SACE stage 2 Chemistry Topic 1.1

Global Warming and Climate Change

What is global warming?

The increase in Earth's average surface temperature due to the greenhouse effect caused by greenhouse gases.

Name three major greenhouse gases.

Carbon dioxide (CO₂), methane (CH₄), and nitrous oxide (N₂O).

How does the greenhouse effect work?

1. Solar Radiation: The Earth receives incoming short-wavelength solar radiation from the sun. Approximately half of this radiation is absorbed by the Earth's surface, warming it.

2. Infrared Emission: The warmed Earth's surface then re-emits this energy as long-wavelength infrared (IR) radiation.

3. Absorption by Greenhouse Gases: Certain atmospheric gases, known as greenhouse gases (GHGs), such as carbon dioxide (CO2CO2), methane (CH4CH4), and water vapor (H2OH2​O), have specific molecular structures that allow them to absorb this outgoing long-wavelength IR radiation. The bonds within these molecules vibrate, increasing their kinetic energy.

4. Re-emission of Radiation: These excited GHG molecules then re-emit the absorbed IR radiation in all directions, including back towards the Earth's surface and lower atmosphere.

5. Warming Effect: This re-emission of IR radiation back towards the surface traps heat, preventing it from escaping directly into space, and thereby warming the planet to a temperature suitable for life.Solar Radiation: The Earth receives incoming short-wavelength solar radiation from the sun. Approximately half of this radiation is absorbed by the Earth's surface, warming it.

6. Infrared Emission: The warmed Earth's surface then re-emits this energy as long-wavelength infrared (IR) radiation.

7. Absorption by Greenhouse Gases: Certain atmospheric gases, known as greenhouse gases (GHGs), such as carbon dioxide (CO2CO2), methane (CH4CH4), and water vapor (H2OH2​O), have specific molecular structures that allow them to absorb this outgoing long-wavelength IR radiation. The bonds within these molecules vibrate, increasing their kinetic energy.

8. Re-emission of Radiation: These excited GHG molecules then re-emit the absorbed IR radiation in all directions, including back towards the Earth's surface and lower atmosphere.

9. Warming Effect: This re-emission of IR radiation back towards the surface traps heat, preventing it from escaping directly into space, and thereby warming the planet to a temperature suitable for life.

What human activities contribute to climate change?

burning fossil fuels, deforestation, and intensive agriculture.

What evidence supports global warming?

Rising average temperatures, melting glaciers, sea-level rise, and changing weather patterns

what is the enhanced greenhouse effect?

Human activities, particularly the burning of fossil fuels, deforestation, and industrial processes, release additional amounts of GHGs into the atmosphere. This increases the concentration of these gases, leading to more IR radiation being absorbed and re-emitted, resulting in an enhanced warming of the Earth's climate, a phenomenon referred to as global warming, and intensifies the natural greenhouse effect, accelerating climate change.

From a molecular perspective, explain why greenhouse gases like carbon dioxide and methane can absorb infrared radiation, while diatomic gases like nitrogen and oxygen are not

Greenhouse gases possess specific molecular structures with at least three atoms. These structures allow for asymmetric stretching and bending vibrational modes, which result in a temporary change in the molecules’ dipole moment. This oscillating dipole can then interact with and absorb specific frequencies of IR radiation, increasing the molecules’ vibrational energy. In contrast, diatomic molecules of the same element are symmetrical and do not experience a change in their net dipole moment during vibration, meaning they cannot absorb IR radiation.

Outline the two primary mechanisms by which global warming contributes to a rise in global sea levels.

1. Thermal Expansion: As the Earth's average temperature rises, the oceans absorb a significant amount of this heat. Water expands as it warms, meaning the increase in ocean water temperature leads to an increase in its volume, thereby raising sea levels.

2. Melting of Glaciers and Ice Sheets: Elevated global temperatures accelerate the melting of glaciers, ice caps, and large continental ice sheets (e.g., in Greenland and Antarctica). The meltwater from these land-based ice masses flows into the oceans, directly increasing the total volume of water and contributing to sea-level rise.

Distinguish between the 'natural greenhouse effect' and the 'enhanced greenhouse effect', identifying the main cause of each.

1. Natural Greenhouse Effect: This is a naturally occurring process vital for maintaining the Earth's temperature at a level suitable for life. It is caused by naturally present greenhouse gases (primarily water vapour) in the atmosphere, which trap some of the outgoing long-wavelength infrared radiation from the Earth's surface, preventing it from escaping into space. 2. Enhanced Greenhouse Effect: This refers to the intensification of the natural greenhouse effect, primarily caused by anthropogenic (human) activities. The main cause is the release of additional greenhouse gases (e.g., from burning fossil fuels, deforestation, and industrial processes) into the atmosphere, which increases their concentration and leads to more heat being trapped, resulting in global warming and climate change.

Distinguish between 'global warming' and 'climate change'.

Global warming refers specifically to the long-term increase in Earth's average surface temperature. Climate change is a broader term that encompasses global warming and all other long-term shifts in climate patterns due to human activity, including changes in precipitation, extreme weather events, and ocean acidification.

Beyond sea-level rise, name two other significant impacts of global warming.

Increased frequency and intensity of extreme weather events (e.g., heatwaves, floods, droughts) and significant disruptions to ecosystems and biodiversity (e.g., coral bleaching, habitat loss).

Identify two primary anthropogenic sources of methane (CH₄) emissions.

Livestock farming (enteric fermentation in ruminants), rice cultivation, landfills, and fossil fuel production (leakage during extraction and transport of natural gas).

What is a key mitigation strategy for reducing greenhouse gas emissions?

Transitioning to renewable energy sources (solar, wind, hydro), improving energy efficiency, carbon capture technologies, and sustainable land management (e.g., afforestation, preventing deforestation).

Explain the concept of 'adaptation' in the context of climate change.

Adaptation refers to adjusting to actual or expected future climate. It involves actions taken to cope with the impacts of climate change that are already happening or are projected to happen, such as building sea walls, developing drought-resistant crops, or improving early warning systems for extreme weather events.