Climate Change, Global Warming, Green House Effect.pptx

Climate Change

1. Climate Change Mitigation and Adaptation

2. The main components (ignoring the normally ever-present but variable water vapor) of an unpolluted version of the Earth’s atmosphere are diatomic nitrogen , N 2 (about 78% of the molecules); diatomic oxygen , O 2 (about 21%); argon , Ar (about 1%); and carbon dioxide , CO 2 (presently about 0.04%). The troposphere, the region of the sky that extends from ground level to about 15 kilometers altitude and contains 85% of the atmosphere’s mass. The stratosphere, the portion of the atmosphere from approximately 15 to 50 kilometers altitude that lies just above the troposphere contains ozone layer. The Atmosphere

3. The electromagnetic spectrum. The ranges of greatest environmental interest are shown.

4. Filtering of Sunlight’s UV Component by Atmospheric O 2 As a result of its light-absorption characteristics, the O 2 gas that lies above the stratosphere filters from sunlight most of the UV light from 120 to 220 nm; the remainder of the light in this range is filtered by the O 2 in the stratosphere. Also, fortunately for life on the surface, ultraviolet light that has wavelengths shorter than 120 nm is filtered in and above the stratosphere by O 2 and other constituents of air such as N 2 . Thus, no UV light having wavelengths shorter than 220 nm reaches the Earth’s surface.

5. Filtering of Sunlight’s UV Component by Atmospheric O 3 Diatomic oxygen also filters some, but not all, of sunlight’s UV in the 220--240-nm range. Rather, ultraviolet light in the whole 220--320-nm range is filtered from sunlight mainly by molecules of ozone, O 3 , that are spread through the middle and lower stratosphere. Ozone, aided to some extent by O 2 at the shorter wavelengths, filters out all of the Sun’s ultraviolet light in the 220--290-nm range, which overlaps the 200---280-nm region known as UV-C. Thus, ozone is not completely effective in shielding us from light in the UV-B region, defined as that which lies from 280 to 320 nm. Because neither ozone nor any other constituent of the clean atmosphere absorbs significantly in the UV-A range, i.e., 320--400 nm, most of this, the least biologically harmful type of ultraviolet light, does penetrate to the Earth’s surface.

6. The Deleterious Effects of UV Light on Human Skin A reduction in stratospheric ozone concentration allows more UV-B light to penetrate to the Earth’s surface. A 1% decrease in overhead ozone results in a 2% increase in UV-B intensity at ground level. This increase in UV-B is the principal environmental concern about ozone depletion, since it leads to detrimental consequences to many life forms, including humans. Exposure to UV-B causes human skin to sunburn and suntan; overexposure can lead to skin cancer, the most prevalent form of cancer. Increasing amounts of UV-B may also adversely affect the human immune system and the growth of some plants and animals.

7. Air Pollution & Smog Screenshots have been shared in the group

8. The Earth’s surface and atmosphere are kept warm almost exclusively by energy from the Sun, which radiates energy as light of many types. In its radiating characteristics, the Sun behaves much like a blackbody, i.e., an object that is 100% efficient in emitting and in absorbing light. The wavelength, λ eak , in micrometers, at which the maximum emission of energy occurs by a radiating blackbody decreases inversely with increasing Kelvin temperature T according to the relationship λ peak = 2,897/ T Since for the surface of the Sun, from which the star emits light, the temperature T ~5800 K, from the equation it follows that peak is about 0.50 µm, a wavelength that lies in the visible region of the spectrum (and corresponds to green light). Indeed, the maximum observed solar output (see the dashed portion of the curve in Figure 5-1) occurs in the range of visible light, i.e., that of wavelengths between 0.40 and 0.75 µm. Beyond the “red limit,” the maximum wavelength for visible light, the Earth receives infrared light (IR) in the 0.75–4 µm region from the Sun. Of the energy received at the top of the Earth’s atmosphere from the Sun, slightly over half the total is IR and most of the remainder is visible light. At the opposite end of the visible wavelength spectrum from IR, beyond the “violet” limit, lies ultraviolet light (UV), which has wavelengths less than 0.4 µm, and is a minor component of sunlight.

