Climate Change: Measurement, Causes, Impacts, and International Response

Climate Change: Measurement, Causes, Impacts, and International Response

Student Learning Objectives

• Understand how variables associated with climate change are measured, both for current atmospheric changes and past, historic climates.

• Understand the sources and causes of stratospheric ozone depletion, as well as the global efforts to mitigate this crisis.

• Explain the greenhouse effect, including the role of anthropogenic greenhouse gases and their effect on the climate.

• Explain various climatic changes (e.g., changes in precipitation patterns, intensity of tropical storms) correlated with the enhanced greenhouse effect.

• Identify and explain the role of two major United Nations institutions that address climate change: the IPCC and the UNFCCC.

Measurement of Climate Change

Current and Past Climate Measurement

Understanding climate change requires accurate measurement of atmospheric variables both in the present and the past. Scientists use a combination of direct measurements and proxy methods to reconstruct climate history.

• Direct Measurements: Modern instruments record temperature, atmospheric gas concentrations, and precipitation patterns.

• Proxy Methods: Indirect evidence from natural recorders of climate variability, such as ice cores, tree rings, and sediment layers, is used to infer past climates.

• Landform Analysis: The study of glacial features and sediment deposits provides evidence of historical climate cycles.

• Ice Cores: Trapped air bubbles in ice cores from glaciers and ice sheets reveal past atmospheric composition and temperature.

Milankovitch Cycles: These are long-term variations in Earth's orbit and tilt that drive natural cycles between glacial and interglacial periods.

Glacial and Interglacial Periods: Earth's climate has alternated between cold (glacial) and warm (interglacial) periods over the past 2.6 million years (the Quaternary period).

Stratospheric Ozone Depletion

The Ozone Layer and Its Importance

The ozone layer is a region of high ozone concentration in the stratosphere, approximately 10–50 km above Earth's surface. It absorbs most of the Sun's harmful ultraviolet (UV) radiation, protecting living organisms.

• Ozone Hole: A region of significant ozone thinning, especially over Antarctica, observed since the late 20th century.

• Upper Air Temperature Inversion: The ozone layer causes a temperature increase with altitude in the stratosphere due to UV absorption.

• CFCs (Chlorofluorocarbons): Synthetic chemicals once widely used in refrigeration and aerosols, which catalyze ozone destruction in the stratosphere.

• Montreal Protocol (1987): An international treaty to phase out ozone-depleting substances, resulting in significant recovery of the ozone layer.

• Impacts of Ozone Depletion: Increased UV exposure leads to higher rates of skin cancer, cataracts, and ecological damage.

The Greenhouse Effect and Greenhouse Gases

Mechanism of the Greenhouse Effect

The greenhouse effect is a natural process where certain gases in Earth's atmosphere trap heat, maintaining a habitable temperature. Human activities have enhanced this effect, leading to global warming.

• Greenhouse Gases: Key gases include carbon dioxide (CO2), methane (CH4), nitrous oxide (N2O), and water vapor.

• Anthropogenic Greenhouse Gases: Human activities, such as burning fossil fuels and agriculture, increase concentrations of these gases.

Equation (Greenhouse Effect):

$\text{Incoming Solar Radiation} - \text{Reflected Solar Radiation} = \text{Outgoing Longwave Radiation} + \text{Trapped Heat by Greenhouse Gases}$

Carbon Dioxide (CO2)

• Significance: CO2 is the most important anthropogenic greenhouse gas due to its abundance and long atmospheric lifetime (centuries).

• Main Source: Fossil fuel combustion (coal, oil, natural gas).

• Secondary Source: Deforestation and land use changes.

• Historical Increase: Atmospheric CO2 concentrations began rising rapidly with the Industrial Revolution (~1750).

Methane (CH4)

• Potency: Methane is over 25 times more effective at trapping heat than CO2 over a 100-year period.

• Sources: Agriculture (especially livestock), landfills, fossil fuel extraction, and wetlands.

• Atmospheric Lifetime: About 12 years.

Surface Albedo

Albedo is the fraction of solar energy reflected by Earth's surface. Changes in albedo (e.g., from melting ice) can amplify warming.

Climatic Changes Associated with Global Warming

Observed and Predicted Changes

Global warming leads to a variety of climatic changes, including altered precipitation patterns, increased frequency and intensity of extreme weather events, and sea level rise.

• Precipitation Patterns: Wet regions are expected to get wetter, while dry regions become drier.

• Droughts and Floods: Increased frequency and severity due to changes in atmospheric circulation and moisture content.

• Melting Arctic Sea Ice: Reduces albedo and accelerates warming.

• Sea Level Rise: Caused by thermal expansion of seawater and melting glaciers/ice sheets.

• Coastal Impacts: Increased flooding, erosion, and habitat loss in coastal zones.

• Hurricanes: Potential increase in intensity due to warmer ocean temperatures.

International Response to Climate Change

Key United Nations Institutions and Agreements

• IPCC (Intergovernmental Panel on Climate Change): Provides scientific assessments on climate change, its impacts, and potential response strategies. Its reports have evolved to show increasing confidence in the role of human activities in recent warming.

• UNFCCC (United Nations Framework Convention on Climate Change): Established in 1992 to coordinate international efforts to address climate change.

• Kyoto Protocol (1997): Introduced legally binding emission reduction targets and emissions trading mechanisms.

• COP15, Copenhagen (2009): Sought to establish a global agreement but resulted in non-binding commitments.

• Paris Agreement (2015-16): Aims to limit global warming to well below 2°C above pre-industrial levels, with "no regrets" initiatives encouraging actions with co-benefits.

• Recent Developments: As of January 2026, the United States formally withdrew from the Paris Agreement.

Climate Models and Attribution

Global Climate Models (GCMs)

GCMs are complex computer simulations that use physical principles to project future climate changes based on different greenhouse gas emission scenarios. They help distinguish between natural variability and human-induced changes.

Natural vs. Anthropogenic Climate Variability

• Climate varies naturally due to factors like volcanic eruptions, solar cycles, and Milankovitch cycles.

• Current warming trends cannot be explained by natural factors alone; human activities are the dominant cause.