Can A Cold Object Warm A Hot Object?
No, according to the Second Law of Thermodynamics.
( But a greenhouse gas can leave our planet's surface warmer than it would otherwise be, in the absence of greenhouse gases. )
The Second Law of Thermodynamics states that the net flow of thermal energy (aka "heat") goes from hot to cold, without exception.
The Second Law says nothing about individual flows of energy, only the net flow.
Heat can’t flow from cold to hot, but radiated energy can.
An object emits radiation until it hits something that absorbs it, and it's converted to thermal energy.
The individual temperatures of the emitting and absorbing objects are not the net energy flow, called “heat” = no violation of the Second Law
Net energy is the sum of individual energy flows -- gains minus losses.
The larger flow minus the smaller flow.
Greatly simplified balanced (constant global average temperature) global energy budget (chart below) patterned after the unbalanced ( shows global warming ) Kiehl/Trenberth budget
The temperature and the radiation are related to each other by the Stefan-Boltzmann equation.
When we apply the S-B equation to the 321 W/m2 of down welling “back radiation” shown in the chart below, it tells us that the effective radiating level is somewhere around freezing, much colder than the surface.
BUT a cold atmosphere can leave the earth warmer than it would be without the atmosphere because it is hiding something even colder from view, the cosmic microwave background radiation that is only 3 W/m2 …
And as a result, with the cold atmosphere shielding us from the nearly infinite heat sink of outer space, the earth ends up much warmer than it would be without the cold atmosphere.
• Heat cannot flow from cold to hot, but radiated energy can.
• A cold atmosphere radiates about 300-plus W/m2 of down welling radiation measured at the surface.
This 300-plus W/m2 of radiated energy leaves the surface warmer than it would be if we were exposed to the 3 W/m2 of outer space."
