The levels of the heat-trapping gas called carbon dioxide have gradually risen and fallen during the past 800,000 years — that is, until recent decades, when carbon dioxide levels shot up far higher than in the past.
Why have the carbon dioxide levels jumped so much in our own lifetimes? Here’s a quick explanation and one that’s handy when we’re chatting with people who insist that the climate crisis is just one more in a series of atmospheric shifts — nothing to look at here, move along.
Small Changes to the Earth’s Orbit & the Tilt of its Axis
Tiny wobbles caused by the gravitational tugs of the sun, moon, Saturn, and Jupiter can slightly alter the amount of sunlight reaching our planet. Even minimal shifts in the amount of energy reaching the planet can cause climate transformations that reveal themselves over millennia.
These tiny changes in Earth’s orbit and the tilt of its axis can nudge the Earth into and out of ice ages. Katharine Hayhoe, a Texas Tech climate scientist, explains, “If we look at Earth’s history, we see that warming after the last ice age peaked about 6,000-8,000 years ago. Since then, the Earth’s temperature has been very slowly, gradually decreasing, on a long slide into the next ice age.” That means the Earth would have entered a new ice age – except that it was interrupted by the recent precipitous warming.
For example, Yale Climate Connections, which conducts scientific research on public climate change knowledge, attitudes, policy preferences, and behavior at the global, national, and local scales, offers the example of how small smatterings of additional sunlight reaching the Earth can cause a slight warming of the oceans. What’s the result? The oceans release carbon dioxide to the atmosphere. Because carbon dioxide captures heat, oceans that release it to the atmosphere cause the oceans to warm even more. The oceans release even more carbon dioxide, and the cycle continues.
The Discovery of Global Warming, by science historian Spencer Weart, narrates how, starting in the 1800s, scientists sought to explain the causes of Earth’s periodic ice ages. Their research led to a better understanding of our planet’s climate system and the eventual discovery that people were warming the climate.
What’s Changed? The Way Humans Use Energy Sources
Rebecca Lindsey at NOAA’s climate.gov explains that the global average atmospheric carbon dioxide in 2018 was 407.4 parts per million (ppm). Carbon dioxide levels today are higher than at any point in at least the past 800,000 years. Fossil fuels like coal and oil contain carbon that plants pulled out of the atmosphere through photosynthesis over the span of many millions of years.
Beginning only a little more than 2 centuries ago, humans have returned that carbon to the atmosphere through burning fossil fuels. Carbon dioxide concentrations are rising mostly because of the fossil fuels that people are burning for energy.
Lindsey goes on to describe how, based on air bubbles trapped in mile-thick ice cores (and other paleoclimate evidence), scientists can determine that during the ice age cycles of the past million years or so, carbon dioxide never exceeded 300 ppm. Before the Industrial Revolution started in the mid-1700s, the global average amount of carbon dioxide was about 280 ppm.
In the 1960s, the global growth rate of atmospheric carbon dioxide was roughly 0.6 ± 0.1 ppm per year. Over the past decade, however, the growth rate has been closer to 2.3 ppm per year, according to Lindsey. The annual rate of increase in atmospheric carbon dioxide over the past 60 years is about 100 times faster than previous natural increases, such as those that occurred at the end of the last ice age 11,000-17,000 years ago.
Increases in atmospheric carbon dioxide are responsible for about 2/3 of the total energy imbalance that is causing Earth’s temperature to rise. Keep in mind you’re probably living in one of the highest carbon-emitting countries in the world.
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Final Thoughts about Carbon Dioxide Levels
Focusing on topics like rising and falling carbon dioxide levels offers us a good chance to compare what we think we know to what science says, and having a solid grasp of what’s changed can help us to inform others. There are many different viewpoints as to how we should tackle the untenable amounts of carbon dioxide in the atmosphere. In an exclusive comment for CleanTechnica, for example, Senator Sheldon Whitehouse (D-RI) argued that a carbon fee is the best method to limit emissions and mitigate ocean quality loss.
If you’d like to track carbon dioxide levels in the atmosphere, the Keeling Curve is a significant source of scientific evidence that shows that CO2 is accumulating in our atmosphere. Indeed, Ralph Keeling, professor at the Scripps Institution of Oceanography in San Diego and son of founder Charles Keeling, is one of many scientists who are now studying data from Mauna Loa observatory in the middle of the Pacific Ocean for signs that the economic slowdown linked to the coronavirus could reduce the rise in atmospheric carbon concentrations.
“There has never been an economic shock like this in the whole history of the curve,” he argues.