Climate Change: Mechanisms, Evidence, and Biological Impacts

Climate Change: Mechanisms, Evidence, and Biological Impacts

Introduction to Climate Change

Climate change refers to significant, long-term changes in the global climate, particularly increases in average surface temperature. It is driven by both natural processes and human activities, with profound impacts on Earth's systems and living organisms.

• How global climate change works: Involves the greenhouse effect, energy balance, and feedback mechanisms.

• Causes of climate change: Includes natural variability and anthropogenic (human-driven) factors.

• Monitoring changes: Scientists use temperature records, ice cores, and other proxies to track climate trends.

• Impacts on natural resources: Affects water, forests, wildlife, and human societies.

Evidence for Climate Change

Global Temperature Trends

• Instrumental records show a marked increase in global average surface temperature since the late 19th century.

• 2023 was the warmest year on record (NOAA data), with no colder-than-average year since 1976.

• Temperature anomalies are calculated as differences from a baseline average (e.g., 1951–1980).

Convergence of Evidence

• Multiple independent datasets (surface, satellite, ocean) confirm the warming trend.

• Consistent increases across months and years reinforce the reliability of the observed changes.

Natural Causes of Climate Variation

Earth's climate has always changed due to natural factors, leading to cycles of warming and cooling.

• Changes in orbit (Milankovitch cycles): Variations in Earth's orbit and tilt affect solar energy distribution.

• Solar activity: Fluctuations in the sun's output can influence climate.

• Volcanic activity: Eruptions inject aerosols into the atmosphere, temporarily cooling the planet.

• Meteor impacts: Large impacts can cause abrupt climate shifts.

The Anthropocene Epoch

The Anthropocene is a proposed epoch marking the period when human activity became the dominant influence on climate and the environment.

• Key environmental processes (carbon cycle, land use) are now heavily shaped by humans.

The Greenhouse Effect

The Natural Greenhouse Effect

The greenhouse effect is the process by which certain gases in Earth's atmosphere trap heat, keeping the planet warm enough to support life.

• About one third of the sun's energy is reflected back into space by the atmosphere and surface.

• The rest is absorbed by Earth's surface and atmosphere, warming the planet.

Process	Percentage of Solar Energy
Absorbed by Earth	51%
Reflected by clouds	20%
Scattered by atmosphere	6%
Absorbed by atmosphere/clouds	19%
Reflected by surface	4%

Human Influence on the Greenhouse Effect

• Human activities increase greenhouse gas concentrations, intensifying the greenhouse effect and causing more heat to be trapped.

• Key activities: burning fossil fuels, deforestation, agriculture, and industrial processes.

Greenhouse Gases

Greenhouse gases (GHGs) absorb and emit infrared radiation, contributing to the greenhouse effect.

• Carbon dioxide (CO2)

• Methane (CH4)

• Nitrous oxide (N2O)

• Ozone (O3)

• Chlorofluorocarbons (CFCs)

• Water vapor (H2O)

CO2 Concentrations and Sources

• CO2 levels have risen from pre-industrial values (~280 ppm) to over 420 ppm today (Mauna Loa Observatory).

• Major sources: electricity generation, transportation, industry, and deforestation.

Source	Percentage of U.S. CO2 Emissions
Electricity	33%
Transportation	28%
Industry	16%
Residential/Commercial	12%
Other	8%

Methane (CH4)

• Accounts for 12% of human-contributed GHGs.

• 20 times more effective than CO2 at trapping heat.

• Sources: natural gas/petroleum systems, enteric fermentation (livestock), landfills, coal mining, manure management.

Nitrous Oxide (N2O

)

• Accounts for 6% of human GHGs.

• 265–310 times more potent than CO2.

• Sources: agriculture, industrial activities, combustion.

Fluorinated Gases

• Account for 3% of human GHGs.

• High global warming potential (GWP), trapping thousands of times more heat than CO2.

Water Vapor

• Most abundant greenhouse gas, but its concentration is controlled by temperature.

• Plays a key role in positive feedback loops (e.g., as Earth warms, more water vapor increases warming).

Carbon Cycle and Human Perturbation

Pre-Industrial Carbon Cycle

Reservoir	Size (GtC)
Atmosphere	420
Terrestrial Biosphere	2160
Ocean Surface	900
Ocean Deep	36,400
Earth's Crust (Rocks)	90,000,000

Anthropogenic Perturbation (1980–1999)

• Atmospheric CO2 increased to 750 GtC (+3.3 GtC/yr).

• Land use change and fossil fuel combustion are major contributors.

Determining Past Climate Patterns

• Dendrochronology: Tree rings reveal past climate conditions (droughts, fire intervals).

• Ice cores: Contain trapped air bubbles with ancient atmospheric gases, revealing past CO2 levels and temperature.

• Other proxies: Sediment cores, pollen, and fossils.

Impacts of Climate Change

Changes in Precipitation and Extreme Weather

• U.S. receives 6% more rain than 100 years ago, but distribution is uneven.

• Increase in hurricanes, droughts, floods, and fires.

Phenology

Phenology is the study of the timing of biological events (e.g., migrations, flowering, emergence dates) and how they are influenced by climate.

• Climate change shifts the timing of these events, affecting ecosystems and species interactions.

Impacts on Wildlife

• Range shifts: Species move to new areas as their habitats change.

• Species with narrow niches may face extinction.

• Hybridization and altered disease rates may occur.

• Food and habitat availability may change.

Impacts on Fish

• Growth and development are temperature-dependent.

• Fewer coldwater species, more disease and invasive species.

• Changes in food web (phytoplankton, zooplankton) and physical lake processes (ice cover, turnover cycles).

Impacts on Forests

• Warmer, drier, or wetter conditions alter forest composition.

• Increased prevalence of pests and diseases.

• Some tree species may not migrate fast enough to suitable climates.

• Loss of carbon sequestration capacity.

Other Environmental Changes

• Decreased ice cover duration on lakes and rivers.

• Reduced water transparency due to increased runoff and algal blooms.

Mitigation and Adaptation

• Mitigation: Actions to reduce greenhouse gas emissions (e.g., renewable energy, reforestation).

• Adaptation: Adjusting to climate impacts (e.g., infrastructure changes, conservation strategies).

Climate Change Perceptions and Local Impacts

• Public perception varies by region and is influenced by local impacts and information sources.

• Understanding and addressing climate change requires both scientific knowledge and societal engagement.

Key Equations

• Radiative Forcing (RF): $RF = ext{Incoming Energy} - ext{Outgoing Energy}$

• CO2 Concentration (ppm): $C_{t} = C_{0} + ext{Emissions} - ext{Uptake}$

Summary Table: Major Greenhouse Gases

Gas	Contribution to Warming	Major Sources
CO2	~76%	Fossil fuels, deforestation
CH4	~16%	Agriculture, landfills, fossil fuels
N2O	~6%	Agriculture, industry
Fluorinated gases	~2%	Industrial processes

Example: The loss of burbot from Otsego Lake in the 1980s is a local example of how climate change can lead to species extirpation.

Additional info: This guide integrates content from lecture slides and academic context to provide a comprehensive overview of climate change mechanisms, evidence, and biological impacts, suitable for General Biology students.