Climate Change Models: Understanding The Basics

With an incoming U.S. President vowing to seriously address climate change, and his cabinet filling with outspoken advocates for such action, the United States, its economy, and its approach to the climate issue are poised to change in profound ways.

The science motivating this political momentum is based largely on global-scale climate models, so these research tools have the very real potential to change the world they are designed to describe. In some instances, they already are doing so.

Yet to most people, including politicians and policy makers acting on the messages these models convey, climate models remain a black box of sorts. Given their importance, though, those who teach, cover, or otherwise act as explainers of climate science to policymakers and regular folks will do well to better understand how global climate models work, and how confident we can be in what they tell us.

Intertwined and stacked cubes blanketing the globe

In simplest terms, a modern global climate model is a computerized grid of millions of mathematically intertwined and stacked cubes blanketing the globe, with each representing a specific spot around the globe. Cubes represent the ocean, land, sea ice, and the atmosphere, and modelers essentially create separate models for each of them and then tie them together to project how they interact to govern the planet’s climate.

Researchers work to program models to calculate as accurately as possible what will happen to temperatures, winds, water currents, and other parameters as appropriate in each cube under various scenarios, for instance a doubling of the current atmospheric carbon dioxide concentration. (The realclimate.org website in early January posted an informative “FAQ on climate models“.) Analyzing and combing data from such calculations allows a model to combine the results for all the individual cubes to project the larger picture of what might happen to the global climate.

Each cube is really just a collection of formulas mathematically describing processes within that area that are relevant to climate. Many of these formulas are based simply on the rudimentary physics that govern motion on a rotating sphere. The laws of gravity, Newton’s laws of motion, and other basics are all tapped to answer such questions as how hypothetical winds will move through cubes, affecting temperatures as they go.

Other formulas needed to calculate a modeled cube’s environment address things Newton likely never pondered. Equations for how sunlight will reflect off a chunk of Arctic ice, warming the air in the cube above it and others nearby, for instance, are based on more recent laboratory experiments. Some important factors, such as how trees might slow a cooling wind, have to be addressed as net effects because attempting to compute the impacts of every individual tree on the planet obviously is impossible.

Clouds, Aerosols Among Modeling Challenges

Much of what will govern the climate at a given point can be well addressed, but other components remain difficult to model. The impacts of clouds as they trap heat and reflect sunlight away from Earth, for instance, are notoriously complex, and clouds’ impacts remain a source of modeling uncertainty. Pollution particles, or aerosols, in the atmosphere can have important cooling effects, but accurately incorporating these impacts remains another modeling challenge. One of the main sources of variation between models from different research groups involves how they incorporate these more difficult components.

Most current models, including the 23 used for the 2007 Intergovernmental Panel on Climate Change report, do not calculate how ocean plankton, trees, and other forms of life process carbon dioxide and other gases to control their fate – whether they end up in the atmosphere providing warming effects or are buried in the ocean or elsewhere. Instead, based on research into how gas cycling occurs, modelers convert greenhouse gas emissions into atmospheric gas concentrations that vary appropriately over time according to the emissions scenario used. The modelers then plug this information into their models.

Earth System Models … ‘The Next Generation’?

Researchers currently are focusing on building new “Earth System Models,” some of which are likely to be used for the next IPCC report. These incorporate biology to generate their own projections for how greenhouse gases will cycle and build up in the atmosphere under a given emissions scenario. Such models are in their infancy, but as they improve they might ultimately reveal important and previously missed controls on climate, such as an unforeseen reduction in carbon dioxide uptake by plankton that would lead to increased atmospheric concentrations.

Modelers also are working to improve the resolution of their models, the number of cubes in the grid that compose a model’s virtual planet and atmosphere. More cubes, just like more pixels in a digital photo, make for a clearer picture. Improved resolution alone does not guarantee a better understanding of climate, but higher resolution, such as incorporating biology, offers the potential to reveal important processes that might otherwise remain unknown.

Studying a Virtual Planet

Once all the equations for the cubes are set, researchers “spin up” a model to run various types of experiments, such as projecting potential future climates based on plausible scenarios specifying factors such as carbon dioxide emissions from human activities. In the case of models used by the IPCC, these scenarios are determined not by modelers, but by social scientists based on studies of population, technology, and other trends. It’s safe to assume the laws of physics will remain constant, but it’s impossible to say what humans are going to do in the future, so filling in these blanks is one of the largest sources of uncertainty in climate modeling.

A model run might begin at some point in the past, say 1860, and run well into the future, often to 2100, calculating a cube’s parameters at specified intervals. Researchers do have to set certain boundaries such as future carbon dioxide concentrations, but they do not plug current and past temperature and other information to fit a model run to the climate that has already been observed. Instead, only initial data for such parameters is set, and the model is then allowed to run on its own. (See article from The Yale Forum.)

Because models are not tweaked to match observations, a key way researchers quantify accuracy involves comparing the trends a model reveals through various runs to what has actually happened. Some subjectivity is involved, for instance in which parameters to compare, but good matches are considered a strong indicator of a model’s reliability in projecting a future climate if a given scenario for human inputs plays out.

