A new look at atmospheric carbon dioxide

’s (2012) conclusion that observed climate change is comparableto projections, and in some cases exceeds projections, allows further inferences ifwe can quantify changing climate forcings and compare those with projections.The largest climate forcing is caused by well-mixed long-lived greenhouse gases.Here we illustrate trends of these gases and their climate forcings, and we discussimplications. We focus on quantities that are accurately measured, and we includecomparison with fixed scenarios, which helps reduce common misimpressionsabout how climate forcings are changing.Annual fossil fuel CO

Abstract. Monitoring annual atmospheric CO2 growth rates is a key constraint on assessing the long-term effectiveness of emission reduction strategies. We analyzed annual growth rates of column-averaged dry-air mole fractions of CO2 (XCO2) using long-term data from 12 sites within the Total Carbon Column Observing Network (TCCON), spanning four regions: the Arctic, two Northern Hemisphere midlatitude bands (40–50 and 30–40° N), and the Southern Hemisphere. While in situ ground-based measurements provide detailed records of near-surface CO2 concentrations, XCO2 reflects the column-averaged abundance across the entire atmosphere, offering a complementary perspective. We compared TCCON-derived growth rates with ground-based in situ observations from the Mauna Loa Observatory (MLO). Three calculation methods – Monthly Mean (MM), Fourier Fit residuals (FF), and Dynamic Linear Model (DLM) – were evaluated, with particular attention to the Eureka site, where polar night introduces substantial data gaps. In addition, the Copernicus Atmosphere Monitoring Service (CAMS) reanalysis product was used to assess consistency with TCCON-based growth rates and to evaluate each method's robustness to missing data. Among the methods tested, the DLM approach proved most resilient to data gaps. Regionally averaged CO2 growth rates, calculated from 2010 or from the earliest available data through 2024, ranged from approximately 2.33 to 2.40 ppm yr−1. The most prominent signal was associated with the 2015–2016 El Niño – Southern Oscillation (ENSO) event, during which growth rates increased by up to 1.7 ppm yr−1. The impact of COVID-19-related emission reductions in 2020 was also examined: a decline of 0.4 ppm yr−1 was observed in the 30–40° N region, whereas other regions showed no significant decline. Correlation analysis between growth rates and ENSO strength revealed significant relationships in the Southern Hemisphere and at Mauna Loa, but not in northern mid- or high-latitude regions.

Earth system models project that the tropical land carbon sink will decrease in size in response to an increase in warming and drought during this century, probably causing a positive climate feedback. But available data are too limited at present to test the predicted changes in the tropical carbon balance in response to climate change. Long-term atmospheric carbon dioxide data provide a global record that integrates the interannual variability of the global carbon balance. Multiple lines of evidence demonstrate that most of this variability originates in the terrestrial biosphere. In particular, the year-to-year variations in the atmospheric carbon dioxide growth rate (CGR) are thought to be the result of fluctuations in the carbon fluxes of tropical land areas. Recently, the response of CGR to tropical climate interannual variability was used to put a constraint on the sensitivity of tropical land carbon to climate change. Here we use the long-term CGR record from Mauna Loa and the South Pole to show that the sensitivity of CGR to tropical temperature interannual variability has increased by a factor of 1.9 ± 0.3 in the past five decades. We find that this sensitivity was greater when tropical land regions experienced drier conditions. This suggests that the sensitivity of CGR to interannual temperature variations is regulated by moisture conditions, even though the direct correlation between CGR and tropical precipitation is weak. We also find that present terrestrial carbon cycle models do not capture the observed enhancement in CGR sensitivity in the past five decades. More realistic model predictions of future carbon cycle and climate feedbacks require a better understanding of the processes driving the response of tropical ecosystems to drought and warming.

Atmospheric carbon dioxide at record high

Atmospheric CO2 measurements made with a nondispersive infrared analyzer during 1974–1985 at Mauna Loa Observatory, Hawaii, are described, with emphasis on the measurement methodology, calibrations, and data accuracy. Monthly mean CO2 data, representative of global background conditions, are presented for the period of record. The monthly means were derived from an all‐data base of CO2 hourly averages archived at the National Oceanic and Atmospheric Administration (NOAA) Geophysical Monitoring for Climatic Change (GMCC) facility in Boulder, Colorado; at the Carbon Dioxide Information Analysis Center (CDIAC) in Oak Ridge, Tennessee; and in the microfiche version of this paper. Flags in the all‐data base identify CO2 hourly averages that have been deemed unreliable because of sampling and analysis problems or that are unrepresentative of clean background air because of influences of the local environment, for example, CO2 uptake by nearby vegetation or contamination and pollution effects. The select NOAA GMCC monthly mean data are compared with similar data obtained independently at Mauna Loa Observatory by the Scripps Institution of Oceanography. The average difference of corresponding monthly mean CO2 values for the two data sets is 0.15±0.18 ppm, where the indicated variability is the standard deviation. Careful scrutiny of the NOAA GMCC measurement, calibration, and data processing procedures that might have caused the small bias in the data has revealed no unusual errors.

