WEATHER CLIMATE WATER The State and the Variations of Greenhouse Gases in the Atmosphere The content of this communication is based on the information that is included in the annual WMO Greenhouse Gas Bulletins produced during the last 14 years on the basis of the long-term high- quality observations undertaken by the global network and taking into consideration the recent advances in greenhouse gas research. The information is prepared by the Scientific Advisory Group on Greenhouse Gases under the Global Atmosphere Watch (GAW) Programme of WMO. 1. Current levels of Greenhouse Gases for carbon dioxide (CO2), methane (CH4) and in the atmosphere and trends nitrous oxide (N2O) reached new highs in the past years. In 2018, the global averaged CO2 mole fraction was 407.8±0.1 ppm, 2.2 ppm higher 1.1 Globally averaged levels in 2018 and 2017 than in 2017. Preliminary data from a subset of The latest analysis of observations from the greenhouse gas (GHG) observational sites for GAW Programme shows that globally averaged 2019 indicate that CO2 concentrations are on surface mole fractions (the quantity representing track to reach or even exceed 410 ppm by the concentration) calculated from this in situ network end of 2019. 410 1900 335 (a) (a) (a) 400 1850 330 390 325 1800 380 320 1750 370 315 1700 mole fraction (ppm) 360 mole fraction (ppb) 310 2 4 O mole fraction (ppb) 2 CH N CO 350 1650 305 340 1600 300 1985 1990 1995 2000 2005 2010 2015 1985 1990 1995 2000 2005 2010 2015 1985 1990 1995 2000 2005 2010 2015 Year Year Year 4.0 20 2.0 (b) (b) (b) 15 3.0 1.5 10 2.0 1.0 5 growth rate (ppb/yr) growth rate (ppm/yr) 4 2 1.0 0.5 O growth rate (ppb/yr) 2 0 CH N CO 0.0 -5 0.0 1985 1990 1995 2000 2005 2010 2015 1985 1990 1995 2000 2005 2010 2015 1985 1990 1995 2000 2005 2010 2015 Year Year Year Figure 1. Evolution of the global averaged mole fractions for the major greenhouse gases CO2, CH4 and N2O from 1985 until 2018, based on the WMO GAW in situ network observations. The red line depicts the de-seasonalized trend. The bottom plots show the respective monthly growth rates derived from the evolution of the global averages for each of the gases during the same period. A full global analysis completed for the three There is to this date no sign of the peaking of the main greenhouse gases shows that in 2017, global greenhouse gas levels and CO2 continued globally averaged mole fractions of CO2 were to increase at the record growth rates during the 405.6 ±0.1 ppm, CH4 at 1859 ±2 ppb and N2O last decade. at 329.9 ±0.1 ppb. These values constitute, respectively, 146%, 257% and 122% of pre- 1.2 The global network industrial levels (pre-1750). The GAW Programme (http://www.wmo.int/ The increase in CO2 from 2017 to 2018 was equal gaw) coordinates systematic observations and to that from 2016 to 2017 but smaller than that analysis of greenhouse gases and other trace observed from 2015 to 2016. This annual increase species. Sites where greenhouse gases have been is practically equal to the average growth rate over measured in the last decade are shown in Figure 2. the last decade. The influence of the El Niño event The GAW greenhouse gas network has been that peaked in 2015–2016 and contributed to the designed to measure the atmospheric content increased growth rate in 2015–2016, has sharply very accurately, with so called compatibility declined in the years 2017 and 2018. The growth goals for CO2 of 0.1 ppm (at a value of about rate of CO2 averaged over three consecutive 400 ppm this is 0.02% accuracy and precision) decades (1985–1995, 1995–2005 and 2005–2015) and 1 ppb for CH4 (at 1850 ppb this is 0.05% increased from 1.42 ppm/y to 1.86 ppm/y and to accuracy and precision). That means that any value 2.06 ppm/y with the highest annual growth rates measured at a GAW station can be compared observed during El Niño events. with any other station within that uncertainty. The greenhouse gas community undertakes For CH4, the increase from 2016 to 2017 is efforts to review the measurement techniques lower than that observed from 2015 to 2016 but and the global requirements for the quality of practically equal to the average over the last measurements and harmonized protocols at the decade. For N2O, the increase from 2016 to 2017 biannual meetings of expert taking place since was higher than that observed from 2015 to 1975 and co-organized by the International Atomic 2016 and practically equal to the average growth Energy Agency since 1997. rate over the past 10 years. Figure 1 shows the evolution of the global mean values derived from Measurement data are reported by participating the WMO GAW global observational network for countries and archived and distributed by the the major greenhouse gases. World Data Centre for Greenhouse Gases (WDCGG) Figure 2. The WMO GAW Ground-based Aircraft Ship GHG comparison sites network of in situ CO2 and CH4 gas observations. 