Your Questions: Carbon Power

Illustration of a carbon atom.

Life, heat, champagne and global warming, all courtesy of the carbon atom. NASA hide caption

itoggle caption NASA
The Keeling Curve i i

The Keeling Curve is named after Charles David Keeling, the first scientist to report that global atmospheric concentrations of carbon dioxide were rising. From the observatory atop Mauna Loa, Hawaii, Keeling began the first continuous record of global carbon dioxide in 1958. Oscillations in the curve represent seasonal fluctuations in carbon dioxide levels. Lindsay Mangum/NPR hide caption

itoggle caption Lindsay Mangum/NPR
The Keeling Curve

The Keeling Curve is named after Charles David Keeling, the first scientist to report that global atmospheric concentrations of carbon dioxide were rising. From the observatory atop Mauna Loa, Hawaii, Keeling began the first continuous record of global carbon dioxide in 1958. Oscillations in the curve represent seasonal fluctuations in carbon dioxide levels.

Lindsay Mangum/NPR

Send Us Your Questions

We want to know what your questions are on climate change. What issues would you like us to explore? What are you confused about? And what are your observations on climate change?

  

Some of the submitted questions may be answered on-air or on NPR.org... or they could be the start of a larger story. This is your chance to help us shape our coverage.

Chart Showing the Global Average Change in Temperature i i

Measurements of temperatures over the course of the 20th century show the planet, on average, has warmed by 1 degree Celsius. Temperature-change computer simulations only match up with observed temperatures if human activity, e.g. burning fossil fuels, is taken into account. The blue-shaded band, based on simulations that only take into account natural systems, such changes in the sun's output or volcanic eruption, falls short of the temperature change actually observed. Lindsay Mangum/NPR hide caption

itoggle caption Lindsay Mangum/NPR
Chart Showing the Global Average Change in Temperature

Measurements of temperatures over the course of the 20th century show the planet, on average, has warmed by 1 degree Celsius. Temperature-change computer simulations only match up with observed temperatures if human activity, e.g. burning fossil fuels, is taken into account. The blue-shaded band, based on simulations that only take into account natural systems, such changes in the sun's output or volcanic eruption, falls short of the temperature change actually observed.

Lindsay Mangum/NPR
Chart showing levels of carbon dioxide over the past 150,000 years. i i

The long-term record of atmospheric carbon dioxide obtained from Antarctic ice cores shows huge fluctuations over the past 150,000 years. Periods of low carbon dioxide concentration correspond to ice ages, while higher carbon dioxide concentrations are linked to warmer periods. Lindsay Mangum/NPR hide caption

itoggle caption Lindsay Mangum/NPR
Chart showing levels of carbon dioxide over the past 150,000 years.

The long-term record of atmospheric carbon dioxide obtained from Antarctic ice cores shows huge fluctuations over the past 150,000 years. Periods of low carbon dioxide concentration correspond to ice ages, while higher carbon dioxide concentrations are linked to warmer periods.

Lindsay Mangum/NPR

"The only constant is change," the Greek philosopher Heraclites once observed. Today, scientists who study climate might have something similar to say: "The only constant in Earth's history is climate change."

Since our planet formed some 4.5 billion years ago, its climate has seesawed — from hot to cold, from wet to dry — and often back again. And over the last 2 million years, humans and our ancestors have struggled to cope with these natural fluctuations. Often, we've successfully adapted, by developing new tools and habits or by fleeing to friendlier climes. Sometimes we failed... and died.

Now, for the first time, scientists say humans are not just trying to cope with Earth's climate, we are shaping it. Our everyday activities – from switching on a light bulb or driving a car, to clearing forests or planting crops — are adding vast quantities of carbon dioxide and other heat-trapping gases to the atmosphere, raising global temperatures.

We don't know for sure what this global warming will bring. But one thing is certain: Once again, our species faces having to adapt to a changing climate.

This year, NPR's Climate Connections is examining how climate changes people, and how people are changing climate. As part of the series, we'll be answering your questions. Below, we start with answers to a few of your fundamental queries, focusing on the prime global warming gas: carbon dioxide.

