As the seas grow warmer the lands grow cooler

This is one of the problems of global warming. Heating is not universal all over the planet. So, as a result there is no one terraforming solution to the problem of global warming.

At least in the beginning if you try to reduce water temperatures around the world, initially you will also reduce land temperatures too (at least in the beginning of this process).

Why?

Because of the present global warming dynamic which is that as seas warm up the cloud cover produced by increased evaporation from the oceans causes lands to decrease in winter in temperature thereby allowing more snow to stick to the ground thereby greatly increasing the chances for a short or long ice age one year in places like the U.S., Europe, China etc. So, it wouldn't take much with presently reducing land temperature from cloud cover to create a fluke 1 year to 5 year to 10 year ice age down to say Northern Mexico or Italy with snow covering everything north of there for 1 or more years time.

But, for example, if you put powdered glass particles in the upper atmosphere like you get from pyroclastic Volcanoes like in Iceland and other countries you not only reduce the water temperatures you also reduce the land temperatures by doing this. So, if you did this you might also create small or longer ice ages on the landed areas of the world north of say Mexico or Italy or north of Thailand or something like that in Asia.

So, as a result reducing water temperatures we also reduce land temperatures initially at least.

Note: The pyroclastic powdered glass particles often that stay in the atmosphere often for years or more after an eruption reduce the amount of sun that gets to the ground over that area of the atmosphere thus affected.

For example, the French revolution in the 1790s was caused by starvation of the French common people because they couldn't grow food from pyroclastic particulate in the air over France during this time. So, the guillotining of all the nobles in France was primarily caused by the eruption of Icelandic volcanoes preventing food from being grown in France.