Is the Last Years Abrupt Warming in the National Observatory of Athens Records a Climate Change Manifestation?

Instrumental data time series show an average global warming of approximately 0.90C over
the last century. Eastern Mediterranean air temperature follows the northern hemisphere (NH)
secular trend till 1970s, while the NH warming of the last 30 years is not noticeable in the
eastern Mediterranean till 1990s. National Observatory of Athens (NOA) meteorological time
series start from the last decades of the 19th Century, therefore are at first suitable for
detection of long term trends in the region. In this study we investigate whether the abrupt
increase of the NOA air temperature time series, which appears during the last few years, is
the finger-print of the broader scale climatic change or it is a discontinuity in the record of
urban effect or of station’s problems origin. It is shown that NOA air temperature records
display a statistically significant discontinuity attributable to change of the station thermometers
on 1995 and therefore NOA records must be treated with caution for long term air temperature
trends detection.