Rain enhancement gas grid

Drought causes more fires (and there have been fires in France, Portugal, Corsica, Florida and so on) and carbon dioxide is being spewed into the air. It would therefore be worth using natural gas, if burning it could create rain - the exploration companies are burning it anyway.

When the methane gas in natural gas is burned, it produces water vapour (methane is the main constituent of natural gas). 
CH4+2O2 gives CO2+2H20, so it humidifies air.
Now convectional rain can be brought about merely by having a piece of darker ground heating up more than surrounding lighter coloured ground (urban heat island effect and so on).

 Why not encourage fracking companies to burn the waste gas in long pipes with lots of holes in to form a sort of huge grid with thousands of flames coming out? This will heat and humidify a large volume of air and could enhance chances of convectional rain, if relative humidity is high (relative humidity usually increases when air gets colder at night). More trees could be grown with more rain (perhaps in deserts) to offset carbon dioxide made from the "rain enhancement gas grid" and less trees would be burned in fires. 

When coal is gasified it produces hydrogen and methane, which could be used, especially hydrogen.

The heat value of natural gas is about 15 kWh per kg and 1 tonne of it could heat a volume of air 200 m deep by 334 m by 334 m, to a temperature 2 degrees C higher than it was (at a temperature of 23 deg C and pressure of 1 atm, air has a volumetric heat capacity of about 1.2 kJ/(deg C.m^3).
If you have 100 tonnes of trees per hectare (100 m by 100 m) then this can create 170 tonnes of carbon dioxide if burned. If one could create rain with a tonne of natural gas over a hectare, it would create 2.75 tonnes of carbon dioxide, but save 170 tonnes of carbon dioxide from being spewed into the air by fire. The natural gas industry could theoretically prevent greenhouse gas emission from forest fires dramatically.
Gas companies could use the following method in deserts to get trees to grow: Use a bulldozer to bulldoze any rocks in the area to a specific location. The rocks will heat up during the day and retain some of their heat during the night.. At night when relative humidity increases, use a gas grid in the rocky area to humidify the air more and cause more convection. The rocks could be dyed a dark colour so they get hotter in the sun (a fairly natural dye such as a dark metal oxide could be used).The amount of water vapour produced by one tonne of gas is about 2.25 tonnes. Because relative humidity is already high at night, this will enhance the chances of rain. For instance Cairo often has a temperature of about 26 deg C at night and an RH of 80% at the same time. A parcel of this air, 100 m by 100 m, by 100 m holds 19.5 tonnes of water vapour. If you add 2.25 tonnes to this from the burning gas grid, you increase the water vapour content significantly.

White clouds to be generated over the ocean.

See http://www.washington.edu/news/2017/07/25/could-spraying-particles-into-marine-clouds-help-cool-the-planet/
I think the idea to create clouds over the oceans by these scientists is an excellent idea, but I do not agree that they should necessarily be brighter. It is a good idea because about 93% of the heat gain is gain into oceans. Creating mist clouds will reflect the light, but clouds are good absorbers of infrared (very roughly 50% of solar energy is infrared), so the clouds will evaporate. These clouds will prevent a lot of solar radiation entering water, because water is a good absorber of just about all solar radiation. Having mist clouds would be fairly natural and evaporation of these would increase relative humidity, which is good for drought areas and for making more clouds, which would reflect sunlight. If ordinary mist clouds are made rather than very white ones I think absorption of solar radiation and more cloud formation will result. However they aim to get other data and information from the creation of the very fine droplets, so perhaps this is a very necessary part of the experiment.
What I think will happen with the generation of the clouds is that the air will cool rapidly because the droplets are to be fine (the air could cool to near wet bulb temperatures - see mist cooling) and they will need some method of getting the cloud to rise (they say they will spray it high into the atmosphere). I think if they generate hot steamy air around their cloud generator the droplets might not evaporate and could rise high. Perhaps they have ideas on how to get the spray to move high up. Possibly they could have hot steamy droplets (heat the water before making the spray).
 Again I mention my Rain Enhancement steam generator as a means of producing hot humid air- see below:
But if your air parcel is at, say, 21 deg C and the surrounding air is at 20 deg C, you can expect immediate acceleration upwards of about 0.03 m/s^2. If your air parcel is saturated you might find that this parcel eventually moves upwards (the moist adiabatic lapse rate situation)  at about 5 m/s. Evaporation and heating by solar energy absorption would, in my opinion, be very difficult to control.
If the parcel of air with fine droplets in is colder, it will sink. It seems that when it reaches the sea and becomes fairly stationary, you could use a terminal settling velocity formula depending on the size and density of droplets, etc, to calculate the velocity of descending droplets. If the top of the cloud is not flat, parts will be differently heated by the sun.

