Post on 30-Jan-2020
Climate Change: Demystifying the Application of Earth Systems Models for
Climate Science Richard B. Rood
Cell: 301-526-85722525 Space Research Building (North Campus)
rbrood@umich.eduhttp://clasp.engin.umich.edu/people/rbrood
June 21, 2017
Some Resources
• Gettelman and Rood: Demystifying Climate Models: A User’s Guide to Earth Systems Models
– Springer, Open Source, (It is free.)
• Introductory Material OpenClimate Mini-page
• Model Introduction OpenClimate Mini-page
• Rood’s Class MediaWiki Site– http://climateknowledge.org/classes/index.php/Climate_Change:_The_Move_to_Action
Outline
• Models– Definition
• Models and Scientific Investigation• Models in Climate Science• Establishing Trust: Numerical
Experimentation • Looking Towards the Future• Summary
Assumption
• I am talking to an audience that knows what “model” means in the context of weather and climate science.
• Knows the jargon of meteorology
From: http://www.halfhull.com/main.jpg
What is a Model?
• Model (Dictionary)– A schematic description of a system, theory, or
phenomenon that accounts for its known or inferred properties and may be used for further studies of its characteristics
We live lives full of models
• Models are everywhere in our lives and work– Architecture– Epidemiology– Aerospace– Computer assisted design– Games– The bridge over the Missouri River– Landing things on Mars– Investing my retirement account– How much rent can I afford– My digital thermometer
What is a Model?
• Model (Dictionary)– A schematic description of a system, theory, or
phenomenon that accounts for its known or inferred properties and may be used for further studies of its characteristics
• Weather and Climate– Provide numerical approximations of the equations that
describe the atmosphere, land, ocean, ice, biology of the Earth –
– process definition, diagnostics, predictions, and projections– Solves conservation equations:
– energy, momentum, mass
Models and Scientific Investigation
OBSERVATIONS THEORY
EXPERIMENT
Models and Scientific Investigation
OBSERVATIONS THEORY
PREDICTION
Models and Scientific Investigation
OBSERVATIONS PROCESSES
SIMULATION
Computational Science (Post and Votta, PhysToday, 2005)
• Computational Science & Numerical Simulation– Given what we know, can we predict what will
happen, and evaluate (validate) that what we predicted would happen, happened?
– Validation: Comparison with observations– Philosophy: Do we ever know if we get the right
answer for the right reason?– Computational and natural science: Establish the
credentials of a model to help inform us about the application for which the model was designed.
Models in Climate Science
Models and Model Infrastructure
Models & Model Simulations
Infrastructure
Solves the conservation equations- Mass- Momentum (~ weather)- Energy (~climate)
Split into “processes”- Fluid dynamics- Radiation- Moist physics- Turbulence
Connects it all together. Critical for- Scientific credibility- Collaboration- Development- Efficiency- Analysis- End user
Observations and Models: Processes
Observations Models & Model Simulations
Define & test model “physics”
Infrastructure
PROCESSES DIAG. & TEST
Diagnostic applications
Observations and Models: Weather Forecasts
Observations Models & Model Simulations
Start Forecasts
Infrastructure
INITIAL COND.
Validation
FORECASTS
Prognostic applications
Observations and Models: Assimilation
Observations Models & Model Simulations
Assimilation & Reanalysis
Infrastructure
MELD
Initial ConditionsValidationScientific InvestigationData System Monitoring
Observations and Models: Predictions and Projections
Observations Models & Model Simulations
Assimilation & Reanalysis
Infrastructure
PROCESSES
INITIAL STATE
PREDICTIONS
PROJECTIONS
Diagnostic applications
Prognostic applications
Define & test model “physics”
Start Forecasts Validation
Complexity / Types of Models(Rood, Perspective)
• Conceptual / Heuristic Models– Integrated, theory based (ex. Geostrophic
balance) • Statistical models
– Past behavior and correlated information used to make predictions
• Physical models: First principle tenets of physics (chemistry, biology)– Mechanistic: some aspects prescribed– Comprehensive: coupled interactions, self-
determining
(State Earth will Warm)
(Details of Warming, Feedbacks)
BIOLOGY
CLOUD-WORLD
The Earth System Model: Climate Models
ATMOSPHERE
LAND
ICE(cryosphere)
SUN
BIOLOGY
OCEAN
Establishing Trust: Numerical Experimentation
• Hindcasting• Historical simulation
Let’s look at observations from the last 1000 years
Surface temperature and CO2 data from the past 1000 years. Temperature is a northern hemisphere average. Temperature from several types of measurements are consistent in temporal behavior.
Medieval warm period
“Little ice age”
Temperature starts to follow CO2 as CO2increases beyond approximately 300 ppm, the value seen in the previous graph as the upper range of variability in the past 350,000 years.
