Dr. Ricky Rood's Climate Change Blog

Point of View

By: RickyRood, 6:03 AM GMT on August 23, 2012

Point of View: Models, Water, and Temperature (6)

This is a series of blogs on models, water, and temperature (see Intro). I am starting with models. In this series, I am trying to develop a way to build a foundation for nonscientists to feel comfortable about models and their use in scientific investigation. I expect to get some feedback on how to do this better from the comments. In order to keep a solid climate theme, I am going to have two sections to the entries. One section will be on models, and the other will be on a research result, new or old, that I think is of particular interest.


Doing Science with Models 1.3: In the previous entry of this series I used the example of balancing a monthly checking account to make the point that studying the Earth’s climate is very much like balancing a budget. Rather than money, we calculate a budget of energy.

Energy is one of the attributes used by scientists to describe the physical world, and it is a basic law of classical physics that energy is conserved. There are the laws of conservation of energy, conservation of mass, and conservation of momentum. Momentum describes how an object is moving: its mass, its speed, and its direction.

I introduced the concept of making a mathematical representation of the real world with this equation for money

Today’s Money = Yesterday’s Money + Money I Get – Money I Spend

and I came to point where I said we have a similar equation for energy

Earth’s Energy Today = Earth’s Energy Yesterday + Energy Gained – Energy Lost

These equations are the most basic models for the process that they describe. In fact, these equations could be said to be the perfect model for your personal budget of money or the Earth’s budget of energy. In the jargon of the scientist who builds models, this perfect model is often called the “analytic” model because it can be solved exactly, or analytically, by arithmetic.

The next idea I want to introduce is point of view. In the first instance, above, the equation represents a personal budget. In the second instance, the equation represents the energy budget of the whole Earth. Recall in the previous entry when I set up the problem of looking at the Earth’s energy, I said to imagine a person not on Earth, but who is observing the Earth. The observer, perhaps on Mars, sees the Earth as a small dot with energy coming in from the Sun, which the Earth then emits back to space from the Earth. If the Earth is in an energy balance, then the amount on energy coming back to space equals that coming in from the Sun.

That’s interesting to think about for a minute. Let’s assume that the Sun is constant. Then if the Earth is in an energy balance, the energy coming back to space is the same no matter the amount of carbon dioxide in the atmosphere. So to the person on Mars, the Earth would look the same. But the conditions on Earth might be quite different if the atmosphere had 600 rather than 300 molecules of carbon dioxide per every million molecules of air. This is because the point of view that we are interested in is from the surface of the Earth.

In 2010 I had a series of blogs called Bumps and Wiggles (here, go back and give it some “likes”). In the third of that series, I introduced Simple Earth. Here is that figure, which is described more completely in the original blog.





Figure 1: Simple Earth 1: Some basic ingredients of the Earth’s climate.

The problem of climate and climate change is important because of our point of view. If we are to continue to build thriving economies in our societies, we need a stable climate. In this case, stable really means that we know what to expect. Therefore, the climate of the Earth that might be of interest to that person sitting on Mars is not especially relevant to the person sitting on the surface of the Earth. Therefore, we need to think of models that are from the point of view of the person on the surface of the Earth. Again, energy and the law of conservation of energy come to the forefront.

In the figure, if the stick man looks around there is energy everywhere. It comes as heat from the Sun. It comes as wind from the air. It comes as waves from the sea. It comes as food from the land. So the accounting problem becomes more complex. We need the budget of energy for the atmosphere, the oceans, the land, and the glaciers and ice sheets. This energy needs to be balanced with what comes in from the Sun and what goes back to space. It is the same simple-to-conceive classical physics, but since we are in the middle of it all, the problem becomes complex. Still though, it is only a matter of balancing the books.

