The Oceans 2015 Initiative, Part I

Description

The report “The Oceans 2015 Initiative, Part I” aims to review knowledge published following AR5 and update understanding of the observed and projected impacts of climate change on physical and biological processes in the oceans. Key messages emerging from the report can be summarised as follows:

• The oceans have absorbed approximately 93% of the excess heat caused by global warming. Warming increases stratification, limiting the circulation of nutrients from deep waters to the surface. There is evidence that enhanced stratification and increasing temperature are causing a decline in dissolved oxygen concentration and expanding existing oxygen minimum zones (OMZs). Approximately 26% of anthropogenic CO₂ is absorbed by the oceans, resulting in a reduction in pH and carbonate ion concentration, termed ocean acidification.
• The ocean ecosystems are responding to the changing environment, but at different rates and magnitudes and with interspecific and geographic variation in responses. Warming causes shifts in species’ geographic distribution, abundance, migration patterns and phenology. Organisms that produce shells and skeletons from calcium carbonate are at most risk from ocean acidification. Decreasing dissolved oxygen concentrations and expanding OMZs will favour anaerobic metabolisers such as bacteria and small microbes whilst reducing habitat for larger, oxygen dependant organisms.
• The interaction of multiple drivers can amplify or alleviate each other’s effects. It is likely that marine organisms will experience a combination of warming, acidification and declining oxygen concentrations as well as regionally specific local stressors. This makes it difficult to predict the responses of individual species to multiple drivers, and species interactions make ecosystem-based projections challenging.

The report is complemented by “The Oceans 2015 Initiative, Part II - An updated understanding of the observed and projected impacts of ocean warming and acidification on marine and coastal socioeconomic activities/sectors”.

Reference information