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British Columbia is expected to experience more warming than the global average [70,71]. Even though air temperature is moderated by the ocean, air temperatures are projected to increase by 1.8°C by the 2050s and 2.7°C by the 2080s, and could reach of 3-5⁰C by the end of the 21st century if emissions continue at current rates [70–72]. On average, air temperatures are likely to increase by 0.1-0.6⁰C per decade [73].

The summer growing season is projected to lengthen and frost-free days to increase by 20-30 days by 2050-2080 [73] (see MaPP region Summary Table). Winter minimum temperatures across BC may increase by 4-9°C by 2080, and summer maximum temperatures may increase by 3-4°C [70,73].

Projected changes in precipitation in BC are expected to be relatively minor, especially when compared to the historical variability in the province. The Pacific Climate Impacts Consortium (PCIC) projections show that annual precipitation may increase by about 9% by the end of the 21st century, relative to the 1961-1990 baseline (see MaPP region Summary Table), while summer precipitation is projected to decrease by 10% [27,28].

Wetter winters are projected to lead to increased runoff in rivers and streams in the winter. Less precipitation will fall as snow in the winter, which is likely to result in a reduction of the spring snowpack by 55% by 2050 [41]. Glacial runoff in the spring has already declined in southern BC, and this is projected to occur for northern BC glaciers through 2050 and beyond [10,42]. Due to this reduction in snowpack, the spring freshet will likely occur earlier in the spring in many rivers. By the end of the century, spring streamflow will likely have increased significantly, while summer river levels will have decreased [44].

Extreme precipitation events will likely increase during some seasons and in some areas of the province [5,41,70,72]. Heavy precipitation events in BC include phenomena known as ‘atmospheric rivers’ where highly concentrated water vapour streams move moisture from tropical regions towards the poles. These occur frequently in the fall and winter in BC, and impact coastal areas with periods of intense precipitation and flood events [41,70,74]. More frequent atmospheric river events after 2040 (approximately double the current number per year) will affect ecosystems along the coast [74].

Global climate models project that the average global sea level will rise by up to 100-120cm by 2100 [10]. The rate of sea level rise will vary, depending on variations in ocean temperature increase and ocean current patterns. Relative sea level across the coast of BC is projected to rise by an average of 20-30 cm by 2100 (90% confidence interval of 10-50 cm) (MaPP regional table).

However, there are many uncertainties in the projections for sea level rise. Localized ocean currents, tidal patterns, and river discharge rates will also influence the observed rate of sea level rise to particular areas. For instance, some models project higher observed sea surface height (SSH) values along the northern coast of BC during the next century in winter and spring related to wind patterns and increasing river discharge [21].

Warming ocean temperatures will affect ecosystems and species across the world and within this region. In BC, sea surface temperatures are likely to increase by between 0.5°C to 2.0°C by the end of the century (2065-2078, relative to a 1995-2008 baseline) ([21]; see MaPP Regional Table; Maps). The rate of ocean temperature increase may accelerate, as consistent with the accelerating rise in global sea surface temperatures [14,75].

Ocean acidification is occurring faster as higher latitude areas, due to the effects of temperature on carbon dioxide absorption [76–78]). Globally, ocean acidification is projected to increase by 100% or more by 2100, but there is large uncertainty and variation among regions and climate scenarios [32,52,79]. Within the MaPP region, acidification is projected to continue to increase as carbon dioxide emissions continue to rise. Average pH levels could decline to between 7.69-7.96 (RCP8.5 and RCP2.6, respectively) by 2091-2100 [32,80].

Ocean oxygen concentrations have been declining in both pelagic (open ocean) and coastal waters for at least the past half-century [81]. Oxygen minimum zones in the open ocean have increased in area, and some coastal areas have low enough oxygen concentrations that marine species distributions and abundances have been affected [81]. Oxygen levels are likely to continue to decline in the northeast Pacific ocean, and coastal shelf and slope marine ecosystems are likely to lose well oxygenated habitats [57]. Seafloor habitats in the North Pacific could experience a reduction of 0.7-3.7% in oxygen levels by 2100 [54].

Ocean salinity is declining globally, along the BC coast, and within the MaPP region [82]. Freshwater discharge from glaciers is a significant contributor to the nearshore waters of BC. Coastal runoff contributes to maintaining the salinity levels along the coast, driven by glaciers, as well as watersheds driven by fall and winter seasonal precipitation. Large river systems (Fraser River, Naas River, Skeena River) also drain large watersheds and experience pronounced spring freshets. Coastal salinity levels are controlled mainly by these processes at the local scale rather than large-scale climate changes [55]. Salinity effects also influence total sea level rise through ocean expansion through global ocean warming [32,83,84].

Changes in wind and wave patterns may interact with other climate change projections such as sea level rise, but the projections of future winds and storm events are highly uncertain [36]. Storm intensities in the North Pacific increased during 1940-1998, and storm surge related winds and storms may become more frequent and intense as air and ocean temperatures increase [44,85].