Lecture 31 - Climate of the Earth

ASTR 1210 (Exam 3)

What Factors Can Cause Long-term Climate Change?

• Energy in = energy out 

• When those two things find equilibrium on a planet, that leads to getting the temp of a planet

• Sun creates all the energy in the solar system = affects equilibrium temp 

• Can take a planet and push it closer to the sun = equilibrium temp goes up because energy goes up and vice versa 

• Can make my star hotter = increase energy even if planet is same distance

  • What is happening to the Sun 

• Stars get hotter and hotter as years go on 

Solar Brightening

• Rate at which sun is fusing at = as it runs out of hydrogen, it has to fuse hydrogen faster

• Sun very gradually grows brighter with time, increasing the amount of sunlight warming the planets

• In Goldilocks Zone to allow liquid water exist on the Earth 

• Mars will be pushed into the Goldilocks Zone

Temperature vs Solar Activity

• Sunlight is decreasing and relatively stable

• Sun is getting colder, Earth is getting hotter

• Has to do with the gases around the planet’s atmosphere

Changes in Axis Tilt

• Earth’s climate is affected by seasonal temperature changes

• Has to do with the axial tilt of the Earth - tilt more extreme = seasons more extreme

• Over many years, about 22 to 25 degrees - our tilt is stable because of the Moon

• Moon acts as a gravitational sounding board that allows the tilt to stay the same

• Mars has had more extreme tilts = more extreme climate change because it doesn’t have a big moon

Changes in Reflectivity

• If planet more reflective - energy in going down

• Less reflective - energy in is gonna increase

• Can change energy of the planet

Changes in Greenhouse Gases

• Cause the potential for significant temp change

• Greenhouse gases are also vital for the Earth’s life to thrive

Evolution of the Earth’s Atmosphere 

• When Earth first formed, it was situated in gas and dust that was the solar nebula 

  • Hydrogen and helium made up Earth’s early atmosphere

• Earth eventually lost the H and He over time - has to do with Earth’s gravity - can’t hold on to H and He

  • If planet was bigger, it could retain H and He - gas giants retained it

• Ammonia and methane went away and atmosphere dominated by nitrogen, carbon dioxide, and water

Sources of Gas

1. Impacts — impacts vaporize rock 

2. Outgassing — volcanos can significantly change the amount of gas in our atmosphere 

3. Vaporization — ice or liquid vaporizes 

Losses of Gas

1. Reversible loss

   1. Condensation

   2. Chemical reactions with the surface

      1. Rust removes oxygen from the atmosphere

2. Permanent loss — losing gas to space

   1. Thermal escape due to planet’s temperature

   2. Escape via the Solar World - particles from Sun smack into planet’s atmosphere and the energy can cause particles to escape the planet’s atmosphere

Thermal Escape from an Atmosphere 

• Average speed or thermal velocity of particles move at tells you the temperature 

• Some of those particles travel faster/ some will travel slower

• Some will be traveling GREATER than escape velocity - velocity of an object so that it escapes a planet 

Thermal Velocity Equation

• Particles that have less mass will be moving much faster than the other particle to reach escape velocity

Escape Velocity from Solar System Planets

• Low-mass particles will move fastest at any given speed

• Further from sun - colder you’re going to be 

• Gravity affects escape velocity

Exospheres of the Moon and Mercury

• Very, very thin atmosphere

• Dominated by things smacking into these objects, vaporizing them…

What is Mars like Today?

• Thin atmosphere but it has some stuff

• Impacts of weather on Mars - seasonally has dust storms

• Dust in the Martian atmosphere that’s been blown around as a result of windstorms that has blurred features

Seasonal Ice Caps of Mars

• Polar ice cap biggest during winter, smallest during summer - made up of carbon dioxide (dry ice)

• Going to increase/decrease CO2 seasonally on Mars

How Has Mars’s Climate Differed in the Past? 

• Likely had water on the surface 

Changing Axis Tilt

• layers of ice and rock that Mars goes through freezing and non-freezing periods - these layers were explained by axial tilt from Mars (0 to 60 degrees)

• Could’ve cause Mars to lose atmosphere

Why the Climate Change?

• Loss of atmospheric gas

• Loss of water

• Size is a critical factor in the timescale for climate change on a planet

Climate Change on Mars 

• Magnetic field may have perserved early Martian atmosphere

• Solar winds stripped atmosphere after field decreased because of interior cooling 

What is Venus like today?

• Much thicker than the Earth

• Dominated by CO2

• 90 times thicker atmosphere than Earth

Venus has a very slow rotation. How would the Coriolis effect on Venus compare to the Earth?

• Slow rotation —> most spherical planets in the solar system

• Coriolis is a byproduct of the speed at which an object is spinning - Venus would have a much weaker Coriolis effect

• Probably no hurricanes

• No strong weather features

Atmosphere of Venus

• Venus has thick CO2 atm with a surface pressure 90 times that of Earth

• Little weather - little wind - slate like rocks, no wind erosion

Greenhouse Effect on Venus 

• Thick CO2 produces strong greenhouse effect 

• Earth escapes this because most of its carbon and water is in rocks and oceans 

Runaway Greenhouse Effect

• Venus is super hot because of the runaway greenhouse effect

• Result of the fact that gases in Venus are transparent to visible, opaque to infrared

• Earth escaped this fate because we have water - water causes rain, taking away CO2 from the atmosphere

What is the main reason why Venus is hotter than Earth?

• Because of the greenhouse effect

How Did Earth’s Atmosphere become different? 

• Water on the surface - Venus is too close to the Sun

• Carbon cycle - because Earth is geologically active and because of water

Carbon Dioxide Cycle

1. Atm CO2 dissolves in rainwater

2. Rain erodes minerals that flow into ocean - CO2 in minerals

3. Minerals combine with carbon to make rocks on ocean floor

4. Subduction carries carbonate rock down into mantle

5. Rock melts in mantle and CO2 is outgassed back into atmosphere through volcanoes

Earth’s Thermostat

• Cooling allows CO2 to build up in atmosphere

• Heating causes rain to reduce CO2 in atmosphere