One of the better general articles on the arctic ice cap (via Scientific American)
The arctic icecap covers about two percent of the planet in June when sunlight is constant. Shifting from reflective white ice to darker seawater and land would catch about as much added heat per year as human caused global warming does now ...
not a good thing
One September, perhaps as early as 2015, perhaps decades later, we’ll learn that the Arctic is ice-free. There will still be ice bergs and occasional floes of ice in the Arctic, but they’ll be scattered, surrounded by far more water than ice. Nowhere will ice constitute the majority of the Arctic.
You’ll probably hear this referred to as the first ice-free Arctic summer. But, in reality that first “ice-free Arctic” will most likely be a period of a few days or a week or two in mid-to-late September. August will still have an ice cap, if a small one. July will have a larger one than that. June larger still. And March, the month of the year when the Arctic ice cap is at its maximum, will still have seen plenty of ice.
Yet from that year on, the ice-free period will likely grow, expanding in duration to start earlier and end later year over year. Most likely, it’ll follow the same jagged, two-steps-forward one-step-back progression we see in climate in general. The first year after the first “ice-free Arctic” year, we may see some ice cap persist all the way through the summer again. For that matter, next year, 2013, it’s quite possible that we’ll see more ice than this year. Climate is bumpy that way. But, if recent history is any lesson, bit by bit, step by jagged step, the ice free period will lengthen, and the ice coverage in other months of the year will shrink.
This is particularly important because September is not a very sunny month in the Arctic. The sun never rises high above the horizon, and so its heating power is muted. Those dark waters are absorbing more of the solar energy that strikes them than ice would, but there’s simply less solar energy striking the arctic in September than there is for the spring and summer months leading up to it.
The sunniest time of year in the northern hemisphere is the summer solstice, in late June, and the weeks preceding and following it. For several weeks the sun’s rays are at their most intense and the Arctic receives 24/7 sunlight, giving it a double whammy of heating. In fact, in June, July, and the latter half of May, the Arctic receives more total solar energy per day than regions at the equator do at any time of year. The sun’s rays are never as powerful in the Arctic as they are at the equator, but the 24/7 availability of sun more than makes up for that. (If you doubt this, see NASA’s Earth Observatory page on the topic or use NASA’s monthly insolation-by-latitude calculator.)
Thus, every patch of dark ocean water revealed by melting ice in June, or May, or July, has a warming effect much larger – as much as five or six times larger – than the same change in ice coverage in September, when the ice hits its minimum today. The loss of ice in September is one thing. Loss of ice in June would have a far bigger impact on the region and the planet.