Climate Science 101 with Science Alliance member Dr. Jen Kay

Photo by Donny O’Neill

97% of climate scientists researching climate change agree that it’s happening and that it’s human-caused. Data shows that humans have put two trillion tons of carbon dioxide into the atmosphere and that it’s changing the planet. Temperatures are going up, sea levels are rising, and extreme weather is becoming more common.

Despite the large consensus of the scientific community, climate change is a politicized issue. We sat down with Jen Kay, an Associate Professor at CU Boulder and a member of the Protect Our Winters Science Alliance, to go back to the basics of the science itself and dive into the most common questions she gets from students. 

“The science isn’t political,” said Professor Kay, who does research and teaches at CU. Professor Kay is passionate about communicating climate science. “The science is just physics, chemistry, and math.”

How do we know that global warming is caused by humans?

Professor Kay: The first way is just accounting. In fact, scientists assess the carbon budget every year. We can figure out how many greenhouse gasses are in the atmosphere by knowing the sources and sinks: Volcanoes, rocks, and us. These things all have different timescales and we do our best to constrain them. The budget analysis shows fossil fuel burning and land use change explains the recent increases in atmospheric carbon dioxide.

Second, the carbon dioxide in the atmosphere is not all the same. The carbon that’s in fossil fuels has an isotopic signature. If we measure the chemistry of the carbon dioxide that’s in the atmosphere—and we see more of the flavor of fossil fuels—then we know that the increased carbon dioxide in the atmosphere is coming from burning fossil fuels and not from volcanoes or other natural sources of carbon. Finally, burning things consumes oxygen. When we burn fossil fuels atmospheric carbon dioxide goes up, and atmospheric oxygen goes down. There’s been a detectable decrease in the amount of oxygen in the atmosphere. It’s small, but we can measure it. We know from multiple lines of scientific evidence and direct measurements that the recent additional carbon dioxide in our atmosphere is due to our burning of fossil fuels.  

How do we know that the extra carbon in the atmosphere is affecting the temperature of the planet?

Professor Kay: We know that when you put more greenhouse gasses into the atmosphere, it increases the surface temperature.

(This peer-reviewed video by Professor Kay explains both human-caused climate change and the greenhouse effect). 

Are you sure that this isn’t all just part of a natural process?

Professor Kay: Yes, I’m sure “it’s us.” What we are observing today cannot be explained by natural processes alone. We know where the carbon comes from, and we know that with more carbon dioxide in the atmosphere the climate warms. One analogy is fingerprints at a crime scene: the climate system has the fingerprints of burning fossil fuels and warming all over it. 

The climate has changed in the past, why should we worry now?

Professor Kay: Yes, the climate has changed in the past, and it will change in the future. Climate change now is especially concerning because we are causing it and it directly affects us. It’s important to understand our role in this change. Whether the climate changes or not, there will always be variability. It’s not one or the other. On short timescales and small spatial scales, the variability dominates. Like today it’s sunny and tomorrow it’s going to snow. The day-to-day shifts in weather patterns are not caused by us and are only predictable for a week or so. We cannot control where a hurricane goes, but thankfully we can predict the path a few days in advance. But by increasing greenhouse gasses we are changing the statistics of the weather, i.e., the climate. The chances of warm weather are increasing, while the chances of cold weather are decreasing. The chances of large rain events causing floods are increasing. The chances of extreme drought are increasing. The chances of strong hurricanes are increasing. These shifts in the statistics are caused by us and affect us.   

It’s also important to look at timescales. Things like volcanoes and the geologic movement of plates are things that change on million-year timescales, and they’ve been huge in terms of explaining for example why 50 million years ago there were crocodiles living in the Arctic and there aren’t now. We don’t live on 50 million-year timescales, and by the way, the primary driver of change on those 50-million-year timescales is atmospheric carbon dioxide. It’s a consistency check: atmospheric carbon dioxide is an important driver of change.

Another common process that gets brought up is Earth’s orbit around the sun, and that has been important for driving glacial-interglacial variations. There used to be two miles of ice over Boston, there’s not anymore. That’s not on the millions of years timescale, that’s more on the tens of thousands of years timescale and we observe that better. We have ice cores that tell us about those changes. We have that data. But even that is talking about tens of thousands of years. Right now, we’re talking about decades. The climate is changing in front of our eyes. 

Where can I find resources that show the climate is changing?

Professor Kay: Every year in my teaching materials I’m updating how much carbon dioxide is in the atmosphere because that has actually really changed over the decade that I’ve been a professor. You can look at what carbon dioxide concentrations are doing today, the data from flasks where people have been going out since the 1950s and measuring it by direct air capture, and then there’s the ice core records which go back 800,000+ years. There are good resources at the National Snow and Ice Data Center; I often look at the sea ice. We have a number of groups globally that put together the instrumental record for global temperature.

How reversible, or irreversible, is human-caused climate change?

Professor Kay: This is a very human question, because if you mess something up, you want to undo it, right?

For things like global temperature and carbon dioxide, if we reduce the amount of carbon dioxide in the atmosphere, temperatures will come down. There’s reversibility in that on human timescales. But for example, sea level rise associated with melting land ice, where we lose all of Greenland. That’d be 24 feet of sea level rise. Florida is underwater. How long does it take to build up a new ice sheet? A long time. Thousand-year time scales, not the decadal timescales of humans. So there are aspects of the climate change we are causing now that are irreversible on human timescales. 

What are the solutions here?

Professor Kay: We have three options: Adaptation, mitigation, or geoengineering.

Adapting is changing our behavior as the climate changes. Mitigation is reducing greenhouse gasses in the atmosphere by changing its sources or sinks (e.g., by reducing fossil fuel burning or by removing carbon dioxide from the atmosphere). Geoengineering is deliberately altering the climate system to alleviate the impacts of increasing greenhouse gasses (e.g., by increasing the number of small particles in the atmosphere so that less solar energy reaches the surface).  

We’re already having to adapt. We have to deal with more wildfires and more floods, and it’s costing us a lot of money in some cases to do that. We can see what this kind of climate change imprint is on an event by running simulations and models where we can compare a warmer atmosphere and the original atmosphere. The models can tell us, in the case of Hurricane Helene in North Carolina for example, how much more rain they got, and that they got more rain because the atmosphere was warmer. Would the hurricane still happen either way? Yes! The point is it is not possible to “do nothing” about climate change; There is a cost associated with adaptation that we’re already bearing. 

Then there’s mitigation, which is reducing carbon dioxide in the atmosphere. To me, that’s the easiest in terms of the climate science part of it because you’re basically undoing what you did. You’re trying to fix problem A by doing A. If you reduce carbon dioxide, many (but not all) of the impacts can be reversed. 

The third option is geoengineering. For example, if we put small particles into the upper levels of the atmosphere we could cool the climate. Volcanoes cool the climate by doing this. Why shouldn’t we? A serious concern with geoengineering is that we are fixing problem A by doing B. The climate impacts of A (greenhouse gas increases) are not the same as the climate impacts of B (geoengineering). For example, a geoengineering strategy that mimics volcanoes will have regional impacts that differ and impact other climate variables like precipitation. For now, geoengineering is being studied to get more information about its climate impacts and its feasibility. 

This conversation has been edited for length and clarity.

Thanks to the research of our Science Alliance members like Dr. Kay, we’re able to better understand the environment we live in and things we can do to help protect it.

Do you want to continue to level up your climate IQ? Check out our Climate Advocate’s  Guidebook to deepen your knowledge. From responsible banking to imperfect advocacy, the guidebook has all the resources and ideas you need to be an advocate – every day.