Abrupt climate change

1
Abrupt climate change

• Climate change and its impacts
• October 9

2
Outline

• Feedbacks and interactions within the climate
  system
• Climate equilibrium and stability
• Examples of abrupt changes

3
Hydrosphere-atmosphere interactions

• Cloudiness
• Salinity changes
• Circulation changes
• Latent and sensible heat fluxes

4
Cryosphere-atmosphere interactions

• Ice cover eliminates 99 of ocean, ground heat
  flux
• Change in albedo
• Change in infrared radiation
• Alters latent/sensible heat balance
• Affects ocean salinity
• Affects circulation / development of storm
  systems
• Sudden ice sheet melting could significantly
  affect climate system

5
Methane release

• Oceans and bogs
• Near Arctic, significant release currently
  observed in oceans and bogs
• Estimates as high as 50GT of CH4 could be
  suddenly released (this would increase
  atmospheric CH4 12-fold)

USGS
6
Biosphere-atmosphere interactions

• Albedo changes
• Forest vs. grassland
• Water budget changes
• Sensible vs. latent heat
• Carbon and methane cycles
• Atmospheric composition

7
Carbon cycle
Global carbon project
8
Carbon storage with change
Global carbon project
9
Feedbacks within the climate system

• Positive feedback
• Initial response is amplified
• Negative feedback
• Initial response is damped

10
Ice-albedo feedback
11
Water vapor feedback
12
CO2 - plant feedback
13
Carbon feedback
14
Cloud feedback

• Increase in temperature increases cloudiness
• Low clouds Negative feedback
• Increase in LW lt Decrease in SW
• High clouds Positive feedback
• Increase in LW gt Decrease in SW

15
Compounding of feedbacks

• Feedbacks within the climate system can compound
  each other
• DTeq f DT
• With two feedbacks, the interaction is
• F f1f2 / (f1 f2 f1f2)
• Models suggest a doubling of CO2 would lead to DT
  1.2 C (in and of itself).
• If the ice/albedo feedback is f11.2 and the
  water vapor feedback is f21.6, then the joint
  value is f2.18.
• DTeq f DT 2.18 x 1.2 2.6 C.

16
Climate equilibrium
17
Hysteresis
18
How an abrupt change might occur

• Response to a rapidly varying external force
• Response to a slow change that eventually crosses
  a tipping point
• Spontaneous transition if a system is chaotic
  enough

19
Potential triggers of abrupt changes

• Sea ice anomalies
• Snow cover anomalies
• Thermohaline changes
• Outburst floods
• Greenhouse gas fluctuations
• Land-surface albedo changes
• Volcano

20
Thermohaline collapse

• Collapse observed in Younger Dryas and
  significant weakening in 8.2-ka event
• Connection to freshwater output in North Atlantic
• Solar connection proposed
• Collapse could occur with high rate of change or
  high absolute amount of CO2

Source Schneider (2004)
21
El Nino

• Multiple equilibria possible
• La Nina, El Nino, or in between (present)
• Model studies suggest connection with orbital
  parameters
• Younger Dryas connected with La Nina
• Teleconnected via snow cover and ice anomalies
• Future association to permanent El Nino?

22
Asian Monsoon

• Connected to snow cover anomalies, temperature
  anomalies, and potentially El Nino
• Greater snow cover, warmer Indian Ocean lead to
  weaker monsoon
• Strength also correlated with North Atlantic
  temperatures
• Abrupt shifts on century- or shorter timescales

23
Regional drought / flood

• Clear multiple equilibria across many regions,
  including Desert Southwest and Great Basin
• Connection with Sea surface temperatures
• Connection with tropical cyclone activity
  (temperature / circulation)
• Mechanisms still not well understood

24
Teleconnections

• Significant abrupt shift somewhere can lead to
  significant teleconnective changes elsewhere
• E.g. Broeckers article and ITCZ shift in
  response to sea ice