Ordinarily, the bright, white surface of glacial ice found in ice sheets such as the ones that cover Greenland and Antarctica serve to function as reflectors that bounce a certain amount of solar radiation back into space — this effect also helps prevent the ice from being directly warmed too much by the sun. The effect of the ice’s reflectiveness, or albedo, can be compromised by changes in its color, for instance by soot being deposited on the surface from large wildfires ravaging a different part of the globe. The darkening of the ice causes it to absorb more sunlight, and in turn this increases the temperature of the ice, hastening its rate of melt. Now, a new factor has been identified that can darken the albedo of Greenland’s ice: the spread of simple algae.
The UK-based Black and Bloom project is currently investigating the different species of algae found in Greenland, how they spread, and their effect on the albedo of the ice, in order to add these factors into future climate change models. Current climate models didn’t incorporate the effect of the albedo of Earth’s ice sheets until 2013, meaning that these models might be underestimating melt rates.
Greenland’s ice sheet is the second largest on the planet, following Antarctica, and is currently contributing to 1 millimeter of sea level rise per year. The ice in Greenland holds enough water to raise ocean levels by 7.2 meters (24 feet) — thankfully, it won’t melt all at once, but researchers are concerned that the rate of melt could accelerate due to the algal growth.
Typically, clean snow reflects about 90 percent of the solar radiation that hits it back into space, but areas darkened by algae can reduce this to 35 percent, and even less. There is also a feedback effect to the presence of the algae: as the area is warmed by the change in color, this warmth also encourages the growth of more algae.
When the BBC’s science editor David Shukman accompanied the research team to Greenland, he initially thought the ice had been covered in soot, due to the extent that the resident algae had changed the color of the ice.
"This is a living landscape," explains glacial microbiologist Dr. Joe Cook, with at Sheffield University.
"This is an extremely difficult place for anything to live but, as we look around us, all this darkness we can see on the ice surface is living – algae, microbes, living and reproducing in the ice sheet and changing its colour."
Additionally, the team has also identified a trend for there to be 15 percent less cloud cover over Greenland over the past 20 years during the summer months, increasing the amount of sunlight getting to the ice. The research team believes this factor has been contributing to two-thirds of additional melt over the long-term average.