Monday, July 21, 2014

New paper finds a decrease of sunshine in Iran since 2000. A cause of the 'pause'?

A paper published today in the International Journal of Climatology finds dimming of sunshine occurred in Iran from the early 1960's to late 1970's [during the 1970's ice age scare], followed by sunshine brightening from the early 1980's through the end of the 20th century [in alignment with global warming], and a renewed dimming during the 2000's [in alignment with the 'pause' of global warming]. 

According to the authors,
"The annual sunshine duration mean time series shows a decrease from the early 1960s to the late 1970s, in line with the widespread dimming of surface solar radiation observed during this period. By the early 1980s, there is an increase in sunshine through the end of the 20th century, aligning with a well-known and well-documented brightening period. In addition, a renewed dimming is observed during the 2000s, with a sharp drop in 2009."
Many other peer-reviewed papers have documented "global dimming" and "global brightening" observed worldwide during these same approximate periods, and which correlate remarkably well to global temperature changes. Sunshine [solar radiation which reaches the surface after clouds/aerosols] is much better correlated to global temperature changes than CO2 levels [of which only 15 ppm or 0.0015% of the atmosphere is from burning of fossil fuels]. 



New evidence on the dimming/brightening phenomenon and decreasing diurnal temperature range in Iran (1961–2009)

Fatemeh Rahimzadeh et al

For a better understanding of multidecadal climate change, as well as for the production of solar power, there is a growing need for knowledge of the trends in incident sunlight at the Earth's surface, but a lack of a long-term sunlight time series dictates that a proxy measure is needed. In this study, variations of sunshine duration and diurnal temperature range (DTR) are used as proxies for surface solar radiation. Annual and seasonal composites of both variables from 29 stations are analyzed from 1961 through 2009 across the different types of climates of Iran. The annual sunshine duration mean time series shows a decrease from the early 1960s to the late 1970s, in line with the widespread dimming of surface solar radiation observed during this period. By the early 1980s, there is an increase in sunshine through the end of the 20th century, aligning with a well-known and well-documented brightening period. In addition, a renewed dimming is observed during the 2000s, with a sharp drop in 2009. A linear trend estimated over the 1961–2009 period was not found to be statistically significant. However, the annual DTR [daily temperature range] time series shows a widespread and statistically significant decrease since the 1960s, although the series ends without relevant variations after the 1990s. An agreement in the interannual variability of sunshine and DTR is observed except for the summer season. On decadal time scales, only the spring DTR series shows a partial agreement with sunshine series. Nevertheless, the recent leveling off in the DTR series supports a transition in the radiative regime.

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