Closing the CO2 window: New research is precise about human contributions to climate change

Co2 Emissions
Human-caused CO2 emissions are roughly halfway to doubling atmospheric carbon dioxide levels, which would represent a grim milestone for Earth's climate (Gerd Altmann/pixabay)

By Thomas Smith

Medill Reports

While carbon and oxygen are necessary for human life, CO2 is also a thermostat for the planet and carbon dioxide buildup in Earth’s atmosphere has the potential to cause irreversible damage to the planet’s climate. Although the window to counteract human contributions to global warming is closing, scientists are more certain than ever about what exactly that window is.

New research presented at the Comer Climate Conference, an annual conference that brings together climate experts from around the world but convened virtually this fall, has clarified that ocean temperatures were colder during the ice age than scientists previously thought.

Geologist Jeff Severinghaus, a professor with the Scripps Institution of Oceanography at the University of California, San Diego, said this is significant because it indicates how much the Earth warms when carbon dioxide levels increase rapidly, as they are doing now.

“A lot of effort has been spent over the past 45 years trying to figure out exactly how much the Earth warms when CO2 doubles, and this is known as the climate sensitivity to CO2,” Severinghaus said. “That’s a really important number because it kind of tells us just how bad our future will be.”

The Earth naturally had about 280 parts per million of carbon dioxide during the warm spells between ice ages and that level is documented in ancient air pockets from ice cores dating across nearly 1 million years. Severinghaus said the current carbon dioxide level is approximately 415 parts per million, which means human activity has come about half way to doubling Earth’s atmospheric CO2.  Doubling CO2  levels has been estimated to mean a global warming of about 5.5 degrees Fahrenheit, or about 3 degrees Centigrade, which is double the safe level identified by the U.N. Intergovernmental Panel on Climate Change and the Paris Agreement.

However, scientists have always had a margin of error of about 3 degrees Fahrenheit, until now. A new report from University of Arizona climate and geosciences researcher Jessica Tierney puts temperature increase from carbon dioxide doubling in a range of roughly 4 to 8 degrees Fahrenheit, with a 6-degree increase in temperature being most likely.

The abundance of biological organisms has been used in the past to deduce temperatures during the ice age, but this metric was flawed insofar as biological organisms can migrate and independently react to climate conditions. Severinghaus said gases, which are his area of expertise, make a much better thermometer for ocean surface temperatures. Past research using biological organisms as a metric was also out of sync with data that uses noble gases, and Tierney’s new data is in line with previous findings.

Reducing the margin of error could have profound ramifications, with global warming and CO2-driven climate change linked to more intense flooding, hurricanes, drought, hunger, melting ice sheets, and widespread loss of coastal lands and islands. Severinghaus said fossil fuel companies have optimistically projected the lowest possible value, a 2.7-degree Fahrenheit global temperature increase, to help assuage their contributions to climate change.

“We cut the uncertainty in half,” Severinghaus said. “So this is a big scientific advance in a sense, with obvious implications for policy. The fossil fuel companies can no longer say, ‘Oh, there’s no problem.’ We know from other lines of evidence that there definitely is a problem, but this was just one little annoying thing that kept coming back, so this is progress.”

Richard Alley, a geoscientist at Pennsylvania State University and MC of the Comer Conference, said extensive scholarship shows that responding efficiently to rising carbon dioxide levels would be good for the economy, with wide-ranging positive impacts.

“If you want a big economy you deal with this,” Alley said, “if you want an economy with employment you deal with this. You have to do it carefully because we rely on fossil fuels, but the best scholarship at this point says economy and employment and ethics and environment and security and health are all in the same direction.”

Thomas Smith is a science reporter at Medill. You can follow him on Twitter at @TomGoodwinSmith.