CLIMATE CHANGE AT GLOBAL LEVEL

INDEX The first studies: climate changes Albedo Volcanoes and volcanic eruptions Ocean currents and C O 2 Change in temperature and greenhouse gases over time Permafrost Water vapour and clouds Solar variation Displacement of the tropics

The first studies: the climate change It is argued that the current change of the climate is provocated by careless actions of people. The Earth has the ability to react to this change but in a very long time so, for this reason, people risk to self-destruct. Scientists believe that: ⋆ The average temperature of Earth’s atmosphere is increasing; ⋆ The concentration of greenhouse gases in the atmosphere is increasing; ⋆ There is a correlation between the increase in temperature and the increase in the concentration of green house gases in the atmosphere; ⋆ The increased concentration of green house gases in the atmosphere is due to anthropogenic emissions.

Scientists suppose that there are effects due to global warming : ⋆ Reducing volume of glaciers: since the end of the little ice age, glaciers of mountain ranges are in sharp decline over the whole earth. ⋆ Oceans are warmer and acids : the ocean surface is 30% more acidic than it was in 1800, and 50% of this change has come from the increament of CO2 in the atmosphere, endangering coral reefs and various species of plankton that form the base of the food chain of the sea. ⋆ Average temperature difference between day and night is easing: another change concerns the thermal shock that occurs between the day and the night, and that turns out to be stronger than in previous years.

⋆ Animals are shifting their habitat poleward: climate change means also changes in the life of animals which make a considerable effort to adapt, hence the pole shift. ⋆ Plants bloom days or weeks earlier than in the past: the percentage of endangered species compared to those analyzed is 69%, while compared to the known ones is 2%.

Factors that affect the climate The climate changes and this depends on various factors: the albedo; volcanoes and volcanic eruptions; the absorption of Co2 and oceans currents; changes of the temperature and greenhouses gases over time; the permafrost; water vapor and clouds; the variation of solar activity; the displacement of the tropics.

Albedo The albedo is the ratio between the amount of solar energy reflected from the Earth-atmosphere system and the total energy coming into the system. The albedo of the Earth-atmosphere is 0,35.

A completely white surface has an albedo of 1, because it reflects all the light. A completely black surface has an albedo of 0 because it absorbs solar rays. Therefore a surface without snow or ice absorbs more radiation.

Consequences of the albedo One of the more evident consequences is the melting of the ice, that, being white, reflects a very effective radiation, while the water and the soil, being darker, reflects less. The more ice melts because of the increment in temperature, the more soil and water become widespread, and the greater the absorption of heat by the planet is.

Volcanos and volcanic eruptions A volcano is a geologic, complicated rocky structure, which is generated in the Earth’s crust by the ascent of the magma formed below or in the Earth’s crust. A volcanic eruption is the leakage of magma and other gaseous materials in the Earth’s surface from the mantle or the crust. Typically a volcanic eruption happens either in the main crater of a volcano or in the minor craters of the volcano. The classification is based on the characteristics of magma and on the type of eruption.

Consequences of the vulcanic activities ⋆ Volcanic eruptions are capable of triggering climate change in a short time with an efficiency that is unmatched in nature. ⋆ In a few months, the atmospheric temperature of the Earth can drop, causing droughts, floods and cold weather.

C O 2 ABSORPTION AND OCEANIC CURRENTS Not all of the carbon dioxide we produce stays in the atmosphere, oceans absorb 1/3 and ¼ of C O 2 every year. This gas dissolves in salty water, creating carbonic acid. Since the concentration of atmospheric C O 2, keeps increasing, oceans absorb more and more C O 2, thus producing more and more carbonic acid. This acid is changing the chemical balance of the oceans: the process is known as “ocean acidification”. Thermohaline circulation: this is the global oceanic circulation due to the variation of density of the water masses. A oceanic current is a mass of sea water in movement with respect to the surrounding water and from which it is different in density, salinity, temperature or colour.

Trends in temperature and green house gases during time The greenhouse gases present in the atmosphere are about 30 and they can capture heat. The water vapour is the most efficient gas in the control of the air temperature of the Earth’s surface. Greenhouse gases are necessary to trap the energy irradiated by surface of the Earth which, otherwise, would be extremely cold. This process limits the flux of energy going outside.

The results show that the Earth's temperature will increase as the greenhouse gases increase. The gas considered as the most important for the green house effect is the CO2 issued into the atmosphere from the consumption of fossil fuels for human activities. In addition to carbon dioxide, there are other greenhouse gases whose quantity is increasing.

The datas of the Earth’s athmosphere in the past were obtained from the growth of rings of the trees or by the relationships between the isotopes of various elements in the glaciers of Antarctica and Greenland, and in the corals or in lake sediments. From all these data we obtain the average global temperature in the past, and these data are essential to defeat the "global warming". The reconstruction of past temperatures based on indirect data is a very difficult path.

Permafrost In areas in high latitudes, where temperatures are very low, the soil is called permafrost, namely "permanently frozen." It is divided into several layers that can be up to a hundred meter deep. Permafrost was formed by the last glaciation and permafrost is divided into: saturated and supersaturated soil. Due to the increment in temperature, permafrost is starting to melt permanently.

Some plants can live into the melting and when they die they don’t decompose but with permafrost remain intact for thousands of years and this has made the permafrost a big carbon sink. With the increase of temperature, however, the planet warms and the permafrost may start to emit greenhouse gases that can amplify the effects of global warming.

Clouds The clouds occupy about half the atmospheric surface and this have a significant effect on the budget radioactive terrestrial based on their thickness. According to the Iris effect a warmer Earth would produce more water vapor in order to protect the Earth from the sun's rays limiting warming. But according to another hypothesis the clouds should trap heat and strengthen the heating. But the cloud cover increase the green effect.

Variation of the sun activity The sun, our star, gives us heat, light and energy. It is a great nuclear power and hydrogen presents sudden changes in its active phase. In the past we had several epochal climate change going from a tropical climate in the Jurassic erato glaciation in the Quaternary Ice Age. This is caused by an important change in energy production of the Sun.

The displacement of the tropics According to a survey the displacement of the tropics coincides with the rise in temperature of 0.8 degrees Celsius. Because the masses of warm tropical air-move away from the equator. The Hadley cells are a type of convective circulation and precipitation determine both the equatorial and subtropical drought.