Changing Climate Revision Notes

Natural Causes of Climate Change

Natural factors have historically influenced Earth's climate. Volcanic eruptions release ash and aerosols into the atmosphere, which can block sunlight and lead to short-term cooling. For example, the 1991 eruption of Mount Pinatubo caused a global cooling of about 0.5°C for a year or two. Variations in solar output, known as sunspot cycles, can also cause slight changes in the amount of solar radiation reaching Earth, impacting global temperatures. Milankovitch cycles describe long-term changes in Earth's orbit and axial tilt, affecting the distribution of solar energy and leading to glacial and interglacial periods over tens to hundreds of thousands of years. These natural processes typically operate over much longer timescales than the rapid warming observed in recent decades.

Human Causes: The Enhanced Greenhouse Effect

The primary human cause of current climate change is the enhanced greenhouse effect. Greenhouse gases (GHGs) like carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O) naturally trap heat in the atmosphere, keeping Earth warm enough to support life. However, human activities have significantly increased the concentration of these gases since the Industrial Revolution. This 'enhancement' means more heat is trapped, leading to a rise in global temperatures. CO2 is the most significant contributor, largely from burning fossil fuels.

Sources of Human-Emitted Greenhouse Gases

The burning of fossil fuels (coal, oil, and natural gas) for electricity generation, industrial processes, and transportation is the largest source of CO2 emissions. Deforestation also contributes significantly, as trees absorb CO2 through photosynthesis; cutting them down not only releases stored carbon but also reduces the planet's capacity to remove CO2 from the atmosphere. Agriculture, particularly livestock farming (due to methane from animal digestion) and rice cultivation (due to methane from flooded fields), is a major source of methane and nitrous oxide. Industrial processes, waste decomposition in landfills, and the use of certain synthetic chemicals also release GHGs.

Evidence from Ice Cores

Ice cores are cylindrical samples drilled from glaciers and ice sheets. They contain trapped air bubbles that preserve ancient atmospheric gases like carbon dioxide and methane, indicating past greenhouse gas concentrations. Layers within the ice also reveal information about past temperatures (using oxygen isotopes), precipitation, and volcanic activity (from ash layers). These records can extend back hundreds of thousands of years, offering a detailed timeline of Quaternary climate fluctuations, showing clear cycles of warming and cooling.

Ocean Sediments and Microfossils

Layers of sediment accumulated on the ocean floor contain fossilized remains of marine organisms, known as microfossils (e.g., foraminifera). The types of microfossils present and their chemical composition (e.g., oxygen isotope ratios) indicate past sea surface temperatures, salinity, and ocean current patterns. Cooler water conditions favour certain species, while warmer conditions favour others, creating distinct patterns in sediment layers that correspond to glacial and interglacial periods, providing a long-term climate record.

Tree Rings (Dendroclimatology)

Tree rings provide annually resolved records of climate for several hundred to several thousand years. The width of a tree ring is influenced by environmental factors such as temperature and precipitation during the growing season. Wider rings generally indicate favourable conditions (e.g., warmer temperatures, sufficient moisture), while narrower rings suggest less favourable conditions (e.g., colder temperatures, drought). By studying patterns in tree ring width across different regions, scientists can reconstruct past climate variability and identify extreme weather events.

Milankovitch Cycles as Drivers

Milankovitch Cycles describe long-term cyclical variations in Earth's orbital parameters: eccentricity (shape of Earth's orbit, ~100,000 years), obliquity (tilt of Earth's axis, ~41,000 years), and precession (wobble of Earth's axis, ~23,000 years). These cycles alter the amount and distribution of solar radiation received by Earth, particularly at high latitudes, which is a major factor in initiating glacial and interglacial periods during the Quaternary. These natural cycles explain the rhythm of past climate change.

Social Impacts of Climate Change

Climate change significantly affects human populations. Rising temperatures lead to an increase in heat-related illnesses and deaths, particularly among vulnerable groups like the elderly and young children. Changes in precipitation patterns and increased extreme weather events (e.g., droughts, floods) threaten food security by reducing crop yields and impacting livestock. This can lead to malnutrition and famine. Water scarcity becomes more prevalent in many regions, affecting drinking water supplies and sanitation. The spread of vector-borne diseases (e.g., malaria, dengue fever) can increase as warmer climates expand the range of disease-carrying insects. Displacement of populations due to rising sea levels, desertification, or extreme weather events creates climate refugees, leading to social disruption and potential conflicts.

Economic Impacts of Climate Change

The economic consequences of climate change are substantial and varied. Damage to infrastructure from extreme weather events (e.g., coastal flooding, severe storms) is costly, requiring extensive repairs and rebuilding efforts. Agricultural losses due to drought, floods, or new pest outbreaks can devastate local economies, increase food prices, and impact national GDP. Industries reliant on natural resources or specific climates, such as tourism (e.g., ski resorts, coral reef diving), fisheries, and forestry, face significant economic disruption. Energy demand for cooling increases in warmer regions, putting pressure on power grids and increasing energy costs. Overall economic growth can be hindered by reduced productivity, increased healthcare costs, and the diversion of funds towards adaptation and mitigation measures.

Environmental Impacts of Climate Change

Climate change causes profound and lasting environmental alterations. Rising global temperatures lead to the melting of glaciers and ice sheets, contributing to global sea-level rise, which threatens coastal ecosystems and human settlements. Ocean warming and acidification (due to increased CO2 absorption) severely impact marine ecosystems, leading to coral bleaching, reduced biodiversity, and disruption of food webs. Changes in temperature and precipitation patterns alter ecosystems, leading to habitat loss, species migration, and an increased risk of extinction for many plant and animal species. More frequent and intense extreme weather events, such as heatwaves, droughts, floods, and wildfires, degrade natural landscapes, destroy habitats, and contribute to desertification. These changes disrupt ecological balances and compromise ecosystem services essential for human well-being.