In boreal coniferous areas, there has been an increase in the transporting of terrestrial-derived dissolved organic carbon  into rivers and lakes, which has caused increased opacity and a shift toward a brown colour . There was little assessment of this in AR5. This process is driven by climate change, and stems from hydrological intensification, greening of the Northern Hemisphere and degradation of carbon sinks in peatlands  . These factors enhance terrestrial productivity, alter vegetation communities and affect the hydrological control of the production and transport of DOC . Non-climate-related drivers of browning are: declining atmospheric sulphur deposition, forestry practices and LULCCs .
IPCC
Climate Change 2022: Impacts, Adaptation and Vulnerability
IPCC Report