BUT HERE IS A GOOD IDEA, I THINK: If they used their system to moisten air off coasts that had drought problems, the cooler moist air would be blown onto land with sea breezes and convectional rain could result if the Rain Enhancement Steam Grid were used.

Drought in Cape Town, etc

Drought in Cape Town, West Coast, etc. Contrary to what many believe, there is a lot of moisture in hot fairly dry desert air. The weather report says that at 17h00 Monday 24 July the humidity in Cairo will be 30% and the temperature will be 37 deg C. This air will hold about 13 grams of water vapour in each cubic metre. If the temperature was 15 deg C and the relative humidity was 95% the air would hold only about 12 grams of water vapour per cubic metre. When air cools the relative humidity increases and the weather report says that at 23h00 on Monday 24 July the relative humidity in Cairo will be 65% and the temperature will be 29 deg C. Now if you heat air with a high relative humidity it does not have to rise far before clouds form. If you heat low relative humidity air, it has to rise high before clouds form and you have to heat it a lot to get it to rise so far. So here is the idea: Wait until the air cools and RH is high and then heat air a little to get it to rise and form clouds. My method to heat it is to have pipes with heated water containers at the ends and with holes in the pipes to let steam out. This will humidify and heat the air.

Example. The weather report says that in Cairo on 28 July 2017 at 04h00 the RH will be 86% and the temperature will be 26 deg C. Using Espy's equation, if this 26 deg C air is heated to 28 deg C it only needs to rise 321 metres for clouds to form. By virtue of its temperature (T=28 deg C) it could rise 606 metres. So it can easily reach the height needed for clouds to form (used general sorts of lapse rates).

To summarize, wait until air cools and then use the device shown in the photo.

Frost prevention, rain enhancement, air pollution dilution

Although I do not drink wine, I like grapes, and I read that grapes had been damaged by frost in France. Here is an idea: Have a long pipe running through the vineyards, with holes in to let out water vapour. Boil water at one end of the pipe (or at points along the pipe) and water vapour will come out all along the pipe into the vineyards. This will increase the sky temperature by increasing relative humidity and the greenhouse effect and help reduce frost.
Hot water vapour actually radiates heat. The book "Fundamentals of Thermal-Fluid Sciences" by Cengel and Turner says that a 1-metre thick layer of water vapor at 1 atm pressure and at 100 deg C emits more than 50% of the energy that a blackbody would emit at the same temperature. Energy will therefore be radiated to the vines.
Regarding cold lower valleys, what usually happens is that the cold air comes down the sides of a valley and sinks below the warmer air (which could be only 10 metres above it). Helicopters are used to mix the warmer air above with the colder air to warm up the air immediately above the ground and higher. This method would also cause mixing because the vapour coming out the pipe would be less dense than the air, causing it to rise and mixing warmer air above with the colder air. One could also ensure that the vapour comes out at fairly high pressure to ensure mixing. The system could be used to enhance convectional rain or dilute pollution in cities by means of convection (dirty air rises out of the city).

