What Does 'Carbon-Neutral' Really Mean?

A segment on KCET's award-winning TV show "SoCal Connected" has been produced in tandem with this story. Watch it herenow.

Protesters clogged the streets of New York City on Sunday in the largest march ever focused on the threat of climate change. The People's Climate March in Manhattan, with at least 100,000 participants, is just the latest piece of evidence that more and more people are worried about our warming world. As our concern over climate change mounts, environment-savvy entrepreneurs and others are looking for ways to shift the way we run our society to have less of an impact on the climate.

As businesses start looking for ways not to affect the planet's natural carbon cycles, the phrases "carbon-neutral" and "carbon-negative" have increasingly become industry buzzwords. They're shorthand used to describe that goal of putting fewer greenhouse gases into the atmosphere, or none at all. But what do they really mean?

At first glance, they seem simple. "Carbon-neutral" means that whatever you're doing, making products or shipping them or whatever your business does -- we'll call it a "widget" for simplicity's sake -- you're not adding any greenhouse gases to the air. A carbon-negative widget actually causes greenhouse gases to be removed from the atmosphere. Both are great goals, but it turns out they're not so simple to describe.

The Natural Carbon Cycle

To understand the way your widget affects the planet's natural carbon cycles, we first have to understand what those cycles are. And those cycles are complicated, but they all have their basis in the process that makes life as we know it possible. That process is photosynthesis, the means by which plants create food out of sunlight, air and water.

Without green plants and their forerunners, the cyanobacteria (once called blue-green algae) that first evolved photosynthesis, there would be a whole lot more carbon in the atmosphere than there is now, and the planet would be much warmer. But those ancient cyanobacteria hit on a unique survival strategy: use the energy of the sun to turn carbon dioxide and water into sugars, which are then used to build starches and even more long-lived carbon compounds like cellulose, thus taking that carbon out of the atmosphere -- at least for a while.

That "at least for a while" is a key point. Some of the carbon stored by plants stays stored for just a few hours: when the sun goes down, plants start burning sugar for energy just like us animals do, and they "exhale" carbon dioxide through the pores in their leaves. Some of the carbon is stored for a few weeks, as annual plants grow, die, and decompose, or for a few years in the case of perennial plants. Sometimes the carbon sucked out of the atmosphere gets locked away for centuries or even millennia, as for example the carbon that gets used to build the trunks of long-lived trees.

Even as plant material dies and begins to release its carbon, the rest of the living world can keep a small amount of it from getting back into the atmosphere quite so quickly. About 18 percent of your body weight is carbon, which means a 200-pound adult is carrying around about 36 pounds of carbon in the form of organic compounds such as fats. That 36 pounds of sequestered carbon means 132 fewer pounds of carbon dioxide in the air. (A molecule of carbon dioxide, with its two oxygen atoms, is significantly heavier than a carbon atom alone.)

Carbon also gets stored in soils as humus, in ecosystems like cryptobiotic crust in the desert and peat bogs closer to the poles, and in the constant rain of calcium carbonate -- the bones and exoskeletons of sea life that drizzles down to the floor of shallow seas, eventually forming limestone, which can then lock up its carbon for hundreds of millions of years in rock formations.

And of course, some carbon gets locked out of the atmosphere as fossil fuels, deposits of coal, oil, and natural gas stored in underground deposits. The amount of carbon turned into fossil fuels each year is vanishingly low, but when you have a planet that's been making a very small amount of fossil fuels each year for about 360 million years, that adds up.

What human society has been doing in the last century has been to take a large amount of that fossil fuel carbon, some of it kept out of the atmosphere since before there were dinosaurs, and setting it on fire to capture its energy -- releasing that millions-years-stored carbon into the atmosphere.

But we've also been messing with the planet's carbon cycles in ways that don't necessarily involve burning oil, coal, and natural gas. Agriculture accounts for about a tenth of human society's greenhouse gas footprint, and much of that tenth comes from increasing biological sources of atmospheric carbon: decaying vegetation in fields, disrupting the natural carbon sequestration of soils, and the always popular cow farts.

Life-cycles

Because the planet's natural carbon cycles are so complex, with so many different factors influencing them, you have to do a whole lot of thinking to determine whether your widget is carbon-neutral or carbon-negative.

