Global Warming

Introduction

The phrase global warming refers to a phenomenon in which the Earth's surface temperature increases from its long-term averages generally because of an atmospheric blanket of greenhouse gases (GHGs; primarily carbon dioxide, methane, and chlorofluorocarbons) that serve to trap reradiated solar energy from escaping into space. This blanket of greenhouse gases is responsible for providing Earth a generally temperate, stable, and life-sustaining climate. In common parlance, global warming is often used interchangeably with climate change. In the present context, though, it is used in a more limited sense as a driver of global climate change.

Discussion

The Science

In all of our solar system, Earth is the only planet known to support life. This uniqueness derives in great part from an atmosphere that regulates the Earth's surface temperature within a range conducive to the development of living organisms, including humankind. The explanation for this phenomenon was suspected as early as 1824, when French mathematician and physicist Jean Baptiste Fourier postulated that gases in Earth's atmosphere might influence its surface temperature. In 1859, physicist John Tyndall suggested that changes in the concentrations of some atmospheric gases could result in changes to Earth's climate. The Swedish chemist Svante Arrhenius published an article in 1896 demonstrating that the amount of carbon dioxide in Earth's atmosphere would significantly affect its surface temperature. Arrhenius coined the phrase greenhouse effect and predicted that a geometric (nonlinear) increase in atmospheric carbon dioxide would result in an arithmetic (linear) increase in the Earth's surface temperature (Karl T, Melillo J., & Peterson T, 2009, pp. 13).

Based on this thermal blanket of greenhouse gases, scientists have long understood that the Earth has undergone a series of long-term cyclic cooling and warming phases. The former account, in part, for periods in which glaciers have covered vast areas of the planet; the latter for long periods of regional desertification during which man and beast have populated a greater portion of the Earth and during which their numbers have greatly multiplied. The most recent glacial period ended approximately 10,000 years ago; Greenland and Antarctica are vestiges of that period. The duration of our current interglacial period will be determined in no small part by the extent of warming caused by the greenhouse effect (Rahmstorf S., 2002, pp. 41).

Radiative forcing is a measure of the net solar and infrared radiation trapped in the Earth's atmosphere. Because of its direct relation to global mean surface temperature— positive forcing drives warming, negative forcing drives cooling—scientists use it to study the effects of natural and anthropogenic causes of global warming. Natural sources of radiative forcing include the earth, clouds, and naturally occurring greenhouse gases. Anthropogenic contributions to radiative forcing include greenhouse gas (positive forcing) and particulate (negative forcing) emissions caused by human activity, and land use changes resulting from human development activities (www.foe.co.uk).

A closely related concept is albedo, a measure of the extent to which a surface reflects light from the sun. Dark-colored objects (e.g., oceans and forests) have low albedo values because they absorb a greater percentage of solar ...