Most lakes worldwide are warming, according to a survey of lake summer surface water temperatures (LSSWT) released in late 2015, the most comprehensive of its kind to date. Using both satellite and ground-based data obtained from 1985 to 2009 for 235 globally distributed lakes, the study found the average LSSWT increased 0.34°C/decade. Comparatively, the average air and ocean temperatures increased by 0.25°C/decade and 0.12°C/decade, respectively. The research was the product of an international collaboration among 57 institutions and was reported in Geophysical Research Letters (December 2015). See also: Air temperature; Lake; Ocean warming; Remote sensing; Satellite climatology; Satellite meteorology

Although the overall trend was warming, the degree of lake warming varied both globally and regionally. Factors influencing warming included latitude and elevation (geographic factors), lake depth, volume, and surface area (geomorphic factors), and cloud cover, summer air temperature, and sunlight (climate factors). For example, the highest warming rates were found among ice-covered lakes that experienced shorter ice-cover time, less cloud cover, and increased summer air temperature and sunlight exposure. See also: Climatology; Cloud; Geography; Geomorphology; Heat balance, terrestrial atmospheric

By volume, lakes represent a small portion of the world’s freshwater supply. However, lakes are important freshwater ecosystems and regionally important sources of drinking and irrigation water. The implications of future lake warming do not bode well as they include, for example, lower water levels (from greater evaporation), degradation of water quality, loss of habitat for cold-water species, introduction of invasive species, and harmful algal blooms. See also: Allergenicity of cyanobacteria; Freshwater ecosystem; Invasive species and their effects on native species; Irrigation (agriculture); Phytoplankton; Water resources; Water supply engineering