Climate trends at Diekirch, Luxembourg: part 2b (atmospheric CO2)

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.

 

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The upcoming last part in this 3 part series on CO2 will discuss long time trends.

Climate trends at Diekirch, Luxembourg: part 2a (atmospheric CO2)

CO2, a gas that is essential to life, has become the villain par excellence during the last 20 years. Not because its undeniable positive effect on plant and crops, but because the “consensus” politicized climatology needed an easy to grasp culprit and enemy. CO2 which is after water vapour the second most important greenhouse gas has been chosen as the “climate killer” (what a horrible word!), even if the effect of its increasing atmospheric abundance still can not be quantified with precision and confidence. More than 20 years of lavishly financed climatology still has not delivered a steel-solid answer to the most often asked question: what is the warming potential (i.e. the climate efficiency) of increasing CO2 mixing ratios?

1. Measuring atmospheric CO2

CO2 is a very rare gas, with a relative abundance of about 0.04% in the atmosphere (or 400 ppmV, the unit most often used). Compare this to oxygen (20%) and nitrogen (nearly 80%), and you can imagine that measuring precisely such a small concentration (the correct expression would be “mixing ratio”) is not very easy. Before Keeling started his CO2 measurement series at Mauna Lo in Hawaii, chemical methods were used, often with relative great precision. My coauthor, the late Ernst-Georg Beck, was a specialist of these historical measurements (see here), which often show wildly varying concentrations, mostly due to the fact that these measurements were done in locations where local effects were important (as for instance plant photosynthesis and human/industrial emissions). Keeling’s admirable insight was to choose a location close to nearly always blowing ocean winds, far from vegetation cover and human activity. Mauna Loa was an ideal location, except for the fact that it is on an active volcano with heavy CO2 out-gassing from time to time; these periods have to be carefully monitored, and the CO2 measurements stopped during strong out-gassing events.

Keeling also was lucky to have a new class of gas sensors available: the NDIR ( = non-dispersive infrared) sensors. Many molecules absorb infrared radiation, and that absorption is proportional to the concentration of the absorbing gas. CO2 for instance absorbs IR radiation in the two wavelength regions of  4 and 15 um (the boxes added by me show the absorption at these wavelengths):

Keeling used an SIO infrared CO2 analyzer built by the Applied Physics Company (see here). Later instruments were built by Siemens and many other companies. These IR analyzers killed the chemical methods, as they were much easier to do, more precise and could be added without problems to automatic measurement systems. But as with all measurements, there remain problems.

2. Problems when measuring CO2

A first and obvious difficulty when measuring atmospheric CO2 is to be sure that the air sample to be measured does not contain other gases absorbing IR radiation at the same wavelength as CO2 does. As water vapour is the most important gas with overlapping absorption regions, the air sample must be dry. Expressing the measurement as a “mixing ratio” in ppmV makes adjustments to standard temperature and pressure conditions superfluous; this would not be the case if CO2 concentration would be given as a mass per unit volume (as xx ug/m3). All measurement systems have problems with stability. One solution to avoid drifts is to make correlation measurements: all sample measurement is followed by a dry clean air measurement (to give a zero level) and by a measure of a an air sample containing a precisely known amount of CO2. These zero and reference samples may be held in capsules mounted on a rotating disk which lies in the path of the IR radiation. As the CO2 concentration in ambient air is usually so low, the IR rays should make a very long path through that sample. This means that the IR rays make many paths between two mirrors mounted at the end of the sample chamber. The quality and cleanliness of these mirrors (often gold coated) is essential for proper operation.

On top of these continuous zero/span measurements, zero and span measurements using real gas samples filling the measuring chambers must be made at certain intervals. At meteoLCD we (i.e. Raoul Tholl and myself) do these calibration checks about every three weeks.

Making zero air is not too difficult: we use either a Sonimix zero air generator from the Swiss company LNI or a chemical drying/absorber column. Sample air with a given CO2 concentration is difficult to obtain when the concentration has to been known with great precision. Keeling’s son (Charles Keeling) long time had a near monopoly for delivering precise CO2 sample gas. At meteoLCD the best we can afford if a “primary standard” gas from PRAXAIR where the concentration is known to 1%. As we use bottles with about 600 ppmV CO2, this means that our uncertainty to the real concentration lies between 594 and 606 ppmV, a not negligible 12 ppmV amount! A bottle of such a gas costs close to 1000 Euro, including the location of the metallic container itself. It does not last much more than a year.

3. The instruments used at meteoLCD

Over the year, we used three different CO2 sensors, with only the last two being good enough for precise measurements and trend detection. From 1998 to 2001 we used a Gascard sensor made by Edinburgh Instruments (UK); from 2002 to 2007 an expensive MIR9000 from the French company Environnement SA was in action. Finally from 2008 on an E600 instrument from the US company Api-Teledyne is measuring atmospheric CO2. The MIR9000 was replaced because its mirrors started degrading. In an ideal world, one everlasting non-degrading sensor would have made us happy. Alas, reality bites hard when it comes to long-time precise measurements. These are never easy to do, and one can not but warn of the often naive and extreme confidence that the public (and even many scientists!) has on many climate related measurements. As the German say “wer misst, misst Mist!”.

The last figures shows the yearly mean CO2 mixing ratios measured with these three instruments:

The Gascard sensor clearly can not be relied upon for a correct investigation into increasing atmospheric CO2 concentrations.

 

(to be continued)

Climate trends at Diekirch, Luxembourg (part 1: air temperature)

I finished a couple of days ago the annual computation of climate trends calculated from the measurements at meteoLCD, Diekirch (Luxembourg). As usual, the numbers show a much less spectacular evolution than the emotional media reports suggest.

1. Lets start by the ambient air temperature:

The thermometers have not been displaced since 2002: the calculated blue regression line for 2002 to 2015 shows no warming, but a very small cooling!

A very similar picture is given by the temperature data of our national meteorological station at the Findel airport. The next graph was made using the homogenized data of NASA’s Gistemp:

Here the cooling rate for the 2002 to 2015 period is -0.0058 °C/year, quite negligible!

 

Did you hear the anthem  “there are no more winters?” Actually this ongoing 2016 winter really seems absent, but the overall picture for  1998-2015 is a remarkable cooling:

This plot of the December-January-February winter periods shows a visible cooling of 0.6°C per decade at the Findel airport. If we restrict our analysis to the 2002-2015, there still is no serious warming to be seen at the Findel: just a meager +0.08 °C warming per decade, very close to zero.

Our Diekirch data for the 2002-2015 winters also show only a modest winter warming of 0.5°C/decade and a good correlation with the NAO (North Atlantic Oscillation), a natural phenomenon which has a big influence on European climate: note how the trend lines of Diekirch, the Findel, Germany (DE) and the NOA index are very similar.

You might compare this  with the January trend of the German weatherstations given at the NoTricksZone blog!

 

Finally let us finish this first part with a look on the DTR = daily temperature range = daily Tmax – daily Tmin. The global warming advocates always point to this measure as a sign for an ongoing warming caused by human activity: global warming should decrease the DTR, because it would make the nights warmer than the afternoons, and as a consequence decrease the DTR. Here our Diekirch data:

All trends are practically zero: +0.2 °C/decade from 1998 to 2015 and -0.1 °C/decade for 2002-2015.

So lets finish this first part with a first conclusion: no big warming seen here in Luxembourg since at least 14 years!

 

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to be continued…..