Episode #2 is the second half of Markham’s interview about climate science basics with David Herring, director of communication and education for NOAA (National Oceanic and Atmospheric Administration), a US government science agency whose work focuses on the oceans, major waterways, and the atmosphere.
Herring is a science writer and editor trained in journalism, science education, and science communication. Before joining NOAA in 2008, he worked for 16 years in the Earth Sciences Division at NASA’s Goddard Space Flight Center, where he served as Project Manager for Education and Outreach. He is an elected Fellow of the American Association for the Advancement of Science (AAAS).
Below the video, readers will find a transcript and links to climate science websites.
David, thank you very much. And we’re going to do episode number two of our climate one-on-one series today, and we’re going to be talking about carbon dioxide. So why is CO2 central to global warming?
David : 00:22
CO2 is central to global warming in…I’d like to use an analogy to sort of explain if solar energy is the fuel that powers the earth furnace and carbon dioxide, it’s like the thermostat that changes or is temperature setting up and down climate scientists have understood for more than a century that increasing the amount of carbon dioxide in the atmosphere would cause the globe to warm. We see unequivocal evidence of that, the relationship between carbon dioxide and temperature in the ice core data record going back more than 800,000 years.
Where is that CO2 coming from?
David : 01:06
Today the increase in atmospheric carbon dioxide is coming mostly from human activities, including burning fossil fuels, like coal, oil and natural gas. As well as, a large amount is coming from cement production and a large amount coming from biomass burning, such as in deforestation, as well as other large scale land-use changes.
How do scientists know when they’re measuring the CO2 concentrations that a carbon atom came from a fossil fuel as opposed to some other source?
David : 01:43
That’s a good question. By monitoring changes in carbon isotopes in the atmosphere, scientists have shown that the rapid build-up of carbon in the atmosphere is coming primarily from burning fossil fuels. Specifically, they’re observing an increase in the abundance of carbon 12 compared to carbon 13 in the atmosphere. Now, that may sound like jargon to your listeners. So let me explain. There are three types of carbon atoms called carbon isotopes. They differ from one another and that they have different numbers of neutrons in their nucleus. They all have six protons, but they may have seven neutrons or eight neutrons or six neutrons. We know that carbon 12 and carbon 13 are stable carbon isotopes, meaning they do not radioactively decay over time. We know they’ll always remain carbon 12 and carbon 13 respectively.
David : 02:41
We also know that plants prefer carbon 12 over carbon 13 during the photosynthesis process. And so they take in much more carbon 12 during photosynthesis. And when they photosynthesize they’re taking those carbon atoms and using them to build plant structures. And so over millions of years, when the plants die or leaf litter falls to the ground, there are many billions of tons of plant structure falling to the ground where it gradually fossilizes, hence the term fossil fuels. That’s where coal and oil come from. And this is made up mostly of the carbon 12 atoms in fossilized form underground. So as humans, mine and burn more fossil fuels, we’re basically taking all that and putting it back up into the atmosphere. And so by monitoring this change in the ratio of carbon 12 to carbon 13, it’s a clear indicator that the increased carbon is coming from burning fossil fuels and biomass burning by humans.
Final question for you. What other gases are responsible for global warming?
David : 03:56
As I said earlier, a lot of the focus is on carbon dioxide because we put so much of it into the atmosphere, but there are other heat-trapping gases such as methane. Methane is a concern as well because it too has a complex molecule and so it’s even more efficient than carbon dioxide. It’s about 30 times greater in its heat-trapping capacity than carbon dioxide. But luckily for us, methane is much less abundant in the atmosphere than carbon dioxide. We measure methane in parts per billion, whereas we measure carbon dioxide in parts per million. I could also add that when we combine methane with all the other known human-produced heat-trapping gases, that adds up to about one watt per square meter or one little Christmas tree light bulb for every square meter of surface area in sustained forcing on the planet. And carbon dioxide is about twice that amount or two watts per square meter in sustained forcing. So CO2 is about twice as great as all as methane and all other heat-trapping gases combined in terms of radiative forcing on the planet. And altogether, that’s a combined total of about three watts per square meter in radiative forcing on the system. I can put that number into context for you if you’d like.
Sure. Why not? We’ve got about 30 seconds left.
David : 05:35
Yeah. To put that number into perspective, scientists estimate that over geologic time on roughly 100,000-year cycles, earth’s orientation changes relative to the sun and as you tilted the northern hemisphere towards the sun that increases in exposure to sunlight averaged over the whole planet was about one per square meter. That one little Christmas tree light bulb per square meter. So it took Mother Nature about one watt in radiative forcing to warm up our planet out of an ice age. Today, we see that humans have exceeded that amount by about three times what it took Mother Nature to warm up our planet. But the difference is the rate of warming over the is projected over the course of this century to be about 50 times faster than earth warming due to mother nature’s forcing. So that helps put it into context.