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Improved understanding of past climatic variability from early daily European Instrumental Sources

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Exploitable results

The main results are: 1) To produce daily pressure and temperature series for carefully selected examples from European archives, i.e. Padova (It., 1725-present), Milan (It., 1763-present), Central Belgium (Be., 1767-present, temperature only), Uppsala (Se., 1722-present), Stockholm (Se., 1756-present), San Fernando/Cadiz (Es., 1776-present) and St Petersburg, Russia (1743-present). These series have been augmented with newly-produced series (Central England, UK., 1772-present). Another important aspect is the high (daily) resolution of the series, which allows more insight into past variability, as monthly averages smooth out and mask many important climatic features; 2) To analyse and correct errors in homogeneities in the long series. Metadata is considered as important as data, since metadata is fundamental not only to correct, make homogeneous and interpret data, but also to distinguish apparent climatic changes, due to variations in observational methodology, from real climatic changes. The long series are affected by a huge number of problems, and not only casual reading errors. Reading errors are mainly randomly distributed and they disappear when the averages of many series are calculated. The real problem is the presence of systematic errors that vary in the course of time, the changes in measuring style due to national or international regulations or the simple evolution of technology, that affected the observations in the same way and simultaneously in all sites. The evaluation of the data quality, as deduced from the statistical analysis of the data, appears more optimistic than the errors deduced by looking at the instruments capability and the field practice. One of the aims of IMPROVE is to encourage critical revision and improvement of the quality of existing series, while providing, at the same time, examples of typical errors to be removed and identifying the procedures needed to amend them. 3) The actual warming rate has been proven to be at such a slow rate that temperature change i.e. 0.06 °C /decade that in most cases is smaller than the instrumental resolution and can hardly be directly detected. This occurs especially with temperature averages, for which the climate signal is often below the noise and/or the instrumental limit. However, looking at the frequency distribution of extreme events, things appear differently. Extreme events depart so much from the average, that they can be easily detected, and in computing their signal to noise ratio the observational error becomes less relevant. IMPROVE has clearly demonstrated that this approach is very promising. An analysis of the distribution of extreme events has also shown that recent warming is characterised by an increase in frequency of the hottest days, in association with a decrease in frequency of the coldest. 4) The main results derived within IMPROVE will be published in a number of international journals and in a special issue of Climatic Change (printed also in a hard bound edition together with a CD containing the original series and those obtained with IMPROVE).