Using this handy dandy graph, I estimate that by the time climate change forces a response we will need to reverse 2° Celsius of heating.

The method for temperature control is described in here - a sunlight blocking satellite.

What percent of the sunlight destined for Earth needs to be reflected/redirected?

The question above presupposes 1%. But where I live there is a 14° variance in temperature which happens over 8 hours (1.75° per hour). The satellite would block light 24 hours per day so by my calculations we could cool the Earth 2°C in 5 days.

1% cooling x 1.75° x 24 hours x 5 days = 2.1°

I assume my math is wrong. But assuming we want to cool the earth over 20 years, what percent of sunlight actually needs to be reflected?

  • 2
    $\begingroup$ You should just edit out your math parts, they aren't really valid science. $\endgroup$
    – kingledion
    Jan 18, 2018 at 1:38
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    $\begingroup$ Heating is not measured in degrees, but in Watts.... you want to change the energy flows (Joules per second) $\endgroup$
    – L.Dutch
    Jan 18, 2018 at 5:54

1 Answer 1


0.2 %



According to NASA's energy budget, the Earth is absorbing 0.6 W/m$^2$, average worldwide over a whole year. This is the energy addition that is causing global warming. The Earth receives from the sun 340.4 W/m$^2$, average over the planet and year. Divide the two, and you see that we need to reduce incoming radiation by 0.2%.

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    $\begingroup$ Could you add a link to the article this image came from? First, as an attribution for the image, and second, to make it easier for your readers to search for more data. $\endgroup$
    – Mołot
    Jan 18, 2018 at 18:02
  • $\begingroup$ Although 0.2% would put the current energy budget in balance and prevent immediate further heating, it's important to remember that the system is dynamic and present imbalances may drive further heating such as further loss of sea ice as the polar ice coverage reaches equilibrium. Also, we'd need further reductions in sunlight to reverse the heating already experienced and keep up with continued carbon emissions. $\endgroup$ Dec 28, 2019 at 20:57

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