Let’s look at just the last 1000 years
Surface temperature and CO2 data from the past 1000 years. Temperature is a northern hemisphere average. Temperature from several types of measurements are consistent in temporal behavior.
Note that on this scale, with more time resolution, that the fluctuations in temperature and the fluctuations in CO2do not match one-to-one.
What is the cause of the temperature variability? Can we identify mechanisms, cause and effect? How?
{
What do we do?
• We develop models based on the conservation of energy and mass and momentum, the fundamental ideas of classical physics. (Budget equations)
• We determine the characteristics of production and loss (forcing) from theory and observations of, for instance, the eruption of a major volcano and the temperature response as measured by the global observing system.
• We simulate the temperature (“Energy”) response.• We evaluate (validate) how well we did, characterize the
quality of the prediction relative to the observations, and determine, sometimes with liberal interpretation, whether or not we can establish cause and effect.
Schematic of a model experiment.
T
T Start model prediction
Model prediction withoutforcing
Model prediction withforcing
Model prediction with forcing and source of internal variability, for example, El Nino, Pacific Decadal Oscillation
Observations
Statistical representation – not deterministic
What do we know from model experiments and evaluation (validation) with observations
• With consideration of solar variability and volcanic activity, the variability in the temperature record prior to 1800 can be approximated.
• After 1800 need to consider the impact of man– Deforestation of North America– Fossil fuel emission– Change from coal to oil economy– Clean Air Act
• Only with consideration of CO2, increase in the greenhouse effect, can the temperature increase of the last 100 years be modeled.
Let’s look at the “modern” record.
• Modern ~ Industrial Revolution~ Last half of 1800s
• When we have direct temperature measures
Figure TS.2320th Century Simulations
Example of Attribution
20th Century Simulations
Meehl et al., J. Climate (2004)
Look towards the future.
• Surface temperature anomaly• Intergovernmental Panel on Climate Change
(IPCC, every ~ 5 years)– IPCC assesses, does not “do” research
• Coupled Model Intercomparison Project (CMIP)– Scientist community designs protocol to evaluate
and establish trustworthiness of climate models • CMIP is not the same as IPCC, but are often
conflated.
IPCC (2007) projections for the next 100 years.
Summary: Models
• Basic scientific principle or law used in climate science is conservation of energy
• Models are an accounting, or calculating the budget, of – Energy– Mass– Momentum
• Credibility established by representation of the past, and, when possible, evaluating predictions and prejections
Summary: Energy Balance of Planet
• Earth’s energy balance– Energy from Sun– Energy sent back to space
• Things that absorb• Things that reflect• Moving energy around• Storing energy at the surface of the Earth
– Greenhouse gases hold the energy a while– Oceans pick it up and hold it longer– Ice takes it up and melts balances change
A fundamental conclusion
• Based on the scientific foundation of our understanding of the Earth’s climate, we know with virtual certainty– The average global temperature of the Earth’s surface
has risen and will continue to rise due to the addition of gases (esp, carbon dioxide) into the atmosphere that hold heat close to the surface. The increase in greenhouse gases is due to human activities, especially, burning fossil fuels.
– Historically stable masses of ice on land have melted and will continue to melt.
– Sea level has risen and will rise.– The weather has changed and will change.
Outline
• Models– Definition
• Models and Scientific Investigation• Models in Climate Science• Establishing Trust: Numerical
Experimentation • Looking Towards the Future• Summary
Some Resources
• Gettelman and Rood: Demystifying Climate Models: A User’s Guide to Earth Systems Models
– Springer, Open Source, (It is free.)
• Introductory Material OpenClimate Mini-page
• Model Introduction OpenClimate Mini-page
• Rood’s Class MediaWiki Site– http://climateknowledge.org/classes/index.php/Climate_Change:_The_Move_to_Action
Poll questions:
• I was formally introduced to weather or climate models in school.
• Our knowledge of climate change is adequate for us to take action to intervene to reduce carbon dioxide emissions.
• Climate models provide adequate information to inform decisions about adaptation.
• Climate models are trustworthy.• Provide any comments, qualifications inspired by the
questions above.• Write any questions or comments about climate
models and climate change you would like to make.• What do you want to get from this presentation?
Background Materials
Roles of Uncertainty / Variability at Different TimesHawkins and Sutton, 2009
Conservation principle
• There are many other things in the world that we can think of as “conserved.” For example, money.– We have the money that we have.
• If we don’t spend money or earn money, then the money we have today is the same as the money we had yesterday.
Mtoday = Myesterday
That’s not very interesting, or realistic
Conservation principle(with income and expense)
Mtoday = Myesterday + I - E
Let’s get some money and buy stuff.
