Paradox about greenhouse effect? I know about the greenhouse effect, but isn't earth receiving the same amount of energy but getting hotter than with that same amount of energy?

My guess is that earth reflects less light, but then wouldn't the Earth get darker?
 A: If you had infrared vision and were able to look down on the Earth from space, most of the light you "saw" would be from the upper regions of the atmosphere (the stratosphere).  Only a small portion would be from the surface.  This is because the atmosphere is largely opaque to infrared radiation, and most (though not all) of the infrared radiation from emitted by the surface is absorbed by the atmosphere.
If the surface warms, this would indeed lead to more radiation escaping into space.  But this increase in outgoing radiation is compensated for by a cooling of the stratosphere, since the additional carbon dioxide in the stratosphere radiates heat into space more effectively (remember that absorptivity = emissivity).  We do in fact observe cooling of Earth's stratosphere.

image taken from this blog post
The net result is that the total amount of outgoing energy flux remains basically balanced with the incoming flux.  It's just that now more of the outgoing flux is coming from the warmer surface and less of it is coming from the cooler upper atmosphere.
A: Yes, earth is roughly receiving the same amount of energy from the sun, but you have to remember that earth is also reemitting a lot of the radiation back into space. The greenhouse effect means that some of that reflected/reemitted radiation stays in the atmosphere.
A: Processes of the greenhouse effect happen in the UV and infrared regime of light: on earth the incoming UV is converted to infrared light (both are not visible to the eye).  Due to the greenhouse effect less energy is emitted in infrared then was absorbed in UV, because it's trapped by the atmosphere, leading to heating of the earth and less radiation energy leaving earth.  In the end the total of reflected and emitted energy is less than the incident energy.
If you take brightness/darkness as radiation energy over all wavelengths, indeed the earth becomes darker.  To notice this, however, you have to average out many variations in time (eg. more clouds during monsoon) and place (eg. ice caps reflect more than oceans).
A: As the earth system accumulates energy, it will become less reflective. Ice and snow cover are decreasing. This will increase absorbed solar, which will lead to greater outgoing long wave radiation. Adding CO2 raises the effective radiating level, so the earth will be radiating at a cooler temperature as energy accumulates in the earth system.
A: The total power in has to equal power out if the trapped energy is not going to rise very fast. However, increasing greenhouse gas effect means that the surface temp has to be higher to achieve the same power out. This is because more infrared radiation is trapped by gases. A higher temp increases the amount of energy at higher frequencies which can escape.