Since 1958, the Mauna Loa Observatory (MLO) has continuously monitored carbon dioxide variations using non-dispersive infrared (NDIR) sensors, with the Keeling curve as an early indicator of the anthropogenic contribution to global atmospheric carbon dioxide. The increasing CO2 levels are alarming and have led to international agreements that promote cleaner industrial activities. However, any change in global behavior would not immediately cause detectable changes in the MLO data; the extent to which global and long-term term trends are conflated with local and short-term variations remains unclear. Hence the current paper verifies the performance of the sampling and measurement systems of MLO, using existing data published within the months of October and November 2020, which comply with the temporal continuity requirements of chronostatistics. It has been determined that the components of the MLO air including carbon dioxide are well mixed due to their particular location. Beyond this, the variographic analysis distinguishes between small (<5%) and large (>10%) variability contributions due to sampling, including graphical depictions of MLO data. Coupled with the precision of the method being better than 0.2 ppm, it has been determined that the sampling and measurement protocols are highly suitable to meet the objective of representing CO2 fluctuations over time. The variographic application also manages to quantify short-term variabilities resulting from the local processes of the region where the observatory is located. The results support the furthering of multiscaled temporal analysis of atmospheric CO2, and potentially the incorporation of CO2 variographic parameters into empirical and semi-empirical climate models.

In May 2013, for the first time since its inception in 1950s, Mauna Loa Observatory, on the island of Hawaii, observed that the daily average of atmospheric carbon dioxide concentration exceeds 400 parts per million. It may be a small concentration in atmosphere, but it plays a significant role in dictating surface temperature on earth. Earth receives radiation from the sun and a significant portion of it is reflected and reradiated back into the space. A portion of the total radiation is absorbed by the atmosphere. To reach an equilibrium for the earth’s climatic condition, the absorbed solar radiation should be in exact balance with radiation emitted to the space. In climatic science, externally imposed perturbations that disturb this balance are collectively known as radiative forcing. Carbon dioxide, a greenhouse gas, is one of the main culprits for global warming or increase of average temperature on earth’s surface through radiative forcing. Global warming may have severe impact on earth’s climate such as change in precipitation patterns, expansion of deserts, frequent occurrence of extreme weather conditions, and rise of sea level. Carbon dioxide is not completely unwanted; rather it is essential to support life on earth. Carbon is exchanged between the different zones of overall earth’s ecosystem through a sequence of events. Balance in every steps of this carbon cycle is essential to sustain life on earth. Post industrialization, carbon cycle is altered primarily due to anthropogenic impacts or impacts due to human activities, particularly due to unplanned deforestation and unrestricted use of fossil fuel. To de-carbonize our atmosphere (i.e., to remove excess carbon dioxide), the whole world has agreed to improve energy efficiency, improve energy conversion efficiency, and utilize low-carbon and renewable energy sources. Nuclear energy faces public resistances, especially after the 2011 Fukushima disaster; renewable energy systems face challenges such as low energy density, high initial capital investment, and relatively poor reliability and availability. In the interim period, efficient utilization of energy and energy conservation poised itself as a realizable target to de-carbonize energy system. Improving energy efficiency and conservation of energy in commercial, industrial, and residential sectors can reduce overall energy requirement significantly. Other than reducing carbon dioxide in atmosphere, it offers significant economic benefits. In industrial practices, reduction of energy requirement for a given production is known as energy management. Increase in production by maintaining the energy requirement is known as debottlenecking. Energy management or debottlenecking can reduce the operating cost and lead to significant financial incentives. Furthermore, various energy efficiency measures provide other benefits such as improved energy security and reduction of peak demand. But energy efficiency programs are also not free of concerns. Suppose, a 15 W energy efficient compact fluorescent bulb replaces a 60 W inefficient incandescent bulb; 75 % reduction in energy consumption is expected. Now user of the new bulb realizes that operation of the lighting system is much cheaper and starts using it more. Thus, realized energy conservation is much lower or a portion of energy saving is ‘taken back.’ Increase in energy efficiency leads to extra available income for consumers to utilize it more. For example, increase in efficiency of cars may lead to & Santanu Bandyopadhyay santanub@iitb.ac.in

