Critical thresholds and "tipping points" in the Earth system Stefan RahmstorfPotsdam Institute for Climate Impact Research

Smooth journey or bumpy ride?

Future Climate Change

Main reasons to suspect the latter:

- History of climate is very “bumpy”- Abundance of non-linearities and

threshold effects in the climate system- A number of those are not captured in

current models

-GISP2 ice core, Greenland

112

11109

87 6

5 43

21716 15

14

13

δ18 O

(per

mil)

Millennia before present

Holocene

Abrupt warming and cooling events, up to 12 ºC within a few decadesLikely cause: reorganisation of ocean currents

8k Event

Younger Dryas

Past Abrupt Climate Changes

Ganopolski and Rahmstorf (Nature 2001)

Ganopolski and Rahmstorf (Nature 2001)

Ganopolski and Rahmstorf (Nature 2001)

Risk of Crossing Critical Thresholds?Temperature is rising fast

Typical amount: ~ 0.1 – 0.2 SvHeinrich Events: ~ 0.1 SvRahmstorf et al. (Geophys. Res. Let. 2005)

Ocean Circulation Threshold

1979

2005

Volume loss 1988-2003 is ~ 4.4 x 1011 m3/yr ≈ 0.014 Sv (Lindsay and Zhang 2005)

Volume of GIS: 2.8 x 1015 m3

Time-scale 1000 years ⇒ 2.8 x 1012 m3/yr ≈ 0.1 Sv

Meltwater from Greenland

Current volume loss:2.2 x 1011 m3/yr ≈ 0.007 SvHas doubled over past decade

Increased River Discharge to Arctic

Peterson et al. (Science 2002)

Increase ~ 0.005 Sv from Eurasian rivers alone

Sea ice: 0.014 SvGreenland: 0.007 Sv

Eurasian rivers: 0.005 SvSum of these: 0.026 Sv

A Simple Sum

[Missing: precipitation increase,Canadian river runoff]

How much will this be after 3 or 5 ºC warming?

Observed Freshening Trend

Ice Sheet Threshold

equilibrium lineablation

accumulation

equilibrium lineablation

accumulation

smaller ice sheet

present ice sheet

Ice sheet – elevation feedback

Ice sheet response time “is of the order of centuries, not millennia”.Hansen (2005)

Volume: 2.8x1015 m3 = 7 meters of sea level

Threshold for melting: ~ 3 ºC warming

Greenland Meltdown?

Jan. 30,2002

Scambos,NSIDC

20 km

Mar. 04,2002

Scambos,NSIDC

20 km

Archer (2006)

Past Sea Level vs. Temperature

Storm Surge Risk in New York

Today: once in 100 yearsAfter 1 m sea level rise: every 3-4 years

Rosenzweig and Solecki, 2001

Based on Schellnhuber (2002)

Amazonrainforest

Sahara / Sahel

Boreal forest / tundraBoreal forest / tundra

Great plains

Arctic sea iceArctic sea ice

ENSOsource region

West AntarcticIce Sheet

Methane hydrates

Methanehydrates

Methane

DMS production and cloud albedo

NAO

NADWformation

AABWformation

Atlanticthermohaline

circulation

Greenland Ice Sheet

Acronyms:ENSO = El Nino Southern OscillationNAO = North Atlantic Oscillation

NADW = North Atlantic Deep WaterAABW = Antarctic Bottom Water

SE Asianforest

IndianMonsoon

West AfricanMonsoon

Map of Potential Tipping Points

Risk-Limiting Emission Corridors

Rahmstorf & Zickfeld (Climatic Change 2005)

“probability of shutdown, given certain warming”

“probability of certain warming, given a CO2 scenario”

Science and Policy Implications

Probability of crossing critical thresholds for major qualitative changes is not negligible

Risk assessment approach is needed!

Many would consider a 5% chance of triggering high-impact tipping points “dangerous interference”

“Optimal emissions” based on smooth damage functions are questionable

Policy goal: minimise risk under uncertainty