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
Climate Change 2019:
Rising Risks; Growing Challenges

                   Will Steffen
  Emeritus Professor, Australian National University
    Senior Fellow, Stockholm Resilience Centre
Climate Change 2019: Rising Risks; Growing Challenges - Will Steffen Emeritus Professor, Australian National University
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
Climate Change 2019: Rising Risks; Growing Challenges - Will Steffen Emeritus Professor, Australian National University
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
Climate Change 2019: Rising Risks; Growing Challenges - Will Steffen Emeritus Professor, Australian National University
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
Climate Change 2019: Rising Risks; Growing Challenges - Will Steffen Emeritus Professor, Australian National University
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.
Climate Change 2019: Rising Risks; Growing Challenges - Will Steffen Emeritus Professor, Australian National University
The climate is warming rapidly
 Global Average Temperature Anomaly, 1880-2017

          Baseline is 1951-1980                  NASA 2018
Climate Change 2019: Rising Risks; Growing Challenges - Will Steffen Emeritus Professor, Australian National University
Global Carbon Dioxide Emissions

Gt C yr-1

              1900       1950          2000       2020

                                   Source: Le Quere et al. 2018
Climate Change 2019: Rising Risks; Growing Challenges - Will Steffen Emeritus Professor, Australian National University
Enhanced Greenhouse Effect
Climate Change 2019: Rising Risks; Growing Challenges - Will Steffen Emeritus Professor, Australian National University
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 2019: Rising Risks; Growing Challenges - Will Steffen Emeritus Professor, Australian National University
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. 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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