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According to the Bureau of Reclamation, water covers about 71% of the Earth's surface. Everything from microbes in the ocean releasing greenhouse gases into the air, to the immense amount of water that gets evaporated and rained back into the ocean, what would Earth's climate and ecosystem by like if it was land covering 71% of Earth's surface instead?

My guess is that at the very least, season's would be very different across the Earth but I am not sure how. I think there would be no such thing as hurricane season (or typhoon season in the Pacific) and rain would be much more rare on Earth. This could potentially lead to agriculture being much more difficult and possibly increasing the temperature on Earth dramatically since water cools things down but there is not much water on land to support that.

Would Earth still be habitable? If so, would temperature, humidity, and the weather still be as we know it? Or would Earth be a dry Sahara desert-weather-planet much like Mercury?

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  • $\begingroup$ "My guess is that at the very least, season's would be very different across the Earth": Seasons are already very different across the Earth. Some places have winter and summer, other places don't. Some places have dry and wet seasons, other places don't. Winter in Edinburgh, Scotland and winter in Moscow, Russia are very different, although the two cities are at about the same latitude. $\endgroup$
    – AlexP
    Aug 20, 2021 at 20:46

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Climate would be prone to extremes, but Earth should still be habitable

Water and oceans play important role in development of Earth biosphere, as well as lithosphere. Without them, life as we know it could hardly develop. However, if oceans are just smaller, they can still provide our planet with enough water.

For the planetary development:

  1. Oceans are needed for plate tectonics;
  2. Oceans are needed for carbonate-silicate cycle;
  3. Oceans are needed to build oxygen-rich atmosphere;

At some point an arid planet would not be able to support any of the above 3 processes, which would make it "not Earth", but imho all of them are still possible with half as much water.

For long term climate:

  1. Oceans can absorb and release various gases, particularly carbon dioxide;
  2. Open oceans can not form glaciers, which are providing important feedback in the onset of ice ages;
  3. Oceans saturate atmosphere with moisture and responsible for why most of the Earth's land is not desert;

For seasonal climate:

Oceans level seasonal temperature changes and allow for many biomes to exist in the first place.

Overall, a "small oceans Earth" would be a different place, prone to devastating climate swings like Huronian glaciation, but still very much hospitable to life.

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