Treelines have long been recognized as important ecotones and likely harbingers of climate change. However, over the last century many treelines have been affected not only by global warming, but also by the interactions of climate, forest disturbance and the consequences of abrupt demographic and economic changes. Recent research has increasingly stressed how multiple ecological, biophysical, and human factors interact to shape ecological dynamics. Here we highlight the need to consider interactions among multiple drivers to more completely understand and predict treeline dynamics in Europe.

To support climate research, the World Climate Research Programme (WCRP) initiated a new radiometric network, the Baseline Surface Radiation Network (BSRN). The network aims at providing validation material for satellite radiometry and climate models. It further aims at detecting long-term variations in irradiances at the earth's surface, which are believed to play an important role in climate change. The network and its instrumentation are designed 1) to cover major climate zones, 2) to provide the accuracy required to meet the objectives, and 3) to ensure homogenized standards for a long period in the future. The limits of the accuracy are defined to reach these goals. The suitable instruments and instrumentations have been determined and the methods for observations and data management have been agreed on at all stations. Measurements of irradiances are at 1 Hz, and the 1-min statistics (mean, standard deviation, and extreme values) with quality flags are stored at a centralized data archive at the WCRP's World Radiation Monitoring Center (WRMC) in Zurich, Switzerland. The data are quality controlled both at stations and at the WRMC. The original 1-min irradiance statistics will be stored at the WRMC for 10 years, while hourly mean values will be transferred to the World Radiation Data Center in St. Petersburg, Russia. The BSRN, consisting of 15 stations, covers the earth's surface from 80°N to 90°S, and will soon be joined by seven more stations. The data are available to scientific communities in various ways depending on the communication environment of the users. The present article discusses the scientific base, organizational and technical aspects of the network, and data retrieval methods; shows various application possibilities; and presents the future tasks to be accomplished.

Means and trends of shortwave irradiance at the earth’s surface are calculated from pyranometer measurements stored in the Global Energy Balance Archive (GEBA) database. The GEBA database contains the most comprehensive set of shortwave irradiance monthly means. The relative random error of measurement is approximately 5% of a monthly mean in general and approximately 2% of a yearly mean. The shortwave irradiance yearly means are analyzed in a 2.5° × 2.5° grid. In average example grid cells in Europe (no large altitude differences, no coasts), the difference of shortwave irradiance yearly means measured at different stations (station effect) is less than 5% of the cell mean, and the interannual variability is approximately 4% of the cell mean. On most continents, shortwave irradiance decreases significantly in large regions, and significant positive trends are observed only in four small regions.