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Last Updated: 2:47 PM GMT on May 16, 2013
— Last Comment: 2:46 AM GMT on May 21, 2013
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ABSORBING
The last time I wrote about the role of reflection in the balance of energy of the planet. This time I will write about absorption. First a word about feedbacks--in the last blog I mentioned what is called the ice-albedo feedback. That is, ice melts, less solar energy is reflected, Earth warms, more ice melts. A lot of the comments were about other feedback mechanisms, especially the feedbacks associated with clouds and how aerosols impact clouds. Before I get to feedbacks, I want to make it through absorption, as clouds and aerosols are important in both absorption and reflection. I will use the same figure as last time and show the Sun with the Earth divided into four major components--the atmosphere, the ocean, land, and ice. Since clouds are so important to the climate, I have also explicitly labeled, surrounding the atmosphere, "cloud-world." To emphasize that we are concerned about the surface, I have placed a thin blue atmospheric layer on the top of the ocean, land, and ice. Climate modelers derive and develop the budget equations for each of these components.  Figure 1: Schematic of the Earth System, which shows the component models of a comprehensive climate model as well as the places that are most important to the absorption of radiative energy. When talking about the absorption of radiative energy we have to divide the radiative energy into two major pieces. The first is the solar radiative energy which is mostly visible light. At the Earth's surface, when solar energy is not reflected it is absorbed. Hence the darker parts of the surface, for instance, the ocean, red rocks, and black-top parking lots absorb energy. (What about trees?) Solar energy is also absorbed in the atmosphere. There is solar energy in the ultraviolet portion (shortwave) of the spectrum; most of this energy is absorbed in the stratosphere by ozone. There is also solar radiation in the infrared portion (longwave) of the spectrum. In the atmosphere water vapor and carbon dioxide absorb some of this energy. If we look at the total amount of energy that comes from the Sun, about 22% is reflected back to space before it reaches the surface, about 9% is reflected by the surface, about 20% is absorbed in the atmosphere, and, therefore, 49% is absorbed at the surface. Much of the energy that is absorbed at the surface is ultimately emitted as infrared radiation. This is the energy that is important for keeping the surface warm. Just as the infrared part of the solar spectrum is absorbed by water and carbon dioxide, the terrestrial radiation is absorbed by the atmosphere. After it is absorbed, some of it is emitted back down to the surface, and some is radiated upwards, towards space. Water and carbon dioxide are the most important infrared energy absorbers. Other infrared absorbers are methane, nitrous oxide, and the chlorofluorocarbons. The emission of infrared radiation from the atmosphere back to the surface holds energy near the surface and keeps it warmer than it would be if there was no atmosphere. This is the greenhouse effect and has been known about for more than 200 years. ("Spencer Weart's Carbon Dioxide Greenhouse Effect") If you use the idea that energy is absorbed and re-emitted a number of times close to the surface, slowly making its way back up to space, then you can imagine a certain average amount of time that the energy is held close to the surface. When we add greenhouse gases we increase the amount of time that energy stays close to the surface. Returning to the figure, humans are changing the climate system in two places most importantly. The first and most important is by adding greenhouse gases to the atmosphere. This slows down how fast the planet cools; hence, the surface becomes warmer. The second place we are directly changing the planet is at the land surface. These changes contribute to the greenhouse gas increase. Also, there are changes in the absorption of solar radiation. The changes in the amount and the distribution of energy leads to changes in the motion of the atmosphere and the ocean which, as pointed out by many previous comments to the blog, are trying to move the system towards an equilibrium state. If you want to find out more about coupled climate models, get model data, and even download a model here are links to two of the United States models used in the "IPCC's Climate Change 2007." . National Center for Atmospheric Research Community Climate System Model Geophysical Fluid Dynamics Laboratory (GFDL) Coupled Climate Models ricky (See my new blog at climatepolicy.org) View (8) Comments For This Post
REFLECTIONS
The last time I wrote about the balance of energy of the planet as a whole. There is some "effective" temperature at which the output of energy from the Earth balances the input of the energy from the Sun. While this "effective" temperature is an important concept for understanding the Earth's energy balance, it is not as important when we think about climate and climate change. We need to consider the temperature of the Earth in more detail, and, first and foremost, we need to consider the temperature of Earth at the surface. Where we live. If we return to the idea of a budget that I talked about in the last blog, then the calculation of the energy budget at surface involves more processes than when we want to calculate the average balance of the whole planet. The way climate modelers approach the calculation of this budget is to consider the components of the Earth system. A useful level of granularity is depicted in the figure which shows the Sun and the Earth divided into four major components --the atmosphere, the ocean, land, and ice. Since clouds are so important to the climate, I have also explicitly labeled, surrounding the atmosphere, "cloud-world." To emphasize that we are concerned about the surface, I have placed a thin blue atmospheric layer on the top of the ocean, land, and ice. Climate modelers derive and develop the budget equations for each of these components.  