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
Global Carbon Dioxide Emissions
Gt C yr-1
1900 1950 2000 2020
Source: Le Quere et al. 2018
Enhanced Greenhouse Effect
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: Worsening Extreme Weather
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. 2018Increase 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. 2017Heatwaves
Heatwaves are becoming more intense, lasting
longer and occurring more often. More frequent
and hotter days are projected for the future.
CSIRO and BoM 2015Bushfires
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 2015Changing 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 2015Sea 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 2014Risk 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 2018The 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 2013The 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 2018Emission Reduction Pathways
for Meeting the Paris Target
Figueres et al. 2017Comparison 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 2015Climate Change in a Broader Context
The Earth: Patterns of a Complex System
Image: NASAThe 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 2018Our planet is a single system…
…the Earth SystemHuman 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. 1999Human 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 2004Temperature rise:
Beyond the envelope of natural variability!
Human influence
2000 years of Holocene variability
Summerhayes 2015Rates 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 20136
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 2015Tipping 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. 2011Tipping Cascades
Source: J. Donges and R. Winkelmann
in Steffen et al. 2018Earth System Trajectories
Steffen et al. 2018Is ‘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. 2018The 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. 2017The Canberra Story
Canberra will be
here next year (2020)
Total ACT Emissions in CO2-e
ACT Climate Change Council 2018You can also read
