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By releasing carbon dioxide to the atmosphere, humans are rapidly altering the chemistry of the ocean and affecting marine life. The acidity of the ocean has increased by about 25% since before the Industrial Revolution, greater than any other time within the last two million years. Given the speed at which humans are altering ocean chemistry, marine plants and animals may not have time to adapt or migrate as they did in the past.
Because of acidification, marine life faces a two-fold challenge: decreased carbonate availability and increased acidity. Laboratory studies suggest changing ocean chemistry will 1) harm life forms that rely on carbonate-based shells and skeletons, 2) harm organisms sensitive to acidity and 3) harm organisms higher up the food chain that feed on these sensitive organisms.
However, we do not yet know exactly how ecosystems will be impacted.
The last period of the text expresses a contrasting idea.