Download Climate modeling

By Caroline Brennan & Elizabeth Elbel
Idealized Energy Balance on Earth
Key Aspects of Modeling
Purpose
To produce climate projections for anticipated
changes in the system.
Identify the components of the system
What entities are moving through the system?
What processes are involved in moving the entity
through the system?
What kinds of things do these processes depend on
complete their actions?
Define and consider if conditions could
exist in the real world
Intro to Climate System Modeling
A Model is a Representation of reality that is simple enough to gain
understanding of the many interacting components
Dynamic behavior can be studied experimentally
Physical and chemical processes are incorporated into a
system model.
Interactions and long-term responses to a system disturbance
require modeling
Ecosystems are made up of many interacting components and therefore,
can be modeled to simulate interactions and mechanisms at global and
regional levels.
Once parameters are determined from existing processes, input
values can be manipulated to make predictions on future
outcomes in the system.
Computer modeling programs attempt to mathematically simulate climates
using predetermined parameters.
What Stella Models Looks Like
Aspects of Climate Modeling:
Many interactions and processes need to be incorporated into models to
insure accuracy.
key systems for:
1. Atmosphere
2. Oceans
3. Biosphere
4. Cryosphere
5. Geosphere
Climate Forcing Factors
Internal Factors
Atmospheric composition
Amount of clouds (reflected
radiation and absorption of
radiation)
Chemistry
Surface Characteristics
Amount and location of ice
Amount of incoming solar
radiation
Temperature rise
Precipitation
Soil Moisture
Oceanic Currents
Chemistry
Shape, location and scale of ocean
circulation
Continental Drift
External Factors
Astronomical
Solar Output
Orbital Changes
Interplanetary dust
Collisions with other
interplanetary bodies
comets
asteroids
Feedback Mechanisms
A self-perpetuating mechanism of
change, directed by inputs in and out of
the system which result in a transient
response to that change.
The incorporation of key components of
the earth system requires an
analysis of fundamental feedback
mechanisms.
Modeling Activity
YEAH!!!
We’re Having
FUN!!!!!
Climate Feedback Mechanisms
Coupled reactions influencing climate sensitivity, patterns
of change and transient response of climate.
Examples
Temp & Albedo: Temp increases → Ice cover decreases → Albedo
decreases → Temp(++) positive feedback
Temp &Water Vapor: Temp increases→ Water Vapor increases →
Greenhouse gas increase→ Temp(++) → Water Vapor
increase→ Clouds increase→ Albedo increase→ Temp
decreases negative feedback
Positive Feedback
The response of a system to a variable is to continue on a
destabilizing path. If left unchecked the system becomes
unbalanced and homeostasis is lost.
Negative Feedback
Negative feedback helps to maintain stability in a system in spite of
external changes. The system responds to the variable by reversing
the effects of the change.
Self regulating system that maintains a state of equilibrium despite
perturbations.
Ice-Albedo Mechanism
Temperature goes up, ice
caps melt revealing dark rock,
albedo of surface goes down,
temperature goes up
(Positive Feedback System)
Ice-Albedo Mechanism
Temperature goes up, ice
caps melt revealing dark rock,
albedo of surface goes down,
temperature goes up
(Positive Feedback System)
Cloud-Albedo mechanism
As temperature rises,
evaporation increases, leading
to increased cloud formation,
increasing albedo, thereby
lowering temperature
(Negative Feedback System)
Earth Albedo is a function of surface type
Atmospheric Cooling
High-latitude Vegetation Feedback
Atmospheric
Cooling
Vegetation
Shifts
Surface
Albedo
Increase
More
Cooling
Ecological Model Types Discussed
in Reading
Illustrate high levels of sensitivity in highlatitude vegetation.
Equilibrium Biogeographical Models
Frame-based transient ecosystems models
Dynamic Global Vegetation Models (DGVMs)
Equilibrium Biogeographical Models
Used to model vegetation and climate interactions
• Determine regional distribution of vegetation types
within a given climate scenario
Use a combination of mechanisms to develop model
In general, disturbance regimes are not considered
Examples: BIOME3, MAPSS and DOLLY
Application to high latitude system
In Simulation, the equilibrium response of vegetation to increased
surface warming is that tundra vegetation will decrease in areas of
greenhouse gas induced climate change scenarios and be
replaced by the upward shift of boreal woodlands. Despite this
extension, boreal and woodland forests decrease in total land
area due to a greater pole-ward expansion of temperate forests.