Researchers also run modeling experiments where they change some aspect of the past. For instance, they might run a model holding greenhouse gases constant at their 1860 levels to study the degree to which natural factors such as volcanic gas emissions and variations in the sun’s heat output might control climate without any consideration of increased carbon dioxide emissions or concentrations. Work along these lines has repeatedly suggested that observed warming and other climatic trends can be explained only if the human greenhouse gas emissions are included.

One of the main reasons researchers’ confidence in models is increasing, and the IPCC reports are expressing more confidence in model projections despite remaining uncertainties, is that models have grown better and better at matching observed climate. The projections of models that take different approaches to addressing areas of uncertainty are also telling ever more similar stories about the likely future impacts of large greenhouse gas emissions.

Modeling can never be a perfect science, but as many of those involved have pointed out, unless we figure out a way to build planets identical to Earth on which to perform experiments, the virtual planets they describe will remain the best available laboratories for studying future climate change.

Mark Schrope is a freelance science writer living in Melbourne, FL.

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One Response to Climate Change Models: Understanding The Basics

  1. Michael Ioffe says:

    Al Gore as leader of senate committee in 1880th first politicized science of climate change.
    In his book (the best of his, by the way), Earth in the balance, 1991 he first time use his slogan: “If 98% of scientists…”
    He also used slogan: “Debate is over”.
    It is good for politic, and must be strongly prohibited in science.

    One man-Copernicus had courage to oppose 99.999…% of scientists that earth is not centers of solar system.
    One man-Newton oppose by his laws the same 99.999…%
    If Copernicus, Newton, Einstein, Faraday, Maxwell and many others great scientists will think about opinion of majority, we will be under influence of Aristotle till now, which also was and is a great man for history of science.
    From Wikipedia, the free encyclopedia

    “Outgoing Longwave Radiation (OLR) is the energy leaving the earth as infrared radiation at low energy. Earth’s radiation balance is very closely achieved since the OLR very nearly equals the Shortwave Absorbed Radiation received at high energy from the sun. Thus, the first law of thermodynamics (energy conservation) is satisfied and the Earth’s average temperature is very nearly stable. The OLR is affected by clouds and dust in the atmosphere, which tend to reduce it below clear sky values. Greenhouse gases, such as methane (CH4), nitrous oxide (N2O), water vapor (H2O) and carbon dioxide (CO2), absorb certain wavelengths of OLR adding heat to the atmosphere, which in turn causes the atmosphere to emit more radiation. Some of this radiation is directed back towards the Earth, increasing the average temperature of the Earth’s surface. Therefore, an increase in the concentration of a greenhouse gas would contribute to global warming by increasing the amount of radiation that is absorbed and emitted by these atmospheric constituents.
    The OLR is dependent on the temperature of the radiating body.”

    “The Stefan-Boltzmann T^4 law for blackbody radiation show tendency also for earth.
    In equatorial area, where temperature is bigger, radiation is also bigger.”
    “The temperature falls with height precisely because most of the atmosphere is convecting, which leads to a fall of temperature with height because of pdV work.”

    If we will look at all these statements they are correct and their correctness create huge misunderstanding what is real reason for climate change.
    Main mistakes are mixing all greenhouse gases together and make all of them equally responsible for climate change.
    It is especially wrong for water vapor, which together with others properties of water actually cooling earth atmosphere.
    Water evaporated from all surfaces of oceans, seas, lakes, rivers,
    Water evaporated from leaves of any plants.
    Water evaporated from any wet surfaces.
    In atmosphere we always see dynamic processes of evaporation and condensation of water, as in drops of rain, as in tail after jet, as in clouds, fog, etc.
    Evaporations of water need energy. To evaporate 1 kg of water we need 539 kcal of energy.
    Every condensation of water released energy in the same amount.
    Evaporation of water is cooling surfaces, from which evaporation occur and air close to those surfaces.
    It is reasons, why in summer time is always cooler close to oceans, seas, lakes and rivers.

    We must pay attention, that only methane (CH4) is lighter than water vapor.
    Nitrous oxide (N2O), carbon dioxide (CO2), nitrogen (N2), oxygen (O2), are heavier than water vapor.
    It property of water vapor helps convection forces to mix air with height.
    Here it will be helpful to repeat, what offer to us Wikipedia:
    “The temperature falls with height precisely because most of the atmosphere is convecting, which leads to a fall of temperature with height because of pdV work.”
    Fall of temperature with height helps condense some water vapor and create water droplets.
    This process released heat, which increase temperature of surrounded gases.
    Hotter air recreate convection forces, which bring some of air higher, where again some of water vapor will condensed and released additional heat.
    It dynamic process of partially condensation with height will repeat many times till upper troposphere (around ten kilometers high), where so cold that 99% of water vapor will condensed to water droplets.
    It process helps all gases in air bring energy 10 km close to space, where energy will go to space easy, than from oceans level.

