Unit 5: Global Warming and Climate Change: An Exam-Ready Study Guide

Global warming refers to the long-term heating of Earth's climate system observed since the pre-industrial period (between 1850 and 1900) due to human activities, primarily fossil fuel burning, which increases heat-trapping greenhouse gas levels in Earth's atmosphere. The term is frequently used interchangeably with the term climate change, though the latter refers to both human- and naturally produced warming and the effects it has on our planet.

Trends of Global Warming and Climate Change

Over recent decades, significant trends indicating global warming and climate change have been observed globally:

• Rising Global Temperatures: The average global temperature has risen steadily, with the most significant warming occurring in the last 40 years. Each of the last four decades has been successively warmer than any preceding decade since 1850.
• Melting Ice and Glaciers: Glaciers, ice caps, and ice sheets (like Greenland and Antarctica) are melting at an accelerated rate, contributing to sea level rise. Arctic sea ice extent has significantly decreased.
• Ocean Warming and Acidification: Oceans have absorbed a large portion of the excess heat and carbon dioxide, leading to ocean warming and ocean acidification (a decrease in pH due to CO₂ absorption).
• Extreme Weather Events: There's an observed increase in the frequency and intensity of extreme weather events, including heatwaves, droughts, heavy precipitation, and intense tropical cyclones.
• Sea Level Rise: Global mean sea level has been rising at an increasing rate due to thermal expansion of water and melting ice.
• Changes in Flora and Fauna: Shifts in plant and animal geographic ranges and the timing of biological events (e.g., flowering, migration) are being observed.

Drivers of Global Warming

The primary drivers of global warming can be categorized into natural and anthropogenic (human-induced) factors.

Natural Drivers

While natural factors have historically influenced Earth's climate, their current contribution to the observed rapid warming is minor compared to human activities.

• Solar Irradiance: Variations in the sun's energy output can affect climate, but recent solar activity has not increased to an extent that explains the observed warming.
• Volcanic Activity: Large volcanic eruptions can temporarily cool the Earth by releasing aerosols that block sunlight, but their long-term effect on warming is negligible.
• Orbital Variations (Milankovitch Cycles): Long-term changes in Earth's orbit, tilt, and wobble affect the amount of solar energy reaching different parts of the Earth, driving glacial and interglacial cycles over tens of thousands of years, but are too slow to explain recent rapid warming.

Anthropogenic Drivers

These are the dominant drivers of current global warming.

• Greenhouse Gas (GHG) Emissions: The burning of fossil fuels (coal, oil, natural gas) for energy, industrial processes, transportation, and deforestation releases large quantities of GHGs into the atmosphere.
• Deforestation: Forests act as carbon sinks, absorbing CO₂. Deforestation reduces this capacity and releases stored carbon when trees are cut down or burned.
• Industrial Processes: Certain industrial activities release potent GHGs, such as fluorinated gases.
• Agriculture: Livestock farming produces methane (CH₄), and fertilizer use releases nitrous oxide (N₂O).

Potential of Different Greenhouse Gases (GHGs) Causing Climate Change

Definition: Greenhouse Gases (GHGs)

Greenhouse gases are atmospheric gases that absorb and emit radiant energy within the thermal infrared range, causing the greenhouse effect. They trap heat in the Earth's atmosphere, contributing to global warming.

The main GHGs include Carbon Dioxide (CO₂), Methane (CH₄), Nitrous Oxide (N₂O), and Fluorinated Gases (F-gases like HFCs, PFCs, SF₆, NF₃). Their potential to cause climate change is assessed based on two key factors:

• Atmospheric Lifetime: How long the gas remains in the atmosphere.
• Global Warming Potential (GWP): A measure of how much energy the emissions of 1 ton of a gas will absorb over a given period of time, relative to the emissions of 1 ton of carbon dioxide (CO₂). CO₂ has a GWP of 1.

Here is a comparison of key greenhouse gases:

Important Observation: While CO₂ has the lowest GWP per ton, its vast quantity of emissions makes it the largest contributor to global warming. Other gases like SF₆ have extremely high GWPs but are emitted in smaller volumes.

Impact of Global Warming

Global warming has far-reaching consequences across natural systems and human societies.

• Increased Temperatures: Overall warming of land and ocean surfaces, leading to more frequent and intense heatwaves.
• Changes in Precipitation Patterns: Some regions experience more intense rainfall and flooding, while others face prolonged droughts.
• Melting Cryosphere: Retreat of glaciers, ice sheets, and Arctic sea ice, contributing to sea level rise and impacting regional water resources.
• Ocean Acidification: Absorption of CO₂ by oceans leads to increased acidity, harming marine ecosystems, especially shellfish and coral reefs.
• Disruption of Ecosystems: Shifts in species habitats, timing of biological events, and increased risk of extinction for vulnerable species.
• Human Health Impacts: Increased heat-related illnesses and deaths, expansion of vector-borne diseases (e.g., malaria, dengue), and impacts on mental health.

