Lecture 15 - February 25, 2009

Today

• positive feedback
• "runaway" climate change
• precautionary principle
• climate change model with thresholds and comparing prevention and remediation costs

1. positive feedback

amplifies increase AND decrease

increase in temperature --> multiple processes --> further increase in temperature

decrease in biodiversity --> impoverished ecological niches --> further loss of bodiversity

 

2. Runaway climate change after the "tipping" point

links:

• McKibben - http://e360.yale.edu/content/feature.msp?id=2012
• NASA - http://www.giss.nasa.gov/research/news/20081208/
• Wiki - http://en.wikipedia.org/wiki/Greenhouse_effect
• Wiki - http://en.wikipedia.org/wiki/Runaway_climate_change

surface temperature goes up because of forcing functions

• some forcing functions are natural
  • solar variation
• some are anthropogenic
  • increased CO2, methane and other GHG
• some are responses to increase temperature
  • methane from tundra
  • ice sheet melting
  • methane hydrates in the ocean floor

reinforcing climate change is called "runaway climate"

Jim Hansen

"tipping point" = no additional forcing is required for long term climate change

his estimate is that the "tipping point" CO2 is about 350 ppm - i.e. we're past that now

target CO2 used to be 450 ppm

"point of no return" - reaches a point with unstoppable climate impacts that can't be reversed on practical time scales

3. Global climate change

multiple models

Broeker - is the trigger in the atmosphere or ocean

abrupt change in the past

temperature - WHOI page

Thermo Haline Conveyor model

circulation diagram - WHOI page

 

3. Thresholds, scale and the precautionary principle

threshold response of a system

scale of a shift or of response

Albufera:
shifted - hasn't switched back for about 50 years

UKL example:
P load limitation - decades to centuries
marsh restoration - 5 years

cost of avoiding the shift vs. cost of remediation/restoration

STELLA/global-warm-thresh-remed.stm

• near balance of input and output - with some variability in the input of CO2
• if the atmosphere reaches a threshold (104% of current) then a new flow kicks in
• required repair costs of $100 per unit over 102%
• because of the stochastic nature of the input, it may or may not require repair
• alternative is to remediate and remove carbon from atmosphere at $100 per unit

run the model multiple times

if it exceeds the threshold the repair costs jump

how little can you spend in remediation to avoid that cost