Environment - Global Climate Change

Global Climate Change

Climate Change Facts
July 14, 1998

Issue 9 U.S. House of Representatives

Minority Staff, Committee on Government Reform and Oversight

Weather, Climate Change & El Nino
Many people wonder about the relationship between climate change and the weather. On a particularly hot or cold day, one often hears comments about the presence or lack of a global warming trend. This year's El Nino event sparked a great deal of discussion about weather and global warming. While no specific weather event is an indicator of global warming, trends in regional temperature, precipitation, and weather events over centuries have generated greater understanding of the impacts of global climate change.

Climate and weather are closely related phenomena, the main difference between them being a matter of time scale. Weather is generally studied at a localized scale over short time spans. Climate is the study of regional patterns in weather over longer time spans. The combination of direct and indirect climate records indicates a growing rate of warming, and suggests the rate of global warming over the next century will be greater than anything seen in nature in the past 10,000 years.

Recent Trends in Temperature & Precipitation. According to the National Oceanic and Atmospheric Administration (NOAA), global temperatures for the first five months of 1998 set new all time highs. Combined land and ocean temperatures for January to May exceed the previous record by nearly half a degree Fahrenheit. To put this in context, global temperatures rose about 1 degree over the preceding century. Overall, this century's temperatures have been warmer than anything seen in the past 600 years.

This year has also brought record levels of precipitation to the U.S. Records kept for the past 104 years show there has not been a wetter and warmer January and February than this year. According to William Brown at NOAA's National Climatic Data Center, "During the period January-February the national average temperature was 37.5 degrees Fahrenheit compared with a normal of 32.1 degrees. The previous record was 37.0 in 1990. 6.01 inches of precipitation fell, compared with a normal of 4.05 inches."

Extreme Weather. According to the Intergovernmental Panel on Climate Change (IPCC), a warming climate can cause serious changes in weather extremes. Warmer temperatures lead to a more vigorous hydrological cycle, causing more severe droughts and floods in some regions. For instance, the IPCC finds that "Several models indicate an increase in precipitation intensity, suggesting a possibility for more extreme rainfall events." The IPCC further finds that "a changing climate's near term effects on ecological and socio-economic systems most likely will result from changes in the intensity and seasonal and geographic distribution of common weather hazards such as storms, floods and droughts."

There is evidence that the U.S. is experiencing more extreme weather. According to Dr. Easterling, a meteorologist at NOAA, three and seven-day rainstorms in the United States have increased about 3% per decade since the 1930s. Dr. Thomas Karl, also at NOAA, further documented that since 1910, precipitation has increased by about 10% across the contiguous United States. Scientists at NASA, and the Goddard Institute for Space Studies found that, "in much of the middle and high latitudes, precipitation has increased systematically during the 20th century."

El Nino. El Nino is a disruption of the ocean-atmosphere system in the tropical Pacific having important consequences for weather around the globe. During El Nino events, a change in surface wind patterns in the Pacific Ocean generates a warm ocean current that typically appears around Christmas time (hence the Spanish name, meaning Christ Child), and lasts several months. The warm ocean surface water in the tropical eastern and Central Pacific subsequently alter global weather patterns.

According to NOAA, new data and analysis suggests that global warming is exacerbating the effects of El Nino. While not directly caused by global warming, El Nino events have become more frequent and warmer over the past century. During the recent El Nino, temperature and precipitation records were broken in the United States, and a series of severe tornadoes has killed 122 people so far this year. An El Nino driven drought in Central America has intensified the effects of regional forest fires that are the most devastating wildfires seen in 70 years. El Nino events, which are marked by a warming of the tropical Pacific, alternate with cold La Nina events. Historically, these events alternated every three to seven years. For the past twenty years, however, there have been more warmer El Nino events.