Satellite images analysed by scientists based at Wuhan University in China, have shown that the number of lights visible over Syria at night has fallen by 83% since March 2011.
The work was carried out in co-operation with the #WithSyria coalition of 130 non-governmental organisations including Christian Aid.
"Four years since this crisis began, Syria's people have been plunged into the dark: destitute, fearful, and grieving for the friends they have lost and the country they once knew," said David Miliband, President and CEO of the International Rescue Committee.
"Four years since the crisis began, there is at present very little light in this tunnel. Over two hundred thousand people have been killed and a staggering eleven million have been forced to flee their homes.
"Syrians deserve much better from the international community - it is past time to show that we have not given up and will work with them to turn the lights back on."
The #WithSyria coalition is also calling on world governments to find a lasting peace and boost humanitarian aid.
Dr Xi Li, lead researcher on the project, said: "Satellite imagery is the most objective source of data showing the devastation of Syria on a national scale.
"Taken from 500 miles above the earth, these images help us understand the suffering and fear experienced by ordinary Syrians every day, as their country is destroyed around them.
"In the worst-affected areas, like Aleppo, a staggering 97% of the lights have gone out. The exceptions are the provinces of Damascus and Quneitra, near the Israeli border, where the decline in light has been 35% and 47% respectively."