Climate Change: Demystifying the Application of Earth Systems Models for Climate Science

Transcription

1 Climate Change: Demystifying the Application of Earth Systems Models for Climate Science Richard B. Rood Cell: Space Research Building (North Campus) June 21, 2017

2 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

3 Models Definition Outline Models and Scientific Investigation Models in Climate Science Establishing Trust: Numerical Experimentation Looking Towards the Future Summary

4 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:

5 Model (Dictionary) What is a Model? 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

6 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

7 Model (Dictionary) What is a Model? 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

8 Models and Scientific Investigation OBSERVATIONS THEORY EXPERIMENT

9 Models and Scientific Investigation OBSERVATIONS THEORY PREDICTION

10 Models and Scientific Investigation OBSERVATIONS PROCESSES SIMULATION

11 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.

12 Models in Climate Science

13 Models and Model Infrastructure Infrastructure Connects it all together. Critical for - Scientific credibility - Collaboration - Development - Efficiency - Analysis - End user Models & Model Simulations Solves the conservation equations - Mass - Momentum (~ weather) - Energy (~climate) Split into processes - Fluid dynamics - Radiation - Moist physics - Turbulence

14 Observations and Models: Processes Infrastructure Observations PROCESSES Models & Model Simulations DIAG. & TEST Define & test model physics Diagnostic applications

15 Observations and Models: Weather Forecasts Infrastructure Observations INITIAL COND. Models & Model Simulations FORECASTS Start Forecasts Validation Prognostic applications

16 Observations and Models: Assimilation Infrastructure Observations MELD Models & Model Simulations Assimilation & Reanalysis Initial Conditions Validation Scientific Investigation Data System Monitoring

17 Observations and Models: Predictions and Projections Infrastructure Observations PROCESSES INITIAL STATE Models & Model Simulations PREDICTIONS PROJECTIONS Define & test model physics Diagnostic applications Prognostic applications Start Forecasts Validation Assimilation & Reanalysis

18 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, selfdetermining (State Earth will Warm) (Details of Warming, Feedbacks)

19 The Earth System Model: Climate Models SUN CLOUD-WORLD ATMOSPHERE BIOLOGY OCEAN ICE (cryosphere) BIOLOGY LAND

20 Hindcasting Establishing Trust: Numerical Experimentation Historical simulation

21 Let s look at observations from the last 1000 years Surface temperature and CO 2 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 CO 2 as CO 2 increases beyond approximately 300 ppm, the value seen in the previous graph as the upper range of variability in the past 350,000 years.

22 Let s look at just the last 1000 years Surface temperature and CO 2 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 CO 2 do not match one-to-one. What is the cause of the temperature variability? Can we identify mechanisms, cause and effect? How?

23 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.

24 Schematic of a model experiment. Observations T Start model prediction T Statistical representation not deterministic Model prediction without forcing Model prediction with forcing Model prediction with forcing and source of internal variability, for example, El Nino, Pacific Decadal Oscillation

25 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 CO 2, increase in the greenhouse effect, can the temperature increase of the last 100 years be modeled.

26 Let s look at the modern record. Modern ~ Industrial Revolution ~ Last half of 1800s When we have direct temperature measures

27 20 th Century Simulations Figure TS.23 Example of Attribution

28 20 th Century Simulations Meehl et al., J. Climate (2004)

29 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.

30 IPCC (2007) projections for the next 100 years.

31 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

32 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

33 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.

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35 Models Definition Outline Models and Scientific Investigation Models in Climate Science Establishing Trust: Numerical Experimentation Looking Towards the Future Summary

36 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

37 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?

38 Background Materials

39 Roles of Uncertainty / Variability at Different Times Hawkins and Sutton, 2009

40 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. M today = M yesterday That s not very interesting, or realistic

41 Conservation principle (with income and expense) Income M today = M yesterday + I - E Let s get some money and buy stuff. Expense

42 Conservation principle (with the notion of time) Income M today = M yesterday + N(I E) Salary Income per month = I Rent Expense per month = E N = number of months I = NxI and E= NxE Expense

43 Some algebra and some thinking M today = M yesterday + N(I E) Rewrite the equation to represent the difference in money (M today - M yesterday ) = 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. (M today - M yesterday )/N = I E

44 Introduce a concept The amount of money that you spend is proportional to the amount of money you have: E = e*m How do you write this arithmetically?

45 Some algebra and some thinking (M today - M yesterday )/N = I em 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 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

46 Conservation principle Energy Income from the Sun M today = M yesterday + I - E Earth at a certain temperature, T Let s get some money and buy stuff. Energy emitted Expenseby Earth (proportional to T)

47 Some jargon, language Income is production is source Expense is loss is sink Exchange, transfer, transport all suggest that our stuff is moving around.

48 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

49 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

50 Earth: How Change T? Energy from the Sun Stable Temperature of Earth could change from how much energy (production) comes from the sun, or by changing how we emit energy. Earth at a certain temperature, T Energy emitted by Earth (proportional to T)

51 The first place that we apply the conservation principle is energy We reach a new equilibrium T 0 H - T t Production Loss H T Changes in orbit or solar energy changes this

52 The first place that we apply the conservation principle is energy We reach a new equilibrium T 0 H - T t Production Loss T H Changing a greenhouse gas changes this

53 Balancing the Budget Today s Money = Yesterday s Money + Money I Get Money I Spend Today s CO 2 = Yesterday s CO 2 + CO 2 I Get CO 2 I Spend Today s Energy = Yesterday s Energy + Energy I Get Energy I Spend Or Tomorrow?

