2.1.2 Changes in Global Energy Balance Notes

Changes in the Global Energy Balance Shape the Earth's Climate

1. The Earth's energy balance is a fragile system that regulates global temperatures and climate patterns.
2. Factors like variations in solar radiation as well as natural and human-induced pollution disrupt this balance, impacting weather systems and contributing to global warming and cooling effects.

Variations in Solar Radiation

1. The Earth's temperature is influenced by changes in the Sun's energy output.
2. This is evident in an 11-year solar cycle and longer cycles like the Milankovitch Cycles.
3. Variations in Earth's orbit affect solar radiation distribution, initiating climate changes like ice ages.
4. Albedo also plays a role in global warming: melting ice reduces reflectivity, increasing heat absorption by darker surfaces like rocks, soil, and vegetation.

Global Dimming: A Hidden Cooling Effect

1. Following events like the 1991 Mount Pinatubo volcanic eruption, a temporary temperature decrease of approximately 0.5°C (0.9°F) for about 1-2 years was observed, highlighting the cooling effect of pollution, termed global dimming.
2. The predominant source of air pollution (aerosols, particulate matter) causing global dimming is linked to human-induced activities.
3. Polluted air contains particles like ash and sulfur dioxide, forming smaller water droplets in clouds, which reflect more sunlight and reduce heat reaching Earth's surface.
4. This phenomenon has led to a 9% decrease in solar energy reaching Earth's surface globally between 1950 and 1990.

Feedback Loops Play a Crucial Role in Global Climate Change

1. Feedback loops involve processes where the output of a system influences its own activity, often with cascading effects on global temperatures.
2. These loops can either enhance warming (positive feedback) or counteract it (negative feedback).

Positive Feedback Accelerates Warming

1. Positive feedback loops enhance warming by triggering processes that lead to further increases in temperature. Key examples include:
   1. Melting Ice and Albedo Loss: Melting polar ice caps reduces the Earth's reflectivity (albedo).
      1. Since ice reflects more sunlight than water, its loss increases solar absorption and later long-wave re-radiation, further warming the planet.
   2. Thawing Permafrost and Methane Release: Permafrost contains methane, a potent greenhouse gas.
      1. As the permafrost thaws, trapped methane is released, enhancing the greenhouse effect.
   3. Increased Biomass Decomposition: Rising temperatures accelerate the decomposition of organic matter in forests, releasing more carbon dioxide and amplifying warming.

Negative Feedback Counters Warming

1. Negative feedback loops act to stabilize the climate system by offsetting warming:
   1. Increased Evaporation and Precipitation: Evaporation at low latitudes leads to more precipitation, potentially increasing snowfall in polar regions and reducing global temperatures.
   2. Growth of Vegetation: Higher levels of carbon dioxide enhance plant growth and photosynthesis, absorbing more CO₂ and reducing atmospheric concentrations.
   3. Increased Aerosols: Burning can increase aerosols in the atmosphere, which reflect sunlight and cause localized cooling.

Case study

Negative Feedback at Boyabreen Glacier, Norway

1. In Norway, the Boyabreen Glacier demonstrates a negative feedback loop.
2. Rising global temperatures increase evaporation, leading to more precipitation in mountainous regions.
3. This falls as snow, adding to the glacier's mass and enhancing the albedo effect, which reflects more solar radiation and cools the surface.
4. This process temporarily offsets warming trends in the region, showcasing how local feedback mechanisms can counteract global climate change in specific areas.