The idea of desert flooding has been around for a little while. Its objects and costs, pros and cons, are as follows. Have a read and say if you agree or disagree with the concept in principle: Objects About 10% of the world's surface is desert, which is cheap, uninhabited, unproductive land that is drenched in some of the most powerful solar radiation on the planet. This approach seeks to leverage these attributes by flooding the desert with water to create millions of 1 km2 oases (shallow reservoirs with water) that can absorb and retain carbon with the potential benefit of creating newly habitable areas. This system of oases would be used to grow phytoplankton. With additional desalinated water, it could irrigate the surrounding area to propagate vegetation as well as provide fresh water to nearby communities. So the objects are to both address climate change, and make more land mass habitable. Costs The key components that drive capital costs are: pumping seawater, desalination plants, installed electricity generation capacity and the piping system. Altogether, they put the cost of the project well above $50tn if appled to all deserts across the world. Economies of scale as well as breakthroughs in material science and construction technology will all be necessary for success. The desalination plants need an annual 9 trillion m3 capacity, which translates to a rate of 24.7 trillion liters of water per day. Currently installed plants vary in capital costs from $1 to $10 per liter per day and less than $1 per 1000 liters (m3) in operating costs, but we can expect $1 per liter per day going forward based on low cost plants. This would result in a roughly $25tn capital cost for building desalinating capacity and $25 billion in daily operating costs. Even if we scrap the desalinated water for irrigation, the desalination energy requirements are a decent proxy for the energy needed to just pump water into our phytoplankton reservoirs, given the multitude of variables ranging from elevation variance as well as the distance traveled. For installed electricity generation capacity, the likely option assuming current technologies would be large-scale solar, which we could assume at that scale to fall under $1 per watt of installed cost. The effectiveness of desalination is assumed to be 3.5 wh per liter, which means 31.5 twh needed per year or a 10.8 tw installed capacity. This gives us an installed cost of $10.8 trillion dollars to supply the desalination plants with enough electricity to operate continuously. The cost of installing the piping system with current technologies is also significant, even when stretching them. Assuming each set of 2 reservoirs can be supplied with 1 km of additional piping, 2.25 million km of piping are needed. At a 4m/s flow velocity, which results in average pressures, 2.4m diameter pipe can support about 430k l / hour, which means it can supply 2 reservoirs constantly. At a $48,000/cm-km installed cost for onshore pipeline, the total cost equals $25 tn. We may be able to cut costs another 5-20x by using polymer-based piping, resulting in a still-massive $5tn bill. If we are able to greatly reduce the distance between sea water and our reservoirs by - really reaching here - carving a river from the ocean through the desert, we may be able to further reduce the cost of piping. Cons While any large scale infrastructure project has the potential to fail or have unintended consequences, the benefit of using currently inhospitable land such as deserts is that we constrain the magnitude of risk. In relation to the potential ecological impact of culturing phytoplankton in the oceans, doing so in desert reservoirs reduces systemic risk and exposure of the marine ecosystem to our widespread meddling. On the scale we would need to get to emissions-neutral, there is simply no way around impacting global weather patterns and, consequently, still exposing the entire ecosystem to potential collapse. Pros Making once inhospitable land productive and livable while putting in place a distributed climate control system will allow us to engineer the next phase beyond this climate crisis. We, also, have the means to provide power-water-nutrition around the globe. For humanity to continue to accelerate and thrive we need to optimize our supply chains for sustainability as well as global accessibility. The lessons from developing this idea would have far reaching consequences, from enabling cheaper food production to giving us insight on how to terraform other planets, while deploying the newest technologies to support its operations.