Global Warming

Global Warming

Key Notes

Global warming refers specifically to the long-term increase in the Earth's global average surface temperature, mainly driven by human-caused greenhouse gas emissions.

• Primary cause: Increasing concentrations of greenhouse gases from burning fossil fuels, deforestation and industrial and agricultural activities.

• Industrial Revolution: Large-scale fossil fuel use since the industrial era has substantially increased atmospheric CO₂ concentrations.

• Ice-albedo feedback: Melting snow and ice expose darker surfaces that absorb more solar energy, causing additional warming.

• Sea-level rise: Results mainly from thermal expansion of warming seawater and the loss of land-based glaciers and ice sheets.

• Ocean warming: A large proportion of the excess heat accumulated in the climate system is stored in the oceans.

• Extreme events: Global warming increases the likelihood or intensity of many heat extremes and can worsen certain droughts, heavy rainfall events and fire-weather conditions.

• Ecosystems: Warming can shift species distributions, alter seasonal cycles and increase risks to vulnerable ecosystems.

• Human impacts: Heat stress, agricultural losses, water insecurity, health risks and damage to infrastructure.

• Mitigation measures: Renewable energy, energy efficiency, low-carbon transport, methane reduction, forest protection and carbon removal.

Key Pointers for UPSC

• Global warming is one component of broader climate change.

• The greenhouse effect is a physical process; global warming is the observed long-term rise in temperature associated with its human-driven enhancement.

• The 1.5°C and 2°C goals in the Paris Agreement are measured relative to pre-industrial temperature levels.

• Global warming does not mean every place experiences warming at the same rate or every year.

• Weather refers to short-term atmospheric conditions; climate describes long-term patterns and statistics.

• Melting floating sea ice has little direct effect on sea level compared with the melting of land-based ice, although sea ice loss affects albedo and ecosystems.

MCQs

Q1. The principal cause of current long-term global warming is:

1. Increased human emissions of greenhouse gases

2. Depletion of all atmospheric oxygen

3. Decrease in Earth's gravity

4. Changes in ocean salinity alone

Correct answer: 1) Increased human emissions of greenhouse gases.

Explanation: Human activities have increased atmospheric greenhouse gas concentrations, strengthening the greenhouse effect and warming the planet.

Q2. The ice-albedo feedback refers to:

1. Increased reflectivity caused by melting ice.

2. Reduced reflectivity when bright ice is replaced by darker surfaces, leading to greater heat absorption.

3. Cooling caused exclusively by volcanic eruptions.

4. The transfer of carbon from oceans to rocks.

Correct answer: 2) Reduced reflectivity when bright ice is replaced by darker surfaces, leading to greater heat absorption.

Explanation: Ice and snow reflect a substantial proportion of incoming solar radiation. Their loss exposes darker surfaces that absorb more energy.

Q3. Which of the following is a major direct contributor to global mean sea-level rise?

1. Thermal expansion of seawater as it warms

2. Increased salinity alone

3. Formation of new continental ice sheets

4. Increased reflection of sunlight by clouds alone

Correct answer: 1) Thermal expansion of seawater as it warms.

Explanation: Warming causes seawater to expand. Melting land-based glaciers and ice sheets also contributes significantly to sea-level rise.