ESPM 15 Midterm 1 - Lecture 04: Earth's Energy Balance

What is the primary energy source driving atmospheric circulation?

Sunlight

Order by albedo, low to high: snow, ocean, desert, forest

Ocean < forest < desert < snow

Which emits more short-wave radiation per unit area: a warm object or a cold one?

The warm object (Stefan-Boltzmann — hotter emits more)

Where does incoming solar radiation exceed outgoing radiation?

At the equator (surplus); the poles run a deficit

What exactly do greenhouse gases absorb?

Outgoing long-wave (infrared) radiation re-emitted by Earth's surface

What is latent heat flux?

Energy transfer associated with water evaporation

Shortwave vs longwave radiation?

Shortwave = incoming solar (UV/visible, high energy); longwave = outgoing infrared re-emitted by Earth's surface

What processes transfer energy in the Earth system?

Radiation, conduction, convection, and latent heat (evaporation/condensation)

What determines Earth's surface temperature?

The balance between absorbed incoming solar radiation and outgoing longwave, modified by the greenhouse effect

How are major greenhouse gas concentrations changing?

Increasing, due to human activity

What happens to incoming solar radiation? (the budget)

About a third is reflected by clouds, air, and the surface; the rest is absorbed by the atmosphere and Earth's surface

Why does the equator run an energy surplus and the poles a deficit?

Sunlight hits the equator nearly head-on (more energy per area); at the poles it arrives at a shallow angle and ice reflects more of it

Walk through the greenhouse mechanism step by step

Surface absorbs shortwave solar → re-emits longwave infrared → greenhouse gases absorb the IR → re-radiate it in all directions, including back down to the surface

Without any greenhouse effect, Earth's average temperature would be?

Around -18°C — frozen solid. The natural greenhouse effect is what keeps us habitable

Natural vs enhanced greenhouse effect?

The natural effect keeps Earth livable; human-added greenhouse gases intensify it beyond the natural baseline