CO2 Hansen et al. (2008)Target atmospheric CO2

8. Climate1850-present • Measures of changing global climate from 1850 to present • 10 quantities • All available datasets are shown Air temperature (land) Air temperature (ocean) Arctic sea-ice extent Sea level IPCC AR5 FOD TS Fig TS.1

9. IPCC AR5 FOD TS Fig TS.7 Climate models: testing with data Models (natural + anthropogenic forcings) Santa Maria Krakatoa Pinatubo Agung El Chicon

10. Climate models: future global warming and precipitation Warming • More warming in high latitudes (polar amplification) – already observed Change in precipitation • Increase in global precipitation (and global evaporation) • Changes are highly non-uniform: predicted drying in mid-latitudes Diffenbaugh and Field (2013) Science 341, 486-492

11. Climate models: future warming • 4 scenarios (RCPs) for future human impact on climate system, from low to high • Climate model runs by many teams for each scenario: • ~30 to 2100 • ~10 to 2300 • Warming (1850-2100): mean (5, 95) % • Low: 1.7 (0.7, 2.8) oC • High: 4.7 (3.6, 5.9) oC IPCC AR5 FOD TS Fig. TS.13

12. Atmospheric CO2 budget (1850-2011) Updated from Canadell et al. (2007) and Le Quéré et al. (2009)Data: http://www.globalcarbonproject.org/carbonbudget/index.htm Fluxes in 2011 [PgC/y] 9.5 0.9 Flux [PgC/y] 2.6 4.1 3.6

13. Global warming and the cumulative-emission clock • Reinforcing feedbacks: • Ice-albedo • Carbon cycle • Ecosystem collapse Non-CO2 gasesAerosols CO2 only • Stabilising feedbacks: • Heat loss (Planck) • CO2 removal by carbon sinks • Logarithmic response to CO2 Raupach et al. (2011), revised in Raupach (2012)

14. The carbon budget • To stay below 2 degrees of warming (above preindustrial): Allowed cumulative CO2 emissions (1750 to far future) are • 1000 GtC => 1 in 2 chance of success • 800 GtC => 2 in 3 chance of success • Cumulative CO2 emissions from 1750 to present: 550 GtC • Factored into budget: • Likely emissions of non-CO2 gases, aerosols • Climate feedbacks in present models (including uncertainties) • Not factored in: • Carbon cycle feedbacks – especially release of Arctic C stores

15. Sharing the cumulative emissions pie Inertia: share by current or historic emissions Equity: share by population Compromise: share by mixture of emissions and population Developing USA weight w (0 to 1) is an "equity index" w=0 w=1

16. Sharing the mitigation task Carbon budget: 1000 GtC total Equity Middle Inertia • Mitigation rate characterises mitigation challenge • As equity increases in emissions sharing, mitigation rates pivot around the required world mitigation rate • A little equity goes a long way towards a sharing of the emissions quota that is both achievable and fair

17. Narratives • Definition: Narratives = stories that guide and empower actions • Narratives are very powerful, and fundamental to being human • Narratives are independent of truth • Two broad narrative families for the 21st century: “growth” and “sustenance” • Hypothesis: Narratives are meme sequences that evolve • Diversification, selection, adaptation • Evolution can be understood, influenced, but not controlled • Examples: the Enlightenment, decline of violence, • Implications: • In shaping our shared future, the evolutionary contest between growth and sustenance narratives is just as important as the dynamics of the natural world • Need to guide evolution of resilient narratives that empower transition to a society that is simultaneously sustainable and improves global human wellbeing Raupach, M.R. (2013). The evolutionary nature of narratives about expansion and sustenance. In: Negotiating Our Future: Living scenarios for Australia to 2050, Vol. 2. (eds. Raupach, M.R., McMichael, A.J., Finnigan, J.J., Manderson, L., Walker, B.H.). (Australian Academy of Science), 201-213. (http://www.science.org.au/policy/australia-2050/)

18. Summary • Climate change as one of a set of pressures on the Earth System • Can humankind avoid dangerous climate change? • Objective science • emissions -> concentrations -> climate -> impacts • Thresholds, tipping points in the climate system • Some changes are happening faster than predicted • The dose-response relationship • Subjective values • Two great narratives: expansion versus sustenance • Human actions • Thresholds, tipping points in human behaviour • Whole-system perspective • The goal: coupled environmental sustainability and social equity • Enablers: resilience, innovation, connectivity, strange alliances

19. Development trajectories: coupled growth in economy, energy and emissions Each point represents one year from 1971 to 2011 The resulting wiggly line is a “development trajectory” showing how energy and CO2 emissions are coupled with affluence (per capita GDP) 2011 Per capita resource use 1971 Per capita GDP Per capita energy use (GJ/year/person) Per capita emissions (tC/year/person) Per capita GDP (k$/year/person) Per capita GDP (k$/year/person) IEA (2012)

20. Development trajectories: coupled growth in population, economy, energy and emissions Emissions / Energy (tC/TJ) Where we need to be • Emissions per unit energy(carbon intensity of energy) Per capita GDP (k$/year/person) IEA (2012)

21. E C W Challenges at energy-water-carbon intersections Principles Technologies Resilience Innovation PMSEIC (2010). Challenges at Energy-Water-Carbon Intersections. (Expert Working Group: Michael Raupach (Chair), Kurt Lambeck (Deputy Chair), Matthew England, Kate Fairley-Grenot, John Finnigan, Evelyn Krull, John Langford, Keith Lovegrove, John Wright, Mike Young). Prime Minister’s Science, Engineering and Innovation Council, Canberra, Australia. http://www.chiefscientist.gov.au/wp-content/uploads/FINAL_EnergyWaterCarbon_for_WEB.pdf

22. Abstract The science of climate change receives intense public scrutiny, making it difficult to distinguish signal from noise. A crucial example is the recent slowdown in the rate of warming in the global atmosphere. Does this mean that the scientific consensus on climate change has overstated its threat? In short, no. Two main factors have contributed to the slowdown: heat being drawn down into the deep oceans, and indirect cooling from atmospheric aerosol (partly from coal combustion). Evolving observations of the energy balance of Earth, deep ocean heat content, sea level rise, polar and glacial ice extents, greenhouse gas concentrations and emissions (and more) continue to show that climate change is ongoing and that its broad policy implications have been correctly articulated by the climate science community. The primary implication is that, to avoid dangerous climate change, there is a cap on the amount of fossil fuel that can be burned. As estimates of this cap are refined, the following broad directions remain soundly based: to change the mix of energy resources away from fossil fuels, to limit population growth and wasteful resource consumption, and to keep a large proportion of fossil fuel reserves in the ground.