Climate Change - page 3


Volcanoes and Climate

When some volcanoes erupt, they send gases up into the stratosphere. Emitted sulfur dioxide is converted into sulfate aerosols, which are tiny suspended particles that circle the globe and reduce the amount of solar radiation that reaches the Earth. Although the actual volcanic activity may only last several days, the impacts on climate can last for a few years, which is the time it takes for the aerosols to fall out of the stratosphere.

The eruption of Mount Pinatubo in the Philippines in June 1991 sent about 20 million tons of sulfur dioxide and ash as high as 20 miles into the Earth's atmosphere. The Pinatubo sulfur dioxide cloud was the largest stratospheric disturbance observed since the advent of Earth-observing satellite imagery in the 1970s. Following the eruption, global temperatures decreased by as much as 0.5 degrees C (about 1 degree F) in late 1992.

In addition, sulfate aerosols emitted during the eruption interacted with human-made chlorofluorocarbons (CFCs), which destroy ozone, and led to the lowest-ever recorded levels of stratospheric ozone. Climate models showed that the eruption also caused a change in North Atlantic wind patterns, which led to a warmer winter season in Europe during 1991-92.

Larsen B
This image from the Multi-angle Imaging SpectroRadiometer (MISR) shows the breakup of the Larsen B ice shelf, which collapsed and broke away from the Antarctic Peninsula during February and March, 2002. Scientists believe the collapse was accelerated by warm summer temperatures. (Image credit: NASA/GSFC/LaRC/JPL, MISR Team)

The Larsen B Ice Shelf Breakup

Picture a chunk of ice the size of the state of Rhode Island - about 3200 square km (1235 square miles). That's the approximate size of the northern section of the Larsen B ice shelf, which shattered and broke off from the Antarctic continent in early 2002. Researchers discovered the ice shelf breakup while analyzing satellite data from the Moderate Resolution Imaging Spectroradiometer (MODIS). The shattered ice sent thousands of icebergs drifting across the Weddell Sea.

Ice shelves are immense plates of partially floating glacial ice that are fed by glaciers and also by the accumulation of new snow. The Larsen B event was the largest in a series of ice shelf retreats along the Antarctic Peninsula during the last 30 years. Since the 1940s, temperatures in the region have warmed by about 0.5 degrees C (1 degree F) per decade. If the warming trend continues, scientists believe the next ice shelf to the south, the Larsen C, may also begin to disintegrate.

Sea Leve
This graphic crudely illustrates the effect of hypothetical, spatially uniform sea level rise scenarios. The red areas indicate regions of the southeastern United States that would be below sea level at rises of 1, 2, 4, and 8 meters (about 3, 6.5, 13, and 26 feet), respectively. (Image credit: NOAA, Geophysical Fluid Dynamics Laboratory)

Sea Level Rise

Mean sea level refers to the height of the sea in relation to a surface reference point. Sea level goes through periodic cycles of change throughout geologic time. According to the Intergovernmental Panel on Climate Change (IPCC), average global sea level has risen 10 to 25 cm (4 to 10 inches) during the past century. Recent analyses of satellite data also show that the rate of sea level rise is accelerating - rising by about 5 cm (2 inches) between 1985 and 2005.

The main cause of sea level rise is water expansion due to rising global temperatures, known as thermal expansion. Melting glaciers and ice caps are responsible for about one-third of sea level rise. Many scientists believe that the Antarctic ice sheet is fairly stable and will not pose a threat to sea level within the next 100 years. However, the Greenland ice sheet may gradually melt and add its water to the oceans.

Miami
About one-third of the world's population resides in coastal areas. Miami, Florida is one of many U.S. coastal cities that are vulnerable to rising sea level. (Image credit: NOAA)

Global sea level rise threatens both human development and natural habitats through flooding, coastal erosion, and saltwater intrusion. Natural features such as dunes and wetlands can be destroyed, making certain areas more vulnerable to hurricanes and cyclones.

About one-third of the world's population resides in coastal areas. Even a 0.3-meter (1-foot) increase in average sea level would flood low-lying U.S. coastal cities such as New Orleans, New York, Boston, Charleston, and Miami.

In recent years, Earth-observing satellites, such as TOPEX/Poseidon, have enabled scientists to monitor global sea level and, therefore, predict future changes.