1. Introduction to monitoring of greenhouse gases and aerosols
2.1 Climate gases with natural and anthropogenic sources
2.1.1 Carbon dioxide (CO 2 )
Carbon dioxide (CO2) is the most important anthropogenic greenhouse gas with a radiative forcing of 1.82 W m-2 since the year 1750, and an increase since the previous IPCC report (AR4, 2007) of 0.16 Wm-2 (Myhre et al., 2013b). Etminan et al. (2016) presented revised forcing estimates for all main greenhouse gases (see section 1.4.1 at page 23), and confirmed the forcing estimates for CO2, with only minor changes.
The increase in forcing is due to the increase in concentrations over these last years. CO2 is the end product in the atmosphere of the oxidation of all main organic compounds, and it has shown an increase of as much as 40 % since the pre industrial time (Hartmann et al, 2013).
This is mainly due to emissions from combustion of fossil fuels and land use change. CO2
emissions from fossil fuel burning and cement production increased by 2.3% in 2013 since 2012, with a total of 9.9±0.5 GtC (billion tonnes of carbon) equal to 36 GtCO2 emitted to the atmosphere, 61% above 1990 emissions (the Kyoto Protocol reference year). Emissions are projected to decrease slightly (-0.6%) in 2015 according to Global Carbon Project estimates http://www.globalcarbonproject.org, it is still too early to assess and evaluate this.
NILU started CO2 measurements at the Zeppelin Observatory in 2012 and the results are presented in Figure 9, together with the time series provided by ITM, University of Stockholm, back to 1988. ITM provides all data up till 2012 and we acknowledge the effort they have been doing in monitoring CO2 at the site. After upgrading Birkenes in 2009, there are continuous measurements of CO2 and CH4 from mid May 2009 also at this site.
The atmospheric daily mean CO2 concentration measured at Zeppelin Observatory for the period mid 1988-2016 is presented in Figure 9 upper panel, together with the shorter time series for Birkenes in the lower panel.
The results show continuous increase since the start of the observations at both sites. As can be seen there are much stronger variability at Birkenes than Zeppelin. At Zeppelin the largest variability is during winter/spring. For Birkenes it is high variability all year around. In
summer there is also a clear diurnal variation with high values during the night and lower values during daytime (not shown). This is mainly due to changes between plant
photosynthesis and respiration, but also the general larger meteorological variability and diurnal change in planetary boundary layer, particularly during summer contributes to larger variations in the concentrations. In addition to the diurnal variations, there are also episodes with higher levels at both sites due to transport of pollution from various regions. In general,
Figure 9: The atmospheric daily mean CO2 concentration measured at Zeppelin Observatory for the period mid 1988-2016 is presented in the upper panel. Prior to 2012, ITM University of Stockholm provides all data, shown as orange dots and the green solid line is from the Picarro instrument installed by NILU in 2012. The measurements for Birkenes are shown in the lower panel, the green line is the daily mean concentration.
1988 1990 1992 1994 1996 1998 2000 2002 2004 2006 2008 2010 2012 2014 2016 340
350 360 370 380 390 400 410 420
ppm CO2
Year
2010 2011 2012 2013 2014 2015 2016 2017
370 380 390 400 410 420 430 440 450
ppm CO 2
Year
there are high levels when the meteorological situation results in transport from Central Europe or United Kingdom at Birkenes, and central Europe or Russia at Zeppelin.
The maximum daily mean value for CO2 in 2016 was 439.5 ppm at Birkenes 25th August. In this period there was transport of air from central Europe. At Zeppelin the highest daily mean value was 416 ppm at 20th November 2016, and the air was transported from Kola Peninsula and western Siberia with the large oil and gas installations.
Figure 10 shows the development of the annual mean concentrations of CO2 measured at Zeppelin Observatory for the period 1988-2016 in orange together with the values from Birkenes in green since 2010. The global mean values as given by WMO (WMO, 2017) in black.
The yearly annual change is shown in the lower panel.
Figure 10: Upper panel: the annual mean concentrations of CO2 measured at Zeppelin Observatory for the period 1988-2016 shown in orange. Prior to 2012, ITM University of Stockholm provides all data. The annual mean values from Birkenes are shown as green bars. The global mean values as given by WMO (2017) are included in black. The yearly annual change is shown in the lower panel, orange for Zeppelin, green for Birkenes.
The global mean increase for CO2 from 2015 to 2016 was 3.3 ppm (WMO, 2017), the largest annual increase ever reported by WMO. The annual mean values for Birkenes and Zeppelin are higher than the global mean as there are more anthropogenic sources and pollution at the Northern hemisphere. The mixing to the southern hemisphere takes time, ca 2-3 years. The annual change shown in the lower panel shows an increase of only 1.6 ppm at Zeppelin from 2014 to 2015 which is remarkably low compared to global mean increase and the reason for this would need an in depth analysis. The change from 2015 to 2016 was more as expected with 3.1 ppm compared to 3.3 ppm in the global mean increase. At Birkenes, the increase from 2015 to 2016 was higher; 4,7 ppm in one year. This is higher than the global increase, and also the strongest yearly growth we have detected since the start in 2009. The time series for CO2 at Birkenes is short and the reported trends should be used with caution. In short time series the end years will have relatively high impact on the trends.
A recent paper in Nature Geoscience (Myhre et al, 2017) is commenting on the relation between forcing of CO2 and the CO2 concentrations. Halfway to a doubling in the CO2
concentration is 417 ppm, which will be reached before 2025 with current CO2 growth rates.
However, with a global mean CO2 abundance in 2016 at 403 ppm the halfway point to a doubling of CO2, in terms of radiative forcing, has been reached. Hence, at CO2
concentrations between 393 ppm and 417 ppm we are more than a halfway to a doubling of CO2 in terms of radiative forcing, but not in concentration (see also see section 1.4.1).
Key findings for CO2: CO2 concentrations have increased all years subsequently, in accordance with accumulation of gas in the atmosphere and the global development and increase in anthropogenic emissions. The new record levels in 2016 are 404.3 ppm at Zeppelin and 409.8 ppm at Birkenes. The increase from 2015 to 2016 is 3.1 ppm and 4.7 ppm, respectively, compared to global mean which was 3.3 ppm increase. Generally, the increase is now very high, and higher than previous years both globally, at Zeppelin, and at Birkenes in particular. It is urgent to understand the reasons more in detail, also the impact of natural sources and sinks on the annual variations. It is assumed that El Niño phenomenon in 2015/2016 contributed to increased growth through complex interactions between climate change and the carbon cycle.