Lecture 12: The Greenhouse Effect

The greenhouse effect refers to the process where gases in the Earth's atmosphere trap incident solar radiation.
The average increase in Earth's temperature due to this effect is approximately 0.9^ ext{°C} compared to a scenario without the greenhouse effect.

Defined as the potential future effects on global climate from the accumulation of specific gases, leading to an uncontrollable increase in Earth's temperature.
This can result in devastating consequences for the planet.

Major greenhouse gases include:
- Water vapor (H₂O): most abundant and significant, but its concentration is reactive to temperatures.
- Carbon dioxide (CO₂): levels are rising due to human activities like burning fossil fuels.
- Methane (CH₄): significantly contributes to warming.
- Nitrous oxide (N₂O) and Ozone (O₃): also play roles in trapping heat.

High concentrations of CO₂ have historically correlated with elevated surface temperatures.
Conversely, low CO₂ periods have witnessed lower surface temperatures.

Sea levels have risen between 4-8 inches over the past century.
Global mean surface temperatures have risen by 0.25^ ext{°C} to 0.5^ ext{°C} since the late 19th century.
The longevity of greenhouse gases in the atmosphere varies from 30 years for methane to 300 years for nitrous oxide.

Increases in greenhouse gas concentrations due to human activities may alter Earth's climate for centuries.
The climate system's heat capacity is significantly attributed to water and ocean dynamics, which have long temporal processes.

Models predict continued stratospheric cooling in response to CO₂ reductions, exacerbated by ozone depletion.
Water vapor in the lower troposphere is projected to increase by approximately 0.3% per 1^ ext{°C} of warming while maintaining relative humidity.
By 2100, predicted global temperature increases range from 3^ ext{°C} to 5^ ext{°C}.
Sea-level rise is likely to increase by 16 ext{–}21 cm by the year 2100.
Global precipitation expected to increase by 1.5 to 2 ext{%} per ext{K} of surface warming.

Water vapor accounts for about 95% of Earth's greenhouse effect, indicating its substantial influence on climate dynamics.