2 Atmospheric CO2 at Mauna Loa Observatory Scripps Institution of Oceanography 400 NOAA Earth System Research Laboratory 380 360 ts per million r Pa 340 19 320 Figure 3. The longest time series of high eptember 20 S precision CO2 in the atmosphere is from 1960 1970 1980 1990 2000 2010 2020 Mauna Loa, Hawaii. (https://www.esrl. noaa.gov/gmd/ccgg/trends/) Year at the Japan Meteorological Agency. The data are 2. Variability of greenhouse gas levels available free of charge for interested audience. 2.1 Spatial and temporal variations in the 1.3 Initiation of the greenhouse gas measurements greenhouse gas levels Measurements of atmospheric CO2 can provide There is substantial variability in the levels strong insights into human induced variations in of greenhouse gases within individual years the global carbon cycle. The rise in atmospheric (seasonal cycle), between years and between CO2 has been well documented since 1958, when different geographic regions. An example of the high precision measurements began at Mauna temporal-spatial variability of CO2 is presented Loa, under the direction of C. D. Keeling, as shown in Figure 4. The variability of CO2 in the Northern in Figure 3. The practices applied then to ensure Hemisphere is larger than in the Southern high-quality measurements were adopted for the Hemisphere. The seasonal cycles (the wiggles observations by GAW participants and are currently within one year in Figure 4) are clearly larger in applied at over one hundred stations worldwide. amplitude in northern high and mid-latitudes and small in the Southern Hemisphere. The Figure 3 represents the so called “Keeling curve” seasonal cycle in the Northern Hemisphere is and shows the monthly mean CO2 mole fractions mainly dominated by the land biosphere, and it is measured at Mauna Loa Observatory, Hawaii. The characterized by rapid decreases with 5–20 ppm National Ocean and Atmospheric Administration from June to August and large returns of similar (NOAA) started its own CO2 measurements in magnitude from September to December. May 1974, and they have run in parallel with Large-scale spatial gradient exists for the other those made by the Scripps institute since then. greenhouse gases as well. The Mauna Loa data are being obtained at an altitude of 3400 m in the northern subtropics and 2.2 Variability of the greenhouse gas levels at are very similar to but different from the globally the individual stations averaged CO2 concentration at the surface due to the global mixing and smoothing of the signals All GAW stations show the same global increases, (see section 2.2). Preliminary analysis shows that mixed with more local influences depending CO2 annual mean mole fraction at Mauna Loa in on the station location and height. These local 2018 reached 408.52 ppm (in comparison with influences can be used to study the local and/or 407.8 ppm globally averaged) and the increase regional sources and sinks of the greenhouse from 2017 to 2018 was 1.97 ppm. From January gases. These signals help to reduce uncertainties 2019 to August 2019 the increase in the mole of our emission estimates or warn for emissions fraction (de-seasonalized trend) was 0.85ppm. signals from unknown sources or previously 3 ppm 420 410 400 390 380 370 360 350 340 80N 60N 40N 20N EQ Latitude 20 S 40 S 60 S 2015 2005 2010 Figure 4. Variation of zonally averaged 80S 1995 2000 1985 1990 Year monthly mean CO mole fractions 340 360 380 400 ppm 2 calculated by WDCGG based on the observational data. not captured processes under the influence of latitude in Europe at Pallas station (part of GAW ongoing climate change that feedback into the contributing network ICOS) in northern Finland. greenhouse gas emissions, e.g. droughts, floods, This station, like now many of the GAW stations, land use changes and permafrost melting. has continuous measurements at high temporal hourly resolution, which delivers more information Figure 5 demonstrates the CO2 atmospheric signal than the traditional weekly or bi-weekly flask captured at three stations in Japan over the period measurements. The black dots here identify 1987 until now, showing similar signals as Mauna the hourly observations that show even more Loa but mixed with local variability. The signal variability, linked to signals from the natural from all stations captures the global increase carbon cycle and anthropogenic emissions.