Turn Off the Carbon Dioxide Emissions – It Still Gets Warmer

Published: 04:26 GMT le 12 décembre 2014

Turn Off the Carbon Dioxide Emissions – It Still Gets Warmer

I have a piece that went up today on a new-to-me website called The Conversation. It’s title is: What would happen to the climate if we stopped emitting greenhouse gases today? I try to explain with not so many words - if we stopped emitting carbon dioxide today, why does the temperature keep going up.

In this blog, I will provide some background material that might make things more intuitive for the weather-savvy crowd – or even the wine-growers amongst us. A couple of my previous blogs that I will call upon:

Still Following the Heat
Point of View

If you compare the climate and weather of, say, Kansas and coastal California, there are some distinct differences. Kansas has higher swings of temperature from summer to winter. In the summer, Kansas is often very hot and in winter it can be brutally cold. Along the California coast, such extremes are not as common. In fact, one doesn’t have to go all the way from the Pacific Coast to Kansas to find such extremes of variability. You only have to go, east, over the relatively small Coast Range of mountains in California to find larger swings of temperature. This is especially true in summer, when driving, east, from San Francisco, through Oakland, to Livermore you can go from quite chilly in San Francisco to over 100 degrees F in Livermore. That’s about 50 miles. (Does any one know what ever happened to Roderick’s BBQ? Prefer, local on-ground verification.)

One reason that the temperature variability on the coast is smaller is because of water. In our California example, the Pacific Ocean and San Francisco Bay are quite cold, and they are large enough to influence the temperature over the land for a few miles. By the time you get to Livermore, this moderating effect of the cool water is diminishing. Many of us have the intuitive feeling that large bodies of water moderate the temperature variability that we feel. That’s one of the reasons we like to go to the seashore or lake shore during the summer. Weather and climate scientists call this a marine, maritime or oceanic climate – from the American Meteorological Society (AMS) Meteorology Glossary “A regional climate under the predominant influence of the sea, characterized by relatively small seasonal variations and high atmospheric moisture content; the antithesis of a continental climate.” Another type of climate largely defined by oceanic moderation / modification is the Mediterranean climate, “Characterized by mild, wet winters and warm to hot, dry summers; typically occurs on the west side of continents between about 30° and 45° latitude.”

This moderating effect of water is reasonably well known. It doesn’t require a whole ocean. The same effect is seen in Great Lakes of the United States, which is, really, a coupled lake-land-atmosphere climate. And, of course, on even a smaller scale, people of Michigan have a huge summer lake culture, where to escape the oppressive 85 degree F days of August, they go to the less-than-great lakes that are throughout the state. (Keeping with a recent dubious theme Kid Rock. This pretty much explains at least one of my students.)

Getting to science, we understand that air and land heat up and cool down faster than bodies of water. There are a number of reasons for this. Both water and air are fluids, so when they get heated, there is the possibility of motion, which, ultimately, mixes hot and cold parts of the fluid. It takes, however, more heat to change the temperature of a mass of water than it takes to change the temperature of an equal mass of air. Or, for the same amount of heat, the air warms up faster than the water. Scientists talk about specific heat and heat capacity, and there are definitions, again, in the AMS Glossary, but I prefer Dictionary.com: specific heat is “the number of calories required to raise the temperature of 1 gram of a substance 1°C, or the number of BTU's per pound per degree F.” Generically, the amount of energy required to raise the temperature of a certain amount of mass of a substance a certain number of degrees. The specific heat of water is about 4 times that of air.

From a different perspective, if you take away the heat, the water takes longer to cool down.

Let’s stick with the more intuitive and experiential approach. I spent a lot of youthful time at the mouth of the Neuse River in North Carolina. Here we scooped soft shells, gigged flounder, developed our relationships with eastern diamond backs and stood in the water and felt the shock of distant lightning. (These are Southern things.) Later in life I spent 30 years on the shore of the Chesapeake Bay. One of the things you notice in these places is the slight shift of the seasons. The daffodils were a full two weeks later on the Bay than up in Greenbelt, MD, just 20-30 miles away. In the autumn, frost was reliably two or more weeks later on the Bay. Though we often think of the moderating effect of bodies of water in weather and climate, I want to use this experience as a bit of a re-framing. Specifically, the role of the Chesapeake Bay in autumn and winter is to warm the air. The effect is large enough that it matters to the people within a small number of miles of the shore. This is a case where the water had been accumulating heat all summer. Then in fall, when the air temperature fell below the water temperature it became a source of heat to the air. A really neat thing was to walk into a rough bay or river in late October and early November and feel how warm it is. (Rough needed to mix the warmer, deeper water, with the cooler water at the surface.)

