Long Waves, Short Waves, And Heat Waves: CU Researcher Explains Weather And Climate
For the last two weeks, the Front Range has experienced over 90-degree Fahrenheit temperatures daily, but this is not due to global warming. Colorado is amidst a high-pressure system.
"People tend to think of last week's weather, right? What you have is a warming planet, but regionally and from day to day, there's always going to be variation: that's what we call 'weather,'" said Dr. Mark Serreze, an Arctic climate scientist at the University of Colorado, Boulder and director of the Cooperative Institute for Research in Environmental Sciences (CIRES) National Snow and Ice Data Center.
Right now, Colorado is experiencing a heat wave. A meandering jet stream is partially the cause.
The jet stream is a fast-moving current of air in the atmosphere, circling the globe like a hula hoop. Earth has a few hoop-shaped jet streams. In Colorado, we are impacted by the polar jet stream to the north and the subtropical jet stream to the south. As the jet streams circle the world, they tend to wobble — or meander — bringing warm air north and cool air south.
A wobble in the jet stream can cause a heat wave, and this is normal.
"We've always had them. We'll always have them. They'll always happen in the future," Serreze said. Heat waves are localized and temporary.
To get a grasp on what we call "global warming," we need to zoom out in both time and space, to consider our entire globe over thousands of years. On this scale, Earth naturally goes through warming periods and cooling periods. The last ice age ended approximately 12,000 years ago. Glaciers have been receding ever since.
What makes our current global climate situation unique is the rate of change. Arctic researchers are seeing glaciers recede at alarming rates. Changes that used to take thousands of years are happening in mere decades.
Serreze began his career in the 1980s, when the Arctic was white and covered by snow and ice.
"Thirty years ago, the Arctic was an Arctic that the explorers of the 19th century would have been very familiar with. They would have said, 'This is my Arctic.' But now it's something very different," he said.
Earlier this summer, a town north of the Arctic Circle in eastern Siberia reached 100.4 degrees Fahrenheit. This record high temperature is associated with a heat wave. Here we witness the intersection of a localized event and a global change: when we gather temperature readings from around the globe and compare them to past averages, the trends are clear. The globe is warming faster than it has in the last 12,000 years.
"You cannot deny what the data show. The data show that the globe is warming. That is unequivocal," Serreze said.
Luckily, scientists understand why Earth is warming so quickly. Now may be a good time to brush up on your own understanding. We will begin with some basic physics about light and atoms. We'll tie physics into our atmosphere, and finally, wrap back around to the Arctic.
The first thing we need to understand is wavelength, specifically the wavelengths of light.
Standing on a beach looking out at the surf, you can see the crests of each wave poking up out of the water as the waves move towards the shore. A wavelength is measured by the distance from crest to crest.
X-rays, UV light and the colors purple and blue have shorter wavelengths. Radio waves, microwaves, infrared and the colors red and orange have longer wavelengths. We can't see wavelengths shorter than purple or longer than red. Infrared radiation, also known as heat, is made of wavelengths just longer than the color red.
"You turn on a stove, an electric stove, it'll start to glow red. Now, it's emitting radiation. Some of it in the visible because you see it. You see the red, but most of it is not quite in the visible," said Serreze.
Absorption and Emission
Next, we need to understand absorption and emission. A pan on the stove will absorb heat from the flame underneath it; this is heat transfer. Absorption and emission are more nuanced at the atomic level.
Let's take a neon atom as an example. The light from a lit-up "open" sign in a gas station window is made by filling a glass tube with neon gas and putting a charge across it. Some energy from the charge is absorbed, and due to the specific structure of the neon atom, orange light is emitted. Hydrogen gas gives off red, and helium gas gives off yellow.
"The whole idea of how certain molecules absorb and emit radiation — that's longwave radiation, shortwave radiation — this is a very, very mature science. Anything from your microwave oven to heat seeking missiles depends on understanding this particular science," said Serreze.
Now, we can turn to Earth's climate.
"The energy that comes from the sun, almost all of it is what we call 'shortwave.' And it's in the visible spectrum. It's the light that we see. Our eyes have evolved to sense that," said Serreze. "The shortwave radiation that isn't reflected away by clouds, isn't reflected away by the surface, gets absorbed by the surface."
Shortwave radiation absorbed by the surface can be transformed into longwave radiation. This is what's happening when asphalt feels hot on a sunny day.