Figure 1: Schematic of the Earth System, which shows the component models of a comprehensive climate model as well as the places that are most important to the reflection of the Sun's energy. Also marked on the figure are the parts of the Earth system that are most important for reflecting energy from the planet. The Sun is the ultimate source of climate energy. The amount of energy provided by the Sun to the Earth's climate is determined by the total amount that arrives from the Sun take away the amount that is reflected. Clouds and ice are excellent reflectors. That is one reason that ice and snow are so important in maintaining a balanced climate --if ice and snow decrease the Earth will reflect away less of the Sun's energy. Hence, there will be more energy in the climate system--more heat, and more ice and snow will melt. (This is known as positive feedback--change amplifies change.) Clouds are also important reflectors, and clouds are determined by the amount of water in the atmosphere and temperature. They are also closely related to weather systems, and in particular, air which moves upward. Clouds are difficult to model, and it is also difficult to determine how clouds will change with changing climate. Therefore, it is not as easy to understand the roles of clouds in the planetary energy balance as it is to understand the role of ice. If the atmosphere is warmer, it can hold more water vapor. It's reasonable to expect more clouds, hence increased reflection. Hence, this role of clouds might be to counter some of the warming by increasing reflection. This is, however, only one role that clouds play. I have also marked in the figure that the atmosphere and land are important reflectors. The gases in the atmosphere scatter some of the Sun's energy back to space. The land is complicated. How the land reflects radiation is determined by what is on the land. If snow is on the land it reflects. If it is a black parking lot, it absorbs. This idea of white things reflecting and black things absorbing is something that people have known and used for centuries. The land is one of places where we change things. In "IPCC's Climate Change 2007" two effects of changing land use are noted. The first is changing the balance of reflection and absorption; the second is contributing to the increase of carbon dioxide. So these are the most important pieces of how the Earth reflects energy from the Sun. The comments to some of the previous blogs mentioned that clouds balance out the heating. We will look at this more closely in the future, but the short version is that it only partially balances the warming. Other comments have mentioned the urban heat island effect is important. This has been accounted for in the determination of trends, and it has also been accounted for in the temperature observations. And Gaia... to me Gaia implies that there is something about the Earth system that maintains a balance that is comfortable to humans. I know of no reason this would be true--see evidence to the contrary, and personally would not rely on the notion. If you want to find out more about coupled climate models, get model data, and even download a model here are links to two of the United States models used in the "IPCC's Climate Change 2007." . National Center for Atmospheric Research Community Climate System Model Geophysical Fluid Dynamics Laboratory (GFDL) Coupled Climate Models ricky View (58) Comments For This Post
THOSE CONFOUNDING MODELS
Models are used in just about every field of human endeavor--think architecture. The basic dictionary definition of a model has the following ideas in it; it's a description of a system or phenomena that accounts for its known or inferred properties and may be used for further studies of its characteristics. Models are used to both diagnose cause and effect in observations and to make predictions. Since it is difficult to set up experiments in the atmosphere, the ability to make predictions with models takes on (part of) the role of experimentation in the classical definition of science. If a model makes a bad prediction, then we often get information about how to improve models. If a model makes a good prediction, then... then, we might know something about cause and effect. But, we might have the right answer for the wrong reason. Therefore the ability to make predictions again and again coupled with the ability of multiple independent groups to make high quality predictions add confidence that we do know something about cause and effect. This idea of confidence contributes to the specification of certainty estimates in IPCC 2007. Since models are at the heart and soul of the climate change problem, I will take some time to work through the concepts of a model. First, there are different types of models, some simple, some complex. There are models based on physical principles like Newton's Laws of Motion; there are models based on statistical descriptions of observed variability(for example, average and standard deviations). All of them have their role. It is, however, the physical model that we care most about. This is because if the model can use the laws of physics to both explain cause and effect and to make a good prediction, then we have a solid foundation for determining our confidence in the predictions. Physics: I remember telling people I was a physics major in college, and it being a definitive conversation ender. The physics of the Earth is both simple and complex. It is simple because it is based on well established, tested ideas that have been around hundreds of years. Complex because there are so many things that are important to the climate, and they exist on large and small spatial scales, on fast and slow time scales. The last 3 or 4 blogs are just beginning to hint at this complexity. I usually start to explain models with a household budget. If you have income and expenses, then you have the basic idea. The amount of money that you have tomorrow is equal to the amount that you have today, plus any income, minus any expenses. You could write an equation for this ... but I'll try to use this figure.  