Download The Anthropocene revolution?

The Anthropocene revolution?
Tim Lenton
University of Exeter
(with thanks to Vasilis Dakos, Valerie Livina, Marten Scheffer,
Andy Watson and Hywel Williams)
Evolutionary regime shifts
Evolutionary
innovations
allow access
to underutilised
resources.
Resultant
by-products
drive
environmental
change.
System-wide
transitions to
new steady
state are
coupled to
mass
extinction
events.
Williams & Lenton (2010) Oikos
Sounds familiar?
The Anthropocene
Paul Crutzen
who coined the
term the
‘Anthropocene’
for a new
geologic era
starting c. 1800
W. Steffen et al. ‘Global change and the Earth system: A planet under pressure’
Common properties of revolutions
•  They are caused by (rare) biological innovations
•  They involve step increases in
–  Information processed by the biota
–  Complexity of organisms / ecosystems
–  Energy capture and material flow through the biosphere
•  They rely on the Earth system having some instability, such that new
by-products can cause catastrophic upheavals in climate, etc.
•  They end only when the system arrives at a new stable state, able to
close the biogeochemical cycles again, recycling all the materials.
Increased information processing
Evolution of natural language
•  FOXP2 gene <200 ka
–  Mutations linked to verbal
dyspraxia
•  Syntax
–  Heirarchical relations
–  Subject verb object
–  Creole languages
Kirby (2000) simulation of evolution of syntax
•  Universal grammar
–  Noam Chomsky
–  Nicaraguan sign language
Deaf Nicaraguan children speaking a
language they derived independently
Out of Africa ~65 ka
All humans alive today descend from a founder
group of <10,000 breeding pairs in Africa ~70 ka
Kyr ago
A model of human migration based on mitochondrial DNA
(letters refer to different haplogroups)
New levels of organisation
City of Ur in Iraq (Urim in Sumerian times)
The start of farming (~11.5 ka)
•  Natufian culture collected,
cooked and ate wild cereals,
but then domesticated them
–  Response to climate drying
linked to Younger Dryas?
–  Neolithic revolution 12-10 ka
•  Sahara re-enters wet phase
The Fertile Crescent
–  Fertile Crescent ~10.5 ka
–  wheat, barley, peas,
–  sheep, goats, cows, pigs
•  Independent domestications
–  e.g. rice in China ~11.5 ka
Centres of domestication and modern production
The rise of civilisations (~7.3 ka)
•  Cities of Sumer
supported by
surplus of food
from agriculture
•  Permitted division
of labour
including the first
armies
•  Groups as a
whole were more
successful
Increased energy and material flows
Population growth (since 1800)
•  1 to 3 billion achieved by
–  Increasing cultivated area
–  Tractors replacing horses
–  Irrigation, herbicides
•  3 to 5 billion achieved by
–  Fertiliser nutrient inputs
–  Dwarf varieties; wheat, rice
•  5 to 7 billion achieved by
–  Increases in crop yield
–  Spread of earlier innovations
2
Increased nutrient inputs
•  Nitrogen input to the
biosphere has roughly
doubled due to human
activities
•  Phosphorus input has
increased by a factor >3
•  Causes eutrophication
and anoxia in
freshwaters, coastal
seas, and ultimately the
open ocean
Mackenzie et al. (2002) Chemical Geology 190(1-4): 13-32
Humans as energy consumers
•  Global photosynthesis
–  5000 EJ yr-1 or 150 TW
–  (exajoule: 1 EJ = 1018 J)
•  Total energy input to human
societies
–  500 EJ yr-1 or 15 TW
–  ~87% from fossil fuels
•  Global food production
–  Output 50 EJ yr-1 or 1.5 TW
–  Fossil input 12.8-18.2 EJ yr-1
Fossil fuel CO2 emissions
•  Currently ~9.1 PgC yr-1
+1.9% yr-1 past 25 years
+1.3% yr-1 during 1990s
+3.1% yr-1 2000-2010
•  Decoupled from population
growth, which has been
decelerating since 1960
•  The richest 20% of humanity
are responsible for 80% of
emissions
Data from CDIAC (Marland et al.)
