The Ingredients of Climate

When people think of the part of Earth that affects our climate, they generally focus on the atmosphere. After all, this is where storms develop, winds blow, and clouds form. For that reason, early climate researchers tended to turn their attention to the sky.

But we now know that the atmosphere is just one component of our incredibly complex climate system. Other important components on Earth include:

Oceans. The temperature of surface waters and the movement of salt in the oceans can affect climate across much of the globe.

Land cover. Plants, soil, pavement, and other types of land cover reflect sunlight, cycle energy and water, and store carbon in different ways, thereby affecting temperature and precipitation.

Snow and ice. Regions that remain covered by snow or ice for long periods of time have an important cooling impact on much of the planet, because snow and ice reflect sunlight back into space, preventing it from warming the atmosphere.

When scientists at NCAR and other institutions build computer models of Earth’s climate[link in Our Changing Climate to Computer models], they create a complete picture by incorporating information about the atmosphere, oceans, land cover, and the cryosphere—that part of Earth that is generally covered with snow and ice. Modelers may also look at additional factors, such as volcanic eruptions, solar activity, and emissions caused by human activity.

Major volcanic eruptions can cool large regions or even the entire planet, because they loft ash and other particles into the atmosphere, blocking sunlight. Research at NCAR indicates that major volcanic eruptions tend to follow a cycle of about 75 years, but no one knows the reason such a pattern may exist.

The Sun is a critical area for Earth system research. Not only does it provide the energy that fuels atmospheric circulation, but its energy output also varies over time, with important consequences for global climate. The virtual disappearance of sunspots and an apparent dip in solar radiation between 1645 and 1715 coincided with a period of intensely cold winters in Europe, part of the period dubbed the Little Ice Age. But solar variation is not to blame for Earth's current warming trend. Climate simulations at NCAR have shown that solar changes explain less than a third of the warm-up during the last century.

Human activities also have diverse and important impacts on climate. For example, urban development tends to increase local temperatures. This urban heat-island effect occurs because buildings and pavement retain more heat than undeveloped areas and cause more runoff and thus drier conditions as well. Conversion of natural forest and grassland ecosystems to agricultural land also alters temperature and precipitation by changing the cycling of energy and water between land and atmosphere. Greenhouse gases, emitted when fossil fuels are burned in homes, gas and coal-fired power plants, vehicles, and factories, increase temperatures globally and may alter patterns of rain and snow. Emissions of other pollutants, such as sulfates from industrial facilities, can block sunlight and slightly offset this warming in certain regions.

The many interactions in Earth's climate system pose a highly complex and challenging problem for scientists to unravel. A change in the chemistry of the atmosphere or in the choice of crops planted in one region may set off a chain reaction with impacts for the entire globe.

For example, NCAR research suggests that increased levels of carbon dioxide in the atmosphere will increase precipitation, reduce wind, and spur more vegetation to grow in arid areas. All these factors may work together to reduce the amount of dust from arid regions that gets lofted into the air. Dust is important for a couple of reasons: it blocks sunlight and therefore helps to cool temperatures, and it also deposits iron in the ocean, thereby fertilizing marine organisms that can remove carbon dioxide from the atmosphere. A decrease in dust is thus one of several potential magnifying effects of increased emissions of carbon dioxide—especially through the ocean's reduced capacity to absorb the chemical.

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