Greenhouse effect and greenhouse gases pdf

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greenhouse effect and greenhouse gases pdf

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It is caused by greenhouse gases in the atmosphere Table G6. The natural greenhouse effect is currently being enhanced through human activity via the release of additional greenhouse gases into the atmosphere. The consensus of the scientific community, voiced through reports written by the Intergovernmental Panel on Climate Change IPCC , is that this enhancement of the natural greenhouse effect has caused global warming over the last years and that this warming is very likely to accelerate in the future.

The enhanced greenhouse effect (Global warming)

Not a MyNAP member yet? Register for a free account to start saving and receiving special member only perks. In simplest terms, "greenhouse gases" let sunlight through to the earth's surface while trapping "outbound" radiation.

This alters the radiative balance of the earth see Figure A. The greenhouse gases in the atmosphere act in much the same way as the glass panels of a greenhouse, which allow sunlight through and trap heat inside.

The panel refers to warming due to increased atmospheric concentrations of greenhouse gases as "greenhouse warming. The solar radiation is set at percent; all other values are in relation to it.

About 25 percent of incident solar radiation is reflected back into space by the atmosphere, about 25 percent is absorbed by gases in the atmosphere, and about 5 percent is reflected into space from the earth's surface, leaving 45 percent to be absorbed by the oceans, land, and biotic material white arrows.

Evaporation and mechanical heat transfer inject energy into the atmosphere equal to about 29 percent of incident radiation grey arrow. Radiative energy emissions from the earth's surface and from the atmosphere straight black arrows are determined by the temperatures of the earth's surface and the atmosphere, respectively. Upward energy radiation from the earth's surface is about percent of incident solar radiation.

Atmospheric gases absorb part 25 percent of the solar radiation penetrating the top of the atmosphere and all of the mechanical heat transferred from the earth's surface and the outbound radiation from the earth's surface. The downward radiation from the atmosphere is about 88 percent and outgoing radiation about 70 percent of incident solar radiation. Note that the amounts of outgoing and incoming radiation balance at the top of the atmosphere, at percent of incoming solar radiation which is balanced by 5 percent reflected from the surface, 25 percent reflected from the top of the atmosphere, and 70 percent outgoing radiation , and at the earth's surface, at percent 45 percent absorbed solar radiation plus 88 percent downward radiation from the atmosphere balanced by 29 percent evaporation and mechanical heat transfer and percent upward radiation.

Energy transfers into and away from the atmosphere also balance, at the atmosphere line, at percent of incident solar radiation 75 percent transmitted solar radiation plus 29 percent mechanical transfer from the surface plus percent upward radiation balanced by 50 percent of incoming solar continuing to the earth's surface, 70 percent outgoing radiation, and 88 percent downward radiation.

These different energy transfers are due to the heat-trapping effects of the greenhouse gases in the atmosphere, the reemission of energy absorbed by these gases, and the cycling of energy through the various components in the diagram. This diagram pertains to a period during which the climate is steady or unchanging ; that is, there is no net change in heat transfers into earth's surface, no net change in heat transfers into the atmosphere, and no net radiation change into the atmosphere-earth system from beyond the atmosphere.

Atmospheric CO 2 is increasing at about 0. The concentration of CH 4 is about 1. It is rising at a rate of 0. CFCs do not occur naturally, and so they were not found in the atmosphere until production began a few decades ago. Continued increases in atmospheric concentrations of greenhouse gases would affect the earth's radiative balance and could cause a large amount of additional greenhouse warming. Increasing the capture of energy in this fashion is also called "radiative forcing.

Best estimates are that the average global temperature rose between 0. However, it is not possible to say with a high degree of confidence whether this is due to increased atmospheric concentrations of greenhouse gases or to other natural or human causes. What about CO 2 and temperature in the prehistoric past?

According to best estimates based on analysis of air bubbles trapped in ice sheets, ocean and lake sediments, and other records from the geologic past, there have been three especially "warm" periods in the last 4 million years. The Holocene optimum occurred from 6, to 5, years ago.

The Eemian interglacial period happened with its midpoint about , years ago. The Pliocene climate optimum occurred between 4. The prehistoric temperature estimates are from evidence dependent. The estimate for the Pliocene period is especially controversial. These concepts can be illustrated by referring to what is called the "carbon cycle. The movement of CO 2 among these sinks is not well understood. About 45 percent of the total emissions of CO 2 from human activity since preindustrial times is missing in the current accounting of CO 2 in the atmosphere, oceans, soil, and biomass.

Three possible sinks for this missing CO 2 have been suggested. First, more CO 2 may have been absorbed into the oceans than was thought. Second, the storage of CO 2 in terrestrial plant life may be greater than estimated. Third, more CO 2 may have been absorbed directly into soil than is thought. However, there is no direct evidence for any of these explanations accounting for all the missing CO 2. CO 2 in the atmosphere is relatively "long-lived" in that it does not easily break down into its constituent parts.

