More rain

Asked January 26, 2017, 1:17 AM EST

I would like an opinion on the feasibility of this idea: My guess is that with global warming there are going to be more droughts. The land heats up faster than the sea and if the land is warmer than the sea then air coming from the sea heats up and its relative humidity falls. Example: Air comes off the sea with relative humidity of 70% and temperature at 20 deg C and heats up to 25 deg C over land. The relative humidity drops to 52% and low relative humidity is associated with low rainfall. One needs to get air from the sea flowing over land as it brings moisture. Cold air tends to be denser and so cold air from the sea has more of a chance of flowing onto land. So here is the idea: 1) Make air over the sea fairly cold and very moist so it will tend to move in over land and bring moisture. 2) Over land, heat this air up so it will rise and vapour will condense, making rain.
You can do all this as follows: Use spray pumps operated by waves in the sea to form a mist that is evaporated in sunlight, causing air to be very moist and also cool (because of evaporation). Now use a solar air heater on every rooftop to heat this air when it comes onto land, so it will rise causing rain. Every two seconds one can have 1.2 kJ of solar energy falling on every square metre in many locations and this 1.2 kJ can heat one cubic metre of air 1 deg C. You could move massive volumes of moist air up like this. Another advantage is that low level clouds (and I would think mist) is associated with cooling of Earth. So you should have cooler Earth and more rain.
EXAMPLE: Say you have a 2km stretch of coast with the spray pumps (operated with wave motion). Let the air temperature over this stretch be 18 deg C with a relative humidity of 95%. Suppose the 2 km wide air parcel from the sea blows onto land. If you heat this 18 deg parcel up to 26 deg C with solar air heaters the relative humidity of the parcel falls to 58.3%. Suppose the surrounding air over the rest of the land area (surrounding the 2 km wide parcel) is at 22 deg C. Then the parcel can rise 1212 m (using a fairly standard dry adiabatic lapse rate). Using Espy's equation it only has to rise 1102 m for clouds to form, so it could rain.
QUESTION: Does this seem a feasible idea?

People are always trying to geoengineer the climate. The writer is correct that higher temps will cause more drought because of increased evaporation. I don't think the proposal will work for the following reasons:

1. It would only work very near the coast, and the worst droughts are far from the coast.

2. The water is going to increase in temperature as well as the land, so it might not be a good source of cool air.

3. I don't think it is a good idea to run solar heaters to increase local temperatures even more than they are already rising, just adds more heat to the system.

4. There are no guarantees that just because you bring more moisture onshore that you will be able to generate rain, even with the heaters causing rising air, because the heaters are also reducing RH. You need to have a good mechanism for creating rain. There are a number of deserts around the world with high RH that are dry because there is no way for the air to form rain clouds. Forming clouds might decrease local temperatures a bit but no guarantees of rain.

5. The energy costs to do this would be tremendous even if you are using solar power, because you have to build all of these machines to do with work. Why not just use it to reduce fossil fuel use instead? Plus there is no guarantee there would be enough waves since lower winds are likely in a warmer world.

6. The sprayers in the water would negatively impact sea and lake life, causing environmental issues.

This is just what comes to mind after thinking about it for a few minutes.

Questioner might like to see the recent suggestion about geo-engineering the Arctic sea loss today in guardian news:
https://www.theguardian.com/world/2017/feb/12/plan-to-refreeze-arctic-before-ice-goes-for-good-clima...

Outside United States climate change

2 Responses

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People are always trying to geoengineer the climate. The writer is correct that higher temps will cause more drought because of increased evaporation. I don't think the proposal will work for the following reasons:

1. It would only work very near the coast, and the worst droughts are far from the coast.

2. The water is going to increase in temperature as well as the land, so it might not be a good source of cool air.

3. I don't think it is a good idea to run solar heaters to increase local temperatures even more than they are already rising, just adds more heat to the system.

4. There are no guarantees that just because you bring more moisture onshore that you will be able to generate rain, even with the heaters causing rising air, because the heaters are also reducing RH. You need to have a good mechanism for creating rain. There are a number of deserts around the world with high RH that are dry because there is no way for the air to form rain clouds. Forming clouds might decrease local temperatures a bit but no guarantees of rain.

5. The energy costs to do this would be tremendous even if you are using solar power, because you have to build all of these machines to do with work. Why not just use it to reduce fossil fuel use instead? Plus there is no guarantee there would be enough waves since lower winds are likely in a warmer world.

6. The sprayers in the water would negatively impact sea and lake life, causing environmental issues.

This is just what comes to mind after thinking about it for a few minutes.

Questioner might like to see the recent suggestion about geo-engineering the Arctic sea loss today in guardian news:
https://www.theguardian.com/world/2017/feb/12/plan-to-refreeze-arctic-before-ice-goes-for-good-clima...