IB Environmental systems and societies 6.2A Climate and Anthropogenic GHG Emissions Notes

Climate vs Weather: Climate Is the 30-Year Average, Not Today's Sky

1. Climate is the long-term average and extremes of atmospheric conditions such as temperature, precipitation, humidity, wind and air pressure.
2. Conditions must be measured for at least 30 years to count as climate data.
3. Climate captures the full range of variation and extreme events for a region.
4. Weather describes short-term conditions over hours, days or weeks.

Physical Processes: Uneven Solar Heating Drives Every Climate Zone

1. Solar radiation distribution
   1. The equator receives more intense solar energy than the poles due to Earth's curvature and axial tilt, driving all other circulation.
2. Atmospheric circulation
   1. The Hadley, Ferrel and Polar cells transport heat and moisture, creating tropical, temperate and polar zones.
3. Convection and uplift
   1. Warm air is less dense and rises, then cools to trigger condensation, especially in tropical and monsoon regions.
4. Cloud formation
   1. Clouds both reflect incoming sunlight and trap outgoing longwave radiation, and this balance shapes temperature.
5. Precipitation cycles
   1. Seasonal rainfall patterns govern vegetation, soil moisture, water availability and ecosystem distribution.
6. Evaporation and humidity
   1. Heat evaporates water from oceans, lakes and soils, raising humidity and feeding cloud formation.
7. Natural greenhouse effect
   1. Greenhouse gases trap outgoing heat and keep Earth warm enough to support life.
8. Seasonal variation
   1. Earth's axial tilt drives seasonal cycles like monsoons and Mediterranean dry summers that are part of a region's climate.

Anthropogenic CO₂: Concentrations Have Jumped 50% Since Pre-Industrial Times

1. Before industrialisation, atmospheric CO₂ sat near 280 ppm and stayed stable for about 6,000 years.
2. The late-18th-century Industrial Revolution raised emissions through coal burning, mechanised manufacturing and urbanisation.
3. By the early 20th century levels reached about 300 ppm.
4. Emissions accelerated sharply after 1950 with rising industrial output, fossil fuel use, globalisation and population growth.
5. CO₂ passed 315 to 316 ppm in the late 1950s and surpassed 420 ppm in the early 2020s.
6. This is a 50 percent increase over pre-industrial values.
7. Industrialisation