Figure 1: Schematic of the Earth Sun System to illustrate the conservation of energy during a stable climate. A budget is the idea behind the conservation principle; for instance, the conservation of energy. Consider the Earth sitting in space; draw a circle around the Earth. Assume that the Earth is at an approximately steady temperature over, say, a year. If this balance is true then the energy that comes into the Earth (income) must equal the energy that leaves the Earth (expense). It balances, like a budget. The figure represents this straightforward and meaningful model. The energy that comes to the Earth comes from the Sun. Without the Sun we'd freeze. Yes, there is some geothermal energy, but it would not keep us warm. So if our energy comes from the Sun, then there are two basic ideas that are important for the energy balance. How much of the Sun's energy is reflected and how much of it is absorbed. If absorption and reflection are changed then the temperature of the Earth would change. Models: So with a model we have to identify and quantify all of things that change absorption and reflection. Then we have determine how they relate to each other--if one thing changes, does the other change? This should begin to hint at how model experiments are set up to disentangle, for instance, how we decide whether or not we are seeing a trend or variability due to the North Atlantic Oscillation. We'll do more next time. ricky View (33) Comments For This Post
CONFOUNDING VARIABILITY: MORE WEATHER AND CLIMATE
From the previous blog: Yes - 1993 was the year of the flooded Midwest. If you go back and look at that wavelet analysis figure once again, you will see the northward moisture flux in the long period scale. It builds up over the course of the summer. A couple of weeks ago I gave my climate science 101 lecture to a class. At the end of the class I was asked a question--what did I think were the most credible arguments that the current warming we are seeing is not caused by the carbon dioxide greenhouse effect? At the top of my list is the question of whether or not we have properly accounted for natural variability. So far we have looked at, perhaps, two extremes. We have seen and discussed the record of carbon dioxide and temperature cycles associated with the ice ages and temperate periods. We are currently in a temperate period, and there is no doubt that if human commerce is a measure of success, we have done well when it is temperate--dare I say warm? These oscillations are on periods of tens to hundreds of thousands of years. At the other end of the scale, I introduced the idea that weather-scale events are the mechanisms that make up the climate, and that the low level, diurnal jet stream was a climate feature because it was so important to the seasonal water cycles for the North American continent. There is a whole array stuff in between these two extremes. Two of the most important flavors of natural variability are the El Nino-La Nina cycles and the North Atlantic Oscillation. The observations and analysis of the IPCC 2001 report came to closure at about the time of 1997-1998 El Nino; hence, the Earth was in a warm cycle. That raised doubt that the warm temperatures at the end of the 1990s were part of a trend. This was reflected in the wording of that report. Since that time, the warming trend has continued irrespective of the El Nino-La Nina cycle. There is little debate today about whether or not the planet is warming. The North Atlantic Oscillation (NAO) is familiar to many people reading this blog. The NAO is associated with a change in the surface pressure pattern, which is easily observed in the position of the Icelandic Low. The figures below show the surface pressure field in the two modes of the North Atlantic Oscillation. These are from the Lamont Doherty Earth Observatory's NAO web page. The first figure shows positive phase with the Icelandic Low being deeper and Azores High higher than normal. The second figure shows the opposite phase.  Figure 1: Positive Phase of the North Atlantic Oscillation. from LDEO  Figure 1: Negative Phase of the North Atlantic Oscillation. from LDEO In a general sense, this type of oscillation, which is observed in both the northern and southern hemisphere, is associated with a redistribution of mass between the middle and high latitudes. (more info from the Climate Prediction Center) Remember, pressure at the Earth's surface is a measure of the weight of air above the surface. The oscillation, therefore, is also seen as up and down variations of pressure at the poles. When there is a pressure change on this spatial scale, the storm tracks change. They move north and south. Hence, we can also expect to see some large scale changes in temperature and wind--warming and cooling at the poles. This is a source of natural variability, which like El Nino-La Nina, has significant global signals. I will come back to how researchers have tried to "remove" these sources of natural variability in order to isolate trends. While the North Atlantic Oscillation and El Nino-La Nina are natural, this does not mean that they are independent of climate change. Climate models show that as the Earth warms there will be changes in variability; the period might change, or the Earth may spend more time in one phase than the other. In recent years the mode with low pressure over the North Pole and higher pressure in middle latitudes has been observed. The question arises is this natural, or is the more common appearance of this mode a consequence of forcing by increasing greenhouse gases, changes in stratospheric ozone, or some other process? ricky View (16) Comments For This Post
