Why we should be concerned about the increase in amount of the green house gases in the atmosphere?

We should be concerned about the amount of green house gases released into the atmosphere because the more gases are released, the more they accumulate in the atmosphere and trap heat, which contributes to global warming, which is causing massive changes in our environment all around the world.

not necessarily. higher fitness requires the organism to be reproductive successful. for example, an organism at age 10 with 15 offspring is much more fit than an organism at age 15 with only 5 offspring.