Friday, March 21, 2014

Climate Change: Part 3 Earth Energy Balance

Note: This program first aired on March 15, 2014.

The first thing we need to understand about the Earth’s climate is that it is the result of a balance, what is called the energy balance. When the same amount of energy comes in that leaves, the system is in balance and the average temperature stays the same.  If more energy leaves the system than comes in, the net amount of energy decreases, and the system cools. If more energy comes into the system than leaves, energy builds up and the average temperature rises. Its like your household budget. If you spend more money than you make, your savings account gets smaller. If you save more than you spend, your savings account gets bigger. If you spend what you make each week, no more, no less, your savings account will stay the same.  Earth’s climate works the same way. For the past 10,000 years or so we’ve been in equilibrium, or balance. The energy in has equaled the energy out, and the overall average climate has been stable. We are in a situation now however where we are taking in more energy than we are giving out, and the climate is out of equilibrium. The temperature will shift until the system is back into equilibrium, in this case, it will warm until the inputs and outputs are back in balance.

Recall if you will the law of the conservation of energy: energy is neither created nor destroyed, but it can change form. What is the source of energy that comes to Earth? The source of the energy that Earth runs on is the Sun. The sun’s energy comes to us in the form of visible light. About 30% of that light is immediately reflected back away from Earth as light, and plays no part in the climate system. It bounces off clouds in the atmosphere as well as brightly reflective surfaces on Earth that have what is called a high albedo, or reflectivity, things like snow, ice, light colored desert. That energy that is reflected doesn’t change wavelength, it arrives as visible light and it leaves as visible light. The other roughly 70% of light however enters the Earth’s climate system by getting absorbed by the atmosphere and the surface of the Earth. After getting absorbed, it is reradiated back out as infrared radiation aka heat. Infrared radiation is a longer lower energy wave length, and is not visible to us, but we can feel it. For thermal equilibrium, the Earth would need to reradiate all 70% of that incoming energy back out. The lag time it takes between the light coming in, and the infrared going back out is what creates an average global temperature greater than absolute zero. While that infrared radiation is making its way back into space, its heating up rocks and water and air and gasses in the atmosphere, which then reradiate the infrared radiation back out again.

Of that 70% of the Sun’s energy that makes it into the climate system, 23% is absorbed by the atmosphere. When that energy is reradiated back out, it goes in all directions, some back into space, some towards Earth. The Earth’s surface absorbs the other 48% of energy directly from the Sun (23+48 = 71, or the about 70 % total). A great deal of that energy actually goes into non sensible heat operations. The first and largest is evaporation. Water absorbs the light energy, but since water has such a high specific heat, it takes a lot of energy before the water actually changes temperature. 25% of that energy hitting Earth goes into simply evaporating water. Heat is still moved, in fact evaporation is major component of moving heat around the climate system, but its not like we feel it like we do when we stand next to the woodstove. The next 5% is moved via convection. The heat is moved not by radiation but physically by air warmed by contact with the warm surface of the Earth. The air rises into the atmosphere taking the heat with it. Its only the last 17% that actually gets reradiated back towards space as infrared radiation, and this is where the tally sheet doesn’t balance. Of that 17%, only 12 ultimately makes it back into space. The remaining 5% is left to build up here in the climate system. And when not everything that comes in makes it back out, we have a system out of equilibrium. The only way for a system to get back into equilibrium is for it to shift. That’s what’s going on now.

Next week we’ll take a look at how the pieces of the climate system work together, and why heat is building up here on Earth.


Your tax dollars at work: The NASA Earth Observatory website is a wealth of great earth and sky science. This page on the Energy Budget is very helpful and full of details I couldn’t cover here:

Climate Change: Part 2 How Science Works

Note: This program first aired March 8, 2014.

It’s the nearing the end of winter (we hope), and most of us in North America are sick of the cold, I know I certainly am, and I love winter! Taken in this context, a warmer climate doesn’t sound that bad. Maybe you or some one you know has even questioned how “global warming” (as it is called in the popular literature) can be real if we are having such a cold, hard core winter. Actually, global warming is a misnomer. The warming part refers to the increase in mean or average global surface temperatures, but that is just an average. We can average both 0 plus 10, and 4 plus 6 and get 5 each time. The range between 0 and 10 is much greater than the range between 4 and 6 yet both data pairs tell us the same story when averaged together. Averages are necessary when looking at climate, because climate is a global phenomenon, the result of a global system. The Earth has warmed approximately 0.7 degrees C (or 1.25 degrees F) in the past 100 years. But don’t let the average warming lull you into the dream of the end of winter, while its likely that winters may be getting milder, more heat in the climate system ultimately means more instability, and more chaos in weather patterns. This instability can mean things like what happened this winter, with the polar vortex wandering south, are also likely.