Transport of water vapour in hot deserts

Transporting moist air by means of natural convection in a pipe: Run a huge black pipe, that will get hot in the sun, from the sea to a few hundred metres above the area needing rain. Moist air from the sea will rise in the pipe by means of natural convection and cause convectional rain. This idea could bring rain to many areas. It would be similar to a solar updraft tower, which can deliver huge volumes of air per second to the atmosphere. Heat the seawater by concentrated solar power (or other means) near the inlet of the pipe to increase relative humidity. This system will be cheaper than solar updraft towers. Some calculations: For a 20 m diameter vertical pipe that is 500 m high with air temperature of 25 deg C outside and 30 deg C inside, a flow of about 3340 cubic metres per second can be expected. Eventually you will have a few cubic kilometres of moist air in the region if wind is weak. To do your own calculations search for "stack effect draft."
One could have a few such pipes into a region to spread humid air. One or two cubic kilometres of moist air per day can be delivered like this. Pipes could be heated more by reflecting sunlight onto them with mirrors. Rocks that the pipe rests on could be heated by solar energy so that the pipe stays warm at night and can keep on delivering moist air. It is quite likely that at night the air from just above the sea will be warmer than land air, which will cause it to rise in the pipe. Moist air is less dense than drier air, which will help it to rise in the pipe.
But here is another idea. In desert regions with hot air one can significantly change the density of the air by increasing relative humidity, because hot air holds so much water vapour and water vapour is less dense than air. At a temperature of 40 deg C with RH of 30% and P=101.325 kPa, air has a density of about 1.118 kg/cubic metre. If you raise the RH of this air to 90% it has a density of about 1.099 kg/cubic metre. This is the same as air with an RH of 30% and T=45 deg C. By increasing the RH of the air with RH = 30% to one with RH = 90% (all at T=40 deg C) you have about the same effect on density as raising the temperature of the air by 5 deg C ( from 40 to 45 deg C). In hot deserts It seems you do not have to heat the air to cause natural convection - you can just increase RH and the air will rise by natural convection in the pipe. The RH can be increased by heating seawater at the inlet of the pipe. At T=40 deg C with RH=90%, there are about 46 grams of water vapour in every cubic metre of air transported in the pipe.
What happens when the air comes out the pipe? Well, say the air with RH=90% and T=40 deg C comes out in air with temperature of 35 deg. Clouds will form with bases at about 245 metres above the outlet of the pipe (very low clouds). The clouds could display huge vertical ascent from their bases because of high RH, high dew point and so on (tall clouds with low bases and towering high tops will result). If a rain cycle results maximum, temperatures will be reduced by evaporation and minimum temperatures will increase because of increasing effective sky temperatures. 
This depends on strength of sunlight, temperature of water coming into the greenhouse, heat losses and so on, but it seems that to form 1 cubic metre of 90% RH air at 40 deg C starting with 30% RH air at 25 deg C, every second, will take very roughly 200 square metres of surface irradiated by the sun. A massive greenhouse with water in could suffice to provide all the humid air needed. Similar greenhouses have been proposed for solar updraft towers. A greenhouse 1 km by 1 km could provide 5000 cubic metres of RH=90% with T=40 deg C air every second.

