This study investigates the global responses of microbial metabolism in glacier-fed streams (GFSs) to glacier shrinkage. By analyzing 154 GFSs across major mountain ranges, the research reveals that these ecosystems are generally carbon and phosphorus limited. Threshold elemental ratios and low carbon use efficiencies (median: 0.15) support this resource limitation, aligning with maintenance metabolism of benthic microorganisms. Space-for-time substitution analyses suggest that glacier shrinkage will stimulate benthic primary production, alleviating carbon limitation. However, increasing streamwater temperature may intensify phosphorus limitation due to rising microbial demands and reduced subglacial phosphorus inputs. The study highlights a 'green transition' towards autotrophy in GFSs, shifting their microbial energetics. Fluvial ecosystems are highly heterotrophic and major CO₂ emitters. In contrast, GFSs, which drain poorly developed terrestrial vegetation, are often carbon limited. Glacier shrinkage is expected to alter resource supply and stoichiometry in GFSs. The study shows that GFSs are generally oligotrophic, with low dissolved organic carbon (DOC) concentrations. Nutrient concentrations vary across regions, with higher DIN in the Pamir and Tien Shan and lower in Southwest Greenland. Streamwater SRP concentrations are also regionally variable, with higher values in certain mountain ranges. These patterns are linked to underlying geologies, with higher SRP concentrations in areas with volcanic activity and basalts. The study finds that benthic chlorophyll-a, a proxy for algal biomass, is inversely related to streamwater turbidity, indicating increased algal biomass in GFSs as glaciers shrink. This 'greening' may alleviate carbon limitation and potentially push microbial metabolism towards phosphorus limitation. Resource limitation and microbial metabolism are influenced by threshold elemental ratios, with GFSs showing higher C:P and C:N ratios than the Redfield ratio, indicating widespread carbon limitation. Microbial carbon use efficiency (CUE) in GFSs is low, around 0.15, reflecting high maintenance metabolism and slow growth. CUE is positively related to benthic algal biomass, suggesting that increased autotrophic production may enhance microbial CUE. Temperature dependence of microbial production is observed, with a temperature sensitivity of 0.62 eV. However, temperature does not significantly affect respiration or CUE in GFSs. The study concludes that glacier shrinkage will lead to a 'green transition' in GFSs, with increased primary production and shifts in microbial energetics, potentially altering ecosystem functioning and carbon cycling.This study investigates the global responses of microbial metabolism in glacier-fed streams (GFSs) to glacier shrinkage. By analyzing 154 GFSs across major mountain ranges, the research reveals that these ecosystems are generally carbon and phosphorus limited. Threshold elemental ratios and low carbon use efficiencies (median: 0.15) support this resource limitation, aligning with maintenance metabolism of benthic microorganisms. Space-for-time substitution analyses suggest that glacier shrinkage will stimulate benthic primary production, alleviating carbon limitation. However, increasing streamwater temperature may intensify phosphorus limitation due to rising microbial demands and reduced subglacial phosphorus inputs. The study highlights a 'green transition' towards autotrophy in GFSs, shifting their microbial energetics. Fluvial ecosystems are highly heterotrophic and major CO₂ emitters. In contrast, GFSs, which drain poorly developed terrestrial vegetation, are often carbon limited. Glacier shrinkage is expected to alter resource supply and stoichiometry in GFSs. The study shows that GFSs are generally oligotrophic, with low dissolved organic carbon (DOC) concentrations. Nutrient concentrations vary across regions, with higher DIN in the Pamir and Tien Shan and lower in Southwest Greenland. Streamwater SRP concentrations are also regionally variable, with higher values in certain mountain ranges. These patterns are linked to underlying geologies, with higher SRP concentrations in areas with volcanic activity and basalts. The study finds that benthic chlorophyll-a, a proxy for algal biomass, is inversely related to streamwater turbidity, indicating increased algal biomass in GFSs as glaciers shrink. This 'greening' may alleviate carbon limitation and potentially push microbial metabolism towards phosphorus limitation. Resource limitation and microbial metabolism are influenced by threshold elemental ratios, with GFSs showing higher C:P and C:N ratios than the Redfield ratio, indicating widespread carbon limitation. Microbial carbon use efficiency (CUE) in GFSs is low, around 0.15, reflecting high maintenance metabolism and slow growth. CUE is positively related to benthic algal biomass, suggesting that increased autotrophic production may enhance microbial CUE. Temperature dependence of microbial production is observed, with a temperature sensitivity of 0.62 eV. However, temperature does not significantly affect respiration or CUE in GFSs. The study concludes that glacier shrinkage will lead to a 'green transition' in GFSs, with increased primary production and shifts in microbial energetics, potentially altering ecosystem functioning and carbon cycling.