Nobel Prize-winning physicist
The perception of risk often has little to do with reality. Some never travel by air, even though aeroplanes are much safer than cars. Similarly, the chances of perishing in a cosmic cataclysm are smaller than those of being killed by a lightning storm on the London Underground.
Still, we are fascinated by the notion of dangers from outer space, whereas the real and immediate dangers remain overlooked. We can discuss global warming ad nauseam and feel good about "offsetting our carbon footprint" by paying a few quid for burning the same amount of fuel, but the elephant in the room is blissfully ignored.
The earth's overpopulation is by far the greatest and gravest danger facing the human race; it is the reason behind many other dangers, including global warming. Many of the planet's non-renewable resources will be depleted within this century. The earth is capable of sustaining only a small portion of the present population.
Much of the human race will be wiped out in the next few centuries -- it will be like a cosmic catastrophe but it won't take place in an instant. In what form this will happen and whether the race survives the slow cataclysm depends on our efforts to stop unsustainable human reproduction. At present, most still consider it profane even to raise the matter.