L4 - Observational evidence and uncertainties for climate change Flashcards
When did water vapor condense to form oceans?
3.3 BYA
What was the first form of life to develop oxygen?
Photosynthetic cyanobacteria in shallow waters, around 3 BYA
What process contributed to the development of atmospheric oxygen 3 BYA?
Photosynthesis from blue-green algae (3 BYA) and green plants (2 BYA)
What is the chemical equation for photosynthesis?
nCO₂ + nH₂O → nCH₂O + nO₂
What is the photo-dissociation of water?
2H₂O + hv → 2H₂ + O₂
What major atmospheric change occurred 1.6 BYA?
Oxygen levels reached 1% of today’s levels, leading to ozone formation, which protected life from UV radiation.
What are the current percentages of major atmospheric gases?
Nitrogen (N₂): 78%
Oxygen (O₂): 21%
Argon (Ar): 0.93%
Carbon dioxide (CO₂): 0.03%
Methane (CH₄): 0.0018%
Water vapor: 0.2% - 2.6% (variable)
What did John Tyndall propose in 1863 about atmospheric heat?
The atmosphere allows solar heat to enter but prevents some of it from escaping, leading to heat accumulation.
What instrument did Tyndall use to study atmospheric gases?
A spectrophotometer to measure the electromagnetic spectrum.
What gases did Tyndall identify as absorbing heat?
Water vapor (H₂O) and carbon dioxide (CO2)
By how much have greenhouse gas concentrations increased since 1800?
CO₂: 35% increase
Methane (CH₄): 142% increase
Nitrous oxide (N₂O): 18% increase
How do scientists measure past atmospheric gas concentrations?
By extracting gases from bubbles trapped in ice cores.
What is the Keeling Curve?
The longest unbroken record of atmospheric CO₂ concentrations, showing seasonal variations.
What historical trend does the Keeling Curve show?
CO₂ concentrations have increased by 39% since 1750, peaking at 400 ppmv.
Why is the CO₂ increase considered man-made?
CO₂ from fossil fuels contains no ¹⁴C, unlike natural atmospheric CO₂.
What percentage of CO₂ emissions in the past 20 years came from fossil fuels?
75% from fossil fuels, with the remainder from deforestation and land use changes.
How much anthropogenic CO₂ has the ocean absorbed?
30% of emitted CO₂, causing ocean acidification and a 0.1 decrease in pH.
How do tree rings provide climate data?
They reflect water availability and record changes over 10,000 years.
How do ice cores provide temperature records?
They contain oxygen isotopes and trapped air bubbles that reveal past temperatures up to 800,000 years ago.
What does ocean sediment reveal about past temperatures?
The proportion of heavy oxygen isotopes in seashells increases when temperatures drop.
How does CO₂ concentration correlate with temperature change?
There is a clear correlation over the last 160,000 years
How has the CO₂ level changed in the last 420,000 years?
It is currently outside the natural variability range.
What factors contribute to climate variability?
Solar variation
Volcanic activity
Internal climate variability
Human-induced CO₂ and aerosols
How many temperature observations are recorded monthly?
1.5 million global observations.
