For the past few million years the world’s oceans have existed in a slightly alkaline state, with an average pH of 8.2. Now, with carbon emissions escalating, there is more CO₂ in the world’s atmosphere. This dissolves in the oceans, altering the chemistry of the seawater by lowering the pH and making it more acidic – up to 30% more in the past 200 years. This growing acidification of the oceans is becoming a serious problem for the production of shellfish around the world.