Climate change refers to the variation in Earth’s global climate or in regional climates over time. It describes changes in the variability or average state of the atmosphere over time scales ranging from decades to millions of years. These changes can be caused by processes internal to the Earth, external forces (e.g. variations in sunlight intensity) or, more recently, human activities.
The external factors that can shape climate are often called climate forcing and include such processes as variations in solar radiation, the Earth’s orbit, and greenhouse gas concentrations.
The Earth’s climate is influenced by many factors, mainly by the amount of energy coming from the sun, but also by factors such as the amount of greenhouse gases and aerosols in the atmosphere , and the properties of the Earth’s surface, which determine how much of this solar energy is retained or reflected back to space.
The atmospheric concentrations of greenhouse gases such as carbon dioxide, methane and nitrous oxide have significantly increased since the beginning of the industrial revolution. This is mainly due to human activities, such as the burning of fossil fuels land use change, and agriculture. For instance, the atmospheric concentration of carbon dioxide is now far higher than in the last 650 000 years and has been growing faster in the last ten years than it has been since the beginning of continuous measurements around 1960.

Variations within the Earth’s climate

Weather is the day-to-day state of the atmosphere, and is a chaotic non-linear dynamical system. On the other hand, climate — the average state of weather — is fairly stable and predictable. Climate includes the average temperature, amount of precipitation, days of sunlight, and other variables that might be measured at any given site. However, there are also changes within the Earth’s environment that can affect the climate.
Earth’s climate repeatedly has shifted dramatically and in time spans as short as a decade. And abrupt climate change may be more likely in the future from variations in the frequency and intensity of storms to changes in the incidence of mosquito-borne diseases. Rising sea levels can flood coastal areas, and habitat changes can cause the extinction of some species of plants and animals. Increases in precipitation can cause floods and landslides, while decreases may lead to droughts and wildfires. This range of possible effects is one reason why many types of scientists are keenly interested in understanding the earth’s changing climate.

The ocean:

Today the oceans’ overturning circulation carries a tremendous amount of heat northward, warming the North Atlantic region. It also generates a huge volume of cold, salty water called North Atlantic Deep Water—a great mass of water that flows southward, filling up the deep Atlantic Ocean basin and eventually spreading into the deep Indian and Pacific Oceans.
Paleoceanographers have found evidence for very different patterns of ocean circulation in the past. About 20,000 years ago (bottom), waters in the North Atlantic sank only to intermediate depths and spread to a far lesser extent. When that occurred, the climate in the North Atlantic region was generally cold and more variable.

The greenhouse effect is actually essential to our existence:

The sun warms the earth, and certain gases (including carbon dioxide and water vapor) act like the glass of a greenhouse, trapping heat and keeping the planet’s surface warm enough to support life. However, measuring humanity’s effect on the concentration of greenhouse gases is a key issue in understanding global climate change. Industry and other human activity add carbon dioxide to the atmosphere. This strengthens the greenhouse effect and may cause a significant warming trend.
Understanding how the atmosphere works is fundamental to understanding climate change. The atmosphere is composed of layers of air, each with its own temperature patterns. Researchers must determine whether changes in temperature or air circulation are part of complex, longer-term cycles. And the interconnections between air, sea, and land mean that any change could have multiple causes—and multiple effects.

The effects of climate change on plants and animals:

Many species inhabit precisely bounded ecological niches, and even small changes in climate may cause fundamental disruptions in habitat or food availability. In the past, animals could respond to these pressures by moving from one place to another. Today, however, land development has constrained and fragmented ranges and travel routes, making species migration in response to climate change much more difficult. Moreover, loss of key predator or prey species may affect the life cycles of other organisms in the food chain.
Organic processes can also play an important role in regulating the earth’s climate. Changes in the extent of snow, ice, or vegetation covering the planet’s surface can alter key climatic processes with unforeseeable effects (changing the amount of carbon dioxide consumed by plants, for example, or the proportion of the sun’s heat absorbed by the earth).

Solar variation

Variations in solar activity during the last several centuries based on observations of sunspots and beryllium isotopes.
The sun is the ultimate source of essentially all heat in the climate system. The energy output of the sun, which is converted to heat at the Earth’s surface, is an integral part of shaping the Earth’s climate. On the longest time scales, the sun itself is getting brighter with higher energy output; as it continues its main sequence ,this slow change or evolution affects the Earth’s atmosphere.
On more modern time scales, there are also a variety of forms of solar variation, including the 11-year solar cycle and longer-term modulations. However, the 11-year sunspot cycle does not manifest itself clearly in the climatological data. Solar intensity variations are considered to have been influential in triggering the Little Ice Age, and for some of the warming observed from 1900 to 1950. The cyclical nature of the sun’s energy output is not yet fully understood; it differs from the very slow change that is happening within the sun as it ages and evolves.

What impacts are expected in the future?

  1. Over the course of the 21st century, many impacts are expected to occur in natural systems. For instance, changes in precipitation and the melting of ice and snow are expected to increase flood risks in some areas while causing droughts in others. If there is significant warming the capacity of ecosystems to adapt will be exceeded, with negative consequences such as an increased risk of extinction of species
  2. The most vulnerable people are in general the poor, since they have less capacity to adapt , and their livelihoods are often dependent on resources that are linked to climate.
  3. Africa is found to be particularly vulnerable, because of existing pressures on its ecosystems and its low capacity to adapt . On all continents, water supply and the threat to coastal areas will be an issue. Overall future impacts are expected to be negative, although some positive effects are also expected initially, such as an increase in agricultural productivity at high latitudes accompanying a moderate warming, or decreased heating needs in cold regions
  4. Impacts will depend on the magnitude of the temperature increase. For instance, some crops at mid- to high latitudes will have higher productivity if local temperature increases by 1-3 °C, but will be negatively affected beyond that). If higher temperatures persist after the 21st century it could result in very large impacts. For instance, the large sea-level rise that would result from the melting of the Greenland and Antarctic ice sheets would have major repercussions on coastal areas. The cost associated with the effects of climate change is projected to increase over time with rising temperatures.
  5. A projected increase in the severity and frequency of droughts, heat waves, and other extreme weather events is expected to cause major impacts over the course of this century

Sources: Wikipedia, Explorartorium.

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