Four professors at an undisclosed university receive grants to study global warming. The temperature of the world, measured in units that normalize the current temperature at 1, is predicted to evolve according to the equation

y' = √ y, y(0) = 1.

The professors give the following opinions:
Zweistein: The temperature will become infinite in a finite time. Clearly this will be the end of the world.
Dreistein: The world will continue to warm, but there will be no end of the world. But eventually it will get too hot for everyone.
Vierstein: The world is warming, but it will reach a new equilibrium. If you like hot weather, you will be ok.
Einstein: All this talk about global warming is nonsense. The world is actually cooling.

Who is right?