Income
Expense
Conservation principle(with the notion of time)
Mtoday = Myesterday + N(I – E)
Salary
Income per month = IRent
Expense per month = EN = number of months
I = NxI and E= NxE
Income
Expense
Some algebra and some thinking
Mtoday = Myesterday + N(I – E)
Rewrite the equation to represent the difference in money
(Mtoday - Myesterday ) = N(I – E)This difference will get more positive or more negative as time goes on.
Saving money or going into debt.
Divide both sides by N, to get some notion of how difference changes with time.
(Mtoday - Myesterday )/N = I – E
Introduce a concept
• The amount of money that you spend is proportional to the amount of money you have:
• How do you write this arithmetically?
E = e*M
Some algebra and some thinking
If difference does NOT change with time, then
M = I/e
Amount of money stabilizes
Can change what you have by either changing
income or spending rate
(Mtoday - Myesterday )/N = I – eM
All of these ideas lead to the concept of a budget:
What you have = what you had plus what you earned minus what you spent
Conservation principle
Mtoday = Myesterday + I - E
Let’s get some money and buy stuff.
Income
Expense
Energy from the Sun
Energy emitted by Earth
(proportional to T)
Earth at a certain temperature, T
Some jargon, language
• Income is “production” is “source”• Expense is “loss” is “sink”• Exchange, transfer, transport all suggest
that our “stuff” is moving around.
Equilibrium and balance
• We often say that a system is in equilibrium if when we look at everything production = loss. There might be “exchanges” or “transfers” or “transport,” but that is like changing money between a savings and a checking account.– We are used to the climate, the economy, our cash
flow being in some sort of “balance.”– As such, when we look for how things might change,
we look at what might change the balance.– Small changes might cause large changes in a
balance
Conservation of Energy
• Conceptual model of Earth’s temperature from space
H = Heating = Production = Loss
lT = Cooling = Loss
D means the change in something, a difference
T is Temperature and t is time
DT
Dt= H -lT
Earth: How Change T?
Energy from the Sun
Energy emitted by Earth
(proportional to T)
Earth at a certain temperature, T
Stable Temperature of Earth could change from how much energy (production) comes from the sun, or by changing how we emit energy.
The first place that we apply the conservation principle is energy
• We reach a new equilibrium
HT
THt
T
LossProduction
-0
Changes in orbit or solar
energy changes this
The first place that we apply the conservation principle is energy
• We reach a new equilibrium
HT
THt
T
LossProduction
-0
Changing a greenhouse gas
changes this
Balancing the Budget
• Today’s Money = Yesterday’s Money + Money I Get – Money I Spend
• Today’s CO2 = Yesterday’s CO2 + CO2 I Get – CO2 I Spend
• Today’s Energy = Yesterday’s Energy + Energy I Get – Energy I Spend
Or Tomorrow?
Conservation principle• Conserved Quantities:
– mass (air, ozone, water)– momentum, – Energy
• Need to Define System– Need to count what crosses the boundary of
the system– System depends on your point of view
Point of View
SUN EARTH
EARTH: EMITS ENERGY TO SPACE BALANCE
PLACE AN INSULATING
BLANKET AROUND EARTH
FOCUS ON WHAT IS
HAPPENING AT THE
SURFACE
Simple earth 1
Models and Modeling
Models
• Blogs on Model Tutorial (Start with #3)• Models are everywhere• Ledgers, Graphics and Carvings• Balancing the budget• Point of View• Cloak of Complexity
What is a Model?
• Model– A work or construction used in testing or perfecting a
final product.– A schematic description of a system, theory, or
phenomenon that accounts for its known or inferred properties and may be used for further studies of its characteristics.
• Numerical Experimentation– Given what we know, can we predict what will
happen, and verify that what we predicted would happen, happened?
Models are everywhere
http://www.halfhull.com/main.jpg
How Many Use Spread Sheets?
Ledgers, Graphics and Carvings
• Ledgers • Spreadsheets Computers
Radiation Balance Figure
Let’s build up this picture
• Follow the energy through the Earth’s climate.
• As we go into the climate we will see that energy is transferred around.– From out in space we could reduce it to just
some effective temperature, but on Earth we have to worry about transfer of energy between thermal energy and motion of wind and water.
Building the Radiative Balance
What happens to the energy coming from the Sun?
Energy is coming from the sun.Two things can happen at the surface. In can be:
Reflected
Top of Atmosphere / Edge of Space
Or Absorbed
Building the Radiative BalanceWhat happens to the energy coming from the Sun?
We also have the atmosphere.Like the surface, the atmosphere can:
Top of Atmosphere / Edge of Space
Reflect
or Absorb
Building the Radiative BalanceWhat happens to the energy coming from the Sun?
In the atmosphere, there are clouds which :
Top of Atmosphere / Edge of Space
Reflect a lot
Absorb some
Building the Radiative BalanceWhat happens to the energy coming from the Sun?
