In this second part on CO2 measurements I will talk about short-time and seasonal CO2 variations. The media usually seem to suggest that CO2 levels are something of what the French call “un long fleuve tranquille”, i.e. a more or less uniform mixing ratio that increases steadily with time. Nothing could be more wrong! If stations near maritime borders have relatively small diurnal variations, the situation is very different in continental and rural locations.
1.The diurnal CO2 variations.
Let me start with a very recent example: the CO2 levels at Diekirch during the last 7 days (22 to 28 Feb 2016):
Obviously the daily CO2 variation is far from uniform: during the 22th Feb. the levels were nearly flat at about 375 ppmV, then became really variable during the next 4 days and returned to flat during the last 2 days. The highest peak of 465 ppmV reached during the morning hours of the 25th Feb. represent an increase of 85 ppmV (21%) above the previous low level of 380 ppmV. Why this formidable peak? Let us look at the other meteorological parameters: there was no precipitation, air pressure did not change much, but air temperature and wind speed varied remarkably.
This plot shows wind-chill in red, air temperature in blue and wind-speed in violet. Let us ignore the red curve, which represents a calculated parameter from air temperature and wind speed. The 25th Feb was the coldest day during this period, and wind-speed was close to zero. The 22th Feb. was a very windy day, and it also was warmer. Now we are in February, and CO2 lowering plant photosynthesis is practically in a dormant state. The next plot of solar irradiance (the blue curve) shows that the sun was shining at its best during the 25th, and was nearly absent the 22th.
So we can make an educated guess of the parameter which has the greatest influence on CO2 levels during our period: it can not be temperature, as warmer temperatures increase microbial soil activity and plant rotting, which both are CO2 sources. It can not be photosynthesis driven by solar irradiance , as the highest CO2 readings happen when this potential activity is highest. There remains one parameter: wind-speed! The night of the 25th was very cold, and as a consequence a strong inversion layer with minimal air movements lay as a blanket over the ground. The absence of air movements made ground air mixing with air at higher levels impossible, so all gases accumulated in this inversion layer. A further proof of the correctness of our detective work is given by the plot of the NO/NO2 concentrations, which we restarted measuring after a year long pause:
NO2 (blue) and NO (red) readings also peak the 25th February (a working day, Thursday), at practically the same time: CO2 peak is at 07:30 UTC, NO2/NO peak at 08:00. The first and certainly the latter show the fingerprint of morning traffic through the valley where lies the town of Diekirch.
The conclusion is: wind speed (air movements) are the main cause of high CO2 levels: low wind speed means poor air mixing, and high CO2 levels; high wind speed means the opposite. For many years I tried to push this explanation, which is practically ignored in the usual “consensus research”. The sole consolation was a first price as “best publication” for the paper I wrote in 2009 with the late Ernst-Georg Beck as coauthor, and which was published by Springer.
More information on diurnal CO2 patterns can be found in this paper I wrote with my friends Tun Kies and Nico Harpes in 2007. It contains the following graph which shows how CO2 levels changed during the passage of storm “Franz” the 11 and 12th January 2007.
2. Seasonal CO2 pattern
Seasonal CO2 pattern reflect the influence of vegetation (and microbial soil activity): during warmer sunny summer months, CO2 levels are as a general rule lower than during the colder sunny-poor periods. Plant photosynthesis is a potent CO2 sink, overwhelming the opposite source of microbial outgassing. The following figure shows that this photosynthesis influence is nearly nil at the South-Pole and becomes stronger at more Northern latitudes (last is Point Barrow in Alaska):
At Point Barrow (latitude 71°N) the seasonal swing is about 18 ppmV, at Mauna Loa (latitude 2°N = nearly at the equator), it is only 10 ppmV approx. Here is the 2015 situation at Diekirch (latitude close to 50°N):
The plot shows the monthly mean CO2 levels, together with a best-fit sinus-curve with an amplitude of 11.2 ppmV or a total swing of about 22 ppmV. These values are comparable to those measured at the German Hohenpeissenberg (HPB) and Ochsenkopf (OXK) stations. Be aware: not every year shows such a nice picture (look for instance here). A paper by Bender et al. from 2005 shows a seasonal swing at Amsterdam of about 16 ppmV, a further argument that our Diekirch measurements are not too bad!
A new paper from Boston University shows that urban backyards contribute nearly as much CO2 to the atmosphere as traffic emissions. There is a great discussion on this paper at the WUWT blog, as the paper does not seem to make a yearly balance of sources and sinks. Nevertheless, one commenter (Ferdinand Engelbeen) recalls that the yearly balance between photosynthesis (a sink) and microbial activity (a source) is slightly negative, i.e. photosynthesis removes more CO2 from the atmosphere than soil microbes and decomposing vegetation produce. Soils globally inject ca. 60 GtC (giga tons of carbon) into the atmosphere, to be compared with annual anthropogenic emissions about about 10 GtC.
The upcoming last part in this 3 part series on CO2 will discuss long time trends.