Abstract. SCIAMACHY onboard ENVISAT (launched in 2002) enables the retrieval of global long-term column-averaged dry air mole fractions of the two most important anthropogenic greenhouse gases carbon dioxide and methane (denoted XCO2 and XCH4). In order to assess the quality of the greenhouse gas data obtained with the recently introduced v2 of the scientific retrieval algorithm WFM-DOAS, we present validations with ground-based Fourier Transform Spectrometer (FTS) measurements and comparisons with model results at eight Total Carbon Column Observing Network (TCCON) sites providing realistic error estimates of the satellite data. Such validation is a prerequisite to assess the suitability of data sets for their use in inverse modelling. It is shown that there are generally no significant differences between the carbon dioxide annual increases of SCIAMACHY and the assimilation system CarbonTracker (2.00 &amp;amp;pm; 0.16 ppm yr−1 compared to 1.94 &amp;amp;pm; 0.03 ppm yr−1 on global average). The XCO2 seasonal cycle amplitudes derived from SCIAMACHY are typically larger than those from TCCON which are in turn larger than those from CarbonTracker. The absolute values of the northern hemispheric TCCON seasonal cycle amplitudes are closer to SCIAMACHY than to CarbonTracker and the corresponding differences are not significant when compared with SCIAMACHY, whereas they can be significant for a subset of the analysed TCCON sites when compared with CarbonTracker. At Darwin we find discrepancies of the seasonal cycle derived from SCIAMACHY compared to the other data sets which can probably be ascribed to occurrences of undetected thin clouds. Based on the comparison with the reference data, we conclude that the carbon dioxide data set can be characterised by a regional relative precision (mean standard deviation of the differences) of about 2.2 ppm and a relative accuracy (standard deviation of the mean differences) of 1.1–1.2 ppm for monthly average composites within a radius of 500 km. For methane, prior to November 2005, the regional relative precision amounts to 12 ppb and the relative accuracy is about 3 ppb for monthly composite averages within the same radius. The loss of some spectral detector pixels results in a degradation of performance thereafter in the spectral range currently used for the methane column retrieval. This leads to larger scatter and lower XCH4 values are retrieved in the tropics for the subsequent time period degrading the relative accuracy. As a result, the overall relative precision is estimated to be 17 ppb and the relative accuracy is in the range of about 10–20 ppb for monthly averages within a radius of 500 km. The derived estimates show that the SCIAMACHY XCH4 data set before November 2005 is suitable for regional source/sink determination and regional-scale flux uncertainty reduction via inverse modelling worldwide. In addition, the XCO2 monthly data potentially provide valuable information in continental regions, where there is sparse sampling by surface flask measurements.

Forest change

Abstract. Atmospheric carbon dioxide (CO2) mole fractions were continuously measured from January 2009 to December 2011 at four atmospheric observatories in China using cavity ring-down spectroscopy instruments. The stations are Lin'an (LAN), Longfengshan (LFS), Shangdianzi (SDZ), and Waliguan (WLG), which are regional (LAN, LFS, SDZ) or global (WLG) measurement stations of the World Meteorological Organization's Global Atmosphere Watch program (WMO/GAW). LAN is located near the megacity of Shanghai, in China's economically most developed region. LFS is in a forest and rice production area, close to the city of Harbin in northeastern China. SDZ is located 150 km northeast of Beijing. WLG, hosting the longest record of measured CO2 mole fractions in China, is a high-altitude site in northwestern China recording background CO2 concentration. The CO2 growth rates are 3.7 ± 1.2 ppm yr−1 for LAN, 2.7 ± 0.8 ppm yr−1 for LFS, 3.5 ± 1.6 ppm yr−1 for SDZ, and 2.2 ± 0.8 ppm yr−1 (1σ) for WLG during the period of 2009 to 2011. The highest annual mean CO2 mole fraction of 404.2 ± 3.9 ppm was observed at LAN in 2011. A comprehensive analysis of CO2 variations, their diurnal and seasonal cycles as well as the analysis of the influence of local sources on the CO2 mole fractions allows a characterization of the sampling sites and of the key processes driving the CO2 mole fractions. These data form a basis to improve our understanding of atmospheric CO2 variations in China and the underlying fluxes using atmospheric inversion models.