For convenience “hide” the sunbeam and reflected solar over in “RS”
Top of Atmosphere / Edge of SpaceRS
Building the Radiative BalanceWhat happens to the energy coming from the Sun?
Consider only the energy that has been absorbed.
What happens to it?
Top of Atmosphere / Edge of SpaceRS
Building the Radiative BalanceConversion to terrestrial thermal energy.
1) It is converted from solar radiative energy to terrestrial
thermal energy.(Like a transfer between accounts)
Top of Atmosphere / Edge of SpaceRS
Building the Radiative BalanceRedistribution by atmosphere, ocean, etc.
2) It is redistributed by the atmosphere, ocean, land, ice, life.(Another transfer between accounts)
Top of Atmosphere / Edge of SpaceRS
Building the Radiative BalanceTerrestrial energy is converted/partitioned into three sorts
SURFACE
3) Terrestrial energy ends up in three reservoirs
(Yet another transfer )
Top of Atmosphere / Edge of Space
ATMOSPHERECLOUD
RS
WARM AIR(THERMALS)
PHASE
TRANSITION
OF WATER(LATENT HEAT)
RADIATIVE
ENERGY(infrared or thermal)
It takes heat to• Turn ice to water• And water to “steam;”
that is, vapor
Building the Radiative BalanceWhich is transmitted from surface to atmosphere
SURFACE
3) Terrestrial energy ends up in three reservoirs
Top of Atmosphere / Edge of Space
ATMOSPHERECLOUD
RS
(THERMALS)(LATENT HEAT)(infrared or thermal)
CLOUD
Building the Radiative BalanceAnd then the infrared radiation gets complicated
SURFACE
Top of Atmosphere / Edge of Space
ATMOSPHERECLOUD
RS
(THERMALS)(LATENT HEAT)(infrared or thermal)
CLOUD
1) Some goes straight to space
2) Some is absorbed by atmosphere and re-emitted downwards3) Some is absorbed by clouds and re-emitted downwards
4) Some is absorbed by clouds and atmosphere and re-emitted upwards
Want to consider one more detail
• What happens if I make the blanket thicker?
Thinking about the greenhouseA thought experiment of a simple system.
SURFACE
Top of Atmosphere / Edge of Space
ATMOSPHERE
(infrared or thermal)
1) Let’s think JUST about the infrared radiation• Forget about clouds for a while
2) More energy is held down here because of the atmosphere
• It is “warmer”
3) Less energy is up here because it is being held near the surface.
• It is “cooler”
Thinking about the greenhouseWhy does it get cooler up high?
SURFACE
Top of Atmosphere / Edge of Space
ATMOSPHERE
(infrared or thermal)
1) If we add more atmosphere, make it thicker, then
2) The part coming down gets a little larger.• It gets warmer still.
3) The part going to space gets a little smaller• It gets cooler still.
The real problem is complicated by clouds, ozone, ….
Think about that warmer-cooler thing.
• Addition of greenhouse gas to the atmosphere causes it to get warmer near the surface and colder in the upper atmosphere.
• This is part of a “fingerprint” of greenhouse gas warming.
• Compare to other sources of warming, for example, more energy from the Sun.
Think about a couple of details of emission.
• There is an atmospheric window, through which infrared or thermal radiation goes straight to space.– Water vapor window
• Carbon dioxide window is saturated– This does not mean that CO2 is no longer able to absorb.– It means that it takes longer to make it to space.
Thinking about the greenhouseWhy does it get cooler up high?
SURFACE
Top of Atmosphere / Edge of Space
ATMOSPHERE
(infrared or thermal)
3) Additional CO2 makes the insulation around the window tighter.
1) Atmospheric Window 2) New greenhouse gases like N20, CFCs, Methane CH4 close windows
The real problem is complicated by clouds, ozone, ….
So what matters?
Things that change
reflectionThings that
change absorption
Changes in the sun
If something can transport energy DOWN from the surface.
THIS IS WHAT WE ARE DOING
Think about the link to models
• energy reflected = (fraction of total energy reflected) X (total energy)
• energy absorbed = total energy - energy reflected = (1-fraction of total energy reflected) X (total energy)
• fraction of total energy reflected – Clouds– Ice– Ocean– Trees– Etc.
Radiation Balance FigureIn this figure out = in
Energy in Earth System: Basics
Can we measure the
imbalance when the Earth is
not in equilibrium?
Science Observations Evaluation Measurement
Can we do the counting to balance the budget?
Radiative Balance (Trenberth et al. 2009)In this figure out does not = in
IPCC (2001) projections for
the next century
IPCC (2007) projections for the next century
IPCC (2013) projections for the next three centuries
Radiative Forcing Changes
Interesting History of This Plot at RealClimate
• Questionnaire: Kansas City, AMS, Broadcast Meteorologists, Model Short Course