The Ocean - the great big puddle which covers most of the surface of our Earth to a average depth of about 4 kilometres - is absorbing about 30% of all carbon dioxide released into the atmosphere. This is causing a reduction to the pH of ocean water such that before the end of this century the ocean may have become slightly acidic. This will make a very different world for the creatures which live in the ocean because the ocean has been slightly alkaline for hundreds of millions of years.
In combination with warming of the ocean waters which is already occurring, this acidification will kill off most corals and most other creatures which make carbonate shells and exoskeletons.
In addition to wide scale species extinctions, when the ocean waters become saturated with CO2, the ocean will no longer absorb more CO2 than it releases. When that happens the rate of increase of CO2 concentration in the atmosphere will itself increase.
There is much more to be added to this.
I believe however there is a method by which we may overcome the very real problem of ocean acidification and in the process create enormous ecological, economical and social benefits.
Watch this space!