What is Climate Change?

Climate change is a long-term shift in the statistics of the weather (including its averages). For example, it could show up as a change in climate normals (expected average values for temperature and precipitation) for a given place and time of year, from one decade to the next. We know that the global climate is currently changing. The last decade of the 20th Century and the beginning of the 21st have been the warmest period in the entire global instrumental temperature record, starting in the mid-19th century.  The phrase 'climate change' is growing in preferred use to 'global warming' because it helps convey that there are changes in addition to rising temperatures.

What are Greenhouse Gases (GHGs)?

Greenhouse gases (GHGs) are gases in the atmosphere that trap energy from the sun. Naturally occurring GHGs include water vapour, ozone, carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O). Without them, the Earth's average temperature would be about 33°C lower than it is, making the climate too cold to support life. While these naturally occurring gases are what make life possible, a serious concern today is the enhanced effect on the climate system of increased levels of some of these gases in the atmosphere, due mainly to human activities.

Recent data indicate that the global mean surface air temperature has increased by between 0.2 and 0.6°C since the late 19th century, while the United State’s mean has increased by about 1°C (IPCC, 1996b, 2001). Some models predict that the Earth's average temperature might increase by about 0.3°C per decade over the next 100 years if this increasing trend in GHG concentrations is not altered.

A warming of this magnitude could significantly alter the Earth's climate. Storm patterns and severity might increase, a rise in sea level would displace millions of coastal residents, and regional droughts and flooding could occur. In the U.S agriculture, forestry, and energy sectors could all be significantly affected.