Why does temperature change

The lower line that has all of the squiggles up and down is the solar energy, which reaches the surface of the earth. Radiation is being absorbed at infrared wavelengths, primarily by water vapor. Water in the atmosphere and other greenhouse gases absorb part of the shorter wavelengths in sunlight and much of the longer wavelengths. They are even more important and effective in absorbing radiation beyond the sunlight into the thermal radiation bands.

Here are some of the so-called greenhouse gases and what they absorb. Water is the greatest absorber here. At longer wavelengths nitrous oxide and methane also made a radiation influence in their respective bands. Water is the most important of the greenhouse gases. Huge amounts of water cover the planet. Water vapor is necessary in the atmosphere to provide rain for life on the planet. There are big differences in way the sun heats water and land. Water surface temperature change much less rapidly than land--so land areas are often hotter than the nearby ocean during the day, and cooler during the night.

Solar warming is generally greater at the equator where the sun shines directly and much less at the poles where the sun is low in the sky. This differential heating is passed on to the air above by conduction which causes air expansion and changes in pressure. Wind is the result of pressure changes in the atmosphere. Any shoreline is a wind machine, because of solar heating effects.

Over the whole year, polar regions are cold or cool and the tropics are warm or hot. Winds blow from high pressure areas to low pressure ones. It has followed its natural year cycle of small ups and downs, but with no net increase bottom. Over the same period, global temperature has risen markedly top. Climate is influenced by natural changes that affect how much solar energy reaches Earth.

The intensity of the sunlight can cause either warming during periods of stronger solar intensity or cooling during periods of weaker solar intensity. These changes appear to be the primary cause of past cycles of ice ages, in which Earth has experienced long periods of cold temperatures ice ages , as well as shorter interglacial periods periods between ice ages of relatively warmer temperatures.

Click to learn about how rates of climate change have varied over time. Changes in solar energy continue to affect climate. However, over the last year solar cycle, solar output has been lower than it has been since the mid th century, and therefore does not explain the recent warming of the earth.

When sunlight reaches Earth, it can be reflected or absorbed. Light-colored objects and surfaces, like snow and clouds, tend to reflect most sunlight, while darker objects and surfaces, like the ocean, forests, or soil, tend to absorb more sunlight.

The term albedo refers to the amount of solar radiation reflected from an object or surface, often expressed as a percentage. Reflectivity is also affected by aerosols. Aerosols are small particles or liquid droplets in the atmosphere that can absorb or reflect sunlight. Unlike greenhouse gases, the climate effects of aerosols vary depending on what they are made of and where they are emitted.

Those aerosols that reflect sunlight, such as particles from volcanic eruptions or sulfur emissions from burning coal, have a cooling effect. Those that absorb sunlight, such as black carbon a part of soot , have a warming effect.

Natural changes in reflectivity, like the melting of sea ice, have contributed to climate change in the past, often acting as feedbacks to other processes.

Volcanoes have played a noticeable role in climate. Volcanic particles that reach the upper atmosphere can reflect enough sunlight back to space to cool the surface of the planet by a few tenths of a degree for several years.

Volcanic particles from a single eruption do not produce long-term change because they remain in the atmosphere for a much shorter time than GHGs. Processes such as deforestation, reforestation, desertification, and urbanization often contribute to changes in climate in the places they occur.

These effects may be significant regionally, but are smaller when averaged over the entire globe. In addition, human activities have generally increased the number of aerosol particles in the atmosphere.

Overall, human-generated aerosols have a net cooling effect offsetting about one-third of the total warming effect associated with human greenhouse gas emissions. Reductions in overall aerosol emissions can therefore lead to more warming. However, targeted reductions in black carbon emissions can reduce warming. Richmond, and Gary W. Yohe, Eds. Global Change Research Program. Qin, G. Plattner, M. Tignor, S.

Allen, J. Boschung, A. Nauels, Y. Xia, V. Bex and P. Midgley eds. Advancing the Science of Climate Changes. National Research Council. Periods of relative stability Interglacial climate periods such as the present tend to be more stable than cooler, glacial climates. The glacial period was characterized by widespread, large, and abrupt climate changes.

In contrast, the previous interglacial period was similarly stable. Periods of abrupt climate change Abrupt climate change refers to sudden on the order of decades , large changes in some major component of the climate system, with rapid, widespread effects.