Calentamiento Global“Mito o realidad” Hernán Santos Departamento de Geologia UPR-Mayagüez G eM Geology Museum
¿Que es el Calentamiento Global? • Calentamiento Global se refiere al aumento de la temperatura promedio en los océanos y en la superficie de nuestro planeta durante las pasadas décadas. (0 en esta grafica representa la temperatura promedio entre 1961 y 1990, IPCC, Global Warming Art)
La temperatura del aire en la superficie aumento 1.3+/-0.32 ºF en el ultimo siglo. • ONU-ICPP (Intergovernmental Panel on Climate Change) concluyo que este aumento se debe al aumento de gases de invernadero en nuestra atmósfera como resultado de actividades antropogénicas.
¿Que son los gases de invernadero? • Los gases de invernadero son componentes de nuestra atmósfera que contribuyen al efecto de casa de invernadero. • Algunos ocurren de forma natural en nuestra atmósfera mientras que otros son el resultado de actividades humanas como la quema de combustibles fósiles (carbón, petróleo y gas natural). • Los gases de invernadero son: vapor de agua, bióxido de carbono, metano, oxido nitroso y ozono.
¿Qué es el efecto de Casa de Invernadero? • Cuando los rayos del sol llegan a la superficie de la tierra algunos son reflejados al espacio y otros son absorbidos por los gases de invernadero calentando la misma.
Este proceso es importante ya que mantiene la temperatura de nuestro planeta. Sin el efecto de casa de invernadero,la temperatura de nuestra planeta seria cerca de 20º C por debajo de la temperatura actual. (-6.6 º F)
Gases de invernadero naturales • Vapor de agua (sin nubes) causa 36-70% del Efecto de Casa de Invernadero (ECI) • Bioxido de carbono 9-26% ECI • Metano 4-9% ECI • Ozono 3-7% ECI • Oxigeno (O2) y nitrogeno (N2), los gases mas abundantes en la atmosfera no producen ECI.
Gases de invernadero originados por el ser humano • La concentracion de Gases de invernadero ha amunetado mayormente por la liberacion de CO2. Principalmente por la quema de combustible fosil y deforestacion • Metano ha aumentado por la ganaderia y sembradios de arros. Tambien por los vertederos.
This map depicts the unequal distribution of industry in the world. The significant part of carbon dioxide emissions comes from energy production, industrial processes and transport. The industrialised countries consequently must bear the main responsibility of reducing emissions of carbon dioxide.
Emissions of carbon dioxide due to changes in land use mainly come from the cutting down of forests and instead using the land for agriculture or built-up areas, urbanisation, roads etc. When large areas of rain forests are cut down, the land often turns into less productive grasslands with considerably less capacity of storing CO2.
Volume of GHG calculated per nation and per capita. The rich countries of the world historically has emitted most of the anthropogenic greenhouse gases since the start of the industrial revolution in the latter half of the 1700s. Per capita, the significant emissions still are produced by the OECD countries.- A major issue of debate is the sharing of responsibility. Non-industrialised countries strive to increase their population's standard of living, thereby also increasing their emissions of greenhouse gases, since economic development is closely associated with energy production. The volume of GHG thus will probably increase despite the efforts to reduce emissions in industrialised countries. China has the second biggest emissions of GHG in the world. However, per capita the Chinese emissions are very low compared to the no. 1 on the list, the USA.
The global carbon cycle shows the carbon reservoirs in GtC (gigatonne= one thousand million tonnes) and fluxes in GtC/year. The indicated figures are annual averages over the period 1980 to 1989. The component cycles are simplified and the figures present average values. The riverine flux, particularly the anthropogenic portion, is currently very poorly quantified and is not shown here. Evidence is accumulating that many of the fluxes can fluctuate significantly from year to year. In contrast to the static view conveyed in figures like this one, the carbon system is dynamic and coupled to the climate system on seasonal, interannual and decadal timescales.
The amount of aerosols in the air has direct effect on the amount of solar radiation hitting the Earth's surface. Aerosols may have significant local or regional impact on temperature. Water vapour is a greenhouse gas, but at the same time the upper white surface of clouds reflects solar radiation back into space. Albedo - reflections of solar radiation from surfaces on the Earth - creates difficulties in exact calculations. If e.g. the polar icecap melts, the albedo will be significantly reduced. Open water absorbs heat, while white ice and snow reflect it.
The figure shows the combined land-surface air and sea surface temperatures (degrees Centigrade) 1861 to 1998, relative to the average temperature between 1961 and 1990.The mean global surface temperature has increased by about 0.3 to 0.6°C since the late 19th century and by about 0.2 to 0.3°C over the last 40 years, which is the period with most reliable data. Recent years have been among the warmest since 1860 - the period for which instrumental records are available.Warming is evident in both sea surface and land-based surface air temperatures. Urbanization in general and desertification could have contributed only a small fraction of the overall global warming, although urbanization may have been an important influence in some regions. Indirect indicators such as borehole temperatures and glacier shrinkage provide independent support for the observed warming. It should also be noted that the warming has not been globally uniform. The recent warming has been greatest between 40°N and 70°N latitude, though some areas such as the North Atlantic Ocean have cooled in the recent decades.
