If absorption and re-radiation are equal on average, then the Earth's temperature remains constant. A little too much radiation absorbed and not re-radiated and the Earth warms. There has been a great deal of scientific inquiry as to whether carbon dioxide emitted by fossil fuel burning by man may be altering this balance. This is a difficult question for which there not yet an unequivocal answer. Nonetheless, a great deal of public attention has been paid to speculating on global warming.
Asteroids hurl through the solar system.
Small space chunks regularly strike the atmosphere forming meteor showers. Sporadically, on geological time scales, an asteroid large enough to create massive destruction strikes the Earth. Despite their rarity and unavoidability, the potential of such an impact titillates the popular imagination. There is however, a catastrophe lurking within the next few decades, that will, if unchecked, cause profound social disruption. In the coming years, there will be a collision between the increasing numbers of elderly, the aging children of the Baby Boom, collecting Social Security and Medicare and the diminishing number of workers supporting them.