REVIEW
CLAIM: CO2 concentrations are increasing in Earth’s atmosphere faster than they have in the last 50,000 years. They have recently risen 10 times faster.
In May 2024, a number of articles and Facebook posts claimed that carbon dioxide (CO2) concentrations are increasing in Earth’s atmosphere faster than they have in the last 50,000 years. So what sparked this claim?
The original source appears to be a paper published on 13 May 2024 in the Proceedings of the National Academy of Sciences (PNAS) journal. For a press release about this research, the paper’s lead author, Dr. Kathleen Wendt, and co-author, Dr. Christo Buizert, were interviewed by the media team at Oregon State University (OSU), where both professors are faculty. Science Feedback contacted these professors, who confirmed that the claim in question is an accurate interpretation of their findings. They also explained that they vetted and approved the OSU press release about their research, including the quotes provided below.
In their paper, titled “Southern Ocean drives multidecadal atmospheric CO2 rise during Heinrich Stadials”, the authors discuss evidence of abrupt jumps in CO2 that occurred during the last glacial period (ending ~11,700 years ago), which they discovered by analyzing ice cores from Antarctica. Though comparing these changes to those observed in modern times was not the focus of the study, the authors explain that “these rates of CO2 increase are among the most rapid seen in the ice core record, yet still about an order of magnitude slower than the current rate of anthropogenic CO2 rise[1]”[2].
In a comment to Science Feedback, Dr. Wendt explained that although comparing the current rise of CO2 to that of the past was not the focus of their research, the OSU press release adds perspective on this to explain why the research is relevant to peoples’ lives. In the press release, Dr. Wendt explains that “studying the past teaches us how today is different. The rate of CO2 change today really is unprecedented”. She also explained that “our research identified the fastest rates of past natural CO2 rise ever observed, and the rate occurring today, largely driven by human emissions, is 10 times higher.” When asked for more context about this, she explained that in the paper, they found that the largest rise in CO2 occurred roughly 40,000 years ago – rising 14 parts per million (ppm) in roughly 50 years[2]. However, the same increase occurred in the last 5 years – a 10 times shorter period – as revealed by data from the National Oceanographic and Atmospheric Association (NOAA). But why is a more rapid CO2 increase in the atmosphere relevant to humans?
CO2 raises Earth’s global temperatures by increasing radiative forcing – trapping outgoing radiation (i.e., heat) that is released from Earth’s surface after absorbing sunlight[3-6] – a process we explain in a past review linked here. There is unequivocal evidence that this process has been exacerbated by human greenhouse gas emissions, which is the primary driver of recent climate change[3,7,8]. Thus, as CO2 continues to increase, so will global temperatures. This sheds light on the rate of CO2 increases, but what about overall concentrations – how do they compare to the past?
Beyond just the current rate of increase of CO2 compared to the last 50,000 years, CO2 concentrations are also higher. The Intergovernmental Panel on Climate Change (IPCC), the world’s leading scientific authority on climate change, explains that “there is high confidence that current CO2 concentrations are higher than at any time over at least the past two million years”[7]. Figure 1 shows the trends in CO2 and global temperatures based on paleoclimate records going back 800,000 years before present. This figure demonstrates how unusual current CO2 concentrations are compared to the past, and how CO2 and temperature have tracked together throughout the past.
Figure 1 – Graphs showing CO2 and temperature oscillations over the last 800,000 years for the global average and Antarctica (data from Parrenin et al. 2013; Snyder et al. 2016; Bereiter et al. 2015). Source: Ben Henley and Nerilie Abram, The Conversation.
But what do very recent trends look like? The daily record of global atmospheric CO2 – known as the Keeling Curve – set a new record in May 2024 for the fastest yearly rise in atmospheric CO2 ever observed. As announced on Scripps Institute of Oceanography’s Keeling Curve webpage:
“The monthly average concentration of carbon dioxide in the atmosphere measured at NOAA’s Mauna Loa Observatory in March 2024 was 4.7 parts per million (ppm) higher than that recorded in March 2023, setting a new record and revealing the increasing pace of CO2 addition to the atmosphere by human activities.”
REFERENCES
- 1 – IPCC (2021) 2021: Technical Summary. In Climate Change 2021: The Physical Science Basis. Contribution of Working Group I to the Sixth Assessment Report of the Intergovernmental Panel on Climate Change
- 2 – Wendt et al. (2024) Southern Ocean drives multidecadal atmospheric CO2 rise during Heinrich Stadials. Proceedings of the National Academy of Sciences.
- 3 – IPCC (2021). Sixth Assessment Report.
- 4 – Kaufman et al. (2020) Holocene global mean surface temperature, a multi-method reconstruction approach. Nature.
- 5 – Raghuraman et al. (2023) Greenhouse Gas Forcing and Climate Feedback Signatures Identified in Hyperspectral Infrared Satellite Observations. Geophysical Research Letters.
- 6 – Zhong and Haigh (2013) The greenhouse effect and carbon dioxide. Royal Meteorological Society Weather.
- 7 – IPCC (2023) Climate Change 2023: Synthesis Report.
- 8 – Santer et al. (2013). Human and natural influences on the changing thermal structure of the atmosphere. Proceedings of the National Academy of Sciences.