9. Of the total incoming sunlight of all wavelengths that impinges upon the Earth, about 50% is absorbed at its surface by water bodies, soil, vegetation, buildings, etc. A further 20% of the incoming light is absorbed by water droplets in air (mainly in the form of clouds) and by molecular gases—the UV component by stratospheric ozone, O3, and diatomic oxygen, O2, and the IR by carbon dioxide, CO2, and especially by water vapor. A small amount of sunlight is absorbed by suspended particulates of black soot. The remaining 30% of incoming sunlight is reflected back into space by clouds, suspended particles, ice, snow, sand, and other reflecting bodies, without being absorbed. The fraction of sunlight reflected back into space by an object is called its albedo, which therefore is about 0.30 for the Earth overall. Clouds are good reflectors, with albedos ranging from 0.4 to 0.8. Snow and ice are also highly reflecting surfaces for visible light (high albedos), whereas bare soil and bodies of water are poor reflectors (low albedos). Thus, the melting of sea ice in polar regions to produce open water greatly increases the fraction of sunlight absorbed there and decreases the Earth’s overall albedo. Planting trees in snow-covered forests reduces the albedo of the surface and may actually contribute to global warming.

10. Like any warm body, the Earth emits energy; indeed, the amount of energy that the planet absorbs and the amount that it releases into space must be equal over the long term if its temperature is to remain level. (Currently the planet is absorbing slightly more than it is emitting, thereby warming the air and the oceans.) The emitted energy (see the solid portion of the curve in Figure 5-1) is neither visible nor UV light, because the Earth is not hot enough to emit light in these regions. Since the temperature of the Earth’s surface is approximately 300 K, then according to the equation above for peak, if the Earth acted like a blackbody, its wavelength of maximum emission would be about 10 m. Indeed, the Earth’s emission does peak in that general region, actually at about 13 m, and consists of infrared light having wavelengths starting at about 5 m and extending, albeit weakly, beyon 50 m (Figure 5-1, solid curve). The 5–100-m range is called the thermal infrared region since such energy is a form of heat, the same kind of heat energy a heated iron pot would radiate. Infrared light is emitted both at the Earth’s surface and by its atmosphere though in different amounts at different altitudes since the emission rate is very temperature sensitive: in general, the warmer a body, the more energy it emits per second. The rate of release of energy as light by a blackbody increases in proportion to the fourth power of its Kelvin temperature: rate of energy release = k T 4 where k is a proportionality constant. Thus, doubling its absolute temperature increases sixteenfold (24) the rate at which a body releases energy. More realistically, for contemporary surface conditions of planet Earth, a one degree rise in temperature would increase the rate of energy release by 1.3%.

11. Some gases in air absorb thermal infrared light—though only at characteristic wavelengths—and therefore the IR emitted from the Earth’s surface and atmosphere does not all escape directly to space. Very shortly after its absorption by atmospheric gases such as CO2, the IR photon may be re-emitted. Alternatively, the absorbed energy may quickly be redistributed as heat among molecules that collide with the absorber molecule, and it may be eventually re-emitted as IR by them. Whether re-emitted immediately by the initial absorber molecule or later by other ones in the area, the direction of the photon is completely random (Figure 5-3). Consequently, some of this thermal IR is redirected back toward the Earth’s surface, and is reabsorbed there or in the air above it. Indeed, the atmosphere is fairly opaque to infrared, in contrast to its near transparency to sunlight. The water droplets and vapor in clouds are also very effective in absorbing infrared light emitted from beneath them. The temperature at the tops of clouds is quite cool relative to the air beneath them, so clouds do not radiate as much energy as they absorb. Overall, air temperatures increase only enough to re-establish the planetary equality between incoming and outgoing energy.

12. The phenomenon of interception of outgoing IR by atmospheric constituents and its dissipation as heat to increase the temperature of the atmosphere is called the greenhouse effect.

