Facing the Wind: Protecting the Environment through Education and Action

4/9/2014, 3 p.m.
Recent climate changes cannot be explained by natural causes alone.
Courtesy photo

As the world prepares to commemorate Earth Day 2014 (April 22), the Informer begins a series of print and e-articles to raise awareness of the destruction everyday industrial and human activity has on the health of the Earth and our natural environment. In addition to presenting prudent information on greenhouse gases, climate changes, and tips to lessening (or halting) the damage, our examination will include the impact of poverty and race-based environmental injustice on the health of the nation. — Shantella Y. Sherman, Editor, Special Section

The Earth’s temperature depends on the balance between energy entering and leaving the planet’s system. When incoming energy from the sun is absorbed by the Earth system, Earth warms. When the sun’s energy is reflected back into space, Earth avoids warming. When energy is released back into space, Earth cools. Many factors, both natural and human, can cause changes in Earth’s energy balance, including, changes in the greenhouse effect, which affects the amount of heat retained by Earth’s atmosphere; Variations in the sun’s energy reaching Earth; and Changes in the reflectivity of Earth’s atmosphere and surface.

Scientists have pieced together a picture of Earth’s climate, dating back hundreds of thousands of years, by analyzing a number of indirect measures of climate such as ice cores, tree rings, glacier lengths, pollen remains, and ocean sediments, and by studying changes in Earth’s orbit around the sun.

The historical record shows that the climate system varies naturally over a wide range of time scales. In general, climate changes prior to the Industrial Revolution in the 1700s can be explained by natural causes, such as changes in solar energy, volcanic eruptions, and natural changes in greenhouse gas (GHG) concentrations.

Recent climate changes, however, cannot be explained by natural causes alone. Research indicates that natural causes are very unlikely to explain most observed warming, especially warming since the mid-20th century. Rather, human activities can very likely explain most of that warming.

The power of a process to alter the climate is estimated by its “radiative forcing,” the change in the Earth’s energy balance due to that process. Some climate forcings are positive, causing globally averaged warming, and some are negative, causing cooling. Some, such as from increased CO2 concentration, are well known; others, such as from aerosols, are more uncertain. The slide shows a relatively small net change in energy from the Sun, large positive changes in energy from greenhouse gas emissions from human activities, and negative changes in energy from aerosols in the atmosphere. The net effect of human activities is positive (an increase in net energy).

Radiative Forcing is a measure of the influence of a particular factor (e.g. greenhouse gases (GHGs), aerosols, or land use changes) on the net change in Earth’s energy balance. On average, a positive radiative forcing tends to warm the surface of the planet, while a negative forcing tends to cool the surface.

GHGs have a positive forcing because they absorb energy radiating from Earth’s surface, rather than allowing it to be directly transmitted into space. This warms the atmosphere like a blanket. Aerosols, or small particles, can have a positive or negative radiative forcing, depending on how they absorb and emit heat or reflect light. For example, black carbon aerosols have a positive forcing since they absorb sunlight. Sulfate aerosols have a negative forcing since they reflect sunlight back out into space.