They acidified due to man's mismanagement. Just like Saddam Hussain made the Iraq' marshes dry and lifeless.
So problem 1 – get the water back. Not via boiling or high pressure desalination. We use low pressure desalination.
1 E=PV so energy is proportional to pressure.
Even sea water boils at 1m – so we make P=0.1 – and vacuum is very cheap to produce. For high pressure desalination we want p=8 – so 80 times as much power.
So the UN gives us solar driven vacuum pimps – the 1m solar panel charges up batteries during the day, so we suck out 20,000 L of water vapour a minute. When condenses this gives us 20 L of water.
This cleans up both sea and river water – so we can suck fresh water from brown river water, and within 2 days, it will have returned to the river.
So we are sucking fresh water from sea water – losing all the salts. The UN will give us the solar vacuum pumps, as it is cheaper than coping with drought and famine.
So we can make Ethiopia green and lush again. We can pump the fresh water to the Saudi high desert – so adding water to the ecosystem.
We dredge up silt from the sea floor, and wash it is river estuaries. We then process it into soil pads – impregnated with grass seed – and fertilized with cow waste or urine.
We scatter these around our water vapour outflows.
We also have tree seedlings in soil balls, we plant – to act as windbreak. And to prevent the soil being washed off.
So in countries like Chilli, we have all of the interior lush and fertile. And all this extra plant growth will convert CO2 into biomass.
But this process happens naturally on the land and seas. CO2 can only rise in a natural ice-age. The Jurassic had 3 – one lasting 650 million years, with 3 times the level of CO2 in the air.
But we end global hunger and thirst. So a decrease in crop yields in the temperate areas of the world is a price worth paying: burn more gas, oil and coal.