The point here, there were situations when the heat in the water, in concert with the contrast between air temperature and water temperature, the heat from the water starts to warm the atmosphere. Look around and you can find examples on this at many different spatial sizes on many different spans of time. In a paper with my student Evan Oswald, we found that on hot days in Detroit, the presence of Lakes Huron, St. Clair and Erie kept downtown Detroit cooler than the inland suburbs in the hot part of the day, but warmer at night. Again, here is a moderating perception to people, caused, in part, by the water heating the air at night when the air temperature was low.

Let’s take this to the global scale. Energy comes from the Sun and heats the Earth. Our “extra” carbon dioxide holds a little more of that energy near the Earth’s surface than compared to, say, a 100 years ago. Some energy goes to heat the land surface and the air. Energy goes into melting ice – sea ice, glaciers and ice sheets. Most of the energy goes into the ocean, increasing the heat content of the ocean. Though most of the energy goes into the ocean, because of the large mass of the ocean, the mixing of ocean, and relative to air, the large specific heat, the temperature of the ocean takes a long time to increase. In this way the ocean actually moderates the air temperature – or, without the ocean, the Earth would be heating up a lot faster. Alternatively, the ocean is taking heat from the atmosphere. (Without the ocean, we also would be less likely to have things like The whole silly warming pause, warming hiatus thing.)

We are already seeing now, in 2014, how a relatively small change in the ocean surface temperature related to a weak, almost El Niño is leading to record surface air temperatures. This is a case of the ocean heating, relatively to last year, the atmosphere. In fact, reaching back to Ocean Hot and Hotter Still, I cite “Oceanic influences on recent continental warming,” that appeared in Climate Dynamics. This paper concludes that much of the “recent warming” observed on land can be traced to heating from the ocean. "Recent" in this paper is, more or less, the last half of a century, fifty years. The authors trace the heating of the land to increases of heat in the ocean.

I have tried to establish an intuitive and experience-based demonstration of the role of large bodies of water in the determination of air temperature. I have described an example, my experience at the coast during autumn, where as the heating by the Sun decreases, the heat from the water serves to warm the air. On a global scale, we are at this very moment living the fact that warming water in eastern Pacific Ocean is pushing the global-average surface (air) temperature to record highs. Therefore, it should logically follow that if we were to stop our emissions of carbon dioxide, thereby stopping the increase of energy being held at the Earth’s surface, that the energy being stored in the ocean will serve to heat the air and continue to warm the Earth’s average surface temperature, until a balance is reached.

I want to end by introducing the role that Point of View plays. Because we are most interested in how climate affects us, we are most interested in the surface air temperature, especially over land. You can imagine, that if you were in space studying the Earth, rather than surface air temperature being your primary focus, you might focus first and foremost on what is happening in the ocean. We would, then, not think so much of the ocean’s ability to heat the air, to increase the average surface temperature. Rather you would think of all of the heat stored in the ocean maintaining the planet in a more or less stable climate, with fluctuations in air temperature. Then the air temperature could be viewed as a low heat capacity envelope around the ocean that amplifies ocean temperature variability. Then, in our thought experiment of the carbon dioxide emissions halting, we would be seeing the atmosphere catching up with the more stable, perhaps more important ocean. It is our presence, our point of view, that makes the surface air temperature the important parameter, that frames our thinking of the ocean catching up and “heating” the planet.

Have a look at What would happen to the climate if we stopped emitting greenhouse gases today?

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Figure 1: Simple Earth 3: Some basic ingredients of the Earth’s climate. There is heat going into the ocean. Ultimately, there is exchange of heat between the ocean and atmosphere. The same amount of heat in the atmosphere has a larger impact on temperature, than in the ocean. (This is simple Earth, so this is vastly over simplified heat transport.)

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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.

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