"The surface now heats up, and it emits long wave radiation upward. Some of that longwave radiation just escapes into space, but some of it is absorbed by the greenhouse gasses," Serreze said.
We hear the term "greenhouse gases" a lot, but what does it mean? It's directly related to absorption/emission.
Our atmosphere is about 80% nitrogen and 20% oxygen, but there are trace amounts — like 0.005% — other gases, including gases that contain carbon: carbon dioxide and methane.
Just like neon emits orange and hydrogen emits red, "there are certain gasses that absorb what we call infrared or longwave radiation emitted from the surface," explained Serreze. Remember, infrared radiation is also known as heat.
"Oxygen doesn't do that. Nitrogen doesn't do that. Argon doesn't do that. But those certain gasses, very important, carbon dioxide, methane; it is these particular gases and they basically absorb this infrared or longwave radiation in particular wavelengths," Serreze said.
It is like these gases are playing tennis with the earth. Infrared radiation is the ball, and the more tennis players there are on the other side of the court (in the atmosphere), the harder it is to get a ball past them. These gases — carbon dioxide and methane — are the tennis players we call "greenhouse gases."
The amount of greenhouse gas in our atmosphere is directly proportional to how warm the planet is. Without these gasses, the earth would be too cold to inhabit.
Serreze says that the earth can cool itself by releasing radiation, but, "If you've got more energy coming in than going out, you've gotta warm up. You can't get around it."
Sometimes a tennis player will walk over to the earth's side of the court, but it doesn't stay there for long. We call this the carbon cycle.
"Plants draw down carbon dioxide from the atmosphere to grow. They release it back to the atmosphere when the plants die and rot. There are big fluxes of carbon dioxide from the atmosphere to the ocean, the ocean to the atmosphere. There are huge transfers going on, but the levels keep going up and that's us," said Serreze.
If atmospheric carbon dioxide was locked exactly as it is today, we'd still get a little warmer, but then plateau.
"It's warming that they call 'in the pipeline.' But we'd equilibrate at a higher temperature. If you continue to add carbon dioxide to the atmosphere and kept doing it and kept doing it, yeah, warmer and warmer and warmer, and that's where you don't want to go. Some warming we can live with. A lot of warming? That's going to be a problem," Serreze said.
In the 1980s, climate scientists predicted that the warming of the Arctic would signal if their theories were right. So far, they've been right.
The Arctic is warming more quickly than the rest of the globe. Serreze says there are two reasons: "One of them is simply feedbacks in that the Arctic has a lot of snow and ice and that is white; it reflects most of the sun's energy. But as the Arctic warms, you lose that snow and ice cover and now you start to absorb more solar radiation, because the surface is darker and that warms it up more."
As Arctic snow and ice melts, the earth's surface becomes exposed. In the Arctic, this surface layer is called "permafrost."
Here's the second reason: "A lot of carbon is locked up in that permafrost, in things like old peatland," said Serreze. As the Arctic warms, "you start to thaw that permafrost, and the microbes in the soil start to become active. They eat the carbon, and what do they breathe out? Carbon dioxide or methane."
This carbon will be released into the atmosphere, further increasing the amount of carbon-containing gases.
We don't know exactly how much carbon is currently trapped in the permafrost, but Serreze said, "The estimates of how much is there seem to keep going up, but it's something like twice as what is in the atmosphere today that's locked up in these peatlands as carbon."
What Does This Mean For Our Planet?
To get some perspective, we can compare Earth to Venus . It's about the same size and also has an iron core and an atmosphere.
Venus is closer to the sun but absorbs less than a quarter of the sun's radiation. It reflects the rest with dense cloud cover. Earth absorbs almost half of the sun's radiation. Our atmosphere is ~0.005% carbon dioxide. The atmosphere on Venus is ~96% carbon dioxide.
Three missions to Mars are planned to launch this July (two of which were built in collaboration with CU Boulder). We hardly ever hear of a mission to Venus. This may be because probes sent to Venus tend to break down from the extreme heat; scientists think the surface is about 880 degrees Fahrenheit.
Serreze doesn't believe that a carbon tax is the right fix for global warming. As a professor, he said that education followed by a cultural paradigm shift is what needs to happen.
"If we're going to beat it, we have to change the mindset," he said, adding that when he began his career as a climate scientist, "it took a lot of evidence, scientific evidence, to even turn me to see it. I was actually kind of a skeptic at one point, but that's what scientists are supposed to be, right?"
Serreze says that what's important is, "recognition that we've only got this one planet. We've got nowhere to go."