Global Warming, What Is it?

Scientists have concluded that human activities are contributing to global warming by adding large amounts of heat-trapping gases to the atmosphere. Our fossil fuel use is the main source of these gases. Every time we drive a car, use electricity from coal-fired power plants, or heat our homes with oil or natural gas, we release carbon dioxide and other heat-trapping gases into the air. The second most important source of greenhouse gases is deforestation, mainly in the tropics, and other land-use changes.

Since pre-industrial times, the atmospheric concentration of carbon dioxide has increased by 31 percent. Over the same period, atmospheric methane has risen by 151 percent, mostly from agricultural activities like growing rice and raising cattle.

As the concentration of these gases grows, more heat is trapped by the atmosphere and less escapes back into space. This increase in trapped heat changes the climate, causing altered weather patterns that can bring unusually intense precipitation or dry spells and more severe storms.

The Causes of Global Warming

• Carbon dioxide (CO2) during the last 400,000 years and the rapid rise since the Industrial Revolution;
• Changes in the Earth's orbit around the Sun, known as Milankovitch cycles, which are believed to be the pacemaker of the 100,000 year ice age cycle;
• Recent increases in atmospheric carbon dioxide (CO2).

The monthly CO2 measurements display small seasonal oscillations in an overall yearly uptrend; each year's maximum is reached during the Northern Hemisphere's late spring, and declines during the Northern Hemisphere growing season as plants remove some CO2 from the atmosphere. The Earth's climate changes in response to external forcing, including variations in its orbit around the sun (orbital forcing), volcanic eruptions, and atmospheric greenhouse gas concentrations. The detailed causes of the recent warming remain an active field of research, but the scientific consensus identifies elevated levels of greenhouse gases due to human activity as the main influence.

Changes In Greenhouse Gas Concentrations

In the figure above are the fluctuations in temperature (red line) and in the atmospheric concentration of carbon dioxide (yellow) over the past 649,000 years. The vertical red bar at the end is the increase in atmospheric carbon dioxide levels over the past two centuries and before 2007.

Is There Anything We Can Do about Global Warming?
Yes! The most important action we can take to slow global warming is to reduce emissions of heat-trapping gases. Governments, individuals, and businesses can all help. Governments can adopt a range of options for reducing greenhouse gas emissions, including

• increasing energy efficiency standards
• encouraging the use of renewable energy sources (such as wind and solar power)
• eliminating subsidies that encourage the use of coal and oil by making them artificially cheap
• protecting and restoring forests, which serve as important storehouses of carbon

Individuals can reduce the need for fossil fuels and often save money by

• driving less and driving more fuel-efficient and less-polluting cars
• using energy-efficient appliances
• insulating homes
• using less electricity in general

Businesses can increase efficiency and save substantial sums by doing the same things on a larger scale. And utilities can avoid building expensive new power plants by encouraging and helping customers to adopt efficiency measures.

Scientific Frequently Asked Questions About Global Warming

Are humans contributing to global warming?

In 1995, the world's climate experts in the IPCC concluded for the first time in a cautious consensus, "The balance of evidence suggests that there is a discernible human influence on the global climate." In its 2001 assessment, the IPCC strengthened that conclusion considerably, saying, "There is new and stronger evidence that most of the warming observed over the last 50 years is attributable to human activities." Scientists have found significant evidence that leads to this conclusion:

• The observed warming over the past 100 years is unlikely to be due to natural causes alone; it was unusual even in the context of the last 1,000 years.
• There are better techniques to detect climatic changes and attribute them to different causes.
• Simulations of the climate's response to natural causes (sun, volcanoes, etc.) over the latter half of the 20th century alone cannot explain the observed trends.
• Most simulation models that take into account greenhouse gas emissions and sulphate aerosols (which have a cooling effect) are consistent with observations over the last 50 years.

Would a temperature rise of a couple degrees really change the global climate?

An increase of a few degrees won't simply make for pleasantly warmer temperatures around the globe. Even a modest rise of 2°- 3°F (1.1°-1.7°C) could have dramatic effects. In the last 10,000 years, the Earth's average temperature hasn't varied by more than 1.8°F (1.0°C). Temperatures only 5°-9°F cooler than those today prevailed at the end of the last Ice Age, in which the Northeast United States was covered by more than 3,000 feet of ice. Scientists predict that continued global warming on the order of 2.5°-10.4°F over the next 100 years (as projected in the IPCC's Third Assessment Report) is likely to result in:

• a rise in sea level between 3.5 and 34.6 in. (9-88 cm), leading to more coastal erosion, flooding during storms, and permanent inundation
• severe stress on many forests, wetlands, alpine regions, and other natural ecosystems
• greater threats to human health as mosquitoes and other disease-carrying insects and rodents spread diseases over larger geographical regions
• disruption of agriculture in some parts of the world due to increased temperature, water stress, and sea-level rise in low-lying areas such as Bangladesh or the Mississippi River delta.

What is the best source of scientific information on global warming?

In 1988, the United Nations Environment Programme and the World Meteorological Organization set up the Intergovernmental Panel on Climate Change (IPCC) to examine the most current scientific information on global warming and climate change. More than 1,250 authors and 2,500 scientific experts reviewers from more than 130 countries contributed to the panel's most recent report, Climate Change 2007: The Fourth Assessment Report (the full report will be released in November 2007). These scientists reviewed all the published and peer-reviewed scientific information produced during the previous few years to assess what is known about the global climate, why and how it changes, what it will mean for people and the environment, and what can be done about it. The IPCC Fourth Assessment Report is the most comprehensive and up-to-date evaluation of global warming. As the new benchmark, it serves as the basis for international climate negotiations.

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