13. A Very Simple Model of the Greenhouse Effect The greenhouse effect may be better understood by considering the following approximate model. Using physics, the temperature of an Earth that had no greenhouse gases in its air but was balanced with respect to incoming and outgoing energy is calculated to be 18°C, or 255 K. Since, according to the equation above, the rate of energy emission from such a planet would be k (255)4, it follows that the rate of energy input from the Sun, whether or not the Earth’s atmosphere contains greenhouse gases, is also k (255)4. Overall, the real Earth acts as if about 60% of the energy it emits as infrared light is eventually transmitted into space, the remainder being the fraction that is not only absorbed by greenhouse gases, but also reradiated downward and further heats the surface and atmosphere. Thus, the rate at which the Earth loses energy to space as IR is not simply kT 4 , but rather 0.6 kT 4 . rate of loss of energy from Earth = rate of energy input from Sun it follows for the real Earth that 0.6 kT 4 = k (255) 4 Cancelling T and taking the fourth root of both sides, we obtain an expression for the temperature: T = (255)/0.60.25 So, T = 290 K From this model, the Earth’s calculated surface temperature is 290 K, i.e., 17°C, an increase of 35 degrees by the operation of the natural greenhouse effect.

14. The current energy inputs and outputs from the Earth—in watts (i.e., joules per second) per square meter of its surface and averaged over day and night, over all latitudes and longitudes, and over all season s —are summarized in Figure 5-4. A total of 342 watts per square meter (W m -2 ) are present in sunlight outside the Earth’s atmosphere. Of this, 235 W m -2 are absorbed by the atmosphere and the surface; this much energy must be re-emitted into space if the planet is to maintain a steady temperature. Because of the presence of greenhouse gases however, emission of only 235 W m -2 from the surface would not be sufficient to ensure this balance. Because absorption of IR by greenhouse gases heats the surface and lower atmosphere however, the amount of IR released by them is increased . Given the current concentration of greenhouse gases in air, the balance is achieved and 235 W m -2 escapes from the top of the atmosphere into space if 390 W m -2 are emitted from the surface, i.e., when 155 W m -2 of IR does not escape into space. Ironically, an increase in CO 2 concentration is predicted to cause a cooling of the stratosphere. This phenomenon occurs for two reasons. First, more outgoing thermal IR is absorbed at low altitudes (the troposphere), so less is left over to be absorbed by and warm the gases in the stratosphere. Second, at stratospheric temperatures CO 2 emits more thermal IR upward to space and downward to the troposphere than it absorbs as photons—most of the absorption at these altitudes is due to water vapor and ozone—so increasing its concentration cools the stratosphere. The observed cooling of the stratosphere has been taken to be a signal that the greenhouse effect is indeed undergoing enhancement.

15. I was surprised when I learned that what sounded like a small increase in the global temperature— In climate terms, a change of just a few degrees is a big deal. During the last ice age, the average temperature was just 6 ℃ lower than it is today. During the age of the dinosaurs, when the average temperature was perhaps 4 ℃ higher than today, there were crocodiles living above the Arctic Circle. Bill Gates

16. Current Progress in Adaptation and Gaps and Challenges Adaptation planning and implementation has progressed across all sectors and regions, with documented benefits and varying effectiveness. Despite progress, adaptation gaps exist, and will continue to grow at current rates of implementation. Hard and soft limits to adaptation have been reached in some ecosystems and regions. Maladaptation is happening in some sectors and regions. Current global financial flows for adaptation are insufficient for, and constrain implementation of, adaptation options, especially in developing countries (high confidence)

17. Observed Changes and Impacts Human activities, principally through emissions of greenhouse gases, have unequivocally caused global warming, with global surface temperature reaching 1.1°C above 1850-1900 in 2011-2020. Global greenhouse gas emissions have continued to increase, with unequal historical and ongoing contributions arising from unsustainable energy use, land use and land-use change, lifestyles and patterns of consumption and production across regions, between and within countries, and among individuals (high confidence).

18. Current Mitigation Progress, Gaps and Challenges Policies and laws addressing mitigation have consistently expanded since AR5. Global GHG emissions in 2030 implied by nationally determined contributions (NDCs) announced by October 2021 make it likely that warming will exceed 1.5°C during the 21st century and make it harder to limit warming below 2°C. There are gaps between projected emissions from implemented policies and those from NDCs and finance flows fall short of the levels needed to meet climate goals across all sectors and regions. (high confidence)