Page 28 - Alternative Energy Systems in Building Design

NATURAL FACTORS DRIVING CLIMATE CHANGE 5

Volcanoes also contribute to the extended atmospheric pollutants because over
millennia of geologic time periods, they release carbon dioxide from the earth’s interior,
counteracting the uptake by sedimentary rocks and other geologic carbon sinks. However,
CO contribution resulting from volcanic eruptions is considered relatively insignifi-
2
cant compared with current anthropogenic emissions. Recent estimates indicate that
anthropogenic activities generate more than 130 times the amount of carbon dioxide
emitted by volcanoes.

GLACIATION
Glaciers are one of the most sensitive indicators of climate change. They advance
substantially during climate cooling, as in ice ages, and retreat during climate warming
on moderate time scales, a climatic cycle that has been repeating through the ages
(Fig. 1.4). Glaciers are dynamic in nature; they grow in winter and collapse in summer,
contributing to natural climatic variability. These are generally referred to as externally
forced changes. However, in the last couple of centuries, glaciers have been unable to
regenerate enough mass during the winter to make up for ice lost during summer
months. The most significant climate processes that have taken place in the past several
million years have been the glacial cycles that result from planetary gravitational forces
and cause the formation of ice sheets.

OCEAN VARIABILITY
Climate changes also result from the interaction between the atmosphere and
oceans. Many climatic fluctuations are a result of heat accumulation and storage in
the oceans that cause water currents to move between different heat reservoirs. The
movement process of oceanic water, thermoline circulation, plays a key role in
redistributing and balancing heat and, consequently, climatic conditions throughout
the globe.

Figure 1.4 Trend in global average surface temperature. Courtesy of United Nations
Environmental Program/GRID-Arendal.