MEVE 011: Unit 01 - Atmosphere and Climate

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UNIT 1: ATMOSPHERE AND CLIMATE

1.1 Introduction

The Earth’s climate system is largely controlled by the atmosphere—a dynamic layer of gases that surrounds the planet and interacts with incoming solar radiation. This unit introduces the structure and composition of the atmosphere, explains how solar radiation drives climate processes, and distinguishes between weather and climate. It also explores the components that contribute to climate change, including greenhouse gases and aerosols, and introduces the concepts of climate variability and long-term climate change.

1.2 Objectives

By the end of this unit, students will be able to:

·         Understand the structure, layers, and pressure systems of the Earth's atmosphere

·         Learn about the composition of the atmosphere, particularly the role of greenhouse gases and aerosols

·         Understand the concept of solar radiation and the global energy budget

·         Differentiate between weather and climate

·         Identify key climate variables and methods of climate classification

·         Recognize the difference between climate variability and climate change

1.3 The Atmosphere

The atmosphere is a thin, gaseous envelope that envelops the Earth and is vital for life. It provides oxygen, helps regulate temperature, protects us from harmful solar radiation, and enables weather phenomena.

1.3.1 Thermal Stratification of Earth’s Atmosphere

The atmosphere is vertically divided into layers based on temperature changes with altitude:

·         Troposphere (0–12 km): The lowest layer where all weather phenomena occur. Temperature decreases with height.

·         Stratosphere (12–50 km): Contains the ozone layer, which absorbs harmful UV radiation. Here, temperature increases with altitude.

·         Mesosphere (50–80 km): The coldest layer, where meteors burn upon entering the Earth’s atmosphere.

·         Thermosphere (80–700 km): A region of high temperatures due to solar radiation absorption.

·         Exosphere (above 700 km): The outermost layer where atmospheric particles gradually escape into space.

1.3.2 Atmospheric Pressure

Atmospheric pressure is the weight of air exerted on Earth’s surface. It decreases with increasing altitude. Pressure influences wind patterns and is a key factor in weather systems, including storms and cyclones.

1.3.3 Composition of the Atmosphere

The atmosphere is composed of major gases and trace components. The primary gases are:

·         Nitrogen (78%)

·         Oxygen (21%)

·         Argon (0.93%)

·         Carbon dioxide (0.04%)

·         Variable amounts of water vapor, ozone, and other trace gases also exist.

1.3.3.1 Greenhouse Gases (GHGs)

Greenhouse gases trap heat in the Earth's atmosphere, allowing the planet to stay warm enough for life. Major GHGs include:

·         Carbon dioxide (CO₂) – emitted from fossil fuel burning and deforestation

·         Methane (CH₄) – released from livestock, wetlands, and agriculture

·         Nitrous oxide (N₂O) – from fertilizers and industrial activities

·         Ozone (O₃) – a GHG at ground level, though protective in the stratosphere

Excess GHGs due to human activities have intensified the greenhouse effect, leading to global warming.

1.3.3.2 Aerosols

Aerosols are tiny particles suspended in the air, originating from both natural sources (like volcanoes, sea spray, dust) and human activities (such as burning fossil fuels). They can:

·         Reflect sunlight (cooling effect)

·         Absorb heat (warming effect)

·         Act as cloud condensation nuclei, influencing cloud formation and rainfall

1.4 Solar Radiation

Solar radiation is the energy emitted by the sun in the form of electromagnetic waves. It is the primary source of energy that drives Earth’s climate and weather systems.

1.4.1 Global Energy Budget

The global energy budget describes the balance between incoming solar radiation and outgoing terrestrial radiation. About:

·         30% of solar radiation is reflected back by clouds, atmosphere, and Earth's surface

·         70% is absorbed by the Earth’s surface and atmosphere

The absorbed energy is re-radiated as longwave infrared radiation, which is partly trapped by greenhouse gases. An imbalance in this energy budget—due to increased GHGs or aerosols—results in climate change.

1.5 Weather and Climate

1.5.1 Climate Variables

Climate is described using several measurable variables:

·         Temperature – average kinetic energy of air molecules

·         Precipitation – total rainfall or snowfall

·         Humidity – moisture content in the air

·         Wind – air movement driven by pressure gradients

·         Atmospheric pressure – influences wind and storm formation

·         Sunshine duration – affects surface temperature and plant growth

These variables help scientists analyze and predict climatic conditions over time.

1.5.2 Climate Classification

Climate classification helps categorize global climates based on temperature, precipitation, and vegetation. The most widely used system is the Köppen Climate Classification, which divides the world into zones such as:

·         Tropical (A)

·         Dry (B)

·         Temperate (C)

·         Continental (D)

·         Polar (E)

1.5.3 Climate Change and Climate Variability

·         Climate variability refers to short-term fluctuations (years to decades) such as El Niño–Southern Oscillation (ENSO) events. These are natural and cyclical.

·         Climate change is a long-term alteration in average weather patterns, typically measured over decades to centuries. Human activities—especially emissions of GHGs—are the main cause of the current rapid climate change.

1.6 Let Us Sum Up

In summary, this unit explains how the Earth’s atmosphere is structured and functions. It highlights how solar radiation interacts with atmospheric gases to regulate Earth's temperature through the global energy budget. The distinction between weather (short-term) and climate (long-term patterns) is made clear, along with the tools used to measure and classify climate. Finally, it introduces the important concepts of climate variability and climate change, setting the stage for deeper exploration in later units of this course.

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