WEATHER and CLIMATE 1A
I'll try to answer a few of the questions from the last blog. Gravity waves --they are called gravity waves because it is the force of gravity that causes the wave-like motion. If you took an introductory course in meteorology then you should have seen buoyancy waves, which are a type of gravity wave. They occur when air which is a little cooler and heavier than the surrounding air is pulled down. The air overshoots a little, it's then warmer and lighter than the surrounding air, and it is lifted back up by the buoyancy force. I've adapted a picture from one of my lectures to try to make the idea more clear. Remember, as air rises it cools, as it sinks it warms, so it's the difference between the parcel's temperature and the background temperature that's important.  Figure 1: Schematic to demonstrate the role of gravity as a restoring force to a parcel of air. A basic concept in what makes a gravity wave. I want to go back to the figure I showed last time. For you who asked for the data and related figures--well, that figure was made a long time ago and I had to scan it. In the future I will see if I can put some digital information with the figures so you can play with the numbers. Back to the figure--I reproduce it below with some annotation that I hope makes is clearer. (Really, though I want to show Jeff Masters that I figured out how to do that.)  Figure 2: Wavelet analysis of north-south moisture flux at San Antonio, Texas. Since a couple of people asked me to clarify the picture a little bit. The wavelet analysis tells us what period oscillations are evident in the observations. So following the time axis it tells us that on, say, June 1 that the 4-8 day period wave was important. On, for example, August 1 the 1 day period wave was important. The one day period is labeled as the "diurnal time scale." The 4-8 day period is labeled as "baroclinic time scales." Baroclinic and synoptic are terms to describe the waves that are responsible for the ordinary highs and lows we associate with weather over the United States. I find it especially interesting to think about the diurnal period moisture flux and climate. The low level diurnal jet stream is confined in the lower couple of kilometers of the atmosphere and is responsible for a night time river of moist air into the Great Plains. It is bound to the west by the increasing altitude of the plains and, ultimately, the Rockies. It's tremendously important for summertime moisture, and those thunderstorms that excite WU devotees. Because it is to some extent defined and anchored by the topography, it requires pretty high resolution models to represent it. When I start to think about climate predictions that are good enough for water resource managers to use, I want to know how this low level jet, this climate mechanism, will change. I want to know if it will start earlier in the year and last later. Will it penetrate further into the continent? Will it transport more water because the Gulf of Mexico is warmer? More questions? Seriously, if you were in the position to have to use a climate forecast in your job or life to make a decision--what would you want to know? What would give you confidence in the information in the forecast? 1993? Do any of you remember what was special about the summer of 1993? ricky View (11) Comments For This Post
WEATHER and CLIMATE 1
I'm going to change gears a little bit. We've talked some about the planet warming and ice melting. My current research is how are weather and climate related? And, well, this is Weather Underground. (Gee, I just realized that that has a clever 1960's sort of subversion. I'm old and slow.) Okay. For many, many years I have been taught that the climate is the "average weather." But thinking about that, it's not really true. There are a couple of reasons. One, there are many features that are part of "climate" that are not weather. For example there are short waves in the atmosphere caused by flow over the mountains, that are very important to climate, but they drive weather forecasters crazy. They're gravity waves, if you want to look them up. The role of weather in the climate system is to transport stuff. Ultimately, the weather needs to transport an excess of energy at the equator to the poles. The sun places more energy at the equator at the poles, but in an approximate sense, the Earth emits energy to space about the same at the poles as at the equator. The atmosphere and the ocean carry that energy, heat, to the poles. The weather also transports water and momentum. I've studied transport for years, and if there is one thing that I have learned, it is that if you want to calculate how much stuff is transported by the atmosphere, you do not make that calculation by averaging. A lot of the motions in the atmosphere slosh stuff back and forth. For transport to occur there has to be something that interrupts this sloshing. Something has to happen in order for there to be irreversible transport. Something like wave breaking--there has to be something that dissipates the motion so that it doesn't simply return to where it started from. What's really important to climate is - how do the weather systems dissipate? How do these transport events accumulate? Climate is really more of the accumulation of weather than the average of weather. Here's a figure. It's complex and full of information. It may take several blogs to talk about it. At least two. This is a wavelet analysis of the north-south flux of water vapor at San Antonio, Texas. Some meteorologists call flux, "transport" but it is not. Flux is how much stuff goes by you. It might come back the other direction--flux is positive and negative.  