Earth’s changing climate is expected to have significant physical impacts along the coast and estuarine shorelands of Oregon, ranging from increased erosion and inundation of low lying areas, to wetland loss and increased estuarine salinity. The environmental changes associated with climate change include rising sea levels, increased occurrences of severe storms, rising air and water temperatures, and ocean acidification. The combination of these processes and their climate controls are important to beach and property erosion, flood probabilities, and estuarine water quality, with the expectation of significant changes projected for the 21st century.

Coastal change and flood hazards along the Oregon coast are caused by a number of ocean processes, each of which has significant climate controls such that the severity and frequency of the hazards in the future can be expected to increase. There is near certainty that the rate of sea-level rise will increase in the future as a result of global warming, with the portential of greater than a 1.0 meter increase in sea level by 2100. Evaluating the consequences of intensigied and more frequent hazards is complicated by Oregon's tectonic setting, with there being significantly different rates of land uplift along the coast. Taken together, the variable rate of uplift plus the present-day rate of sea level rise, some stretches of the coast are submerging as the sea level rise is greater than the tectonic uplift, whereas other areas are emerging where the reverse is true. The prospects are that with accelerated rates of sea level rise, the entire coast will eventually be submerging and experience significantly greater erosion and flood impacts than at present day.

Another long-term trend is increasing storm intensities and the heights of the waves they generate. In addition, the periodic occurrence of major El Niños in the future will compound the impacts of increasing sea levels and waves, resulting in severe episodes of coastal erosion and flooding, as experienced during the El Niño winters of 1982-83 and 1997-98. At present it is not known whether or not El Niño intensity and frequency will increase under a changing climate. With these multiple processes and their climate controls having important roles in causing erosion and flooding along the Oregon coast, it is challenging to collectively analyze them with the goal of providing meaningful assessments of future coastal hazards during the next several decades.

Coastal infrastructure will come under increased risk to damage and inundation under a changing climate with impacted sectors including transportation and navigation, coastal engineering structures (seawalls, riprap, jetties etc.) and flood control and prevention structures, water supply and waste/storm water systems, and recreation, travel and hospitality.

It is likely that regional coastal climate change will result in changes in the intensity and timing of coastal upwelling, shifts in temperatures and dissolved oxygen concentrations, and alteration of the carbonate chemistry (ocean acidification) of nearshore waters. The combination of these meteorological and nearshore ocean changes will exert stress on the communities of near-coastal and estuarine organisms. The range of community responses to the climate change stressors may include elevational shifts in the distribution of submerged aquatic vegetation, disruption of shell formation for calcifying organisms, alteration of the phenology of phytoplankton blooms, shoreward migration of tidal marshes, and increased colonization by non-indigenous aquatic species.

Unfortunately, significant knowledge gaps remain, impairing our ability to accurately assess the impacts of climate change along our coast and estuarine shorelands. For example, the uncertainty of future global sea level rise is significant with credible projections ranging from less than 0.5 m to as much as 2.0 m by 2100. At present we do not conclusively understand the climate controls on increasing storm intensities and wave heights and therefore have a very limited ability to project future trends in coastal storm impacts. The magnitude and frequency of major El Niños has significant implications for the state of Oregon; however, at this time we are unable to assess whether or not these will increase in the future due to climate change. Further, the long-term time-series data necessary to definitively identify perturbations of estuarine communities that can be attributed to anthropogenic climate change are lacking and therefore our understanding of anticipated shifts remain largely speculative.