What are the causes of climate change?

Climate change is occurring as the result of increased concentrations of so-called greenhouse gases in the atmosphere. Like a warming blanket or the glass panes of a greenhouse, these gases have the effect of trapping heat energy that would otherwise radiate from the Earth’s surface back to space. A number of pollutants associated with human activities have this effect, but the most important is carbon dioxide.

Worldwide, tens of millions of tons of carbon dioxide enter the atmosphere every day as a direct result of burning fossil fuels—coal, oil, and natural gas—to provide the energy we use in everyday activities, from lighting and warming our homes, to operating our factories and fueling our cars. In industrialized countries like the United States, electric power plants and automobiles are the most important sources of carbon dioxide. Worldwide, other activities and sources—such as deforestation—are also important contributors to global climate change.

Fossil fuel combustion is harmful to our environment not only because it creates greenhouse gas emissions and causes global warming, but because it is also a major source of other types of air pollution. Sulfur dioxide emissions from burning coal and oil, for example, play a major role in the formation of soot which has been linked to higher rates of asthma, bronchitis, emphysema, heart disease, and other ailments. Fossil fuel use is also a primary source of the pollutants that create smog, a major public health threat in many urban areas, as well as of mercury and other toxic chemicals.

According to the United Nations’ Intergovernmental Panel on Climate Change (IPCC), evidence that the Earth’s climate is warming is now ‘unequivocal.’ Moreover, the IPCC has concluded that most of this warming is very likely due to human-caused greenhouse gas emissions. Eleven of the twelve most recent years (1995–2006) rank among the hottest years on record since 1850; in addition, scientists have observed an increase in average air and ocean temperatures, widespread melting of snow and ice, and rising global average sea level. If current emissions trends continue, these changes will persist and even accelerate in the decades ahead. In sum, the risks posed by global warming are rising and rising rapidly—unfortunately, the world is not yet doing nearly enough to tackle this problem.