Cooling the Earth

Energy from a body can go in many different directions, but some of the energy heading in the right direction can escape directly to space (see atmospheric window).  Carbon dioxide is a very strong absorber of radiation trying to leave Earth in the about 12 to 13 micron and above range. This is closing the 8 to 14 micron atmospheric window that is allowing energy to escape from Earth on the 14 micron side. Using Planck's law I calculate that with an 8 to 13 micron window only 32% of the energy from a 25 deg C Earth can escape (using a blackbody approximation - the oceans, pavements, vegetation, etc have high emissivities close to that of a blackbody). With an 8 to 14 micron atmospheric window 37.4% of the energy could escape. Now if we had mirrors shading the ocean, that reflected sunlight onto black surfaces, the temperature of the ocean would change very little and we could heat up the black surfaces to high temperatures of 91 deg C. I say 91 deg C because at 91 deg C the highest percentage of energy radiated by the black surface can pass through the atmospheric window to space. At different temperatures only a smaller percentage can leave Earth. At 91 deg C the percentage of energy leaving to outer space is 34.5% of the energy radiated by the black surface. If the black surface were at 25 deg C only 32% of the energy it radiated could escape through an 8 to 13 micron atmospheric window.
With an 8 to 14 micron atmospheric window a temperature of 79 deg C allows the maximum proportion (39.3%) of radiation to escape to space.
Of course if we have higher temperatures more energy is radiated by a black body, but from an "efficiency" point of view, the highest ratios of energy can exit at the temperatures mentioned. Black surfaces heating seawater dripping onto them can also bring more rain, because of evaporation and convection. Clouds formed could cool Earth by reflection and radiation to space.
With increasing global warming it is expected that winters will warm faster than summers, ( see https://skepticalscience.com/The-human-fingerprint-in-the-seasons.html  ) so a question that might arise is this: Will winter rainfall regions have less rain?

Bring rain and reduce air pollution.

Clean up cities and bring rain with solar energy: With global warming the land is heating up faster than the ocean in terms of temperature (although about 90% of the solar energy absorbed by Earth is going into the oceans). When this happens the relative humidity of the air decreases more when blowing from sea to land. One can have floating spray pumps in the ocean to increase relative humidity (the pumps could be operated by wave motion). Another method to get more rain is to have this sort of system near the sea: Where there is land not being used (say on rocky hills, etc) erect pipes a few metres in diameter and a few hundred metres high and reflect sunlight onto these pipes using mirrors. The air in the pipes will be heated and rise and convectional rain is far more likely than usual to occur. It should be very cheap system to implement without the need for machinery to operate it. The bottom part could consist of a greenhouse. Often one will get 6 kWh or so of sunshine per day on a one square metre horizontal surface. Theoretically at 101.325 kPa this could heat 3600 cubic metres of air by 5 deg C (just the solar energy on one square metre could do this) starting off with 24 deg C air. With a 5 deg C temperature difference one can expect about 600 cubic metres per second out of the pipe (tower) if it is 400 m high or so (to research this Google stack effect draft, etc). To supply the energy for heating the 600 cubic metres coming out one needs roughly 5x1.2x600 kJ of energy per second (volumetric heat capacity of air is about 1.2 kJ per cubic metre per deg C and temp rise is 5 deg C and volume is 600 cubic metres). If sun power is 0.5 kW/ sq metre then we need 5x1.2x600/0.5 square metres of radiated surface. ie we need 7200 square metres of radiated surface. Therefore we need an area of about 84 m by 84 metres to supply energy to heat 600 cubic metres of air by 5 deg C every second. Of course there will be heat losses, so a bigger area is needed. This device can also be used to move polluted air out of cities by convection.
Links: 1) Cool roofs could be reducing rainfall https://www.scientificamerican.com/article/cool-roofs-may-have-side-effects-on-regional-rainfall/
2) Colour of land could affect rainfall: https://eos.org/articles/more-intense-rains-in-u-s-midwest-tied-to-farm-mechanization?utm_source=Eos%20Primary%20List&utm_medium=email&utm_content=more-intense-rains-in-u-s-midwest-tied-to-farm-mechanization&utm_campaign=5022c1d8f8-Weekly_All_Content_Digest&utm_term=0_f923f18da4-5022c1d8f8-522497757
3) Regarding cool roofs, etc, http://iopscience.iop.org/article/10.1088/1748-9326/11/6/064004/meta says, 
"The lowered wind speeds and vertical mixing during daytime led to stagnation of air near the surface, potentially causing air quality issues." 

If space is a problem then one could build a greenhouse with black floors to absorb solar energy and holes in the floors to let hot air rise through. See following diagram: