The oceans are buffering temperature increase, by absorbing much of the CO2 that we emit. The oceans are acidifying and the oceans WILL become functionally extinct if this trend continues, not only because the coral reefs- the nurseries of the sea- will no longer exist, but because of other pressures such as over-fishing.
We know the Earth has been far colder and far warmer in its history, there has been more CO2 and less CO2 in the atmosphere while sharks and turtles have survived for aeons, species have come and species have gone, its a long term cycle - even in humanity's time on Earth there have been ice ages and their opposites - even within recorded history the Romans grew grapes and made wine in York and the Vikings had cows in Greenland, and in the 1400 - 1700s there was a mini ice age. We are out of the mini ice age and there are not yet grapes or wine in York, so clearly the temperature trend will predictably continue to be upward for a while.
The problem is not these long cycles, but sadly the whole Global Warming scam has meant that for c15 years we have taken our eyes off the real issue - the problem of the energy and other resource consumption of 7bn (and growing) people.
You don't need Global Warming to predict that breeding millions of people and sticking them on environmentally risky land like wearthquake zones, flood plains and fluctuatingly arid regions invites disasters, nor that cutting down huge swathes of forest for slash and burn agriculture and overgrazing will create starvation and microclimate natural disasters, nor that overfishing is unsustainable. This has got nothing to do with long term Global Warming and everything to do with very predictable short term resource overconsumption.
Populations will collapse (they are collapsing in places, thats sparking many of these small wars going on today) and people will be having more and bigger wars over water, food land and energy long before any ocean turns acidic.