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

Fenner Conference “Population, resources and climate change: implications for Australia’s future” (AAS, Canberra, 10-11 October 2013)

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”

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

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

Angus Maddison (http://www.ggdc.net/maddison/)

100

1000

10000

100000

0 500 1000 1500 2000

Po

pu

lati

on

(m

illi

on

), G

DP

(In

tl $

bil

lio

n)

Population

GDP

100

1000

10000

0 500 1000 1500 2000

Per

cap

ita

GD

P (

Intl

$ p

er p

erso

n)

Per capita GDP

Year AD

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

Earth system: forcing and responses

CO2 emissions (fossil fuels + land use change)

CO2 concentrations(composite record)

Global temperature(land + ocean, HadCRUT3)

Approximately exponential forcing

Response 2: climate change

Response 1: atmospheric GHG concentrations

The climate system

Climate (temperature)

Adapted from: Australian Academy of Science (2010) The science of climate change: questions and answers

Solar radiation

Heat radiation

Aerosols

Water vapour, clouds

Ice sheets

GHGs(CO2, …)

Oceans

Biosphere

Orbital variations

Volcanoes

Human activities

Climate in the distant past (800,000 years)

Present CO2

Hansen et al. (2008)Target atmospheric CO2

Climate1850-present

IPCC AR5 FOD TS Fig TS.1

Measures of changing global climate from 1850 to present

10 quantities

All available datasets are shown

Air temperature (land)

Air temperature (ocean)

Sea levelArctic sea-ice extent

Climate models: testing with data

IPCC AR5 FOD TS Fig TS.7

Kra

kato

a

Ag

un

g

El

Ch

ico

n

Pin

atu

bo

San

ta M

aria

Models (natural + anthropogenic forcings)

Climate models: future global warming and precipitation

Diffenbaugh and Field (2013) Science 341, 486-492

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

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

Atmospheric CO2 budget (1850-2011)

9.5

0.9

2.6

4.1

3.6

Fluxes in 2011

[PgC/y]

Flu

x [P

gC/y

]Updated from Canadell et al. (2007) and Le Quéré et al. (2009)

Data: http://www.globalcarbonproject.org/carbonbudget/index.htm

Raupach et al. (2011), revised in Raupach (2012)

Global warming and the cumulative-emission clock

Reinforcing feedbacks:• Ice-albedo• Carbon cycle• Ecosystem collapse

Stabilising feedbacks:• Heat loss (Planck)• CO2 removal by carbon sinks• Logarithmic response to CO2

CO2 only

Non-CO2 gasesAerosols

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

Sharing the cumulative emissions pie

w=0.0

USAEuropeJapanD1FSUChinaIndiaD2D3

w=1.0

USAEuropeJapanD1FSUChinaIndiaD2D3

w=0.5

Inertia: share by current or historic emissions

Equity: share by

population

Compromise: share by mixture of

emissions and population

1 i ii

F PQ Q w w

F P

ii

FQ Q

F i

i

PQ Q

P

weight w (0 to 1) is an "equity index"

w=0 w=1

USADeveloping

Sharing the mitigation task

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

Inertia

Equity

Middle

Carbon budget: 1000 GtC total

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/)

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

Development trajectories: coupled growth in economy, energy and emissions

Per capita GDP

Per c

apita

re

sour

ce u

se

1971

2011

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)

Per capita GDP (k$/year/person)

Per c

apita

ene

rgy

use

(G

J/ye

ar/p

erso

n)

Per c

apita

em

issi

ons

(t

C/ye

ar/p

erso

n)

Per capita GDP (k$/year/person)IEA (2012)

Development trajectories: coupled growth in population, economy, energy and emissions

Emissions per unit energy(carbon intensity of energy)

Emis

sion

s /

Ener

gy

(tC/

TJ)

Per capita GDP (k$/year/person)IEA (2012)

Where we need to be

E

WC

PrinciplesTechnologies

ResilienceInnovation

Challenges at energy-water-carbon intersections

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

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.