Carbon dioxide is a major cause of global warming; ice core surveys do not prove otherwise

The Context

Social media users shared a video that incorrectly claims carbon dioxide (CO2) is not the cause of global warming, but instead, an increase in carbon dioxide is the product that follows a temperature change. According to the video, ice core studies show that after a few hundred years CO2 increase follows the temperature rise. The caption of these posts reads, "How inconvenient – Ice core surveys show carbon dioxide is not the cause of warming."

The video is a clip captured from a 2007 documentary, "The Great Global Warming Swindle" by Martin Durkin. The documentary argues that man-made global warming is a myth, which is against the consensus of the scientific community.

Most scientists agree that the greenhouse effect is the main contributor to global warming. Carbon dioxide accounts for the majority of emitted greenhouse gases trapping heat on Earth's surface. Logically Facts has previously covered carbon dioxide’s role in global warming and refuted climate change conspiracies and false claims.

In fact

Ice cores refer to cylinders of ice drilled from an ice sheet or glacier. The small air bubbles in the ice contain samples of the atmosphere; this allows scientists to directly measure the past concentration of atmospheric gases, including carbon dioxide.

"Overall, ice cores have confirmed the very tight relationship between CO2 and temperature over the last 800,000 years. That is inclusive of the possibility that in some cases a natural (orbitally-forced) temperature rise led to a CO2 rise. The ice core record also definitely fingerprints the human-caused, CO2-led rise in temperature we know to be the primary challenge of climate change" Dr. Peter Neff from the University of Minnesota explained to Logically Facts.

Similarly, Professor Eric Wolff from the University of Cambridge explained to Logically Facts that the "Ice cores covering 800,000 years show that Antarctic temperature, mean ocean temperature, and CO2 all rise and fall together in the sequence of ice ages and warmer interglacials. This is entirely consistent with the known physics of greenhouse-effect warming, with the changes in CO2 being a major contributor to the observed warmings and coolings.”

According to the British Artic Survey, studies show that during cold periods CO2 concentrations were low, while warm periods saw high concentrations. This phenomenon is known as positive feedback; a strong connection between temperature and CO2, where each factor amplifies changes in the other.

Professor Wolff elaborates, saying “In a positive feedback, where more CO2 makes the temperature rise, and higher temperature promoted the release of carbon particularly from the deep ocean. This positive feedback indicates a role for CO2 in causing much of the warming out of ice ages, which would occur even though an initial trigger started both rising. In fact, the data shown in the clip has anyway been superseded and the latest papers show that the start of the warming and the start of the CO2 rise was simultaneous within uncertainty.”

The verdict

Carbon dioxide is a major contributor to global warming through the greenhouse effect, ice core surveys do not prove otherwise. Ice core studies have confirmed the very tight relationship between CO2 and temperature. The results are consistent with the greenhouse effect warming and human-made global warming. Therefore, we have marked the claim as false.