Causes of Climate Change (Natural & Human)

Natural Causes of Climate Change

Volcanic Eruptions

Volcanic eruptions release large amounts of gases and particles into the atmosphere, including carbon dioxide ($\mathrm{CO_2}$) and sulphur dioxide ($\mathrm{SO_2}$). The ash and sulphur dioxide can reflect sunlight away from Earth, causing short-term cooling. However, the $\mathrm{CO_2}$ released contributes to warming over longer periods.

For example, the 1991 eruption of Mount Pinatubo caused global temperatures to drop by about $0.5^\circ\mathrm{C}$ for a couple of years due to ash and sulphur dioxide reflecting sunlight.

Solar Output Variations

The Sun’s energy output changes in cycles, mainly the 11-year sunspot cycle. More sunspots mean more solar energy reaching Earth, causing slight warming. Fewer sunspots lead to cooling.

These variations affect climate naturally but only cause small temperature changes compared to human impacts.

Orbital Changes (Milankovitch Cycles)

Earth’s orbit changes shape and tilt over tens of thousands of years, affecting how much solar energy reaches the planet. These cycles include:

• Eccentricity: The orbit changes from more circular to more elliptical every 100,000 years.
• Axial tilt: The angle of Earth’s tilt varies between $22.2^\circ$ and $24.5^\circ$ over 41,000 years.
• Precession: Earth’s wobble on its axis changes every 26,000 years.

These changes cause natural ice ages and warm periods by altering the distribution of sunlight on Earth.

Natural Greenhouse Gas Fluctuations

Greenhouse gases like carbon dioxide and methane vary naturally due to volcanic activity, decomposition, and ocean processes. These fluctuations have caused climate changes in the past, such as ice ages and warm interglacial periods.

Natural greenhouse gas levels are generally balanced by natural carbon sinks like forests and oceans.

Human Causes of Climate Change

Burning Fossil Fuels

Burning coal, oil, and natural gas for energy releases large amounts of carbon dioxide ($\mathrm{CO_2}$) into the atmosphere. This is the biggest human cause of climate change.

For example, power stations, cars, and factories burn fossil fuels, increasing greenhouse gases and enhancing the greenhouse effect.

Deforestation

Cutting down forests reduces the number of trees that absorb $\mathrm{CO_2}$ through photosynthesis. This means more $\mathrm{CO_2}$ stays in the atmosphere, increasing warming.

Deforestation also releases $\mathrm{CO_2}$ stored in trees when they are burned or decay.

Agriculture and Livestock

Farming activities release methane ($\mathrm{CH_4}$) and nitrous oxide ($\mathrm{N_2O}$), both potent greenhouse gases:

• Methane: Produced by livestock digestion (especially cows) and rice paddies.
• Nitrous oxide: Released from fertilisers used on crops.

Industrial Processes

Manufacturing and chemical industries release greenhouse gases such as fluorinated gases, which have a strong warming effect despite being in smaller quantities.

These gases come from refrigeration, air conditioning, and production of plastics.

Greenhouse Effect and Global Warming

Role of Greenhouse Gases

Greenhouse gases in the atmosphere trap heat from the Sun, keeping Earth warm enough to support life. This natural process is called the greenhouse effect.

Key greenhouse gases include:

• Carbon dioxide ($\mathrm{CO_2}$)
• Methane ($\mathrm{CH_4}$)
• Nitrous oxide ($\mathrm{N_2O}$)
• Water vapour ($\mathrm{H_2O}$)

Enhanced Greenhouse Effect

Human activities have increased greenhouse gas concentrations, trapping more heat and causing global temperatures to rise. This is known as the enhanced greenhouse effect.

Temperature Rise

Since the Industrial Revolution, average global temperatures have risen by about $1^\circ\mathrm{C}$. This rise is linked to increased greenhouse gases from human activities.

Feedback Mechanisms

Climate change can trigger feedback loops that either amplify or reduce warming:

• Positive feedback: Amplifies warming. For example, melting ice reduces Earth's reflectivity (albedo), causing more solar energy absorption and further warming.
• Negative feedback: Reduces warming. For example, more clouds could reflect sunlight and cool the Earth, but this effect is complex and uncertain.

For instance, Arctic sea ice melting reduces the white reflective surface, exposing darker ocean water that absorbs more heat, speeding up warming.

Example: If the concentration of $\mathrm{CO_2}$ in the atmosphere increases from 280 parts per million (ppm) pre-industrial to 400 ppm today, this traps more heat, raising global temperatures.

For instance, the percentage increase in atmospheric $\mathrm{CO_2}$ from 280 ppm to 400 ppm is approximately 42.9%, illustrating how human activities have significantly raised greenhouse gas levels.