It's true that jet airplanes are larger, have more powerful engines and fly more frequently than ever... about 700 million passenger flights per year in the US alone.

For each gallon of jet fuel burned, aircraft produce a gallon of water, because H2O is one of the two chemical byproducts resulting from the combustion of hydrocarbons. Current jet fuel use is about 60 billion gallons per year, so that's also about 60 billion gallons of water being manufactured in the atmoshphere annually, or nearly half a trillion pounds of H2O ... frozen water vapor that doesn't just fall back down to Earth.

In the low air pressure, sub-zero temperatures where contrails form, steam from the exhaust freezes immediately and expands to a much greater area than its sea-level volume. Since the steam is gaseous and warmer than the environment around it, it continues to rise rather than fall. 60 billion gallons of fuel = 60 billion gallons of water = approximately 10 to 20 trillion cubic feet of ice crystal clouds added to the atmosphere every year, most of which is injected into the northern hemisphere of the planet.

But there's more to artificial clouds than just frozen H2O.

Weather modification means cloud seeding with silver iodide (AgI)— hygroscopic metallic aerosols that provide a dense field of cloud condensation nuclei (CCNs) to thicken clouds and induce precipitation. Condensation nuclei are the basis of cloud development. When mixed with moisture, silver iodide promotes cloud formation by providing CCNs that jet exhaust moisture can bond with. The invisible cloud-seeding chemicals are dispersed in the atmosphere at around 20,000 feet, in front of incoming moisture fronts, enhancing contrails from jet air traffic and often spawning cloud cover prior to the storm's arrival.

Silver iodide aerosols are invisible once dispersed, and the contrails from the planes burning the flares are minimal and usually disappear because these are small jets that are already at their cruising altitude; that is, using relatively little fuel. However, when large aircraft ascend through the seeded fields of silver iodide at these higher altitudes, their contrails become instantly visible. The extreme photosensitivity of the crystalline-shaped silver iodide aerosols combine with the highly-reflective ice crystals from the exhaust to form bright white contrail wakes behind the plane that tend to persist rather than disperse.

Weather modification companies use fleets of jets and high-altitude propeller planes that have flares fixed to the wings of the aircraft. When the flares burn, they release silver iodide, a salt-based chemical (potassium iodide and silver nitrate), which provides abundant cloud condensation nuclei to spawn and thicken clouds.

Cloud seeders ignite as many flares as possible before incoming storms in order to maximize precipitation. There are other less common applications for cloud seeding, such as breaking up hailstorms with surfactants in order to reduce damage, but precipitation enhancement is the primary reason for weather modification.

In the United States, county governments are typically the ones who hire weather modification companies to seed clouds. The programs are designed to enhance precipitation and increase water supplies. These ongoing precipitation enhancement projects are typically paid for by consumers through a Public Purpose Program surcharge on their utility bills.

Local governments see cloud seeding as a good value for obtaining additional water; other sources are more costly, if any are even available.

Some states have had legal disputes about cloud seeding, including New York, Oklahoma, Washington, Nebraska, Pennsylvania, Montana, South Dakota, North Dakota, Texas and California.

Dry states in the US like California have seeded the atmosphere with silver iodide every year since the 1960s. Other states have caught on and, as the worldwide water shortage begins to affect more and more cities, the weather modification industry has expanded drastically over the past few decades.

Counties in these U.S. states have conducted and/or still conduct extended cloud-seeding programs:

• California
• Colorado
• Georgia
• Idaho
• Illinois
• Iowa
• Kansas
• Montana
• Nevada
• New Mexico
• North Dakota
• Oklahoma
• Oregon
• South Dakota
• Texas
• Utah
• Washington
• Wyoming

Most other states have also experimented with weather modification. (For more, just Google "precipitation enhancement" or "cloud seeding" plus your state.)

As global water supplies diminish, few alternatives exist to provide enough water for growing populations and increasing agricultural needs. Just as most western states in the US conduct ongoing cloud seeding programs for precipitation enhancement, almost any country you can name uses cloud seeding to increase rainfall and snowpack that keeps rivers flowing through the summer, including Europe, South America, the Middle East, Asia and even Australia. China seeds the clouds in over 2,000 counties.

The massive amounts of cloud condensation nuclei result in thicker, more persistent contrails, more artificial clouds and hazy skies over Earth's northern hemisphere.

Cloud seeding with AgI began in the 1960s; "climate variation" concerns started in the 1970s.

Like natural clouds, artificial clouds can drastically affect the weather: In the daytime they block the sun, creating shade and reflecting some solar radiation back into space. But at night, clouds have a blanketing effect that keeps warm air trapped.

The coldest nights are usually cloudless ones since the heat can escape from the Earth. Clouds also absorb and re-emit heat, so cloud cover makes it even warmer at night. Warmer air also means higher pressure, and high pressures can also help repel some storms, preventing rain.

When a moisture front presents itself, cloud seeding companies go into action, dispersing silver iodide in front of the incoming storm... specifically, over areas of land where precipitation is desired. These hygroscopic aerosols provide a field of CCNs for jet exhaust moisture to bond with and, combined with the higher ice crystal saturation that comes from moisture preceding the storm, aircraft can spawn thick clouds before the storm clouds arrive.

This creates a shady area in the path of the incoming front, providing a low-pressure "downhill run" for the storm. In fact, this can allow some precipitation to arrive that would otherwise be repelled by higher pressure.

Visible contrail clouds begin to form when jets reach a high enough altitude— around 25,000 feet— and tend to stop when the plane reaches its cruising altitude, where the ice crystal saturation is lower and the jet is using less fuel.

In the United States, weather typically moves across the country from left to right with the jet stream. This means storms we intensify in the western states tend to flow toward the eastern states. Through precipitation enhancement programs, we thicken and accelerate storms, which continue eastward with the winds... along with the extra cloud condensation nuclei we introduce into the atmosphere to enhance precipitation.

How often do the western states seed the clouds? Every time there's potential for rain or snow. We need the water. But who is aware of the downstream consequences?

Recently scientists found that stratospheric water vapor destroys ozone. This is troubling because in addition to adding CO2 directly into the upper atmosphere, jet aircraft inject their water vapor into the lower stratosphere where the ozone layer helps protect the Earth from solar radiation.

NASA researchers also found that high-altitude clouds are formed around condensation nuclei comprised of "metallic aerosols and mineral dust"-- the ingredients that are in cloud-seeding flares.

In addition, our heavy cloud seeding practices using salt-based material may temporarily inhibit evaporation in some areas by increasing the surface salinity of water bodies that provide the humidity for cloud formation.

Just like road flares, which also contain toxic metals, cloud seeding flares have to burn in wet, high-wind conditions.

Besides silver nitrate and potassium iodide (an inorganic salt chemical) cloud seeding flares contain incendiary chemicals and metals that are toxic to living things, including aluminum, strontium and magnesium.

As the big commercial (and military) jet aircraft ascend through areas of high relative humidity (ice crystal saturation) or dense cloud condensation nuclei, exhaust moisture bonds with the nuclei to form ice crystals. Like natural clouds, depending on where the sun is, contrail clouds can appear bright white, dark gray, or colorful.

Artificial clouds change the Earth's weather.