Precipitation has increased over land at high latitudes of the Northern Hemisphere, especially during the cold season. Decrease in precipitation occurred in steps after the 1960s over the subtropics and the tropics from Africa to Indonesia. These changes are consistent with available data analyses of changes in stream flow, lake levels and soil surface. Precipitation averaged over the Earth's land surface increased from the start of the century up to about 1960, but has decreased since about 1980. There is a lack of data on precipitation over the oceans. (Source:WG I SAR, TS p.28)
Using the IS92 emission scenarios, projected global mean temperature changes relative to 1990 were calculated up to 2100. Climate models calculate that the global mean surface temperature could rise by about 1 to 4.5 centigrade by 2100. The topmost curve is for IS92e, assuming constant aerosol concentrations beyond 1990 and high climate sensitivity of 4.5 °C. The lowest curve is for IS92c and assumes constant aerosol concentrations beyond 1990 and a low climate sensitivity of 1.5 °C. The two middle curves show the results for IS92a with "best estimate" of climate sensitivity of 2.5 °C: the upper curve assumes a constant aerosol concentration beyond 1990, and the lower one includes changes in aerosol concentration beyond 1990. (It is assumed that the Greenhouse effect is reduced with increased aerosols.)Note: In IPCC reports, climate sensitivity usually refers to the long- term or equilibrium, change in global mean surface temperature following a doubling of CO2-equivalent atmospheric concentrations. More generally, it refers to the equilibrium change in surface air temperature following a unit change in radiative forcing (°C/Wm-2)
Using the IS92 emission scenarios, projected global mean sea level increases relative to 1990 were calculated up to 2100. Taking into account the ranges in the estimate of climate sensitivity and ice melt parameters, and the full set of IS92 emission scenarios, the models project an increase in global mean sea level of between 13 and 94 cm.During the fist half of the next century, the choice of emission scenario has relatively little effect on the projected sea level rise due to the large thermal inertia of the ocean-ice-atmosphere climate system, but has increasingly larger effects in the later part of the next century. In addition, because of the thermal inertia of the oceans, sea level would continue to rise for many centuries beyond 2100 even if concentrations of greenhouse gases were stabilized at that time.
Some reports suggest that increase in climate variability or extremes has taken place in recent decades. However, there are inadequate data to determine whether such global changes have occurred consistently over the 20th century. On regional scales there is clear evidence of changes in some extremes and climate variability indicators - for example, fewer frosts in several widespread areas; and an increase in the proportion of rainfall from extreme events over the contiguous states of the USA. It can also be seen that the economic damages from weather related disasters have increased dramatically, although much of this may be attributed to a greater number of people living in vulnerable areas..
ea-ice draft is the thickness of the part of the ice that is submerged under the sea. Comparison of sea-ice draft data acquired on submarine cruises between 1993 and 1997 with similar data acquired between 1958 and 1976 indicates that the mean ice draft at the end of the melt season has decreased by about 1.3 m in most of the deep water portion of the Arctic Ocean, from 3.1 m in 1958-1976 to 1.8 m in the 1990s. In summary: ice draft in the 1990s is over a meter thinner than two to four decades earlier. The main draft has decreased from over 3 meters to under 2 meters, and the volume is down by some 40%.
The global conveyor belt thermohaline circulation is driven primarily by the formation and sinking of deep water (from around 1500m to the Antarctic bottom water overlying the bottom of the ocean) in the Norwegian Sea. This circulation is thought to be responsible for the large flow of upper ocean water from the tropical Pacific to the Indian Ocean through the Indonesian Archipelogo. The two counteracting forcings operating in the North Atlantic control the conveyor belt circulation: (1) the thermal forcing (high-latitude cooling and the low-latitude heating) which drives a polar southward flow; and (2) haline forcing (net high-latitude freshwater gain and low-latitude evaporation) which moves in the opposite direction. In today's Atlantic the thermal forcing dominates, hence, the flow of upper current from south to north.When the strength of the haline forcing increases due to excess precipitation, runoff, or ice melt the conveyor belt will weaken or even shut down. The variability in the strength of the conveyor belt will lead to climate change in Europe and it could also influence in other areas of the global ocean. The North Atlantic atmosphere-ocean-cryosphere system appears to have natural cycles of many timescales in switching the conveyor belt. Periodic movement of excessive ice from the Arctic into the Greenland Sea appears to be responsible for the interdecadal variability of the conveyor belt. There is no evidence yet that the influx of interdecadal switching extends beyond the North Atlantic Ocean.