Interesting Research: Warming and Cooling in Ice Sheets - I’m usually not the blogger reporting on the most recent papers and breaking research, but this week I am different. The paper is Recent Antarctic Peninsula warming relative to Holocene climate and ice-shelf history, which was published online on August 22, 2012 in Nature. Robert Mulvaney is the senior author. The press take on this paper is that ice-core data show that over the previous, approximately, 12,000 years (the Holocene), there have been a number of times when there has been warming on James Ross Island, an island off the Antarctic Peninsula. These periods of warming have been comparable to the warming observed in the last 50 years, and hence, there are examples of warming that are not caused by the recent increases in carbon dioxide. There are scientific and political consequences of this paper. I will try to think like a scientist.

What does this paper say about generalized warming of the planet due to green house gases? First, we have to look at the locality of the data. It is from a single small island, in a part of the world that is known to have substantial fluctuations of temperature. We then need to look at how this knowledge fits in with the body of evidence as a whole. For example, Mulvaney and coauthors found a prominent warming period about 600 years ago. Was this warming at James Ross Island accompanied by warming of the same global extent as the currently observed warming? Are there other existing data that suggest natural internal variability during these previous times of warming? Is there something different in the past 50 years that distinguishes the current warming from the previous times of warming? The list goes on. So this result needs to be placed in context of all of the data and knowledge, and the coherence of this new information with the existing information needs to be evaluated.

This paper highlights the difficulty of extracting the contribution of warming due to carbon dioxide increase for any particular event. Ages ago, I had a blog on the breakup of the Larsen Ice Shelf. This new result makes the easy attribution of that ice-shelf collapse to human-caused warming difficult. As above, that attribution problem requires looking at the ice- shelf collapse in concert with other information. Was the event isolated? Is there evidence of other causes of variability? Is there something now that is different from the past? One attribution question that I can see – can the extra warming from carbon dioxide push the melting of the ice shelf over a tipping point?

Finally, I will bring us back to models, as models are ubiquitous in climate science and science in general. Within this paper, a glaciological model is used to determine the age scale. This model represents the flow of ice in the glacier, and that flow is assumed to remain constant over the time of the study. Another place that a model is used is determining the temperature based on the observations of isotopes of oxygen. This requires a melding of theory and application. Therefore, when you say, “but the observations show …” remember the role of models in making those observations.

r

Climate Change Climate Models Climate Change Attribution

Updated: 3:36 PM GMT on August 27, 2012

Permalink

Balancing the Budget:

By: RickyRood, 8:36 PM GMT on August 15, 2012

Balancing the Budget: Models, Water, and Temperature (5)

This is a series of blogs on models, water, and temperature (see Intro). I am starting with models. In this series, I am trying to develop a way to build a foundation for nonscientists to feel comfortable about models and their use in scientific investigation. I expect to get some feedback on how to do this better from the comments. In order to keep a solid climate theme, I am going to have two sections to the entries. One section will be on models, and the other will be on a research result, new or old, that I think is of particular interest.

First, I want to provide an example of model-based science, engineering, and design – the landing of the rover Curiosity on Mars. This effort relied on simulations for the quantitative evaluation of the propulsion of rockets and the drag of the parachute. Computers were programmed to simulate and manage the workflow, the stage separation, and the coordination with the orbiters. The trajectories and orbits were calculated with computer models of the dynamics of objects moving in gravitational fields with atmospheric drag. Observations were made along the way, and they were used to correct errors that were discovered by the discrepancies between model predictions and observations. The validation of these calculations came with a landing on Mars, in a crater, surrounded by steep mountains. A landing where there was one and only one opportunity. A landing, which was the first real-world execution of these quantitative calculations. As best as I can tell the landing was in terrain with characteristics as expected. As best as I can tell, the landing was within a few meters or where the landing was planned. A few meters error – the models were wrong? Useless?



Figure 1: From NASA: "Curiosity Spotted on Parachute by Orbiter: NASA's Curiosity rover and its parachute were spotted by NASA's Mars Reconnaissance Orbiter as Curiosity descended to the surface on Aug. 5 PDT (Aug. 6 EDT). The High-Resolution Imaging Science Experiment (HiRISE) camera captured this image of Curiosity while the orbiter was listening to transmissions from the rover. Curiosity and its parachute are in the center of the white box."