54 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

55 Point of View SUN EARTH PLACE AN INSULATING BLANKET AROUND EARTH EARTH: EMITS ENERGY TO SPACE BALANCE FOCUS ON WHAT IS HAPPENING AT THE SURFACE

56 Simple earth 1

57 Models and Modeling

58 Models Blogs on Model Tutorial (Start with #3) Models are everywhere Ledgers, Graphics and Carvings Balancing the budget Point of View Cloak of Complexity

59 Model What is a 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?

60 Models are everywhere

61 How Many Use Spread Sheets?

62 Ledgers Ledgers, Graphics and Carvings Spreadsheets Computers

63 Radiation Balance Figure

64 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.

65 Building the Radiative Balance What happens to the energy coming from the Sun? Top of Atmosphere / Edge of Space Energy is coming from the sun. Two things can happen at the surface. In can be: Reflected Or Absorbed

66 Building the Radiative Balance What happens to the energy coming from the Sun? Top of Atmosphere / Edge of Space We also have the atmosphere. Like the surface, the atmosphere can: Reflect or Absorb

67 Building the Radiative Balance What happens to the energy coming from the Sun? Top of Atmosphere / Edge of Space In the atmosphere, there are clouds which : Reflect a lot Absorb some

68 Building the Radiative Balance What happens to the energy coming from the Sun? RS Top of Atmosphere / Edge of Space For convenience hide the sunbeam and reflected solar over in RS

69 Building the Radiative Balance What happens to the energy coming from the Sun? RS Top of Atmosphere / Edge of Space Consider only the energy that has been absorbed. What happens to it?

70 Building the Radiative Balance Conversion to terrestrial thermal energy. RS Top of Atmosphere / Edge of Space 1) It is converted from solar radiative energy to terrestrial thermal energy. (Like a transfer between accounts)

71 Building the Radiative Balance Redistribution by atmosphere, ocean, etc. RS Top of Atmosphere / Edge of Space 2) It is redistributed by the atmosphere, ocean, land, ice, life. (Another transfer between accounts)

72 Building the Radiative Balance Terrestrial energy is converted/partitioned into three sorts RS Top of Atmosphere / Edge of Space It takes heat to Turn ice to water And water to steam; that is, vapor 3) Terrestrial energy ends up in three reservoirs (Yet another transfer ) CLOUD ATMOSPHERE RADIATIVE ENERGY (infrared or thermal) SURFACE PHASE TRANSITION OF WATER (LATENT HEAT) WARM AIR (THERMALS)

73 Building the Radiative Balance Which is transmitted from surface to atmosphere RS Top of Atmosphere / Edge of Space 3) Terrestrial energy ends up in three reservoirs CLOUD CLOUD ATMOSPHERE (infrared or thermal) SURFACE (LATENT HEAT) (THERMALS)

74 Building the Radiative Balance And then the infrared radiation gets complicated RS Top of Atmosphere / Edge of Space 1) Some goes straight to space 2) Some is absorbed by atmosphere and re-emitted downwards 3) Some is absorbed by clouds and re-emitted downwards 4) Some is absorbed by clouds and atmosphere and re-emitted upwards CLOUD CLOUD ATMOSPHERE (infrared or thermal) SURFACE (LATENT HEAT) (THERMALS)

75 Want to consider one more detail What happens if I make the blanket thicker?

76 Thinking about the greenhouse A thought experiment of a simple system. Top of Atmosphere / Edge of Space 1) Let s think JUST about the infrared radiation Forget about clouds for a while 3) Less energy is up here because it is being held near the surface. It is cooler ATMOSPHERE (infrared or thermal) 2) More energy is held down here because of the atmosphere It is warmer SURFACE

77 Thinking about the greenhouse Why does it get cooler up high? Top of Atmosphere / Edge of Space 1) If we add more atmosphere, make it thicker, then 3) The part going to space gets a little smaller It gets cooler still. ATMOSPHERE 2) The part coming down gets a little larger. It gets warmer still. (infrared or thermal) SURFACE The real problem is complicated by clouds, ozone,.

78 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.

79 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 CO 2 is no longer able to absorb. It means that it takes longer to make it to space.

80 Thinking about the greenhouse Why does it get cooler up high? Top of Atmosphere / Edge of Space 1) Atmospheric Window 2) New greenhouse gases like N 2 0, CFCs, Methane CH 4 close windows ATMOSPHERE 3) Additional CO 2 makes the insulation around the window tighter. (infrared or thermal) SURFACE The real problem is complicated by clouds, ozone,.

81 Changes in the sun So what matters? THIS IS WHAT WE ARE DOING Things that change reflection Things that change absorption If something can transport energy DOWN from the surface.

82 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.

83 Radiation Balance Figure In this figure out = in

84 Energy in Earth System: Basics Science Observations Evaluation Measurement Can we do the counting to balance the budget? Can we measure the imbalance when the Earth is not in equilibrium?

85 Radiative Balance (Trenberth et al. 2009) In this figure out does not = in

86 IPCC (2001) projections for the next century

87 IPCC (2007) projections for the next century

88 IPCC (2013) projections for the next three centuries

89 Radiative Forcing Changes Interesting History of This Plot at RealClimate

90 Questionnaire: Kansas City, AMS, Broadcast Meteorologists, Model Short Course