1. S. Pavlova and L. Nenova, “Peculiarities in climate variations during last 30-ty years at the Obraztsov chiflik, region Rousse,” in Scientific Works, University of Rousse, Issue 47, Series 1.2 (2008), pp. 75–80. in Bulgarian.
2. http://www.nasa.gov/topics/earth/features/climate by any other name.html.
3. http://earthobservatory.nasa.gov/glossary/?mode=all.
4. National Report on the Status and Protection of the Environment in Bulgaria in 2012 (Executive Environment Agency, Ministry of Environment and Water), available at www.eea.government.bg.
5. V. Alexandrov, P. Simeonov, V. Kazandjiev, G. Korchev, and A. Jotova, Climate Change (National Institute of Meteorology and Hydrology, BAS, Sofia, October 2010), p. 48. in Bulgarian.