This is rocket science – what is rocket science? Rocket science is classical physics, what most physicists would consider simple physics, in a sequence of steps that in their totality are complex. Simple physics in a complex system – the same as a climate model.

Doing Science with Models 1.2: In the previous entry of this series I introduced the fact that many of the tasks of design, manufacturing, and accounting have been encoded as mathematical models executed by computers. And I made this promise: I will return to this idea of mathematical descriptions of objects later. Here we are.

Let’s start with something intuitive, money. The amount of money that I have today is equal to the amount I had yesterday plus the money I get minus the money I spend. In my class, I maintain that this simple equation

Today’s Money = Yesterday’s Money + Money I Get – Money I Spend

is symbolic of all of the mathematics that is required to have a scientific foundation to understand the Earth’s climate and climate change. This equation is, in a literal sense, a budget equation. Assume Yesterday’s Money is the amount in your checking account, you Get some money from working, and you Spend some money writing checks. From this information, you know the amount of money you have today by addition and subtraction. If you add it all up, and then compare with your bank statement, and you and the bank agree, then the budget balances.

There is a concept of classical physics called the conservation law, described by a conservation equation. The equation for money, above, is a conservation equation: the amount of money is conserved. That is you have a certain amount, and that amount changes either by getting money or spending money. If you don’t get or spend money, then the amount of money remains the same; it is conserved. There is nothing else. If you take a personal point of view, you can say that the money I have today is the money I had yesterday plus the money I produced minus the money I lost.

So I have used the words simple and classical to describe “physics.” One of the primary fields of physics is mechanics, which describes the way things move. This is what Isaac Newton described, and the basic idea is that if there are forces acting on an object with mass, then that object will move in response to those forces. A force we are all familiar with is gravity, which we usually think of as an object falling towards the Earth. This object could be Newton’s proverbial apple, rocks coming down the side of a mountain, or the mass of your body settling on your tired feet as you stand up. If we go back to the landing of the Curiosity rover described above, then when the parachute was slowing the landing module, there was gravity that was resisted by the drag of the atmosphere on the parachute. The study of forces and motions, as described in this paragraph, is called classical physics because it is old and describes the way the everyday objects that we can see move as well, as the way that planets and moons move. Classical stands in contrast with, for example, Einstein’s theory of relativity which is required when observing things that are moving very fast, for example, light.

Now back to the idea of the conservation equation, your checkbook. There are some things that are observed to be conserved. This observed conservation is so strong and so intuitive that we call these conservation laws. There are the laws of conservation of energy, conservation of mass, and conservation of momentum. Momentum describes how an object is moving: its mass, its speed, and its direction. I will start with the conservation of energy.

Let’s imagine that we are sitting out in space, perhaps on Mars, observing the Earth. Then we say

Earth’s energy today = Earth’s energy yesterday + energy gained – energy lost

The total energy of the Earth can be related to the temperature of the Earth. If there is more energy, then it is warmer. The primary way the Earth gains energy is through heating by the Sun. The Earth loses energy by emitting it back to space. If the energy lost is equal to the energy gained, then today’s energy is equal to yesterday’s energy. That is energy is constant, conserved; and, by inference, the temperature remains the same from one day to the next – from one year to the next. That is, the climate is stable. The energy budget is balanced.

The budget equation for your checkbook and the budget equation of the Earth’s energy look the same. Therefore, a model of the Earth’s climate can be viewed as an accountant’s spreadsheet. A climate model is the accounting of the Earth’s energy, and from that accounting, we conclude whether the Earth’s energy, temperature, is constant, increasing, or decreasing.

