Earth Science: The Climate System – Natural Climate Phenomena
Historically, the Earth’s climate has gone through natural cycles. These can be detected in climate data of past millennia, recorded in mineral deposits and core samples of polar ice.
Fueled by the sun’s energy, wind and ocean currents continually churn the Earth’s troposphere and hydrosphere, affecting the Earth’s climate. The so-called trade winds significantly influence global climate by carrying large amounts of ocean moisture.
El Nino and La Nina
The southeast trade winds drive the circulation of water in the South Pacific. Cool surface water off the coast of South America moves westward, warming as it goes. As this current nears Southeast Asia, it encounters cooler water, which sinks down into the Pacific and travels along the seafloor toward South America, rising again to renew the cycle. This cold current from the deep Pacific creates an extended high-pressure zone and a dry climate in western South America.
The nutrient- rich water makes fishing ideal near the shores of countries such as Peru. Conversely, in Southeast Asia, warm waters produce sustained low-pressure zones regularly resulting in heavy monsoon rains in Australia and Indonesia. Every three to eight years, an unusual warming event occurs near the South American coast. One potential reason is that trade winds weaken, interrupting the water circulation pattern in the Pacific.
As a result of this, heavy rains and hurricanes often ensue. Without the nutrient-laden, cold current, fish stocks drastically decline. In Southeast Asia, severe droughts cause failed harvests and forest fires. Since this event often occurs around Christmas, Peruvian fishermen dubbed it “El Nino,” (the Christ Child). When rising pressure differences between South America and Southeast Asia allow the trade winds to gain strength, the circulation pattern resumes and the original conditions return. This is known as La Nina (the little sister). Scientists still do not fully understand either phenomenon.
CLIMATE ANALYSIS
The Earth’s climate has been influenced throughout history by natural events such as the formation of the atmosphere and new land masses, tectonic plate movement, meteorite collisions, and massive volcanic eruptions.
Most climate changes were gradual, but they can still be detected from the subtle traces they have left behind. Scientists draw important information from fossils, the chemical composition of minerals, and ice deposits to gain an understanding of past climate conditions.
BASICS
DENDROCHRONOLOGY Tree rings vary in thickness depending on how favorable the growing season was. Thus, growth rings tell us about past climate conditions as well as the tree’s age.