600
500
Earth system instability
400
300
CO2 Concentration
280
CO2 [ppmv]
260
240
220
200
180
600,000
500,000
400,000
300,000
Age (yr BP)
200,000
100,000
0
600
500
Projected Concentration After 50 More Years of Unrestricted
Fossil Fuel Burning
Earth system instability
400
300
CO2 Concentration Temperature proxy
280
CO2 [ppmv]
260
240
220
200
180
600,000
500,000
400,000
300,000
Age (yr BP)
200,000
100,000
0
600
Projected Concentration After 50 More Years of Unrestricted
Fossil Fuel Burning
500
400
Today’s CO2 Concentration
300
CO2 Concentration Temperature proxy
280
CO2 [ppmv]
260
240
220
200
180
600,000
500,000
400,000
300,000
Age (yr BP)
200,000
100,000
0
After 45 More Years of current energy use patterns
600
500
400
Today’s CO2 Concentration
300
CO2 Concentration Temperature proxy
280
CO2 [ppmv]
260
240
220
200
180
600,000
500,000
400,000
300,000
Age (yr BP)
200,000
100,000
0
Recent past climate instability
Livina, Kwasniok & Lenton (2010) Climate of the Past, 6: 77-82
Number of states: 1, 2, 3, 4
Future climate instability?
•  Tipping element
–  A component of the Earth system, at least subcontinental in scale (~1000km), that can be
switched – under certain circumstances – into a
qualitatively different state by a small perturbation.
•  Tipping point
–  The corresponding critical point – in forcing and a
feature of the system – at which the future state of
the system is qualitatively altered.
Lenton et al. (2008) PNAS 105(6): 1786-1793
Two (of many) types of tipping point
Bifurcation
Irreversible transition
Two (of many) types of tipping point
Bifurcation
Irreversible transition
No bifurcation
Reversible transition
Policy relevant tipping elements
•  Human activities are interfering with the
system such that decisions taken within a
“political time horizon” (~100 years) can
determine whether the tipping point is
reached.
•  The time to observe a qualitative change plus
the time to trigger it lie within an “ethical time
horizon” (~1000 years).
•  A significant number of people care about the
fate of the system.
Lenton et al. (2008) PNAS 105(6): 1786-1793
Observations & IPCC projections
= High growth
= Mid growth
= Low growth
IPCC (2007)
Tipping elements in the climate system
Lenton et al. (2008) PNAS 105(6): 1786-1793
Estimates of proximity
Results from literature review and workshop
Lenton & Schellnhuber (2007) Nature Reports Climate Change
Probabilities under different scenarios
  Three different warming scenarios:
  Imprecise probability statements elicited from experts.
  Example of collapse of Atlantic meridional overturning circulation:
Kriegler et al. (2009) PNAS 106(13): 5041-5046
Greenland ice sheet
Net mass balance of Greenland ice sheet
2007 melt days
anomaly relative
to 1988-2006
Low
Expert elicitation
for future warming
scenarios:
Medium
High
West Antarctic ice sheet
Shepherd & Wingham (2007) Science 315: 1529-1532
Net mass balance of Antarctic ice sheet
Low
Expert elicitation
for future warming
scenarios:
Medium
High
Amazon rainforest
Malhi et al. (2009) PNAS 106: 20610-5; Jones et al. (2009) Nature Geosci. 2: 484-487
See also: Cox et al. (2000) Nature 408: 184-187; Cook and Vizy (2009) J. Climate
Low
Expert elicitation
for future warming
scenarios:
Medium
High
El Niño / Southern Oscillation
Guilyardi (2006) Clim. Dyn. 26: 329-48; Yeh et al. (2009) Nature 461: 511-4;
Collins et al. (2010) Nature Geosci. 3: 391-7
  Increase in ENSO amplitude
occurs in some realistic models
under global warming (but
others show decrease).
