Archive for August, 2013

The O’Dowd paper on aerosols and global warming.

August 26, 2013


There is a lot of discussion in the blogosphere on the paper Cleaner air: Brightening the pollution perspective?” by  O’Dowd et al. (paywalled!) which suggests that European warming of the last decade(s) is (also) caused by a sky brightening: the good results of air-pollution control lead to a rise in the negative radiative forcing of the aerosols (i.e. the negative forcing becomes less negative), and as a consequence solar irradiance at ground level increases. This increase is at least partially responsible for the observed warming.

Colin O’Dowd and co-authors have published a similar free-access article in issue 11 of the bulletin of Royal Irish Academy’s Climate Change Sciences Committee (here). Wang et al published in 2012 a paper “Atmospheric impacts on climatic variability of surface incident solar radiation” which essentially follows the same path.

What makes me uncomfortable, is that both authors clearly affirm that we have an ongoing solar brightening in Europe (brightening and dimming is a seen as a decadal change in solar irradiance). Here is a figure from Wang’s paper showing the situation in Europe:

Wang_Climate_variabilityThe green line shows the anomaly (5 years smoothing applied) of solar irradiance, the blue of the inverted atmospheric optical depth (-AOT) and the red of the free (= cloudless) sky fraction. Clearly AOT declines after 2000, and solar irradiance increases.

O’Dowd et al conclude their investigation with “…the trends of reducing anthropogenic aerosol emissions and concentrations, at the interface between the North-East Atlantic and western-Europe, lead(ing) to a staggering increase in surface solar radiation of the order of ∼20% over the last decade.”

These are strong words, and paint a situation that is the contrary of what I have been measuring since about 15 years. Actually, in Diekirch (Luxembourg) we have an ongoing solar dimming since 1998, which has even become stronger after 2003 (the heat-wave year I would not dare to take as a starting point for a regression line!)


There also is no warming here, but we even measure a slightly cooling since 2002 (see here). What gives me some comfort that our measurements are not picked out of the blue, are the satellite data from Helioclim for Luxembourg (which alas stop at 2005):

Helioclim_solar_dimming_Luxbg_1985_2005The Helioclim plot shows a long-time dimming over two decades for Luxembourg!

Martin Wild from ETH (Zürich, Switzerland) is one of the world specialists in global dimming/brightening, and co-author of the Wang and Norris papers. He asserts that there was a dimming in Europe from 1950 to 1980, followed by two brightening periods of different magnitude from 1980 to 2000 and after 2000 (see here). So he is in consensus with the two other authors.

Assuming these authors correct, global European trends may clearly be very different from those of smaller specific regions. So one should be cautious to generalize a broad picture to regional scale, where the exact opposite might go on.

Let us conclude with another paper by Norris et al. “Trends in aerosol radiative effects over Europe inferred from observed cloud cover, solar ‘‘dimming,’’ and solar ‘‘brightening’’” which use the GEBA archive (Global Energy Balance Archive) and which give this picture:

GEBA_global_radiation_trendsGEBA_global_radiation_trends_legendThe blue dots correspond to decreasing, the red to increasing irradiance. Now watch the right part and the legends: all crossed circles correspond to statistically not significant trends, and clear circles to a situation where 25% or more data are missing. If we leave out these measurements, not much remains in the 1987-2002 part which allows to conclude to a brightening. Here the right part magnified:


If you keep only the statistically significant points and those with enough data you have 3 cooling points (Germany, France, Bulgaria) and three brightening (2 in northern Italy and one in Finland), see the arrows. Not so impressive!



  • Colin O’Dowd, Darius Ceburnis, Aditya Vaishya, S. Gerard Jennings, Eoin Moran : Cleaner air: Brightening the pollution perspective? AIP Conf. Proc. 1527, pp. 579-582; doi: (4 pages)
  • K. C. Wang, R. E. Dickinson, M. Wild, S. Liang: Atmospheric impacts on climatic variability of surface incident solar radiation. Atmos. Chem. Phys., 12, 9581–9592, 2012. doi:10.5194/acp-12-9581-2012 (link)
  • Joel R. Norris, Martin Wild:  Trends in aerosol radiative effects over Europe inferred from observed cloud cover, solar ‘‘dimming,’’ and solar ‘‘brightening’’. JOURNAL OF GEOPHYSICAL RESEARCH, VOL. 112, D08214, doi:10.1029/2006JD007794, 2007 (link)

Klima Angst article in Lëtzebuerger Land weekly

August 19, 2013


The weekly journal d’Lëtzebuerger Land has in its actual issue#33 from the 16th August 2013 an article by myself on 25 years of climate fear titled “Zeit zur Rückbesinnung” (in German); the layout is quite impressive, even if I had preferred a larger font :-).

A text-only PDF version is here.

Ambient air radioactivity peaks due to radon washout?

August 7, 2013

The last 7 days from 01 to 07 August 2013 give a nice example of the increase of ambient air radioactivity with precipitation. During these days we had at Diekirch 3 very short precipitation events, which leave a visible fingerprint in the data series of the gamma Geiger counter:

rain_and_rad_01to07Aug2013 We see that the short precipitation events (in blue on the top plot) correlate perfectly with activity peaks (in red on the bottom plot). The first event in the night of the 03 August has 3.4mm precipitation and an increase of radioactivity by about 19 nSv/h, to be compared to the “normal” increase for this period of the day of 3 nSv/h. So this rainfall event produced  approx. a 500% higher radioactivity level. The 3 events are too few to look for a relationship; but obviously the greatest precipitation event also produced the highest radioactivity rise.

This phenomenon is well-known and usually attributed to radon washout, with radon daughters like the gamma emitter Pb214 gathering on the instrument in the wet rainwater film. After evaporation has removed this wet cover, levels return to normal.

I found some discussions on this effect here:
If you have more to say on this, thank you for a comment.


08 Aug 13:  corrected units typing error: activity is nanoSv/h (nSv/h), not microSv/h (uSv/h)

10 Aug 13:  Two readers sent me interesting comments (thank you!), and I will summarize these here with their tacit authorization:

Antoine KIES is a friend, emeritus professor of physics of the University of Luxembourg (Laboratoire Physique des Radiations), and a well known radon and ambient radioactivity  specialist. He says this (translated from Luxembourgish): “This is a normal and well-known situation, as a short rain fall deposits the daughter products (as polonium, lead, bismuth) of radon which are attached to aerosols. As the periods of these radioactive daughters are short, the increase in measured gamma activity is a short peak. Precipitation can block the out gassing of radon from the soil, so usually one observes a minimum of activity when the soil is wet. The diurnal variation of ambient air activity is mostly caused by radon.”

Marcel Severijnen is a former head of the Environmental Monitoring Department of the Province of Limburg in the Netherlands and also has a climate blog. He writes (translated from German): “Twenty years ago I had in my room a terminal from the BMNI (Binnenlandse Zaken Meetnet Nucleaire Incendenten) which is a network with over 300 measuring stations (now integrated into the LMR (Landelijk Meetnet Radioactiviteit, see The peaks during heavy rain showers were always very visible, and represented something like a precipitation radar. Today values below 200 nSv/h are considered normal. Above this limit the RVIM makes an analysis of the situation and when 2000 nSv/h is reached, the local fire brigades are set on alert…”

The link to the Dutch network is very interesting. Luxembourg also has many “official” measuring stations (see here) but no website with real-time data (except our “unofficial” meteoLCD). Nevertheless monthly reports are available here.