Ocean Acidification in Canada's Changing Climate Report 2026

The second Canada's Changing Climate Report (CCCR) has been released, and features ocean acidification, along with other changes to our oceans.

Of note, Headline statement 14 is clear on the causes and consequences of OA:

"The oceans around Canada have warmed and acidified because of greenhouse gas emissions from human activity. Marine heatwaves have become more frequent and intense. The oceans will continue to warm, absorb carbon dioxide, and acidify as long as air temperature and carbon dioxide continue to rise. (7.2, 7.7, 7.8)"

Ocean acidification, along with other stressors, are discussed in more detail in Chapter 7: Changes in the oceans. 

• 7.7: Ocean chemistry (start here for the scientific content)

• 7.9.5: Key knowledge gaps and emerging issues - Ocean chemistry

•  FAQ 7.3: Why does the carbon dioxide that humans emit into the atmosphere cause ocean acidification?

Figure 7.33 from CCCR 2026: Surface ocean carbon and acidity in the waters around Canada

Key messages from Chapter 7 related to OA (and other stressors) include:

Key message 7.12

"At the surface, observations over the last three decades show that the oceans around Canada have absorbed anthropogenic carbon dioxide from the atmosphere, causing ocean acidification (very high confidence). This higher-carbon, acidified water is carried beneath the surface by ocean circulation."

Key message 7.13

"Beneath the surface, oxygen has declined over many decades in the offshore and coastal waters of the northeast Pacific, in the Estuary and Gulf of St. Lawrence, and on the Scotian Shelf (high confidence), but the processes responsible vary by region and are not fully understood. Since biological respiration both consumes oxygen and adds carbon dioxide, acidification is exacerbated in regions experiencing oxygen declines (high confidence). Year-to-year variations in water circulation and biological activity have caused extreme low-oxygen and high-acidity events in the subsurface oceans around Canada (medium confidence)."

Key message 7.14

"Over the rest of the 21st century, the oceans around Canada are projected to continue to absorb anthropogenic carbon dioxide, to increase in acidity (very high confidence), and to lose oxygen in the subsurface (medium confidence). The level of projected acidification in the latter half of this century will strongly depend on the level of future carbon dioxide emissions (very high confidence)."

Key message 7.15

"The oceans slow the rate of climate-driven atmospheric warming by absorbing heat and carbon dioxide; however, this absorption, in turn, warms and acidifies the oceans around Canada (very high confidence). Impacts on the ocean include more frequent and intense marine heatwaves, increasing stratification, rising sea levels in many regions, more frequent coastal flooding events, and decreasing ocean oxygen levels (high confidence). Continued emissions will intensify these changes, but with impacts varying substantially along Canada’s coastlines, which will result in differing needs for climate change adaptation (high confidence)."

Read the CCCR 2026 here!

Citation for Chapter 7:

Greenan, B.J.W., Hamme, R.C., Casas-Prat, M., Hannah, C.G., James, T.S. & Zhai, L. (2026). Changes in the oceans. In Canada’s Changing Climate Report 2026. (pp. xx–xx). Government of Canada.