Editor’s note: “Doomsday” author and  WRAL TechWire contributor Marshall Brain says these eight geoengineering ideas could combat climate change. Here’s a look at each:

Geoengineering Option #1 – Adding Sulfur Dioxide to Earth’s Stratosphere

Scientists have known for a long time that volcanic eruptions can cool the planet. For example, when Mt. Pinatubo erupted in 1991, average temperatures around the world dipped by 0.5 degrees C. Why? Because the eruption sent 20 million tons of sulfur dioxide into the stratosphere. It turns out that sulfur dioxide reflects incoming sunlight back into space, meaning less sunlight hits the Earth’s surface. The whole planet cools down after a big volcanic eruption.

Humans could mimic this effect by letting high-altitude airplanes release sulfur dioxide into the stratosphere. See this video for a nice description of both the idea and the controversy: https://www.youtube.com/watch?v=WR6uSXW-8p4

People who don’t like this approach argue that this is a bad idea because we don’t know about the unintended side effects. The counter to this argument is that we do know that things could become catastrophically awful if we allow the planet to keep warming up via fossil fuel emissions. We may have no choice about cooling the planet down.

Geoengineering Option #2 – Putting Orbiting Mirrors in Space to Block Sunlight

If you don’t like the idea of blocking sunlight with sulfur dioxide in the stratosphere, then how might you feel about using mirrors in space to do the blocking? The idea here is to put mirrors in orbit and use them in a controlled way to lower the amount of sunlight reaching the planet.

This approach would likely be more expensive and more difficult than Option #1, but it might give us more control. For example, if we wanted to put the Arctic and Antarctica in the shade to cool them down specifically, rather than blocking sunlight globally, it might be possible to imagine this using orbiting mirrors. But a lot of research and money would be required to bring this idea to fruition, as well as to understand/mitigate potential side effects.

Geoengineering Option #3 – Creating More Clouds Over Oceans

If we could add more clouds covering the Earth, these clouds would reflect sunlight back into space. Clouds can also have different levels of brightness when doing this reflecting, so we would want to make clouds brighter if we could. This is where the idea of Marine Cloud Brightening comes in.

This idea is simple at the core:

  1. We build large floating machines to spray seawater mist into the air
  2. In the process, lots of salt gets into the air
  3. The tiny salt particles in the air help to form bright clouds over the oceans

If we did this at a large enough scale, it would help cool down the planet. We could also turn the effect on and off very quickly.

Geoengineering Option #4 – Adding Iron to the Ocean to Increase Plankton

This option may initially sound weird to you, but this one has actually been tried several times in the real world at a small scale. It turns out that adding iron to plankton dead zones in the ocean can radically increase the growth of plankton there. This one nutrient is the thing holding back plankton growth in the dead zones. So the idea is to add iron, let the plankton grow and die as they naturally would, and then these dead plankton sink to the bottom and take a bunch of carbon with them. In the ideal case, the plankton stay in the sediments on the ocean floor without decomposing, and the carbon stays there for many years.

Initial experiments showed that the basic idea works, but also showed that there may be unintended side effects and caveats. Therefore, much more research is needed.

Geoengineering Option #5 – Making Arctic Ice More Reflective with Glass Beads

Have you ever looked at a highly reflective roadside sign or stripe at night and wondered what causes it to be so reflective? In many cases, the reflectivity is caused by tiny glass beads. When light enters one of these beads, it happens to get reflected back out of the bead pretty efficiently. And glass beads are a lot like sand, meaning they tend to be harmless in the environment.

Therefore, one idea is to use glass beads in mass quantities to reflect sunlight back into space. And one place where this is being considered is in the arctic, where the ice has been melting rapidly. If we use glass beads to brighten the ice, then the ice will melt less. More ice in the arctic is good because it means more sunlight reflecting back into space and less sunlight warming the arctic ocean.

Geoengineering Option #6 – Create Ponds and Lakes in Desert Areas

The Sahara Desert is gigantic at 3.5 million square miles. What if we flooded parts of it with seawater or desalinated water? Or what if we flooded Death Valley in the United States, which is 5,000 square miles and already below sea level? These projects would be expensive, but they would cool things down and they would give us more room to grow plankton for carbon sequestration. See this video for some perspective on these ideas – https://www.youtube.com/watch?v=Cg7aGjIlfEU.

Geoengineering Option #7 – Adding Yellow Dye to the Arctic Ocean

Kim Stanley Robinson is a popular science fiction author whose book entitled “The Ministry of the Future” has found a wide audience. In this book he talks about two geoengineering techniques that have become better known because of the book’s popularity. The first involves adding a yellow dye to the arctic ocean to cool it down.

The problem we face in the arctic is that the sea ice is melting. With less ice there is more open water. The open water absorbs a lot more sunlight than the ice would, because the white ice is reflective. Therefore, the ocean warms up and melts the ice even faster in a destructive feedback loop.

By adding vast quantities of bright yellow dye to the seawater on a regular basis, the lighter color means that the seawater absorbs much less sunlight and therefore heat, keeping more of the ice around.

Geoengineering Option #8 – Slowing Down Glaciers like the Thwaites Glacier

In this article we talked about the gigantic global risk created by the Thwaites glacier and other nearby glaciers in Antarctica. The problem is that these glaciers naturally flow downhill toward the sea, and their speed has been increasing. If the Thwaites glacier collapses into the ocean, the rate of sea level rise would be catastrophic for beaches and coastal cities.

In his book, Robinson’s fictional scientists hypothesize that a layer of meltwater under these glaciers is lifting them up off their rocky beds and lubricating their decent. Therefore, the geoengineering idea is to drill holes through the glaciers and pump the meltwater out. The glaciers then reconnect with the rock underneath them and slow back down, preventing sea level rise from glacier collapse.