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 Dynamic behavior can be studied experimentally Physical and chemical processes are incorporated into a system model. Physical and chemical processes are incorporated into a system model. Interactions and long-term responses to a system disturbance require modeling 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. 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 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 The incorporation of key components of the earth system requires an analysis of fundamental 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.

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. system responds to the variable by reversing the effects of the change. 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 Cooling Vegetation Shifts Surface Albedo Increase More Cooling Atmospheric

Ecological Model Types Discussed in Reading Illustrate high levels of sensitivity in high- latitude vegetation. Equilibrium Biogeographical Models Frame-based transient ecosystems models Dynamic Global Vegetation Models (DGVMs)

Equilibrium Biogeographical Models 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. 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

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 Examples of Plant Functional Types:  Broadleaf trees  Needle leaf trees  Shrubs  C3 Grass  C4 Grass 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.

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.