Chapter 4 Effects on the Climate System

CHAPTER 4 EFFECTS ON THE CLIMATE SYSTEM

Ocean Circulation

Driven by overlying winds such as the great global subtropical anticyclones that exist in ocean basins centered near the 30° parallel

Driven by thermohaline currents that flow in response to temperature and/or salinity
Deep water currents are usually found layered with the Antarctic Bottom Water (AABW) at the bottom, the Antarctic Deep Water (ADW) above the AABW, and the North Atlantic Deep Water (NADW) above the ADW in the Atlantic
Deep water currents in the Pacific are also usually found layered with the Common Water (CW) current and the Pacific Subarctic Water (PSW) at the bottom and the Antarctic Intermediate Water (AAIW) and the North Pacific Intermediate Water (NPIW) above them

El Niño/Southern Oscillation Events

Walker Circulation– refers to the connection between atmospheric pressure centers in the equatorial Pacific that are associated with the Southern Oscillation, the sea surface temperatures, and the tropical trade winds that blow from east to west near the surface in the tropics

Indirect data sources such as tree rings, flood frequency, sediment cores, and coral reef growth suggest that anomalous weather events associated with ENSO events have been occurring for thousands of years

Coincides with a reversal of the normal Walker Circulation, occurs once every three to seven years, and usually lasts ten to fourteen months

Trade wind flow along the equatorial Pacific Ocean becomes even stronger than normal, which increases warm water accumulation in the western equatorial Pacific and cold water upwelling in the east

Higher than normal air pressure and subsiding airflow over tropical eastern South America, causing many rainforests in the area to experience a drought
The relatively-high-pressure regime that normally prevails over eastern equatorial Africa becomes an area of lower atmospheric pressure and the region becomes anomalously wet
Other effects elsewhere

A trough in the northern branch of the polar jet streams can cause colder air to infiltrate the eastern U.S.all the way to the Gulf coast
In the northeastern United States, El Niño causes slightly higher temperatures and slightly drier conditions caused by a net reduction of snowfall
Other effects elsewhere

It is widely assumed that global warming is caused by human emission of pollutants known as greenhouse gases and that global warming causes more extreme ENSO events, but increased frequency of ENSO events could be causing increased global temperatures

Volcanic Activity and Climate

Volcanic activity contributes to both short and long term climate fluctuations and is encouraged in certain locations as Earth’s crustal plates move slowly

The Dust Veil Index (DVI) and the Volcanic Explosivity Index (VEI) were created to estimate the amount of aerosols (especially those caused by volcanoes) in the atmosphere

Mount Pinatubo’s eruption in the Philippines on June 25, 1991, led to surface global cooling
In 1815, Tambora’s eruption in Sumbawa, Indonesia, caused the “year without a summer”
Krakatau’s eruption in Indonesia in 1883 and is believed to have killed up to 40,000 people
Laki Fissure erupted in 1783 and was responsible for devastating most of the human and animal population of Iceland
The eruption of MountToba in Sumatra approximately 71,000 years ago is believed to be the most catastrophic of all volcanic eruptions, and is believed to have accelerated the onset of the last glacial advance

Deforestation and Desertification

Humans play a role in climatic variation through fossil fuel combustion, deforestation, slash and burn agriculture, and desertification

Cryospheric Changes

The cryosphere existsin the form of continental ice sheets, semi-permanent alpine glaciers, seasonal sea ice, and/or seasonal snowpack

Feedback systems, whereby changes can either be magnified (positive feedback system) or dampened (negative feedback system), are important in climatology, and particularly in the cryosphere
Addition of snow and ice increases albedo, causing a reduction in temperature, more extensive snow and ice, and a positive feedback system
Likewise, melting of snow and ice decreases albedo, raising the temperature, melting more snow and ice, and a positive feedback system
Some researchers now estimate that the Greenland ice sheet, the largest in the northern hemisphere, could lose as much as one-half of its mass over the next thousand years, leading to an increase in global sea level of about 2.7 m (9 ft)
If all permanent continental ice were to melt, sea levels would rise about 67 m (220 ft)