Atmospheric Chemistry Flashcards
Why did our atmosphere go from weakly reducing to an oxidising atmosphere?
Photosynthetic organisms evolved, reducing the concentration of carbon dioxide and producing oxygen
Why did it take so long for life to migrate from the ocean to land?
The build-up of oxygen produced ozone which is required for UV protection
What are the three natural cycles that influence Earth’s climate?
The Obliquity Cycle (Axial Tilt)
The Eccentricity (Elliptical) Cycle
The Precession Cycle (Wobble)
What is the obliquity cycle?
The axial tilt is usually around 23.5 degrees, but can vary between 22 and 24.5 degrees over a period of 41,000 years.
When obliquity increases, the Earth gets hotter
What is the eccentricity cycle?
The Earth’s orbit is elliptical, but the exact orbit path depends on the gravitational pull from other planets.
This is the longest cycle, about every 100,000 and 400,000 years
What is the precession cycle?
Precession is the trend in the direction of the Earth’s axis of rotation relative to the fixed stars, and this occurs every 26,000 years.
Driven by tidal forces (position of sun and moon)
When does warming occur?
Warming occurs when our northern hemisphere (landmass) is pointed towards the sun (increased obliquity) and our orbit is more elliptical.
When does cooling occur?
Cooling occurs when we attain a more circular orbit and tilt decreases (decreased obliquity)
Why is the current climate not solely due to these natural cycles?
The effects we are seeing exceed the cause
What is the probable sequence of events for the heating of the climate?
1) Changes in the obliquity and eccentricity causes the Earth to warm
2) Warming oceans cause emissions of CO₂ to rise about 200-500 years later
3) CO₂ further warms the whole planet, leading to even further CO₂ release e.g. melting of permafrost
What role does the ocean play in the carbon cycle?
It absorbs CO₂ - 26% of the CO₂ released between 2002 and 2011 was absorbed
During the pre-industrial era, this value is estimated to be around 98%.
What is the chemical equation for the uptake of CO₂ by the ocean?
CO₂ + CO₃²⁻ + H₂O ⇌ 2HCO₃⁻
Does the ocean have an infinite capacity for CO₂ uptake?
1) As water temperature increases, its ability to dissolve CO₂ decreases
2) As surface water warms, the harder it is for winds to mix the surface layers with the deeper layers, limiting infusion of fresh carbonate-rich water from below
3) The stagnant water also supports fewer phytoplankton, therefore carbon dioxide uptake from photosynthesis slows
What is radiative forcing?
It is the change in net irradiance (solar plus long-wave) at the tropopause.
It is normally calculated as the change since the industrial revolution.
What are the advantages of showing the effects of emissions compared to concentrations?
It is emissions that can be directly controlled
It allows for many of the indirect effects to be seen e.g. reaction with other gases
It shows that air quality (CO, VOCS, NOₓ) affects climate via indirect effects on ozone
What does the radiative efficiency depend on?
1) Strength and spectral location of absorption of IR radiation
2) Atmospheric lifetimes
3) The time period over which the radiative forcing (RF) will be calculated
What is the equilibrium climate sensitivity (ECS)?
The equilibrium change in global temperature that occurs in response to doubled CO₂ since the pre-industrial era.
What is the equation for equilibrium climate sensitivity (ECS)?
ECS: ΔT / ΔF
Why does temperature decrease with height in the troposphere?
Most heat is absorbed by the planet surface. The warmed air at the surface rise and cools.