Figure 1: Wavelet analysis of north-south moisture flux at San Antonio, Texas. Back to the Figure. On the horizontal axis is time. On the vertical axis is period in days, as in the period of a wave (Labeled on the right hand side). First you see the sloshing. The flux is first to the north (positive, red), then to south (negative, blue). It is also organized into periods. Through the month of May, there is a lot of activity in the 4-8 day period. These are the ordinary high and low pressure systems that we normally associate with weather, and take 4-8 days to cross Texas. Then starting in June this period stops, and there is the start of this short period, 1 day, oscillation. This is the flux associated with the low level jet in the Great Plains. Getting back to climate--these mechanisms, synoptic waves and the low level jet are important for carrying moisture to the continent, especially from the Gulf of Mexico. This is an important climate parameter. The mechanism of the transport changes with the season, and the seasonal transition is definitive. Seasonal transitions are part of the climate of a region. These mechanisms which are local in nature determine the regional climate and it is important to understand how these mechanisms will change with time. ricky View (15) Comments For This Post
WEATHER and CLIMATE 1
I'm going to change gears a little bit. We've talked some about the planet warming and ice melting. My current research is how are weather and climate related? And, well, this is Weather Underground. (Gee, I just realized that that has a clever 1960s sort of subversion. I'm old and slow.) Okay. For many, many years I have been taught that the climate is the "average weather." But thinking about that, it's not really true. There are a couple of reasons. One, there are many features that are part of "climate" that are not weather. For example there are short waves in the atmosphere caused by flow over the mountains, that are very important to climate, but they drive weather forecasters crazy. They're gravity waves, if you want to look them up. The role of weather in the climate system is to transport stuff. Ultimately, the weather needs to transport an excess of energy at the equator to the poles. The sun places more energy at the equator at the poles, but in an approximate sense, the Earth emits energy to space about the same at the poles as at the equator. The atmosphere and the ocean carry that energy, heat, to the poles. The weather also transports water and momentum. I've studied transport for years, and if there is one thing that I have learned, it is that if you want to calculate how much stuff is transported by the atmosphere, you do not make that calculation by averaging. A lot of the motions in the atmosphere slosh stuff back and forth. For transport to occur there has to be something that interrupts this sloshing. Something has to happen in order for there to be irreversible transport. Something like wave breaking - there has to be something that dissipates the motion so that it doesn't simply return to where it started from. What's really important to climate is - how do the weather systems dissipate? How do these transport events accumulate? Climate is really more of the accumulation of weather than the average of weather. Here's a figure. It's complex and full of information. It may take several blogs to talk about it. At least two. This is a wavelet analysis of the north-south flux of water vapor at San Antonio, Texas. Some meteorologists call flux, "transport" but it is not. Flux is how much stuff goes by you. It might come back the other direction - flux is positive and negative. Figure 1: Wavelet analysis of north-south moisture flux at San Antonio, Texas. Back to the Figure. On the horizontal axis is time. On the vertical axis is period in days, as in the period of a wave (Labeled on the right hand side). First you see the sloshing. The flux is first to the north (positive, red), then to south (negative, blue). It is also organized into periods. Through the month of May, there is a lot of activity in the 4-8 day period. These are the synoptic waves that are normally associated with weather. Then starting in June this period stops, and there is the start of this short period, 1 day, oscillation. This is the flux associated with the low level jet in the Great Plains. Getting back to climate - these mechanisms, synoptic waves and the low level jet are important for carrying moisture to the continent, especially from the Gulf of Mexico. This is an important climate parameter. The mechanism of the transport changes with the season, and the seasonal transition is definitive. Seasonal transitions are part of the climate of a region. These mechanisms which are local in nature determine the regional climate and it is important to understand how these mechanisms will change with time. ricky View (7) Comments For This Post
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