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First, Earth gets darker as white snow and ice melt and vanish. Vegetation, ocean water, or rock is revealed underneath. They are darker, so they absorb much more energy than white surfaces of snow or ice do. This heats Earth up. Second, Earth is also more reflective from more aerosols in the air, from burning coal, so they usually cool off Earth’s surface. As we burn less coal, we lose this cooling effect. Third, it turns out that Earth has fewer low clouds as it warms up; being reflective on balance, missing those clouds heats Earth up.
To reverse Earth getting darker, we need to undo these three ways Earth darkens. First, there are proposals to grow ice (net), by spraying water on top of ice in winter. Second, put aerosols (sulfur or calcite) high up in the stratosphere; this is doable and relatively cheap. Third, increase low clouds, with marine cloud brightening or thin high (warming) cirrus clouds by spraying cloud condensation nuclei high in the troposphere. One can use mirrors on the ground to reflect sunlight, even paint roof white. There are other proposals as well.
