10 Recent Climate-Induced Changes in Freshwaters in Denmark Erik Jeppesen 1,2,3 , Brian Kronvang 1 , Torben B. Jørgensen 1,4 , Sø re n E. Larse n 1 , Hans E. Andersen 1 , Martin Søndergaard 1 , Lone Liboriussen 1 , Rikke Bjerring 1 , Liselotte S. Johansson 1 , Dennis Trolle 1 , and Torben L. Lauridsen 1,2 1 Department of Bioscience, Aarhus University, Denmark 2 Sino-Danish Centre for Education and Research ( SDC) , Beijing, China 3 Greenland Climate Research Centre ( GCRC) , Greenland Institute of Natural Resources, Nuuk, Greenland 4 Limfjordssekretariatet, Nørresundby, Denmark 10.1 I ntroduction As a result of the Intergovernmental Panel on Climate Change reports, it is now widely accepted that global warming is a fact. It is also recognized that the extent of the effects will differ at different locations, being stronger at high latitudes and less strong at lower latitudes (IPCC 2007). According to a set of regional climate models, Denmark can expect an overall warmer climate and particularly higher temperatures in late summer and winter (van Roosmalen et al . 2010). An overall wetter climate can be expected, with more precipitation during winter, but likely lower precipitation during summer (van Roosmalen et al . 2010). Such changes will have profound effects on discharge, nutrient input, temperature, water column stability (in lakes), nutrient dynamics as well as biological structure and dynamics. In this chapter we show that Danish freshwaters are already facing changes that can be attributed to the recent warming during the past two decades. We use long-term data from 18 streams and between 20 and 250 lakes. Climatic Change and Global Warming of Inland Waters: Impacts and Mitigation for Ecosystems and Societies, First Edition. Edited by Charles R. Goldman, Michio Kumagai and Richard D. Robarts. © 2013 John Wiley & Sons, Ltd. Published 2013 by John Wiley & Sons, Ltd.