Chajes: Drivers of climate change differ over time
Beth Chajes is the Delaware state coordinator for the national nonpartisan nonprofit Citizens’ Climate Lobby. She holds a master’s degree in ecology from the University of California, Davis and is the former communications manager for the Delaware Environmental Institute at the University of Delaware.
When I talk to people about climate change, one of the most common responses I hear is “Climate is always changing.”
It’s true. Natural forces have caused Earth’s climate to vary widely over the millennia. We have oscillated from ice ages, with deep sheets of ice covering large land areas, to warm periods with no ice, not even at the poles. Variability in the intensity of the sun, the tilt and wobble of Earth’s orbit, and volcanic activity have all contributed to climatic changes in the past.
However, none of these factors adequately explains the planet’s current warming trend. In fact, our position in the tilt-and-wobble cycles that have largely driven the planet in and out of ice ages in the past should currently place us on a cooling trajectory — a long, gradual slide into the next ice age. Yet, this is not what we are observing.
We cannot assume that the drivers of climate change today must be the same as the drivers of climate change in the past. Yet, that’s the basic logical fallacy made by the author of a recent Opinion in the Daily State News, who asked, “Which came first, CO2 or air temperature?” He points out that the ancient atmospheric record preserved in bubbles in Antarctic ice cores reveals that a rise in temperature preceded a rise in carbon dioxide — evidence, he claims, that carbon dioxide must not be the cause of global warming, then or now.
Climate scientists were not, in fact, surprised by this finding; they had predicted it. They understood that, in the past, a large-scale warming trend was usually initiated by cyclical shifts in Earth’s tilt and orbit that caused sunlight to strike the surface of the planet more directly. Since warm water can’t hold as much dissolved carbon dioxide as cold water, once the oceans began to warm, they began to release CO2 to the atmosphere, similar to the way a warm soda releases its CO2 bubbles much faster than a cold one.
Thus, the initial warming caused by Earth’s wobbly orbit was then amplified by a temperature-carbon dioxide feedback loop. Once in the atmosphere, carbon dioxide acts like a blanket to trap heat emitted from the Earth — the more CO2 piles up in the atmosphere, the “thicker” the blanket and the warmer the Earth’s surface becomes. Without some CO2 in the atmosphere, the Earth would be a frozen ball of ice. This basic physics has been understood by scientists for 160 years.
Both processes — wobbly orbit and temperature-carbon dioxide feedback — operating simultaneously over long timescales, can result in the time lags preserved deep in Antarctic ice cores. Without interference, we might well expect this pattern to continue. However, since the end of the last ice age about 18,000 years ago, a new force has arisen on the planet — human civilization. We have developed sufficient numbers and technology to become the dominant climate-forcing factor. We became experts at removing carbon-based fuels from deep underground and using controlled fires to release and harness the fuels’ energy. In the process, we have transferred millions of tons of carbon to the atmosphere as carbon dioxide and methane, on a timescale equivalent to the blink of an eye, geologically speaking.
The current level of carbon dioxide in the atmosphere is about one-and-a-half times higher than it ever was in the ice core record. For the last 800,000 years, CO2 in the atmosphere never exceeded 300 parts per million. As recently as 1880, it was 280 parts per million. But, by 2021, it exceeded 420 for the first time. We are sleeping under an ever-thicker, heat-trapping blanket.
The author of the previously cited Opinion suggested that we should be grateful, since carbon dioxide is “food for plants,” one of the essential inputs for photosynthesis, along with water. It’s true that, under highly controlled conditions in a laboratory or a greenhouse, enriching the air with carbon dioxide can accelerate plant growth. But that happens only when plants have plenty of everything else they need to grow, including water and nutritious soil. It’s highly improbable that a warming planet will replicate these ideal growing conditions in nature. Instead, the plants of our planet are more likely to encounter droughts, fires and more intense storms and floods capable of washing precious soil nutrients away.
Half-truths can have a reassuring ring to them, especially when the whole story tells us something we don’t want to hear. But the climate story doesn’t have to have a tragic ending. The same human ingenuity that enabled us to harness the power of carbon-based fuels is being used to innovate technological and policy solutions. Clean, renewable energy and alternatives to the fuel-burning technologies that make our lives convenient and comfortable are rapidly improving and are cost-competitive. Policies to speed up this transition, while protecting people’s pocket books — such as Canada’s carbon rebate program — are being adopted around the world. It’s time for Americans to decide whether we will lead the way to a safe and healthy future.
Reader reactions, pro or con, are welcomed at civiltalk@iniusa.org.
