Glossary Terms
Climate change and variability are governed by complex land, sea, and air interactions occurring across a range of temporal and spatial scales, such as the Pacific Decadal Oscillation, or PDO; the El Niño/Southern Oscillation, or ENSO; and the Madden-Julian Oscillation. These complex interactions affect not only the locations of storms, but also their frequency and intensity.
Long-term trends of climate change, in particular global warming and relative sea level rise, are also an important consideration in the Pacific Islands. The U.S. Environmental Protection Agency has prepared a four-page document titled "Climate Change and Hawai‘i." This document provides more detail on the causes and possible impacts of global warming and sea level rise, specific to the State of Hawai‘i.
"But that reservoir can hold the water from one week's rain, two week's rain. That is how it used to be over here. But now the world is turning around. We are getting different kinds of weather, a different climate."
– Samuel M. Kaahaaina, Sr., Wai‘anae resident
Surface water temperatures during El Niño, La Niña, and normal conditions.
Source: National Oceanic and Atmospheric AdministrationEl Niño Southern Oscillation (ENSO). El Niño is a disruption of the normal ocean patterns of the tropical Pacific. Its consequences are felt around the globe. Under normal conditions, the trade winds force the warmer surface water of the Pacific toward the west. During El Niño, the trade winds relax, allowing the warmer surface water amassed in the western Pacific to migrate east, toward the west coasts of North and South America. Precipitation associated with the warmer water moves with the tide, bringing increased rainfall and flooding to the west coast of the continents. The movement of the moisture also causes droughts in the western Pacific, including the Hawaiian Islands. Although the warm surface water migration is located in the Pacific Ocean, weather patterns are impacted around the globe. The most severe droughts affecting the State of Hawai‘i in the past 15 years have occurred in association with El Niño.
La Niña is in some ways the opposite of El Niño, and its impacts tend to be the opposite of El Niño's. La Niña is characterized by the warm surface water being pushed farther west than normal. La Niñas are associated with some El Niño events but do not occur as frequently as El Niños.
Global Warming. The Earth's surface temperature has risen by about 1°F in the past century (U.S. Environmental Protection Agency [EPA] 1998). In Honolulu, the average temperature has increased 4.4°F over the last century (USEPA 1998). There is strong evidence that most of the warming over the last 50 years is attributable to human activities. Human activities have altered the chemical composition of the atmosphere through the buildup of greenhouse gases, primarily carbon dioxide, methane, and nitrous oxide. As buildup of these gases continues, scientists expect that the average global surface temperature could rise an average of 1.6 to 6.3°F in the next century (USEPA 1998). In Hawai‘i, it is projected that temperatures could increase by an additional 3°F by the year 2100.
Increasing concentrations of greenhouse gases are likely to accelerate the rate of climate change. Rising global temperatures are expected to change precipitation and other local climate conditions. It is not possible at this time to predict the impacts to individual areas, such as Hawai‘i. Changing regional climate could alter forests, crop yields, and water supplies. It could also affect human health, animals, and many types of ecosystems. For example, deserts may expand into and replace existing rangelands. The increased temperature is also expected to cause a melting of fresh water currently reserved in snow and ice, which would result in rising of the sea level.
Sea Level Rise. Globally, sea level has risen four to eight inches over the past century. The snow cover in the Northern Hemisphere and floating ice in the Arctic Ocean have decreased, which is assumed to have contributed to the global increase in the sea level. In various areas in the Hawaiian Islands, sea level already is rising at a rate of 6 to 14 inches per century, and it is likely to rise another 17 to 25 inches by 2100. The impacts of rising sea levels will be felt most immediately along coastal areas throughout the Hawaiian Islands and the world. Following are brief descriptions of areas of the anticipated impacts:
Floods. Low-lying coastal areas will begin to be inundated with the rising sea level. The impacted communities will need to build infrastructure to mitigate against the rising water levels, which will include dikes and pumping facilities. The City of New Orleans, Louisiana, currently uses pump stations and levees to control flooding as portions of the city are constructed below the current sea level. Locations along rivers influenced by tidal action of the oceans may also be affected by the sea level increase, although they may be situated miles from the ocean. The higher water surface elevation at the downstream end of rivers discharging into the ocean will translate upstream, creating an increase in the flood stages miles upstream of the coast.
Possible responses to rising sea levels in coastal areas of Hawai‘i, such as the Wai‘anae coast, include building walls to hold back the sea, allowing the sea to advance and adapting to it, and raising the land by replenishing beach sand or elevating structures. All of these responses would be costly.
Beach Erosion and Barrier Islands. Beach erosion is associated with the volume of water interacting with the land as well the location of the interaction. The increased sea level will be associated with an increase in the total volume of water in the oceans and the higher sea levels will also allow tides to impact shorelines at locations that are not currently protected. Barrier islands may be inundated, which will lessen their effectiveness in dissipating the energy of incoming tides and waves. This will allow for more energy to reach inhabited shorelines, increasing the erosion rate.
Saltwater Intrusion. Coastal areas where groundwater is used as a water supply source may experience impacts of the rise in sea level. Because of density differences, fresh water floats on top of saltwater, with a transition zone located at the interface. If the sea level rises, it will force the fresh water in the ground to rise also. Deep wells that currently are pumping only fresh water may experience a rise in the transition zone to the well level, causing the well to pump water with a higher salinity content.
Coastal Wetlands. These wetlands naturally developed due to the inundation action of the tidal zone. The location of flora found in a wetland is based on water levels experienced at the site. If seawater levels increase, the existing plant communities may be destroyed by the increased inundation and salinity. Channel formation within the wetland is based on the volume of water interacting with the site. As the sea level increases, the volume of water impacting the wetland area increases, modifying the channel.
U.S. Environmental Protection Agency (USEPA). 1998. Climate Change and Hawai‘i. September 1998. EPA 236-F-98-007e. Climate and Policy Assessment Division. On-line address: http://yosemite.epa.gov/oar/globalwarming.nsf/UniqueKeyLookup/SHSU5BUNQM/$File/hi_impct.pdf
Alu Like, Inc. 1989. Oral Histories of the Native Hawaiian Elderly: On the Island of Oahu. Native Hawaiian Resource Center. Honolulu, HI.
National Oceanic and Atmospheric Administration (NOAA). 2004b. What is an El Nino? http://www.pmel.noaa.gov/tao/elnino/el-nino-story.html
National Oceanic and Atmospheric Administration (NOAA). 2004c. What is an La Nina? http://www.pmel.noaa.gov/tao/elnino/la-nina-story.html
