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Long-term trends and spatial distributions of CO2, CH4, N2O and SF6 from NOAA’s global background measurements
by Dr. Xin Lan, Dr. Ed Dlugokencky, Dr. Sylvia Michel , Dr. Pieter Tans, Dr. Kirk Thoning , Dr. Don Neff, Dr. Andrew Crotwell, Mrs./Ms. Molly Crotwell, Mr. Eric Mogli, Dr. Monica Madronich, Mr. John Mund


NOAA’s Global Monitoring Laboratory began monitoring CO2 from weekly discrete air samples collected at Niwot Ridge, Colorado and Ocean Station M in 1968. Since then, the network of flask-air sampling sites has grown, with about 50 active sites in early-2022, and we now precisely measure CO2, CH4, N2O, and SF6. Atmospheric burdens of these long-lived greenhouse gases (LLGHGs) have been increasing significantly in the past few decades, according to our global background measurements. Global mean CO2 has risen steadily at a rate from 0.8 ppm yr−1 in the 1960s to an average of 2.4 ppm yr−1 during the last decade, reaching to 414.7 ± 0.1 ppm in 2021. Since the beginning of our systematic CH4 measurements in 1983, global CH4 rose and then flattened prior to 2006, followed by rapid increases since. In the past two years, we observed the largest increases of CH4 in our record, 15.1 ppb yr−1 during 2020 and 18.1 ppb yr−1 during 2021. Global mean CH4 just passed the 1900 ppb benchmark in fall 2021. Global mean N2O and SF6 have been increasing steadily in the past two decades and reached 334.31 ± 0.14 ppb and 10.63 ± 0.005 ppt in 2021. These long-term, internally consistent measurements are at the core of understanding LLGHG budgets. Total global missions of these LLGHGs are now undoubtedly greater than any time since our measurements began. In addition to these LLGHGs, we also measure carbon isotopes in CO2 and CH4, in partnership with INSTAAR (Institute of Arctic and Alpine Research), to better understand different source and sink processes. The impacts of these LLGHGs on global climate are estimated based on their abilities to change the global radiative energy balance. Based on our measurements, we found that the increase in atmospheric CO2 contributes 66% of the increase in all LLGHG radiative forcing since the pre-industrial era while the increase in CH4 contributes 16%. If we want to track future changes in LLGHG budgets and their climate impacts, including potential climate feedbacks, we need to expand high-quality observations to under-sampled regions, such as the tropics, Siberia, Africa and South America. Continuous monitoring of LLGHGs with high measurement quality is also essential for tracking progress in mitigating climate change.

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Topic : Theme 1: Atmospheric Chemistry and Physics.
Reference : T1-A12

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