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 under- utilised 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 Kirby (2000) simulation of evolution of syntax – Subject verb object – Creole languages
• 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
2 • 5 to 7 billion achieved by – Increases in crop yield – Spread of earlier innovations 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 CO
280 2 2 260 Concentration 240 220 [ppmv]
2 200
CO 180
600,000 500,000 400,000 300,000 200,000 100,000 0 Age (yr BP) 600 Projected Concentration After 50 More Years of Unrestricted Fossil Fuel Burning
500 Earth system instability
400
300 CO
280 2 2 260 Concentration 240 220 [ppmv]
2 200 CO
180 Temperature proxy
600,000 500,000 400,000 300,000 200,000 100,000 0 Age (yr BP) 600 Projected Concentration After 50 More Years of Unrestricted Fossil Fuel Burning
500
400
Today’s CO2 Concentration
300 CO
280 2 2 260 Concentration 240 220 [ppmv]
2 200 CO
180 Temperature proxy
600,000 500,000 400,000 300,000 200,000 100,000 0 Age (yr BP) 600 After 45 More Years of current energy use patterns
500
400
Today’s CO2 Concentration
300 CO
280 2 2 260 Concentration 240 220 [ppmv]
2 200 CO
180 Temperature proxy
600,000 500,000 400,000 300,000 200,000 100,000 0 Age (yr BP) 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 sub- continental 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 No bifurcation
Irreversible transition 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 Medium High
Expert elicitation for future warming scenarios: West Antarctic ice sheet
Shepherd & Wingham (2007) Science 315: 1529-1532
Net mass balance of Antarctic ice sheet
Low Medium High
Expert elicitation for future warming scenarios: 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 Medium High
Expert elicitation for future warming scenarios: 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 Medium High
Expert elicitation for future warming scenarios: Combined likelihood of tipping
Kriegler et al. (2009) PNAS 106(13): 5041-5046
Imprecise probability Atlantic statements from experts formally combined Greenland Under 2-4 °C warming: >16% probability of passing at least one of Antarctica five tipping points
Under >4 °C warming: Amazon >56% probability of passing at least one of five tipping points 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
Khvorostyanov et al. (2008) GRL 35, L10703 Archer et al. (2009) PNAS 106(49): 20596-601 )
Extent of permafrost melt and -2 methane hydrate dissociation both forecast proportional to warming kgC m (i.e. not tipping elements)
But Yedoma, containing up to 500 PgC, could undergo runaway
meltdown due to biochemical heat Releasable methane ( release
Estimated threshold is a 9 °C regional warming, but note this region warmed >3 °C in 2007 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
Comparison of indicators on Real geophysical data (air temperature, river flux, etc.) artificial data tending to random walk 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 Model tests of early warning Slowly forced collapse of the Atlantic Thermohaline Circulation
GENIE-1 intermediate complexity model GENIE-2 atmosphere-ocean GCM MOC (Sv) MOC (Sv)
Lenton (2011) Nature Climate Change Paleo-data tests of early warning
End of the last ice age in Antarctica End of the Younger Dryas in Cariaco Basin δ D (per mil) Greyscale (0-255)
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 Attribution-NonCommercial-ShareAlike 3.0 Unported You are free: to Share - to copy, distribute and transmit the work to Remix - to adapt the work Under the following conditions: Attribution. You must attribute the work in the manner specified by the author or licensor (but not in any way that suggests that they endorse you or your use of the work).
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