With respect to life counteracting increased solar flux, here's what my idle mind came up with.
Coconut trees currently absorb large quantities of silica and integrate it into their tissues. This is why coconut tree logs, although not technically wood, can be denser than teak.
Coconuts currently float for only a few months before they start sprouting or become waterlogged and sink. This is why the transpacific spread of coconut trees is believed to be partially due to humans carrying the nuts with them.
Imagine a coconut tree that creates a silicate shell around its nut, impervious to water. The nut would not be able to sprout until the shell had been abraded or cracked on a distant beach, years, decades, or even centuries after it fell into the sea. Nuts that fell on land would not germinate until after a fire or other disaster had cracked the silicate (and destroyed all competing trees). Failing that, they would rest in stasis forever, until a hurricane or erosion washed them into the sea. This would be an obvious evolutionary advantage, aiding the spread of the tree's genome. There are precedents, such as some pine cones that do not release their seeds unless exposed to the heat of a wildfire.
Now, after the coir around the nut had come off in the ocean, you would have a hard, shiny, glassy sphere, bobbing for centuries in the ocean. World commercial production of coconuts is around 6 x 10^10 kg, at around 1.5 kg/nut, so there are currently at least 40 billion nuts produced each year. Let's suppose silicate coconuts became the dominant tree on the planet, and we went up to a trillion nuts per year, each surviving for a century or more. Let's assume each of the 10^14 shiny nuts was equivalent to a perfect reflector with an area of 0.05 square metres. This would be the same as a mirror of about five million square kilometers, reflecting sunlight light back into space to keep the earth cool.
But that's only about 1% of the earth's surface.
Drat, not enough.