The Nile Delta is one of the oldest intensely cultivated areas on earth. It is very heavily populated, with population densities up to 1600 inhabitants per square kilometer. The low lying, fertile floodplains are surrounded by deserts. Only 2,5% of Egypt's land area, the Nile delta and the Nile valley, is suitable for intensive agriculture. Most of a 50 km wide land strip along the coast is less than 2 m above sea-level and is protected from flooding by a 1 to 10 km wide coastal sand belt only, shaped by discharge of the Rosetta and Damietta branches of the Nile. Erosion of the protective sand belt is a serious problem and has accelerated since the construction of the Aswan dam.
Rising sea level would destroy weak parts of the sand belt, which is essential for the protection of lagoons and the low-lying reclaimed lands. The impacts would be very serious: One third of Egypt's fish catches are made in the lagoons. Sea level rise would change the water quality and affect most fresh water fish. Valuable agricultural land would be innundated. Vital, low-lying installations in Alexandria and Port Said would be threatened. Recreational tourism beach facilities would be endangered and essential groundwater would be salinated. Dykes and protective measurements would probably prevent the worst flooding up to a 50 cm sea level rise. However, it would cause serious groundwater salination and the impact of increasing wave action would be serious.
Greenhouse effectThe "greenhouse effect" is the warming that happens when certain gases in Earth's atmosphere trap heat. These gases let in light but keep heat from escaping, like the glass walls of a greenhouse.First, sunlight shines onto the Earth's surface, where it is absorbed and then radiates back into the atmosphere as heat. In the atmosphere, “greenhouse” gases trap some of this heat, and the rest escapes into space. The more greenhouse gases are in the atmosphere, the more heat gets trapped.Scientists have known about the greenhouse effect since 1824, when Joseph Fourier calculated that the Earth would be much colder if it had no atmosphere. This greenhouse effect is what keeps the Earth's climate livable. Without it, the Earth's surface would be an average of about 60 degrees Fahrenheit cooler. In 1895, the Swedish chemist Svante Arrhenius discovered that humans could enhance the greenhouse effect by making carbon dioxide, a greenhouse gas. He kicked off 100 years of climate research that has given us a sophisticated understanding of global warming.Levels of greenhouse gases (GHGs) have gone up and down over the Earth's history, but they have been fairly constant for the past few thousand years. Global average temperatures have stayed fairly constant over that time as well, until recently. Through the burning of fossil fuels and other GHG emissions, humans are enhancing the greenhouse effect and warming Earth.Scientists often use the term "climate change" instead of global warming. This is because as the Earth's average temperature climbs, winds and ocean currents move heat around the globe in ways that can cool some areas, warm others, and change the amount of rain and snow falling. As a result, the climate changes differently in different areas.Aren’t temperature changes natural?The average global temperature and concentrations of carbon dioxide (one of the major greenhouse gases) have fluctuated on a cycle of hundreds of thousands of years as the Earth's position relative to the sun has varied. As a result, ice ages have come and gone.However, for thousands of years now, emissions of GHGs to the atmosphere have been balanced out by GHGs that are naturally absorbed. As a result, GHG concentrations and temperature have been fairly stable. This stability has allowed human civilization to develop within a consistent climate.Occasionally, other factors briefly influence global temperatures. Volcanic eruptions, for example, emit particles that temporarily cool the Earth's surface. But these have no lasting effect beyond a few years. Other cycles, such as El Niño, also work on fairly short and predictable cycles.Now, humans have increased the amount of carbon dioxide in the atmosphere by more than a third since the industrial revolution. Changes this large have historically taken thousands of years, but are now happening over the course of decades.Why is this a concern?The rapid rise in greenhouse gases is a problem because it is changing the climate faster than some living things may be able to adapt. Also, a new and more unpredictable climate poses unique challenges to all life.Historically, Earth's climate has regularly shifted back and forth between temperatures like those we see today and temperatures cold enough that large sheets of ice covered much of North America and Europe. The difference between average global temperatures today and during those ice ages is only about 5 degrees Celsius (9 degrees Fahrenheit), and these swings happen slowly, over hundreds of thousands of years.Now, with concentrations of greenhouse gases rising, Earth's remaining ice sheets (such as Greenland and Antarctica) are starting to melt too. The extra water could potentially raise sea levels significantly.As the mercury rises, the climate can change in unexpected ways. In addition to sea levels rising, weather can become more extreme. This means more intense major storms, more rain followed by longer and drier droughts (a challenge for growing crops), changes in the ranges in which plants and animals can live, and loss of water supplies that have historically come from glaciers.Scientists are already seeing some of these changes occurring more quickly than they had expected. According to the Intergovernmental Panel on Climate Change, eleven of the twelve hottest years since thermometer readings became available occurred between 1995 and 2006.