Earth's Climate Zones: Tropical, Arid, Temperate

• Climate zones are influenced by latitude, atmospheric and ocean circulation, and geographic features.
• The Köppen Climate Classification categorizes Earth's climate zones.

Major Climate Zones

• Tropical zones (0°–30° latitude) like the Amazon and Congo Basin have high solar radiation, consistent warm temperatures, and strong convection, leading to heavy rainfall.
• Hadley cells, with rising air at the equator, control tropical climates.
• Arid zones (around 30° latitude) such as the Sahara and Australian Outback are caused by descending dry air from Hadley Cells, suppressing precipitation.
• Temperate zones (30°–60° latitude) like the Mediterranean and U.S. East Coast experience seasonal variations due to Earth's tilt.
• Westerly winds bring moisture inland in temperate zones.
• Continental zones (40°–70° latitude) such as Russia and the Midwest U.S. have large landmasses, leading to greater seasonal temperature contrasts.
• Polar zones (above 60° latitude) such as Antarctica and the Arctic have low solar radiation and high albedo, resulting in cold temperatures.

Weather vs. Climate

• Weather constitutes short-term atmospheric conditions.
• Climate represents long-term weather patterns, typically observed over 30+ years.
• Weather is a single game, while climate is the team's performance over the season.

Temperature and Density

• Temperature is the average kinetic energy of molecules.
• Warm air is less dense and rises, while cold air is denser and sinks.
• Hot air balloons rise because heated air inside is less dense.
• Cold water is denser than warm water, and high-salinity water is denser than low-salinity water.
• The Dead Sea's high salinity allows people to float.
• Density differences drive wind and ocean circulation, shaping weather and climate.

Biomes and Their Distribution

• Biomes are large-scale ecosystems shaped by climate, geography, and vegetation.
• Rainforests have high rainfall, warm temperatures, and dense vegetation.
• Savannas feature seasonal rainfall and grasses with scattered trees.
• Deserts exhibit low rainfall and extreme temperature changes.
• Temperate forests have deciduous and evergreen trees with distinct seasons.
• Grasslands possess rich soil and seasonal droughts.
• Taiga (Boreal Forests) are cold, coniferous forests.
• Tundra has permafrost and limited vegetation.

Land Biosphere Processes

• Photosynthesis involves plants absorbing CO₂ and releasing oxygen.
• Respiration involves plants and animals releasing CO₂.
• Decomposition involves dead organisms decaying and releasing carbon and nutrients.
• Forests and soils act as carbon sinks.
• Deforestation in the Amazon reduces CO₂ absorption, accelerating climate change.

Ocean Biosphere Processes

• Phytoplankton photosynthesis involves ocean algae absorbing CO₂, forming the base of the marine food web.
• The biological carbon pump involves dead marine organisms sinking, sequestering carbon.
• Upwelling involves deep-sea nutrients rising to the surface, supporting fisheries.
• Coral reefs are biodiversity hotspots that suffer from ocean acidification.

Atmospheric Circulation

• Earth’s rotation and solar heating create three major circulation cells.
• Hadley Cells (0°–30° latitude) have warm air rising at the equator, causing heavy rain and tropical climates.
• Air moves poleward in Hadley cells and sinks at 30°, creating deserts.
• Ferrel Cells (30°–60° latitude) have mid-latitude westerlies that drive moist, variable climates.
• Storm systems in the U.S. and Europe are driven by Ferrel Cells.
• Polar Cells (60°–90° latitude) have cold, dense air that sinks at the poles.
• Antarctica has extreme cold and ice-covered landscapes because of polar cells.

Ocean Circulation & the Climate

• Surface currents are driven by winds, like the Gulf Stream warming Europe.
• Deep ocean circulation is driven by temperature and salinity gradients (Thermohaline Circulation).
• El Niño-Southern Oscillation (ENSO) is a climate pattern in the Pacific Ocean.
• El Niño involves weak trade winds leading to warming in the Pacific, disrupting weather patterns.
• La Niña involves strengthened trade winds leading to cooling, affecting rainfall and hurricanes.

Global Ocean Conveyor Belt

• The thermohaline circulation is a deep-ocean current system that transports heat and nutrients worldwide.
• Cold, salty water sinks in the North Atlantic, driving deep currents.
• Deep water moves toward Antarctica and into the Indian and Pacific Oceans.
• Warm water moves back toward the Atlantic, completing the cycle.
• The Gulf Stream keeps Europe warm, but melting Arctic ice disrupting the current could dramatically cool Europe.

Climate Change Policies

• The Montreal Protocol (1987) aimed to reduce CFCs to protect the ozone layer; it prevented millions of skin cancer cases and stabilized the ozone hole.
• The Paris Agreement (2015) aims to limit global warming to well below 2°C and preferably 1.5°C.
• The Paris agreement encourages renewable energy and carbon pricing, with countries setting nationally determined contributions (NDCs) to reduce emissions.

Renewable and Negative Emission Tech

• Renewable energy sources include solar, wind, hydro, geothermal, and biomass.
• Negative emissions technologies include direct air capture, afforestation, and ocean fertilization.
• Iceland uses geothermal energy and carbon capture to store CO₂ underground.

Geoengineering

• Geoengineering involves deliberate interventions to counteract climate change.

Solar Radiation Management (SRM)

• SRM reflects sunlight away from the earth.
• SRM can rapidly cool the earth potentially reversing warming trends.
• SRM does not reduce CO₂
• SRM could disrupt weather patterns, and cause risky side effects.
• Examples of SRM are stratospheric aerosol injection, and marine cloud brightening

Carbon Dioxide Removal (CDR)

• CDR removes CO₂ from the air.
• CDR directly addresses the cause of climate change, and is more sustainable
• CDR is expensive, slow to scale, and has potential land-use conflicts.
• Examples of CDR are Direct Air Capture, and ocean fertilization.