Impact of Climate Change on Specific Systems

Impact on Atmosphere

• Temperature Profile Changes: A warming troposphere (lowest layer) and a cooling stratosphere (layer above) are observed. This is a clear fingerprint of GHG-induced warming, as increased GHGs trap heat in the lower atmosphere, preventing it from reaching the stratosphere.
• Increased Water Vapor: Warmer temperatures lead to more evaporation, increasing atmospheric water vapor, which is itself a potent greenhouse gas, creating a positive feedback loop.
• Changes in Atmospheric Circulation: Large-scale atmospheric patterns like the jet stream can be altered, potentially influencing regional weather and climate. For example, some studies suggest a weakening of the polar vortex.
• Air Quality Degradation: Warmer temperatures can exacerbate ground-level ozone formation and increase airborne particulate matter, worsening respiratory health issues.

Impact on Weather Patterns

Climate change is intensifying and altering weather patterns globally:

• Extreme Heat: Frequency and intensity of heatwaves are increasing, leading to heat stress and mortality.
• Droughts: Many regions are experiencing more prolonged and severe droughts due to higher temperatures and altered precipitation.
• Floods and Heavy Rainfall: Paradoxically, some regions are experiencing more intense rainfall events and flooding, as a warmer atmosphere can hold more moisture.
• Tropical Cyclones (Hurricanes/Typhoons): While the overall frequency might not change significantly, there is evidence of an increase in the intensity of the strongest storms, along with higher rainfall rates.
• Winter Storms: Some regions may experience more intense blizzards due to increased moisture in a warmer atmosphere, even as overall snowfall declines in others.

Impact on Sea Level Rise

Sea level rise is a critical consequence of climate change, with significant implications for coastal areas.

The two main drivers are:

1. Thermal Expansion: As ocean water warms, it expands, taking up more space. Oceans have absorbed over 90% of the excess heat from global warming.
2. Melting Glaciers and Ice Sheets: Ice from mountain glaciers and the massive ice sheets of Greenland and Antarctica is melting at an accelerated rate, adding vast amounts of water to the oceans.

Consequences of Sea Level Rise:

• Coastal Inundation: Low-lying coastal areas and islands face increased flooding and eventual permanent submergence.
• Coastal Erosion: Higher sea levels lead to increased erosion of beaches, dunes, and cliffs.
• Saltwater Intrusion: Seawater can intrude into freshwater aquifers, contaminating drinking water supplies and affecting agricultural lands.
• Increased Storm Surge Damage: Higher sea levels amplify the destructive power of storm surges during coastal storms.
• Displacement of Populations: Coastal communities may be forced to relocate due to uninhabitable conditions.

Impact on Agricultural Productivity

Climate change presents both challenges and potential, mostly negative, for global agriculture:

• Reduced Crop Yields: In many regions, rising temperatures, changes in precipitation patterns (droughts or floods), and increased frequency of extreme weather events lead to reduced crop yields.
• Water Scarcity: Increased evaporation and altered rainfall patterns can exacerbate water scarcity for irrigation.
• Pest and Disease Outbreaks: Warmer temperatures can expand the geographical range and accelerate the life cycles of agricultural pests and diseases, increasing crop losses.
• Soil Degradation: Intense rainfall can lead to soil erosion, while droughts can increase soil degradation and desertification.
• Longer Growing Seasons (in some areas): In some temperate regions, a warmer climate might initially extend growing seasons, potentially boosting yields for certain crops, but this benefit is often offset by other negative impacts.
• Impact on Livestock: Heat stress can reduce livestock productivity (milk, meat, egg production) and increase susceptibility to diseases.
• Food Security Concerns: Overall, these impacts threaten global food security, especially in vulnerable regions.

Impact on Biological Responses

Ecosystems and species are responding to climate change in various ways:

• Species Range Shifts: Many plant and animal species are shifting their geographical ranges towards poles or higher altitudes in search of cooler temperatures and suitable habitats.
• Phenological Changes: The timing of biological events (phenology) such as flowering, breeding, migration, and hibernation is changing. For example, spring events are occurring earlier.
• Biodiversity Loss: Species unable to adapt, migrate, or compete in new conditions face an increased risk of extinction. Ecosystems with specific climate requirements (e.g., coral reefs, polar bears) are particularly vulnerable.
• Ecosystem Disruption: Changes in species composition and interactions can disrupt entire ecosystems, affecting food webs, pollination, and nutrient cycling.
• Ocean Acidification and Marine Life: Marine organisms that build shells and skeletons from calcium carbonate (e.g., corals, shellfish, plankton) are directly impacted by ocean acidification, making it harder for them to grow and survive.
• Changes in Species Interactions: Shifts in timing can lead to mismatches between predators and prey or between plants and their pollinators, affecting reproductive success and survival.