The combined land and ocean surface temperature in 2007 fell within the 10 highest on record, while the average land temperature was the warmest since global records began in 1880. In the low to midtroposphere, the annual global mean temperature was among the five warmest since reliable global records began in 1958, but still cooler than the record warmest year of 1998. For the fourth consecutive year, the annual precipitation averaged over global land surfaces was above the long-term mean, although the anomaly was significantly less than in 2006 when the annual value was the eighth wettest since 1901. The globally averaged concentration of carbon dioxide (CO2) continued to increase in 2007, having risen to 382.7 ppm at the Mauna Loa Observatory in Hawaii. The average rate of rise of CO2 has been 1.6 ppm yr−1 since 1980; however, since 2000 this has increased to 1.9 ppm yr−1. In addition, both methane (CH4) and carbon monoxide (CO) concentrations were also higher in 2007. Over the oceans, global SST during 2007 showed significant departures from the 1971–2000 climatology. Annual average upper-ocean heat content anomalies declined between 2006 and 2007 in the eastern equatorial Pacific and increased in off-equatorial bands in that ocean basin. These changes were consistent with the transition from an El Niño in 2006 to a La Niña in 2007. The global mean sea level anomaly (SLA) in 2007 was I.I mm higher than in 2006, which is about one standard deviation below what would be expected from the 15-yr trend value of 3.4 mm yr−1. In the tropics, the Atlantic hurricane season was near normal in 2007, although slightly more active than in 2006. In the north and south Indian Ocean Basins, both the seasonal totals and intensity of tropical cyclones (TC) were significantly above average, and included two Saffir-Simpson category 5 TCs in the north Indian Ocean and a world record rainfall amount of 5510 mm over a 3–8-day period on the island of Reunion in the south Indian Ocean. In the polar regions 2007 was the warmest on record for the Arctic, and continued a general, Arctic-wide warming trend that began in the mid-1960s. An unusually strong high pressure region in the Beaufort Sea during summer contributed to a record minimum Arctic sea ice cover in September. Measurements of the mass balance of glaciers and ice caps indicate that in most of the world, glaciers are shrinking in mass. The Greenland ice sheet experienced records in both the duration and extent of the summer surface melt. From the continental scale, as a whole the Antarctic was warmer than average in 2007, although the Antarctic Peninsula was considerably cooler than average. The size of the ozone hole was below the record levels of 2006, and near the average of the past 15 yr, due to warmer springtime temperatures in the Antarctic stratosphere.

The combined land and ocean surface temperature in 2007 fell within the 10 highest on record, while the average land temperature was the warmest since global records began in 1880. In the low to midtroposphere, the annual global mean temperature was among the five warmest since reliable global records began in 1958, but still cooler than the record warmest year of 1998. For the fourth consecutive year, the annual precipitation averaged over global land surfaces was above the long-term mean, although the anomaly was significantly less than in 2006 when the annual value was the eighth wettest since 1901. The globally averaged concentration of carbon dioxide (CO2) continued to increase in 2007, having risen to 382.7 ppm at the Mauna Loa Observatory in Hawaii. The average rate of rise of CO2 has been 1.6 ppm yr−1 since 1980; however, since 2000 this has increased to 1.9 ppm yr−1. In addition, both methane (CH4) and carbon monoxide (CO) concentrations were also higher in 2007. Over the oceans, global ...

Carbon dioxide (CO2) growth rates are estimated for a period 1959–2004 from atmospheric CO2 measurements at Mauna Loa by the Scripps Institute of Oceanography. Only during a few short periods, 1965–1966, 1972–1973, 1987–1988 and 1997–1998, in the last 45 yr have growth rates of atmospheric CO2 been of a similar magnitude or higher than that due to the total emission from burning of fossil fuels. Using results from a time-dependent inverse (TDI) model, based on observations of atmospheric CO2 at 87 stations, we establish that El Nino-induced climate variations in the tropics and large-scale forest fires in the boreal regions are the main causes of anomalous growth rates of atmospheric CO2. The high growth rate of 2.8 ppm yr−1 in 2002 can be predicted fairly successfully by using the correlations between (1) the peak-to-trough amplitudes in the El Nino Southern Oscillation (ENSO) index and tropical flux anomaly, and (2) anomalies in CO2 flux and area burned by fire from the boreal regions. We suggest that the large interannual changes in CO2 growth rates can mostly be explained by natural climate variability. Our analysis also shows that the decadal average growth rate, linked primarily to human activity, has fluctuated around an all-time high value of ~1.5 ppm yr−1 over the past 20 yr. A statistical model analysis is performed to identify the regions which have the maximum influence on the observed growth rate anomaly at Mauna Loa.

Effects of fuel and forest conservation on future levels of atmospheric carbon dioxide

Between Scylla and Charybdis: energy, carbon dioxide, and indoor environmental quality