Past trends and future projections of key atmospheric, oceanic, sea ice, and biogeochemical variables were assessed to increase our understanding of climate change impacts on Canadian Arctic marine ecosystems. Four subbasins are evaluated: Beaufort Sea, Canadian Arctic Archipelago, Baffin Bay/Davis Strait, and Hudson Bay Complex. Limited observations, especially for ecosystem variables, compromise the trend analyses. Future projections are predominately from global models with few contributions from available marine basin scale models. The assessment indicates a significant increase in air temperature, slight increases in precipitation and snow depth, and appreciable changes in atmospheric circulation patterns. Projections suggest an increase in storm strength and size, leading to enhanced storm surges and coastal erosion, a slight increase in wave heights, increases in gustiness, and small changes in mean wind speed. An Arctic-wide decrease in the extent of multiyear ice and a spatial and temporal increase in ice-free waters in summer have been observed and are projected to continue into the future. Limited observations of ocean properties show local freshening (Beaufort Sea) and summer warming (Baffin Bay). These trends are projected to continue along with localized strengthening in stratification. Increased ocean acidification has been observed and is projected to continue throughout the Canadian Arctic, leading to severely decreased saturation states of calcium carbonate (aragonite and calcite). Qualitative analysis of biological observations indicate large regional differences. Increased primary production and double bloom development is seen in areas of sea ice retreat where nutrient supply is sufficient, and unchanged or reduced production is seen where nutrients are low or suppressed in response to enhanced stratification. Future primary production projections show inconsistent results, with light-dependent increase or nutrient-limited decrease dominating, dependent on the model. For the next decade, natural intradecadal variability is expected to be of similar importance as longer-term trends. To improve our capacity to assess and project climate change adaptation in marine ecosystems, more consistent observations are needed, especially over marine areas and for biogeochemical variables. Higher resolution basin-scale models are also required to provide locally applicable projections relevant for Arctic communities and management units.