Deferred rendering is a rendering technique that allows for flexible lighting and effects by rendering the scene to textures first before applying lighting and shading. It works by rendering the scene to color and depth buffers, then applying textures, lighting, and effects in a pixel shader. While it has issues like memory usage, it enables many lights and complex effects. Atmospheric scattering simulates how light interacts with particles in the air to produce realistic skies and aerial perspective. It is complex to implement as it involves integrating scattering equations along light rays. While attempts to include it have been partially successful, it remains challenging to code and debug.