Interesting Research: The State and Fate of Himalayan Glaciers - The State and Fate of Himalayan Glaciers appeared on April 20, 2012 in Science and got some press at the time. Tobias Bolch is the senior author. This is a review paper, which is interesting from perspectives that are scientific and the practice of science.

With regard to the practice of science, some will recall that in the Intergovernmental Panel on Climate Change (IPCC) Fourth Assessment Report an incorrect statement was made about the rate of melting of the Himalayan Glaciers. This review paper is an assessment of the literature and the knowledge on the Himalayan Glaciers. It was motivated, at least in part, by addressing this erroneous statement. It is members of the scientific community reacting to and correcting incorrect information that made it into the public domain. (see also Glacier Misinformation and IPCC Statement) This error was caused by a breakdown of protocol and review.

With regard to the conclusions of the Bolch et al. paper, they state their correction to the original error, “The statement that most Himalaya and Karakoram glaciers will likely disappear by 2035 is wrong …” They conclude that most of these glaciers have lost mass since the mid-19th century, that this lose has accelerated in recent decades, and that mass loss will continue through the 21st century. They also detail the complexity of the problem, ranging from the terrain, to the regional role of the South Asian monsoon in summertime accumulation of snow at high altitudes, to the role of rocky debris in the reduction of glacial melting. There is also complexity in the impacts that the glacial changes have on water supply.

How are these conclusions reached? The primary tool is the conservation equation for the mass of glaciers.

Today’s Glacial Mass = Yesterday’s Glacial Mass + New Glacial Ice – Glacial Melt

An accounting is made from observations of the processes that form glacial ice and that cause glacial melt. There is input from snow. There is loss measured by stream flow. It is a counting problem, another calculation of a budget.

r




Climate Models Climate Change

Updated: 4:18 PM GMT on August 27, 2012

Permalink

Ledgers, Graphics, and Carvings

By: RickyRood, 7:47 PM GMT on August 07, 2012

Ledgers, Graphics, and Carvings: Models, Water, and Temperature (4)

This is a series of blogs on models, water, and temperature (see Intro). I am starting with models. In this series, I am trying to develop a way to build a foundation for nonscientists to feel comfortable about models and their use in scientific investigation. I expect to get some feedback on how to do this better from the comments. In order to keep a solid climate theme, I am going to have two sections to the entries. One section will be on models, and the other will be on a research result, new or old, that I think is of particular interest.

Doing Science with Models 1.1: In the previous entry of this series I argued that if one considered the types of models used in design and engineering, then we use models all of the time. In fact, when we build or do just about anything, we use some sort of model to get us started. I ended the previous entry with the example of building a simple picnic bench that would hold three, two-hundred-pound men. Not only do the materials need to be of sufficient strength, but the legs of the bench need to be attached in a way that they form a solid and stable foundation. If the bench wobbles and the legs spread apart, then it will be unsafe. If we have experience of some sort, we construct a model from this experience. For example, if we have built or repaired tables and benches we have some ideas of good and bad construction. If we have no direct experience then we can find or ask about plans. These plans might be a schematic, a graphic model of the bench.

For those who do not build benches, but who, say, balance their checkbooks, there are models as well. The forms in a ledger represent models that have proven usable through practice or that have become standard approaches. Information is collected and organized: the check number, the date, the payee, the amount, the purpose and the category of expenditure.

These graphic, tabular, or touchable models are common enough that we develop intuition about their use. Introductory materials to climate models often use the words “mathematical,” “numerical,” and “computational.” These words take us not only away from our intuitive notions of models, but also into subjects that many of us find difficult and obscure. However, in the past couple of decades we have seen the tabular models of checkbook balancing coded as computational products such as Quicken. Design and architecture move to tools such as Computer-assisted Design. Recently, we have seen this combination of the world of digital models and touchable products come full circle with the advent of three-dimensional printing. In three-dimensional printing, solid objects made of plastic and metal are rendered from mathematical descriptions of the objects. I will return to this idea of mathematical descriptions of objects later. The point that I would like to make now is that using computers as tools to represent the real world has in the last two decades become routine. Therefore, in and of itself, the use of computers to make numerical calculations of the real world is common. It might not be as universally intuitive to people as a ledger or a wooden design of a boat, but there is large body of experience that affirms the value of computer-based modeling.