You'd think it would be straightforward, a matter of asking two questions: "How much carbon is released into the atmosphere when we make the widget?" and "how much when the widget gets used?" Both questions are important parts of assessing a widget's carbon footprint. You might have a factory that builds widgets without using any fossil fuels or releasing any greenhouse gases, but if those widgets are gasoline-powered SUVs, they aren't going to be carbon-neutral. The same might be true for a hypothetical factory that builds solar panels, but which runs off electricity from an inefficient coal-fired power plant. Those solar panels may well generate carbon-free electricity, but it would take a whole lot of them to make up for the carbon spilled into the atmosphere by the factory power plant.

Seems straightforward enough. But for a fair assessment of your widget, you really need to consider a few other factors.

First off, what is your widget used for? Orange County-based Newlight Technologies creates a form of plastic they call Air Carbon, made from greenhouse gases such as carbon dioxide and methane in a process that uses biocatalysts. From the plastic's feedstock (those greenhouse gases) to the finished plastic product, the process actually seems to take more greenhouse gases out of the atmosphere than it puts in from the energy the process uses.

So Newlight's plastic would seem, on the face of it, to be carbon-negative. But let's say that plastic made by a similar process was used to make disposable foam clamshell containers used by a fast food chain. (Newlight's plastic isn't: it's mainly used for durable items. But let's use the clamshell as a hypothetical.) The clamshell's carbon footprint doesn't end once it leaves the factory: it also bears some "responsibility," for lack of a better word, for allowing the fast food chain to sell its products. One could reasonably wonder whether the clamshell's climate footprint should include at least some of the greenhouse gases spewed into the air by vehicles idling in the drive-through, or released by the feedlot cows who become the ground beef in the hamburgers inside the clamshells.

We also have to think about how the widget ends its useful life. Can it be reused or recycled, further reducing the impact the materials in it have on the environment? Can it be composted, potentially adding the carbon in it to a healthy soil? Or will it end up in a landfill, potentially adding to the methane leaking into the atmosphere?

Looking at every aspect of a widget's life from its manufacture to its use to its ultimate disposal is called a "cradle-to-grave analysis," and that kind of analysis is crucial in assessing a widget's climate footprint. Sometimes the impacts are direct, like the gasoline the above-mentioned green-factory-built SUVs burn. Sometimes the impacts are less direct and hard to evaluate, as in determining how much blame for cow methane those clamshells ought to bear. But looking at everything from a widget's water use (pumping water takes energy, which can mean greenhouse gas emissions) to factory worker commutes to how much energy gets used shipping widgets back and forth is necessary to get a true picture of that widget's climate footprint.

Offsets

Some companies claim carbon-neutrality or -negativity based on their funding climate-beneficial projects to make up for the greenhouse gases they emit. Such outside projects used as mitigation for greenhouse gas emissions are commonly called "offsets," since they're used to offset the emissions of the person or company who buys them.

Some examples of offsets include tree planting, landscape conservation (especially of forests and other carbon-sequestering habitats), developing renewable energy capacity, or paying other companies to reduce their own emissions.

Offsets are both widely used and highly controversial. In theory, they're a sensible strategy: reductions in greenhouse gases anywhere on the planet benefit the rest of the world, and projects to reduce carbon emissions or take it out of the atmosphere can often benefit from outside funding. But some environmentalists criticize offsets for the fact that they enable companies to continue on with business as usual, not taking serious measures to reduce their emissions but instead writing a check to cover their corporate consciences.

There are less intangible problems with offsets as well. Tree-planting projects are nice, but their benefit to the climate isn't always easy to figure out. Unless they're tended carefully most newly planted trees die, meaning their climate benefit is negligible. Some trees don't take up all that much carbon for several decades after planting, and the ones that do are often invasive plants like eucalyptus and Monterey pine.

In fact, there's evidence that very old trees may soak up a lot more carbon dioxide than young ones. Which means that the common practice of claiming tree-planting projects as climate offsets for old-growth logging projects may not make any sense at all for the climate.

There are similar issues with regard to funding renewable energy projects as offsets. Again, green energy can be just fine, but whether it's useful as an offset depends largely on 1) whether the renewable energy project would have been built anyway, and 2) whether that project actually replaces a fossil-fueled power plant instead of just adding more energy to the grid as our power consumption climbs.

So, the upshot: being carbon-neutral or even carbon-negative is a fantastic goal, and there are people working in good faith to find ways for our society to get there as a whole. But in a complex world where oversimplified claims are great for selling widgets, it's best to take such claims with a grain of salt -- which, after all, contains no carbon.