Climate Change 2019: Rising Risks; Growing Challenges - Will Steffen Emeritus Professor, Australian National University
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Climate Change 2019: Rising Risks; Growing Challenges Will Steffen Emeritus Professor, Australian National University Senior Fellow, Stockholm Resilience Centre
Outline of Talk 1. Basic climate science 2. Risks and impacts 3. Implications for Australia 4. Climate change and the Earth System: Nature of the challenge
January 2019 Flooding in Townsville Massive Flooding in Townsville Region Many sites across tropical Queensland set records for high, multi-day rainfall accumulations. In and around Townsville, consecutive days of heavy rainfall set many new records for cumulative totals. Climate change increases the likelihood of heavy rainfall events in most locations. Andrew Rankin/EPA BoM Special Climate Statement, Feb 2019
Extreme Heat across Australia January heatwave notable for its persistence and spatial extent. During January heatwaves affected every state and territory, with large areas of WA, SA, NSW and Vic affected by either severe or locally extreme heatwaves. January 2019 was hottest month on record nationally. NSW broke its previous hottest month record by more than 2oC. Climate change is increasing the frequency, duration and intensity of heatwaves in Australia
Bushfires in Tasmania Hottest and driest January on record in Tasmania, making vegetation vulnerable to fire ignition by lightning and rapid fire spread. Lightning fires started in remote areas, making them difficult to control. Vast areas of Tasmanian World Heritage area were burnt.
The climate is warming rapidly Global Average Temperature Anomaly, 1880-2017 Baseline is 1951-1980 NASA 2018
Trend in Global Ocean Heat Content Upper 2000 m relative to a 1981-2010 baseline 93% of the extra heat since 1971 stored in the ocean 3% warming land 3% melting of ice (glaciers & ice sheets 1% warming atmosphere Source: Cheng et al. 2019; IPCC AR5 2013
Climate Change is worsening extreme weather: Lines of evidence 1. Basic physics: All extreme weather events are now occurring in an atmosphere that is significantly warmer and wetter than it was 50 years ago (Trenberth 2012). 2. Observations of changes in extreme weather – e.g., the hottest day of a heatwave is getting hotter. 3. Attribution of specific extreme events – e.g., the 2016 bleaching of the Great Barrier Reef was made 175 times more likely by climate change.
Decline and Death of Coral Reefs Change in coral cover Heat exposure: deg C-weeks …throughout the entire GBR,...the cover of corals declined by 30.0% between March and November 2016. Climate change made bleaching of the GBR 175 times more likely (Bleaching would not have happened without climate change). The 2016 mass bleaching event Hughes et al. 2018
Increase in global coral bleaching events: 1960-2010 Time period Number of bleaching events Pre-1980 12 1980s 236 1990s 1874 2000s 5094 Source: Donner et al. 2017
Heatwaves Heatwaves are becoming more intense, lasting longer and occurring more often. More frequent and hotter days are projected for the future. CSIRO and BoM 2015
Bushfires The Forest Fire Danger Index has increased at 16 of 38 weather stations, mostly in the southeast, over the past 40 years. Even harsher fire weather is expected in the future. CSIRO and BoM 2015
Changing rainfall patterns Rainfall has declined in southwest Australia since the 1970s and in southeast Australia since the 1990s, mainly in the cooler months of the year. In southern Australia cool-season rainfall is projected to decrease. More time will be spent in droughts, and severe droughts will become more frequent. CSIRO and BoM 2015
Sea level and coastal flooding Sea level has risen by 20 cm since the 1980s. The frequency of coastal flooding has increased 3-fold in Sydney and Fremantle through the 20th century. Sea level is projected to rise by between 30 and 100 cm by 2100 compared to the 1986-2005 average. IPCC AR5 2013 and Climate Council 2014
Risk of Accelerating Sea-level Rise Collapse of West Antarctic ice sheet would raise sea-level by ~3 metres Ice loss there has tripled over last 25 years Episodes of sea-ice melting increase risk of ice sheet collapse. Strong evidence that this process has already begun in Amundsen Sea sector Antarctic Peninsula, February 2019 Source: Future Earth 2018
