Global Warming and Climate Change Notes

Greenhouse gases trap heat in the Earth's atmosphere, leading to the greenhouse effect.

Studying Earth's temperature history involves analyzing water molecules and CO2 in ice cores.
The Earth has gone through cycles of warm and cold periods on a ~100,000-year timescale.

Understanding where CO2 comes from (sources) and where it goes (sinks) is crucial.

Global warming refers to the increase in Earth's average surface temperature.
Climate change encompasses broader changes, including temperature, precipitation, and extreme weather events.

Incoming solar energy (100% = $681 W/m^2$ ) is either reflected or absorbed.
Reflected:
- 6% reflected from the atmosphere.
- 20% reflected by clouds.
- 4% reflected by the Earth's surface.
Absorbed:
- 16% absorbed by the atmosphere.
- 3% absorbed by clouds.
- 51% absorbed by land and oceans ( $341 W/m^2$ ).
Energy is radiated to space from clouds and the atmosphere.
Conduction and rising air account for 7% of energy transfer.
Latent heat in water vapor carries 23% of energy to clouds and the atmosphere.
15% of radiation is absorbed by the atmosphere.
6% radiated directly to space from earth.

Radiation absorbed from the Sun: $I \pi R^2 (1 - α)$
Radiation released from Earth: $4 \pi R^2 σ T_E^4$
At equilibrium: $I(1 – α) = 4 σ T_E^4$
$T_E = \sqrt[4]{\frac{I(1-α)}{4σ}}$
$I = 1361 W/m^2$ (solar radiation per unit area)
$α ≈ 30\%$ (albedo - reflected solar radiation).
$T<em>E = 255 K$ or $-18°C$ , actual average Earth surface temperature observed is $T</em>{obs} = 288 K = 15°C$

Main effect: trapping warm air and preventing it from leaving the atmosphere.
Analogy: glass in a greenhouse lets in short wavelength light but blocks long wavelength light.

Gases that absorb long wavelength light (infrared radiation).
Important greenhouse gases: O2, O3, CH4, N2O, Chlorofluorocarbons (CFCs).
Must have suitable molecular vibration modes that can absorb infrared radiation.

Reflection: About 30% of solar radiation is reflected, mainly by clouds, ice, and snow.
Absorption: Up to 85% of radiation from Earth is absorbed in the atmosphere, mainly by clouds and water vapor.
Positive feedback: If Earth heats up, ice melts (less reflection), leading to more water vapor (more absorption), amplifying global warming.

Emits pollutants (kg / $10^{12} J$ ).
- CO2 (GHG): Natural Gas (50,400), Oil (70,700), Coal (89,600)
- CO: Natural Gas (17.2), Oil (14.2), Coal (89.6)
- Nitrogen oxides: Natural Gas (39.6), Oil (193.0), Coal (196.9)
- Sulphur dioxide: Natural Gas (0.4), Oil (483.4), Coal (1116.3)
- Particulate: Natural Gas (3.0), Oil (36.2), Coal (1182.2)
- Mercury: Natural Gas (0.000), Oil (0.003), Coal (0.007)
Global carbon emissions increased from 0.5 Gt in 1900 to 5.5 Gt in 2000, and 9 Gt in 2018.
43% of CO2 emissions come from burning coal, 56% from burning hydrocarbons.

The 400,000-year temperature history obtained from ice cores shows cycles of warm and cold periods on a 100,000-year timescale.
We should be heading for another ice age.

Caused by variations in:
- Eccentricity of Earth's orbit (E)
- Tilt of Earth's rotation axis (T)
- Wobble of the axis (P)
Affect the intensity of solar radiation received by Earth.
Period: 100 thousand years.

1 to 1900: continuous decline in average temperature (consistent with onset of an ice age).
1900s: sudden sharp increase of average temperature (