Causes
For the last 200 years, the burning of fossil fuels — coal, oil, natural gas — for energy, cement production, and deforestation pumps carbon dioxide or CO2 into the atmosphere. Photo © Wolcott Henry 2005/Marine Photobank
Ocean acidification is the reduction of ocean pH due to the absorption of anthropogenic carbon dioxide (CO2) released from the burning of fossil fuels, into surface seawaters. Present-day atmospheric CO2 is almost 40% higher than pre-industrial levels due to human fossil-fuel combustion and deforestation, and atmospheric CO2 could reach double or triple historical levels by the end of the century.1 The oceans constitute a critical sink for CO2 and currently absorb approximately one-third of the excess CO2 injected into the atmosphere from human fossil fuel use and deforestation.2,3,4,5
The uptake of the additional CO2 in ocean waters increases the hydrogen ion (H+) concentration and thus decreases the pH of ocean surface waters. The present average surface ocean pH of ~8.1 is 0.1 pH units lower than in pre-industrial times, representing a 30% increase in the concentration of H+ ions. At the projected rate of CO2 production, acidity is predicted to increase 150% to a pH of 7.8 units by the end of this century.6
Resources
NOAA's State of the Science FACT SHEET: Ocean Acidification, May 2008
NOAA's Pacific Marine Environmental Laboratory Carbon Dioxide Program