Is carbon dioxide a pollutant? A small but vocal group of researchers, authors and US government officials say it is time to change the definition.
Most climate and atmospheric scientists say rising levels of CO2 are raising the planet’s temperature, which in turn is leading to more intense storms, rising sea levels and the risk of more intense drought and wildfires that endanger human health and welfare.
The Trump administration is asserting that CO2 isn’t a threat to public health, as part of a new effort to undo some of the Environmental Protection Agency’s responsibilities for regulating emissions.
CO2 “is a greenhouse gas. It absorbs infrared radiation, but it’s not a pollutant,” said Energy Secretary Chris Wright in an interview with the Journal. “It does not cause acute harm to humans.”
The definition of CO2’s role is central to the EPA plan, which would eliminate the so-called endangerment finding that followed from the 2007 court ruling. Public hearings start this week, kicking off what is likely to be a lengthy legal battle over whether the government will continue to regulate greenhouse-gas emissions from vehicles, power plants and other industries.
There are both certainties and uncertainties about CO2 and its effects on the planet.
Carbon dioxide is an odorless gas that plants absorb and, together with sunlight, use to produce food and oxygen during photosynthesis. Humans exhale CO2 as a waste product of cellular activity. It isn’t toxic to people at current levels in the atmosphere.
It is also produced by the burning of fossil fuels in vehicles, power plants and other industrial activities.
In a world without human activity, natural sources of CO2 such as volcanoes, decomposing plant material and wildfires, would be balanced by natural “sinks” that absorb it, such as the ocean and plants that take in CO2 during photosynthesis, according to Daniele Visioni, professor of earth and atmospheric sciences at Cornell University.
While natural emissions are about 10 times greater than human-caused emissions annually, human activities are the primary cause of the current rise in atmospheric CO2, say climate scientists.
“These human emissions come on top of this perfect balance,” Visioni said.
More than two decades of research from climate scientists and federal agencies have linked rising atmospheric temperatures to rising CO2.
The concentration of CO2 in the atmosphere—the ratio of CO2 to air molecules—has jumped by more than 50% since preindustrial times, from approximately 280 parts per million to 425 ppm today, according to the EPA.
Meanwhile, the average global atmospheric temperature has risen 1.27 degrees Celsius (2.3 degrees Fahrenheit) since the mid-19th century, and the past 10 years have been the warmest since record-keeping began in the 1850s, according to the National Aeronautics and Space Administration.
Members of emergency services and locals work to contain a wildfire near Tepelena, Albania.
As the scientific consensus on CO2’s role in climate change has solidified, so too has the alternative view that more CO2 is good for the planet, and that it was a mistake to classify it a pollutant. This view has been promoted for the past two decades by authors, bloggers and researchers who don’t accept the established scientific findings.
They say that CO2 isn’t directly harmful to humans and has many natural sources, and that since Congress didn’t label CO2 a pollutant when it passed the original 1970 Clean Air Act or its amendments in 1990, changing the gas’s legal definition will require new legislation rather than EPA regulations.
The Energy Department completed a 141-page review of the science of climate change last month that is the scientific foundation of the EPA’s effort to roll back existing emissions rules. It is written by five authors who acknowledge that the atmosphere is warming but cast doubt on the severity of the effects of a changing climate and question the accuracy of climate models that predict future warming.
The report argues that increasing CO2 levels will boost agricultural production, like a massive jolt of plant food. Some experimental studies have found that increasing CO2 boosts plant growth, but other studies have also found that many food crops lose vitamins, minerals and proteins under high CO2 conditions.
The DOE report notes that this loss of nutrients will have to be compensated by using more fertilizers or breeding new strains of food crops to handle the extra growth.
Critics say the DOE report is inaccurate. A lawsuit filed last week by the Environmental Defense Fund and the Union of Concerned Scientists in a federal-district court in Massachusetts contends that agency officials violated federal rules that require them to hold open meetings and disclose the report’s authors beforehand.
A DOE spokeswoman had no immediate comment on the lawsuit.
Determining how much and how fast CO2 emissions will warm the planet in the future is still uncertain. That is because large-scale changes in the Earth’s ecosystem that are occurring as the atmosphere warms are still being studied, according to Michael Diamond, professor of atmospheric sciences at Florida State University.
The warming atmosphere is changing cloud patterns in some parts of the globe, but it isn’t clear whether the changes will warm or cool the planet. Much depends on their altitude and density. The warming atmosphere is also pulling more moisture from plants, he said, offsetting the beneficial growth effects of CO2 and melting permafrost in the Arctic, releasing methane, another greenhouse gas.
Another big question is whether the oceans might be reaching their limit on absorbing excess heat and CO2.
“There’s a lot of things that we still need to understand better about climate change, but we know more than enough to know that it is a threat to human health and wellness and ecosystems,” Diamond said.