What is Radiative Forcing?
Radiative forcing occurs when there’s an imbalance between the energy entering and leaving the Earth’s atmosphere. Energy from the sun reaches Earth as solar radiation, and Earth emits some of this energy back into space as infrared radiation (heat). When more energy comes in than escapes—like today—the atmosphere warms up. This process is called radiative forcing because this energy difference forces changes in Earth’s climate
IPCC.
The Energy Balance: Heat In, Heat Out
Sunlight constantly strikes half of Earth’s surface. About 30% of this energy is reflected back into space, while the remaining energy is absorbed by Earth’s surface. However, as a warm body in a cold environment (space), Earth also radiates heat back out into space.
Radiative forcing measures the difference between incoming solar energy and outgoing heat over a period. Many factors, like cloud cover, polar ice, and atmospheric gases, influence how much energy is absorbed or reflected, and these complicate precise measurements. Yet, scientists have observed that more heat is currently being absorbed than radiated out, contributing to global warming
IPCC
IPCC.
The Balance Shift
Before the industrial era, incoming and outgoing radiation were nearly in balance, keeping Earth’s average temperature relatively stable. Scientists use a baseline, often from around 1750 (before significant human industrialization), to compare changes in radiative forcing. The primary change has been the rise of greenhouse gases, which trap heat and prevent it from escaping, thus warming the atmosphere.
Human activities like deforestation also affect this balance. By removing trees, we expose Earth’s surface, which can absorb more heat if the land is darker than the forest canopy, or reflect more if it’s lighter. This changes Earth’s albedo (reflectivity)
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The Role of Aerosols
Human activities also add aerosols—tiny particles from industrial processes, vehicles, and other sources—into the atmosphere. Aerosols complicate the picture because they can either reflect sunlight (cooling the Earth) or absorb heat (warming the Earth). For example, bright aerosols, like those from sulfur emissions, reflect sunlight, whereas dark aerosols, like black carbon, absorb heat
IPCC
IPCC.
Natural Influences
Radiative forcing also includes natural factors like variations in solar energy output and volcanic activity, which can cause short-term changes in the climate. For instance, volcanic eruptions can release aerosols that reflect sunlight and temporarily cool the planet
IPCC
IPCC.
Image Source: https://climate.mit.edu/explainers/radiative-forcing
