The ocean currently absorbs about a quarter of human-caused carbon dioxide emissions to the atmosphere, leading to ocean acidification that will alter marine ecosystems in dramatic yet uncertain ways.

This finding is from chapter 24 of Climate Change Impacts in the United States: The Third National Climate Assessment.

Process for developing key messages: A central component of the assessment process was the Oceans and Marine Resources Climate assessment workshop that was held January 23-24, 2012, at the National Oceanographic and Atmospheric Administration (NOAA) in Silver Spring, MD, and simultaneously, via web teleconference, at NOAA in Seattle, WA. In the workshop, nearly 30 participants took part in a series of scoping presentations and breakout sessions that began the process leading to a foundational Technical Input Report (TIR) entitled “Oceans and Marine Resources in a Changing Climate: Technical Input to the 2013 National Climate Assessment.”018aba6e-7bff-4124-ae9a-f2521e683bd1 The report, consisting of nearly 220 pages of text organized into 7 sections with numerous subsections and more than 1200 references, was assembled by 122 authors representing governmental agencies, non-governmental organizations, tribes, and other entities. The chapter author team engaged in multiple technical discussions via teleconferences that permitted a careful review of the foundational TIR018aba6e-7bff-4124-ae9a-f2521e683bd1 and of approximately 25 additional technical inputs provided by the public, as well as the other published literature, and professional judgment. The chapter author team met at Conservation International in Arlington, VA on 3-4 May 2012 for expert deliberation of draft key messages by the authors, wherein each message was defended before the entire author team before the key message was selected for inclusion in the report. These discussions were supported by targeted consultation with additional experts by the lead author of each message to help define “key vulnerabilities.”

Description of evidence base: The key message is supported by extensive evidence documented in the Oceans Technical Input Report018aba6e-7bff-4124-ae9a-f2521e683bd1 and additional technical inputs received as part of the Federal Register Notice solicitation for public input, as well as stakeholder engagement leading up to drafting the chapter. Numerous references provide evidence for the increasing acidity (lower pH) of oceans around the world (Ch. 2: Our Changing Climate, Key Message 12).a36b4f01-c7d8-493d-b0dc-7f0f04f73b4b c299055a-259d-4bd5-be87-1dbbba4174d4 There is a rapid growth in peer-reviewed publications describing how ocean acidification will impact ecosystems,2f1dcb89-554b-42ed-86bd-2c6e6a5bb27e e2d475bc-34fd-46f5-9f0a-17cbac654617 but to date evidence is largely based on studies of calcification rather than growth, reproduction, and survival of organisms. For these latter effects, available evidence is from laboratory studies in low pH conditions, rather than in situ observations.d3f2fc9b-6acf-48b0-b5d1-0f8c620e7f35 4b235b7f-7d25-4b2f-919d-89c3fa917803

New information and remaining uncertainties: The interplay of environmental stressors may result in “surprises” where the synergistic impacts may be more deleterious or more beneficial than expected. Such synergistic effects create complexities in predicting the outcome of the interplay of stressors on marine ecosystems. Many, but not all, calcifying species are affected by increased acidity in laboratory studies. How those responses will cascade through ecosystems and food webs is still uncertain. Although studies are underway to expand understanding of ocean acidification on all aspects of organismal physiology, much remains to be learned.

Assessment of confidence based on evidence: Confidence is very high that carbon dioxide emissions to the atmosphere are causing ocean acidification, and high that this will alter marine ecosystems. The nature of those alterations is unclear, however, and predictions of most specific ecosystem changes have low confidence at present, but with medium confidence for coral reefs.

References :

• Meta-analysis reveals negative yet variable effects of ocean acidification on marine organisms (4b235b7f)
• Ocean Acidification: A National Strategy to Meet the Challenges of a Changing Ocean (a36b4f01)
• Ocean Acidification’s Potential to Alter Global Marine Ecosystem Services (2f1dcb89)
• Oceans and Marine Resources in a Changing Climate: Technical Input to the 2013 National Climate Assessment (018aba6e)
• Ocean Acidification: A Critical Emerging Problem for the Ocean Sciences (e2d475bc)
• Evidence for Upwelling of Corrosive "Acidified" Water onto the Continental Shelf (c299055a)
• Impacts of ocean acidification on marine organisms: quantifying sensitivities and interaction with warming (d3f2fc9b)