At least if you are questioning the veracity of climate change this winter, you are doing so based on evidence, the evidence being its cold! How can this be a sign of global warming? I applaud you for looking around and actually observing what is happening in the world around you, and making connections to things you have heard are supposed to be happening. The problem is, climate isn’t quite that simple and as a result, we shouldn’t really be calling it global warming. The phenomenon is global in scale, and most of us operate on a human sized scale of observation. So where you are at any give moment (or many many moments this winter), may seem colder than usual, that doesn’t mean that on average, Earth isn’t warming up, it is.

The hardest conversations to have are those with people who don’t “believe” in climate change. Not believing in climate change is sort of like not believing in gravity. Its not believing in how science explains things in the world. Not believing in how science works is always a choice, but people need to understand the implications of that choice. Science seeks to explain natural phenomena through observing, collecting evidence, testing and establishing attribution or cause and effect.

Sometimes science misses the truth because it isn’t asking the right questions, or asking enough questions. That isn’t the case this time around. There are so many scientists working so hard on this issue, from so many different angles; we’re not missing any big picture components. There is so much evidence that has been documented, about how the climate system works, what makes is shift, how it shifts, how fast it shifts. There is a lot we don’t know in this exciting field of inquiry, but the big picture mechanisms of the climate system are well established.

So do me a favor, and when you want to have a conversation about climate change, don’t start it with anything having to do with belief. While there are philosophical discussions to be had about any topic, including climate change, whether or not it is happening and whether or not it is being caused by our carbon dioxide emissions is a question for science. If you want to deny climate change, you need to do so based on evidence, and good luck with that, because the evidence is pretty overwhelming! And by evidence I don’t mean what the talking heads on CNN or NPR or Fox News or some nutty lady on community radio says. Get as close as you can to the source, the people doing the investigating. They are the ones in the trenches, looking at this day in and day out. And I’ll tell you, they are pretty alarmed with what they are learning.

We’ll look more at the climate system and what scientists are finding so alarming in the coming weeks.

There is SO MUCH information out there on the web about climate change, but some of the nicest and most concise is from NASA’s Earth Observatory:

Climate Change: Part 1 Introduction

Note: This program first aired March 1, 2014.

Its time for another series here on the World Around Us, so the next big thing we’re going to spend a few weeks talking about is something that is happening to the world around us. That big thing has the potential to change where a billion of us live, where and how we grow our food, where it rains and where it doesn’t, how ocean currents circulate around the globe, or not, what can even live in the ocean. In short, this phenomenon stands to transform the world beyond the experience of any of us, of any human being that has ever lived. I’m talking of course about climate change, and we’ll spend the next several weeks looking in detail at science behind this multi faceted phenomenon.

Climate change simply refers to a change in the overall global average temperature and the associated shifts in weather patterns that accompany the change. The Earth’s climate has changed many, many times over the course of Earth’s history, generating climates both colder and warmer than what we experience, on average on Earth today. These shifts typically take thousands of years. There are various reasons the climate changes, for example the intensity of the sun has changed over time, the Earth’s orbit and thus distance from the sun varies, the processes of plate tectonics move the continents around which changes ocean and atmospheric circulation and thus heat distribution patterns, the composition of the atmosphere has changed, climate has even been effect by extra terrestrial objects. For the past 2 million years, the Earth has experienced, not a steady temperature, but a consistent pattern of alternating average temperatures, with cooler periods that resulted in long stretches of glaciation in the northern hemisphere, alternating with warmer periods, during which time the glaciation receded. We’re in one of those warmer in between glacial periods now. But instead of cooling back off and plunging the northern hemisphere back into ice, evidence points to a small increase in average temperature having occurred already, and puts us on the brink of larger increases in the near future. We are perhaps leaving this ice age pattern and moving into a different climate regime.

It should be clear then, that climate change is a normal occurrence on Earth. What is all the fuss about then? Because, just as we have loads of evidence about how climate has changed in the past 500 million or more years, we also have loads of evidence about what the consequences of those climate changes have been. What we find is that rapid and dramatic climate change represents an existential crisis for most living organisms. Rapid changes in climate often accompany mass extinction events, when 60, 70, 80, 90% of families of organisms disappear from the fossil record. So that dear listeners, is the thing to be worried about. If you like how things are on this planet currently, be aware, things are likely to change, not quite on the time scale of your life, but possibly not too much longer than that. The processes of evolution have done an amazing job of repopulating the Earth after these mass extinction events, in fact evolution seems to happen most rapidly when the physical environment changes. Knowing that, I have no doubt that life on Earth will go on and even flourish. No, climate change is ultimately an existential crisis for us. Humans have evolved in a very narrow window of relative climate stability, and all of what we would call the development of agriculture and modern civilization has occurred in this briefest of moments in this interglacial period. As far as we know biologically, its only ever been about this warm, or colder, in our evolutionary period. Its never been warmer, and warmer is where it appears we are going, fast. While the Earth has certainly been there before, we never have, and that reality could have serious consequences.

Join us in the coming weeks as we attempt to explain the science of what is happening, how we know what we know, where all this might be headed and what we can do about it. It’s a topic laden with emotion, political and economic baggage but I think you will find, the science is fascinating. From that point of view, we are truly living in interesting times.