Q. The public needs a lucid explanation of how carbon dioxide warms the atmosphere. — Callan Bentley, Annandale, Va.

It's called the "greenhouse effect," but carbon dioxide (CO2) and the other gases that trap heat on Earth don't actually work exactly like the glass panes in a nursery hothouse. Here's the skinny:

First, the sun bathes the Earth in radiation. Some of that radiation we can see – visible light — and some of it we can't, like ultraviolet light.

When solar radiation strikes Earth, the atmosphere reflects some of it back into space. The rest is absorbed by the atmosphere or penetrates through to the surface, where it is absorbed by land and water. Think of how a paved parking lot or puddle of water warms on a sunny day.

Then — and this is key — the Earth beams part of that heat back up to space — in the form of infrared energy. But while the transparent gases in the atmosphere let incoming sunlight pass through (that's where the name "transparent" comes from) they absorb or trap some of the infrared radiation sent up by the Earth. This infrared energy heats up the gas molecules, which then release some of that heat, helping warm the Earth. (In a real greenhouse, this "re-radiation" doesn't play a big role — the glass simply traps the warm air in the greenhouse.)

Also, it turns out that different atmospheric gases have different abilities to trap and radiate heat. The four major warming gases are water vapor, carbon dioxide, methane and nitrous oxide.

Overall, water vapor plays the most important role in keeping the planet warm, but humans have little influence over how much water vapor is in the atmosphere. Carbon dioxide is the most important warming gas that we do influence, because we create it by burning fossil fuels, cutting or burning forests, and draining wetlands. We also help produce vast amounts of methane and nitrous oxide through farming and industrial practices.

Ironically, these greenhouse gases have helped make life on Earth possible; they've even given us those CO2 bubbles in our champagne and soda. But now, they could profoundly alter life as we know it.

Q. How far outside of the historical range for CO2 levels are we at this point? — Jim Foreman, Sacramento, Calif.

Pretty far. Scientists studying air bubbles trapped in ice cores have found that over the last 650,000 years, CO2 levels in the atmosphere ranged from about 180 parts per million (ppm) to 300 ppm. Just prior to Britain's Industrial Revolution, levels hovered at 280 ppm, according to the latest report from the United Nation's Intergovernmental Panel on Climate Change. CO2 levels had risen to 379 ppm by 2005, and are increasing at an average of nearly 2 ppm per year.

The trend is pretty similar for other major greenhouse gases produced by human activities. Methane concentrations have more than doubled from 715 parts per billion (ppb) in pre-industrial times to 1774 ppb in 2005. And nitrous oxide levels have spiraled from 270 ppb to 319 ppb.

Q: If the globe has been warming since the last ice age, and man has probably only been a potential contributor to climate change for the last 100 years, how is it that man is the greatest contributor to climate change? — John Folinsbee, Kamloops, B.C., Canada

Yes, it is true that Earth's history is full of climatic swings – including the switch from the last "ice age" 12,000 years ago to a relatively warmer period. But human activities played no role in those changes. Now, however, we know that people are influencing Earth's climate by adding massive quantities of carbon dioxide and other warming gases to the atmosphere. That's a whole new situation. But are human activities — burning fossil fuels, clearing land, releasing synthetic chemicals – now the "greatest" single contributor to climate change? That may be debatable. But it is clear that these activities are within our power to influence. Other factors, from changes in solar radiation to wobbles in the Earth's orbit, really are not.

Q. If we can put CO2 into the atmosphere, why can't we devise a simple way to filter it out? — Matthew Woods, Mansfield Center, Conn.

We might be able to. Scientists and engineers around the world are already exploring ways of stripping carbon dioxide and other greenhouse gases out of the atmosphere, and then "sequestering" those gases someplace where they can't re-escape into the atmosphere.

The technical and economic challenges are significant, however. For instance, one popular idea is to trap CO2 before it can escape smokestacks at coal-fired power plants, then pump it deep underground. But so far, the process costs more than many industries are willing to pay; it could add 50 percent or more to the cost of a typical electricity plant. And it is not yet clear how long the carbon gas would stay trapped below ground.

Another problem is that it often takes energy to run carbon-sequestering devices, meaning you may end up producing more CO2 in order to capture it. One solution is to use wind or water power to fuel the process. In general, though, many experts say sequestration is only part of the solution to reducing greenhouse gas emissions. Another key will be finding ways to not produce emissions in the first place.

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