Gerrit's got the technical answer; I'm going to answer for a layperson.

There are two ways objects lose heat.

• The first, and the way people are most familiar with, is conduction. Something touches something else, and the hotter material transfers some of its heat to the colder material. It's why you rapidly lose heat if you wade into cold waters: your body is hot and the water is cold - so the energy from your body seeps into the water you're touching.
• The second, though, is a bit harder to intuitively grasp: radiation. Or if it helps, think of it as light. Everything emits radiation/light - and that light is based on how hot the material is. Ever wonder why every material you heat up really how starts to glow red first (ovens, stoves, campfire embers, etc)? That's because when its that hot, the energy it's giving off is energetic enough to be seen by the human eye as red (the lowest energy color in the spectrum.) Heat it up further, and the color eventually shifts to a white.

Make sense so far?

Okay, Earth doesn't lose heat to conduction. Simply put, it's in a near-vacuum; there's not really anything its touching to transfer its heat to.

Instead, it loses its energy to radiation.

Now, objects emit radiation based on their temperature. So the energy coming from the sun? It's based on the temperature of the surface of the sun: about 6,000 degrees Kelvin (about 10k degrees F). So the light/energy/radiation coming from it is very high-energy. That energy strikes earth and heats it up. But the Earth itself is comparatively cool: an average of 287 kelvin (56 degrees F.) So the radiation that earth emits is much lower in energy.

And that's the key. Gasses like Carbon Dioxide don't allow lower-energy radiation to pass as easily has higher-energy radiation. So while it lets a lot of the sun's energy in, it doesn't let the radiated energy back out as easily.

Gerrit's got the technical answer; I'm going to answer for a layperson.

There are two ways objects lose heat.

• The first, and the way people are most familiar with, is conduction. Something touches something else, and the hotter material transfers some of its heat to the colder material. It's why you rapidly lose heat if you wade into cold waters: your body is hot and the water is cold - so the energy from your body seeps into the water you're touching.
• The second, though, is a bit harder to intuitively grasp: radiation. Or if it helps, think of it as light. Everything emits radiation/light - and that light is based on how hot the material is. Ever wonder why every material you heat up really how starts to glow red first (ovens, stoves, campfire embers, etc)? That's because when its that hot, the energy it's giving off is energetic enough to be seen by the human eye as red (the lowest energy color in the spectrum.) Heat it up further, and the color eventually shifts to a white.

Make sense so far?

Okay, Earth doesn't lose heat to conduction. Simply put, it's in a near-vacuum; there's not really anything its touching to transfer its heat to.

Instead, it loses its energy to radiation.

Now, objects emit radiation based on their temperature. So the energy coming from the sun? It's based on the temperature of the surface of the sun: about 6,000 Kelvin (about 10k degrees F). So the light/energy/radiation coming from it is very high-energy. That energy strikes earth and heats it up. But the Earth itself is comparatively cool: an average of 287 Kelvin (56 degrees F.) So the radiation that earth emits is much lower in energy.

And that's the key. Gasses like Carbon Dioxide don't allow lower-energy radiation to pass as easily has higher-energy radiation. So while it lets a lot of the sun's energy in, it doesn't let the radiated energy back out as easily.

Gerrit's got the technical answer; I'm going to answer for a layperson.

There are two ways objects lose heat.

• The first, and the way people are most familiar with, is transfer. Something touches something else, and the hotter material transfers some of its heat to the colder material. It's why you get cold going out on a winter night: your body is hot and the air is cold - so the energy from your body seeps into the air you're touching.
• The second, though, is a bit harder to intuitively grasp: radiation. Or if it helps, think of it as light. Everything emits radiation/light - and that light is based on how hot the material is. Ever wonder why every material you heat up really how starts to glow red first (ovens, stoves, campfire embers, etc)? That's because when its that hot, the energy it's giving off is energetic enough to be seen by the human eye as red (the lowest energy color in the spectrum.) Heat it up further, and the color eventually shifts to a white.

Make sense so far?

Okay, Earth doesn't lose heat to transfer. Simply put, it's in a near-vacuum; there's not really anything its touching to transfer its heat to.

Instead, it loses its energy to radiation.

Now, objects emit radiation based on their temperature. So the energy coming from the sun? It's based on the temperature of the surface of the sun: about 6,000 degrees Kelvin (about 10k degrees F). So the light/energy/radiation coming from it is very high-energy. That energy strikes earth and heats it up. But the Earth itself is comparatively cool: an average of 287 kelvin (56 degrees F.) So the radiation that earth emits is much lower in energy.

And that's the key. Gasses like Carbon Dioxide don't allow lower-energy radiation to pass as easily has higher-energy radiation. So while it lets a lot of the sun's energy in, it doesn't let the radiated energy back out as easily.

Gerrit's got the technical answer; I'm going to answer for a layperson.

There are two ways objects lose heat.

• The first, and the way people are most familiar with, is conduction. Something touches something else, and the hotter material transfers some of its heat to the colder material. It's why you rapidly lose heat if you wade into cold waters: your body is hot and the water is cold - so the energy from your body seeps into the water you're touching.
• The second, though, is a bit harder to intuitively grasp: radiation. Or if it helps, think of it as light. Everything emits radiation/light - and that light is based on how hot the material is. Ever wonder why every material you heat up really how starts to glow red first (ovens, stoves, campfire embers, etc)? That's because when its that hot, the energy it's giving off is energetic enough to be seen by the human eye as red (the lowest energy color in the spectrum.) Heat it up further, and the color eventually shifts to a white.

Make sense so far?

Okay, Earth doesn't lose heat to conduction. Simply put, it's in a near-vacuum; there's not really anything its touching to transfer its heat to.

Instead, it loses its energy to radiation.

Now, objects emit radiation based on their temperature. So the energy coming from the sun? It's based on the temperature of the surface of the sun: about 6,000 degrees Kelvin (about 10k degrees F). So the light/energy/radiation coming from it is very high-energy. That energy strikes earth and heats it up. But the Earth itself is comparatively cool: an average of 287 kelvin (56 degrees F.) So the radiation that earth emits is much lower in energy.

And that's the key. Gasses like Carbon Dioxide don't allow lower-energy radiation to pass as easily has higher-energy radiation. So while it lets a lot of the sun's energy in, it doesn't let the radiated energy back out as easily.