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 (Alley, 41).

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 (Bengtsson, 69).

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.

By testing polar and glacial ice cores at continuously increasing depths, scientists can determine the composition of Earth's atmosphere as a function of time. For example, an Arctic ice sample will contain minute pockets containing a small amount of air—and its constituent gases—that were trapped at the time the ice froze. Ice samples taken from deeper cores were formed earlier in time. Using these historic data, modern computer models of Earth's climate systems are able to calculate Earth's surface temperature over time. Using this and other proxy data, we have a longitudinal history of Earth's surface temperature stretching back hundreds of thousands of years.

Although global warming can be driven by natural processes (both continuous and sudden), surface temperature data measured and imputed over the past thousand years indicates that human (anthropogenic) forcing is playing a significant role in the present warming trend. These data indicate that the Earth's surface temperature has been increasing at an accelerating rate since the beginning of the Industrial Revolution in the mid-1800s. Analysis of atmospheric greenhouse gas concentrations and computer modeling of interacting land, ocean, and atmospheric systems has led scientists to conclude beyond any reasonable doubt that greenhouse gas emissions from human activity are the primary drivers in this dramatic increase in global warming.

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 ...