The Earth is bathed in a flood of sunlight. A fierce inundation of photons—on average, 342 joules per second per square meter. 4185 joules (one calorie) will raise the temperature of one kilogram of water by one degree Celsius. If all this energy were captured by the Earth’s atmosphere, its temperature would rise by ten degrees Celsius in one day.

Luckily much of it radiates back to space. How much depends on albedo and the chemical composition of the atmosphere, both of which vary over time.

A good portion of Earth’s albedo, or reflectivity, is created by its polar ice caps. If polar ice and snow were to shrink significantly, more solar energy would stay on Earth. Sunlight would penetrate oceans previously covered by ice, and warm the water. This would add heat and melt more ice, in a positive feedback loop.

The Arctic Ocean ice pack reflects back out to space a few percent of the total annual solar energy budget. When the Arctic ice pack was first measured by nuclear submarines in the 1950’s, it averaged thirty feet thick in midwinter. By the end of the century it was down to fifteen. Then one August the ice broke up into large tabular bergs, drifting on the currents, colliding and separating, leaving broad lanes of water open to the continuous polar summer sunlight. The next year the breakup started in July, and at times more than half the surface of the Arctic Ocean was open water. The third year, the breakup began in May.

That was last year.

Weekdays always begin the same. The alarm goes off and you are startled out of dreams that you immediately forget. Predawn light in a dim room. Stagger into a hot shower and try to wake up all the way. Feel the scalding hot water on the back of your neck, ah, the best part of the day, already passing with the inexorable clock. Fragment of a dream, you were deep in some problem set now escaping you, just as you tried to escape it in the dream. Duck down the halls of memory—gone. Dreams don’t want to be remembered.