[To lower Earth’s average temperature by approximately 2 degrees Celsius, a space sunshade at the Sun-Earth L1 Lagrange point would need a total area of several million square kilometers. The exact size depends on the specific design and the target amount of cooling needed to offset ongoing warming, but estimates generally fall within the range of a few million square kilometers.
Key estimates for the required size and related metrics:
Percentage of sunlight blocked: To fully offset global warming (which would include cooling by roughly 2°C), studies suggest blocking around 1.7% to 2% of incoming solar radiation.
Total area: A structure with an equivalent area of approximately 2.6 million square kilometers (or about 1 million square miles) would be required to block this amount of sunlight if positioned at the classical L1 point. Other estimates suggest an even larger area, around 4.5 million square kilometers, might be needed.
Composition: Due to the immense size and mass, a single structure is not feasible. Proposed designs involve trillions of smaller, independent disks or a series of smaller, modular shades acting together as an “archipelago”.
Mass: The total mass of such a system would be substantial, estimated at millions of tons (e.g., about 20 million tonnes in one proposal), posing a significant launch challenge.
The physical scale of such a project is comparable to the size of a large country, such as Argentina or roughly half the size of the contiguous United States, highlighting the monumental engineering and cost challenges involved.]-Gemini
Even with starship it would be millions of launches and trillions and trillions of dollars....or we can just bask in the warmth of a greener and wetter planet for a few thousands years till the ocean and the water cycle via igneous rock weathering pulls all the carbon back down to limestones , corals and deep sea muds.
Crop failures to follow, then blight and starvation.