Glaciers don't just darken from soot. Their surfaces host tiny algae that, as temperatures rise, bloom and turn the ice dark. Dark ice absorbs more sunlight, melts faster, and further warms the planet. It's like how a black t-shirt in the sun gets hotter than a white one.
The second player in overheating is forests. Trees absorb carbon dioxide, but they have a limit. When it gets too hot, plants grow worse and take up less gas. Then more CO2 stays in the air, trapping heat, and it gets even hotter. Forests can't keep up.
Scientists combined these two loops into one computer model: temperature, carbon dioxide, and vegetation. Under strong emissions, the model doesn't heat up smoothly: it abruptly jumps to a new state, a hot 'greenhouse.' The tipping point comes when ice darkens from algae and forests stop taking up carbon.
This isn't a forecast for tomorrow, but a warning: climate has a hidden threshold. Cross it, and there may be no way back. The icy t-shirt will turn black and never go white again.
Microscopic algae on ice can tint an entire glacier red or green in a single season — visible even from space.