Over the last 5 million years the average temperature has been gradually decreasing (fig 1). On a larger scale the earths temperature over the last 65 million years ago, rose, then decreased sharply very sharply.then stayed roughly constant. Then rose sharply and decreased again.(as shown in Fig 1 & 2) On a way larger scale of 540 million years has risen and fallen while going though Glacial Periods and high temperatures. Note: about 150 years ago there was a rise in temperature, although this about the first recorded controlled use of fire I do not believe these two events are connected. (I was joking there) My opinion is that rate of warmth may have been accelerated but i do not believe there is enough recent data to show so. What the Carbon dioxide is doing is causing Ocean Acidification. Ocean Acidification is the name given to the ongoing increase in the pH and increase in acidity of the earths oceans caused by the uptake of carbon dioxide is the atmosphere. Usually when the carbon molecules in the air in increase by 4 one will diffuse into the seawater. mean about one quarter of carbon dioxide in the Earths atmosphere ends up in the oceans. This increased amount of carbon messes up the chemistry of marine organisms. In shellfish this messes up the chemistry of their shells. The carbon bonds with the calcium and creates CaCo3 which when in highly acidic waters dissolves. This means do to carbon dioxide the water become more acidic. This carbon is adsorbed by the shellfish and there shells become weaker. Long story short that's very bad.