The environmental implications of tidal stream energy extraction need to be evaluated against the potential climate change impacts on the marine environment. Here we study how hypothetical very large tidal stream arrays and a business as usual future climate scenario can change the hydrodynamics of a seasonally stratified shelf sea. The Scottish Shelf Model, an unstructured grid three‐dimensional ocean model, has been used to reproduce the present and the future state of the NW European continental shelf. Four scenarios have been modeled: present conditions and projected future climate in 2050, each with and without very large scale tidal stream arrays in Scottish Waters (UK). It is found that where tidal range is reduced a few centimeters by tidal stream energy extraction, it can help to counter extreme water levels associated with future sea level rise. Tidal velocities, and consequently tidal mixing, are also reduced overall by the action of the tidal turbine arrays. A key finding is that climate change and tidal energy extraction both act in the same direction, in terms of increasing stratification due to warming and reduced mixing; however, the effect of climate change is an order of magnitude larger.