There are a number of steps that need to be taken from here to climate models. So far, I have been talking about models that are in the spirit of a work or a structure used in testing or perfecting a final product. In climate modeling, the final product of the construction is a model. It is the purpose of that model to provide a credible representation of the climate. That representation has a number of attributes. There is the attribute of representing what we have already observed. There is also the attribute of predicting what we will observe, that is, predicting the future. Therefore, the final product of the whole process is the simulation of and the prediction of the climate.

As with many words, there is more than one definition of model in the dictionary. Another relevant definition from my print edition (third) of the American Heritage Dictionary is “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.” (American Heritage Dictionary online) This definition is directly descriptive of a climate model. But like those introductions to climate models that I referred to above, it quickly goes to words like “system” and “theory” that are not quite as intuitive as I would like. This is where I will start next time.


Interesting Research: Attribution of 2011 Extreme Weather to Climate Change - Some might recall in 2011, I wandered into the contentious subject of the attribution of climate change to humans (collected here) and talking about communicating extreme weather events in the media (Shearer and Rood). The paper I highlight in today’s blog is a compilation of efforts to understand the role of planetary warming in some of the extreme events of 2011. The paper is Explaining Extreme Events of 2011 from a Climate Perspective edited by Tom Peterson and others and published in the Bulletin of the American Meteorological Society. This paper looks at six of the extreme events of 2011 and tries to attribute, in a variety of ways, the role played by human-caused global warming. (nice summary in New Scientist)

I want to focus on the part of the paper that discusses the extreme heat and drought in Texas in the summer of 2011. Much of that discussion is based on evaluating the effect of sea surface temperature, and specifically, the role of El Nino and La Nina. El Nino and La Nina are the names given to recurring patterns of sea surface temperature distributions in the eastern, tropical Pacific Ocean. The approach to this problem is to use models to make many simulations with sea surface temperature distributions similar to the La Nina conditions of 2011. Simulations were made for times in the 1960s and for the year 2008. The simulations provide an ensemble of many plausible outcomes, and it is possible to investigate the odds of a drought of similar extreme attributes as the 2011 drought occurring in the 1960s. The authors conclude that the warming climate made the 2011 drought 20 times more likely to occur now than in the 1960s. The authors point out that they cannot make statements about absolute probability. That is, they cannot state that in the absence of carbon dioxide increases and associated warming, that the drought would not have occurred.

This approach of using probability to discuss the impact of warming is an active area of research as well as an emerging way to communicate the relation between extreme weather and global warming. In the Washington Post, Jim Hansen has an op-ed piece that describes a paper which was released on Monday, August 6 (reference at end). In this paper Hansen revisits his metaphor that compares extreme weather in a warming climate with playing a dice game with loaded dice. That is, the dice are loaded in a way such that what used to be “extreme” will more likely occur. Going back to the Texas drought, that result mentioned in the previous paragraph says that the dice are loaded so that the extreme attributes of the 2011 drought are 20 times more likely. The takeaway message from Hansen is that we have, so far, underestimated how much the dice are loaded and that we have underestimated the probability of extreme events such as droughts, floods, heat waves, and yes perhaps, persistent cold snaps.

r


Hansen, Early Edition, PNAS, Perception of Climate Change

Hansen, Perception of Climate Change, Public Summary

Climate Models Extreme Weather Climate Change Attribution Climate Change

Updated: 7:58 PM GMT on January 14, 2013

Permalink

About RickyRood

I'm a professor at U Michigan and lead a course on climate change problem solving. These articles often come from and contribute to the course.

Local Weather

Mostly Cloudy
48 °F
Mostly Cloudy