    Mankind activity not only reduces evaporation of water from continents by deforestation, tilling land, growing the same crop on huge area.
    Mankind activity decreased reflection of direct sun radiation, by soot, roads, homes, cities, etc.
    Mankind activity correlate with energy, which we use. Most of energy, used by mankind increased carbon dioxide, which is ease use as coefficient in climate models.
    In reality carbon dioxide is playing not so significant role in climate change, as reduction of evaporation on continents and decreasing reflection of direct sun radiation.

    I understand, that these statements from me are controversial, and to support my view I could only bring next:
    If we will imagine earth without continents and only with one equally deep ocean, will be weather disasters on the earth on recent level in this case?

    Understanding these realities, create new possibilities in fighting climate change.
    It is economically difficult to change reflection of direct sun radiation.
    It is easy to increase evaporation of water on continents by forests.
    We only need to found economical reason to grow forests.

    Even if I am wrong in my conclusions about properties of water, solution, which I could offer will reduce carbon dioxide in the world and be useful for economy.

    Reason for change:

    Transportation system

    Efficiency of engine in most cars moving by gasoline is around 30%.
    Efficiency of gasoline production is less than 45%.
    It means that real efficiency of car movement is around 13.5%
    If person (200 lb.) mostly alone is driving in this car (4,000 lb.) it means that efficiency of movement of this person in this car is 0.67%.

    Perhaps mass (m) of car is 2,000 kg, mass of driver 100 kg and speed (V) of car 65 miles per hour or 110.5 km/hour or 30.7 m/sec

    Kinetic energy of this car will be as follows:

    K=1/2mv²=1/2 x 2100 x 30.7 x 30.7=1/2 x2100 x 942

    As you can see in this case, the mass of car and its driver change the amount of kinetic energy twice more than the speed.
    It is less important, if we drive on strait road without stop on long distance.
    But usually it is traffic, or driving in city with stop on every light.
    We are losing energy in vain.
    If we will analyze situation with public transportation—cars, busses, trains, high speeds transportation situation will be even worst than for car. These types of transportation are heavier than car and Have many people aboard, which will wait few people going in and out.

    It will be better to move one person on small cart with weight 20 lb. moving by electricity directly from grid.

    It will reduce energy for transportation at least ten times.

    We could also reduce energy needs for moving every boat, creating forces, which will reduce underwater part of boat.

    Power plant

    The burning of fossil fuels (coal, natural gas, or petroleum) in power plant.
    In hot gas (gas turbine), turbines are driven directly by gases produced by the combustion of natural gas or oil.
    Gas turbine plants are driven by both steam and natural gas. They generate power by burning natural gas and use residual heat to generate additional electricity from steam. These plants offer efficiencies of up to 60%.”
    In grid we are loosing more than 7% of energy. It means 11.6% of energy of fuel. 60%-11.6%=48.4
    According maximum power theorem, resistance of source of energy must be close to resistance of load. In source of energy we are loosing around 50% of energy. 48.4/2=24.2
    Efficiency of load in average is less than 80%. 24.2 x0.8=19.36
    Not all plant has up to 60% of efficiency. And if you will speak with Engineers from usual power plants it is common – 13% of efficiency.
    As you see efficiency of power plant, which is common for USA is less than 20%.
    If we change power plant to use as heat as electricity power wood could provide more useful energy, than right now coal, natural gas, or petroleum.
    Smoke from coal, natural gas, or petroleum is toxic for forests.
    Smoke from wood we could put in water to watering forests, surrounding power plants.
    Together with ash it will be the best nutrition to grow trees.
    Let compare wood and coal by energy capacity:
    1 ton coal = 16,200,000 to 26,000,000 Btu
    1 ton wood = 9,000,000 to 17,000,000 Btu

    If we will change our transportation system our heat, hot water, and electricity production, we could reduce our needs for energy at least seven times.
    In this case wood will provide more useful energy than coal and oil product right now.
    Of course we could use mix of wood, natural gas and coal in environmentally friendly proportions.

    We could put all gases from oven, which used wood in water, to watering forests around power plants.

    It will be zero emission energy production.

    In 48 states we have 600,000,00­0 acres of forested land.
    300,000,00­0 acres of land are more than enough for USA energy needs.

    It is possible to harvest 5 dry ton/acre, year.
    Average heating value of 8,000 BTU/lb(dry)or 89,596,000BTU/acre, year
    Consumption of energy in 2010 (projection)-
    107,870,000,000,000,000 BTU / 89,596,000BTU/acre year=1,200,000,000
    If our energy needs will reduce 7 times we need only 1,200,000,000/7=171,000,000 acres of forest.

    Changing our transportation system, electricity production, growing forests for wood energy will:
    1. Make North American countries energy independent.
    2. Create 100% of employment in USA, Canada and Mexico.
    3. Create possibilities to fight climate change with help of these three countries. North America between Pacific, Arctic, and Atlantic oceans is influent climate from France to Japan.