Limitations of Model
Lacks consideration of various mechanism
interactions and responses
Model does not include such variables as nutrient
availability and the response of photosynthesis to elevated
CO2.
Permafrost and its role in controlling vegetation disruption
In some models, the total effects of disturbance (ex Fire)
on vegetation composition
Does not simulate the rate of transitions of vegetal
and climate states in response to climate
associated variables.
Frame-Based Transient
Ecosystem Models
Model consists of a series of sub-models within their own barriers, each
simulating transient changes of different ecosystem types
Spatial interactions among neighboring regions can be simulated.
This is described as a GRID BASED SIMULATION.
Each ecosystem type is modeled separately so that differences among
ecosystems are incorporated within each sub-model
Sub-models originally absent from model can be conceived and
added into model simulations.
Individual models can be expanded to simulate other model
variability
Allows modelers to track succession and disturbance (fire and
insect attack)
Can determine probability of switching to one ecosystem type over
another. When switching occurs another sub-model is
activated which then stimulates other factors to activate.
Frame-Based Transient
Ecosystem Models cont.
Application to high latitude system
In simulation, the boreal forests move upwards towards the poles. A
gradual change in tree invasion, climatic probability of fire, and disease
are established as a function of climate.
The rate of vegetation change is dictated by the rate of
climate change.
Climatic changes cause biome composition to
destabilize. Equilibrium is not achieved.
Limitations of Model
Smaller mechanisms and interactions become overlooked
by the larger picture.
Ecosystems are strictly defined within there prescribed
sub-model. Combinations of interactions among
vegetation and other factors are simulated in a manner
where movement of existing plant communities is not
considered. The model’s results are focused on new
associations with vegetation and environment,
Dynamic Vegetation Models
The integration of biogeogeography and biogeochemistry
models into transient models illustrates ecological effects
of climate change, in real time. DGVMs effectively model
disturbances and incorporate natural constraints on
biomass. They are useful for modeling vegetation climate
change reactions and can incorporate disturbances such as fire
or insect infestation.
The Basics:
1. Integrate vegetation structure and function.
2. Simulate the responses of integrated structure and function to
changing climate conditions.
Plant Functional Types
It is not possible to model plant species on
an individual level. The concept of PFTs
allows for the grouping of species,
reducing the variables of the model to a
manageable level.
Plants are classified in a functional way,
however there is no single or universal
format for PFTs. PFTs are thus specific to
the issues being addressed in the model.
Assumptions of PFTs:
1. Species can be grouped according to structural and
functional characteristics.
2. Parameterizations of each functional type represent
the species within the group, with little variance.
3. Biogeography does not matter.
Examples of Plant Functional
Types:
 Broadleaf trees
 Needle leaf trees
 Shrubs
 C3 Grass
 C4 Grass
Biogeochemistry
biogeography
Fire Module
Preliminary Results for NASA DGVM
Studies
Model limitations:
•Does not consider
disturbances such as fire.
•No consideration of Plant
seed limitations or dispersal
mechanisms.
The NASA-CASA DGVM
correctly predicts
forested area in 75%95% of cases worldwide
and 58% of all
grassland scenarios.
Improvements of DGVMs for
Northern Ecosystems
Inclusion of anaerobic soil processes
Permafrost dynamics
Moss-lichen layer dynamics
Broader disturbance regimes (insect outbreaks
and land management changes)
Plant Functional Types schemes specific to
high-latitude environments.
Overall Northern Latitude Climate
Change Projections
Modeled Projections
Upward polar-shift of boreal woodlands and temperate forests
Shifting Plant Communities. An increase in temperature, chemical
abundance and albedo may alter the competitive abilities between two
or more species, thereby affecting the composition of a natural
community. Photosynthesis and period of growth may be enhanced.
Reaction of vegetation to increased saturation and nutrient content.
Rising CO2 will increase temperature and in turn increase evaporation
from tundra.
Arctic tundra may change from net sink to a source of CO2 (Billings et al.
1983).
Increase of organic decomposition rate, which will in turn change soil
composition.
Are climate models reliable?
Models are tested by comparing model
predictions to current and past climates.
A lack of knowledge of biological processes
makes models difficult to verify.
There are flaws in climate models, this must
be considered when using models.