The 2015 Paris Climate Agreement …to hold the rise in global average temperature to ‘well below 2oC’ and to make every effort to limit temperature rise to 1.5oC
Stabilising the Climate: The Carbon Budget Source: IPCC AR5 2013
The Paris 2oC Target: Can We Meet It? The total carbon budget from 1870 is about 1,000 Gt C (emitted as CO2) for a 66% probability of meeting the 2oC target. Cumulative human emissions (fossil fuels, cement, land use) from 1870 through 2018 were about 585 Gt C, leaving 415 Gt C in the budget. Accounting for non-CO2 gases (e.g. CH4, N2O) reduces the C budget by 210 Gt C. The remaining budget is 205 Gt C in total. At current rates 10 Gt C per year at current rates, the budget would last only two decades. Sources; IPCC AR5 WGI SPM; GCP 2018
Emission Reduction Pathways for Meeting the Paris Target Figueres et al. 2017
Comparison of Paris pledges Amongst OECD countries, Australia is the global laggard on climate action. If all countries matched Australia’s level of ambition and current climate policies, we would be headed for a 3 to 4oC world by 2100. The Climate Institute 2015
Climate Change in a Broader Context The Earth: Patterns of a Complex System Image: NASA
The climate is warming rapidly Global Average Temperature Anomaly, 1880-2017 What does this temperature trend mean from an Earth System science perspective? Baseline is 1951-1980 NASA 2018
Our planet is a single system… …the Earth System
Human Development and the Earth System Beginning of agriculture Evolution of fully Hunter-gatherer modern societies only humans in Africa Adapted from Steffen et al. 2004; ice core data from Petit et al. 1999
Human Development and Earth System Dynamics Source: Data from Petit et al. 1999, labeled as in Young and Steffen 2009. Source: J. Rockström and N. Nakicenovic Data from Petit et al. 1999 and Oppenheimer 2004
Temperature rise: Beyond the envelope of natural variability! Human influence 2000 years of Holocene variability Summerhayes 2015
Rates of Change Rate of atmospheric CO2 increase over the past two decades is about 100 times the maximum sustained rate during the last deglaciation. Since 1970 the global average temperature has risen at a rate about 170 times the background rate over the past 7,000 years of the Holocene, and in the opposite direction. De Vos et al. 2014; Wolff 2011; Marcott et al. 2013; NOAA 2016
Implications of accelerating climate change IPCC temperature projections IPCC 2013
6 Earth System moves to a new state? Severe challenge to 5 contemporary civilisation. Possible collapse? IPCC Projections 2100 AD 4 Global Temperature (°C) Tipping Points? 3 2 Committed 1 0 Summerhayes 2015
Tipping Elements in the Earth System 10 years of C storage lost in 2005 and 2010 droughts 50 to 250 Gt C lost by 2100 from thawing permafrost Huber, Lenton, and Schellnhuber, in Richardson et al. 2011
Tipping Cascades Source: J. Donges and R. Winkelmann in Steffen et al. 2018
Earth System Trajectories Steffen et al. 2018
Is ‘Hothouse Earth’ inhabitable? • Most of the tropics and subtropics will be too hot for human habitation. • Changing temperature & rainfall patterns will likely make current large agricultural zones unproductive. • Sea-level rise of 20-40 m ultimately likely, drowning coastal cities, agricultural areas and infrastructure. • Maximum carrying capacity of ~1 billion humans (today’s population is 7.6 billion)
How Plausible is this Scenario? • Complex system behaviour of the Earth System in the late Quaternary • Hothouse Earth conditions accessible with projected CO2 concentration and temperature • Some feedback processes are the same as those in glacial-interglacial cycling • Observations show some tipping elements vulnerable at 1-3ºC temperature rise Steffen et al. 2018
The Nature of the Challenge Bottom Line A worst-case scenario could collapse modern civilisation. 1. MAGNITUDE 2. URGENCY We have 2 years left to get our act together. Delay rapidly increases risk of collapse.
Emission Reduction Pathways for Meeting the Paris Target Figueres et al. 2017
The Canberra Story Canberra will be here next year (2020) Total ACT Emissions in CO2-e ACT Climate Change Council 2018
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