  No clear change in frequency
  Shift toward Central Pacific
Modoki replacing classic East
Pacific El Niño?
Low
Expert elicitation
for future warming
scenarios:
Medium
High
Combined likelihood of tipping
Kriegler et al. (2009) PNAS
106(13): 5041-5046
  Imprecise probability
statements from experts
formally combined
  Under 2-4 °C warming:
>16% probability of
passing at least one of
five tipping points
  Under >4 °C warming:
>56% probability of
passing at least one of
five tipping points
Atlantic
Greenland
Antarctica
Amazon
El Niño
Boreal forest dieback
Lucht et al. (2006) Carbon Balance and Management 1: 6; Kurz et al. (2008) PNAS 105(5): 1551-5
  Canadian forests have recently
switched from carbon sink to source
due to insect outbreaks
  More widespread dieback forecast
under ~3°C global warming (~7°C local
warming)
  Map shows change in
vegetation carbon content
from 2000 to 2100
  LPJ model forced with
SRES A2 climate change
from HadCM3
Permafrost and methane hydrates
  Extent of permafrost melt and
methane hydrate dissociation both
forecast proportional to warming
(i.e. not tipping elements)
  But Yedoma, containing up to
500 PgC, could undergo runaway
meltdown due to biochemical heat
release
  Estimated threshold is a 9 °C
regional warming, but note this
region warmed >3 °C in 2007
Archer et al. (2009) PNAS 106(49): 20596-601
Releasable methane (kgC m-2)
Khvorostyanov et al. (2008) GRL 35, L10703
Revised map
Early warning prospects
Generic early warning signals:
 Slowing down
 Increasing variability
 Skewed responses
System being
forced past a
tipping point
Held & Kleinen (2004) GRL 31: L23207; Lenton et al. (2008) PNAS 105(6): 1786-1793
Scheffer et al. (2009) Nature 461: 53-59; Ditlevsen & Johnsen (2010) GRL 37: L19703
Alternative early warning indicators
Livina & Lenton (2007) Geophysical Research Letters 34: L03712
Real geophysical data (air temperature, river flux, etc.)
carry memory caused by various types of inertia.
Statistically, the memory is described in terms of
correlations, and there exist several methods to
estimate correlations:
1) Power spectrum exponent, β
2) Auto-correlation function (ACF) exponent, γ
3) Detrended fluctuation analysis (DFA) exponent, α
They are related: α = 1 - γ/2 = (1+β)/2
We developed an indicator using DFA:
α = 0.5 uncorrelated data
α > 0.5 correlated data
α = 1.5 random walk with uncorrelated steps
We rescaled: indicator = 1 when α = 1.5
Comparison of indicators on
artificial data tending to random walk
Model tests of early warning
Slowly forced collapse of the Atlantic Thermohaline Circulation
MOC (Sv)
GENIE-2 atmosphere-ocean GCM
MOC (Sv)
GENIE-1 intermediate complexity model
Lenton (2011) Nature Climate Change
Paleo-data tests of early warning
δD (per mil)
Greyscale (0-255)
End of the Younger Dryas in Cariaco Basin
End of the last ice age in Antarctica
Lenton (2011) Nature Climate Change
Early warning of the end of the ice age
GRIP δ18O
data
Detrended
data
Early
warning
indicator
Lenton, Livina, Dakos, Scheffer (in press) Climate of the Past
Atlantic Multi-decadal Oscillation
AMO
index
Detrended
data
Early
warning
indicator
Results from Vasilis Dakos and Valerie Livina
Geoengineering responses
Reflect more sunlight back to
space
Remove CO2 from
atmosphere and store it
Lenton & Vaughan (2009) Atmospheric Chemistry and Physics 9: 5539-5561
Where next?
•  Apocalypse
•  Global tipping into a state unable to
support current societies
•  Retreat
•  Lower energy, lower material
consumption, lower population
•  Revolution
•  High energy, high recycling world
supporting billions of people
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