CH 4 , by contrast, decomposes in the atmosphere in about 10 years. The greenhouse gas with the longest atmospheric lifetime except for CO 2 , CFC, has an average atmospheric lifetime of about years. The overall contribution of greenhouse gases to global warming depends on their atmospheric lifetime as well as their ability to trap radiation.

Table A. Each gas has different radiative properties, atmospheric chemistry, typical atmospheric lifetime, and atmospheric concentration. For example, CFC is roughly 15, times more efficient molecule for molecule at trapping heat than CO 2. Because CFC is a large, heavy molecule with many atoms and a. Current rate of annual atmospheric accumulation b. Estimates of human-induced emissions from the biosphere are controversial.

This time scale also characterizes the rate of adjustment of the atmospheric concentrations if the emission rates are changed abruptly. CO 2 is a special case because it is merely circulated among various reservoirs atmosphere, ocean, biota. The "lifetime" of CO 2 given in the table is a rough indication of the time it would take for the CO 2 concentration to adjust to changes in the emissions.

Houghton, G. Jenkins, and J. Ephraums, eds. New York: Cambridge University Press. Reprinted by permission of Cambridge University Press. Each ton of CFC emissions is about 5, times more efficient at trapping heat than each ton of CO 2. The comparatively greater amount of CO 2 in the atmosphere, however, means that it accounts for roughly half of the radiative forcing associated with the greenhouse effect.

Figure A. The potential increase for each. Emission changes are assumed to be linear from levels to the level selected. The vertical axis shows the change in radiative forcing in watts per square meter at the earth's surface in Each asterisk indicates the projected emissions of that gas assuming no additional regulatory policies, based on the Intergovernmental Panel on Climate Change estimates and the original restrictions agreed to under the Montreal Protocol, which limits emissions of CFCs.

Chemical interactions among greenhouse gas species are not included. For CO 2 emissions remaining at levels through , the resulting change in radiative forcing can be determined in two steps: 1 Find the point on thecurvelabeled "CO 2 " that is vertically above 0 percent change on the bottom scale.

These steps must be repeated for each gas. For example, the radiative forcing for continued level emissions of CH 4 through would be about 0. The figure shows the impact of different percentage changes in emissions compared to emission rates on the radiative forcing.

One example of a greenhouse warming feedback mechanism involves water vapor. As air warms, each cubic meter of air can hold more water vapor. Since water vapor is a greenhouse gas, this increased concentration of water vapor further enhances greenhouse warming.

In turn, the warmer air can hold more water, and so on. This is an example of a positive feedback, providing a physical mechanism for "multiplying" the original impetus for change beyond its initial force. Some mechanisms provide a negative feedback, which decreases the initial impetus. For example, increasing the amount of water vapor in the air may lead to forming more clouds. Low-level, white clouds reflect sunlight, thereby preventing sunlight from reaching the earth and warming the surface.

Increasing the geographical coverage of low-level clouds would reduce greenhouse warming, whereas increasing the amount of high, convective clouds could enhance greenhouse warming. This is because high, convective clouds absorb energy from below at higher temperatures than they radiate energy into space from their tops, thereby effectively trapping energy. Satellite measurements indicate that clouds currently have a slightly negative effect on current planetary temperature.

It is not known whether increased temperatures would lead to more low-level clouds or more high, convective clouds. Can the temperature record be used to show whether or not greenhouse warming is occurring? The estimated warming of between 0. It cannot be proven to a high degree of confidence that this warming is the result of the increased atmospheric concentrations of greenhouse gases. There may be an underlying increase or decrease in average temperature from other, as yet undetected, causes.

General circulation models GCMs are the principal tools for projecting climatic changes. GCMs project equilibrium temperature increases between 1. The midpoint of this range corresponds to an average global climate warmer than. An incremental change in radiative forcing between and due to emissions of greenhouse gases implies a change in global average equilibrium temperature see text. The scales on the right-hand side show two ranges of global average temperature responses. These scales indicate the equilibrium commitment to future warming caused by emissions from through Assumptions are as in Figure A.

To determine equilibrium warming in due to continued emissions of CO 2 at the level, find the point on the curve labeled "CO 2 " that is vertically above 0 percent change on the bottom scale. The equilibrium warming on the right-hand scales is about 0. For CH 4 emissions continuing at levels through , the equilibrium warming would be about 0. Total warming associated with level emissions of the gases shown until would be about 0.

Scenarios of changes in committed future warming accompanying different greenhouse gas emission rates can be constructed by repeating this process for given emission rates and adding up the results. The consequences of this amount of warming are unknown and may include extremely unpleasant surprises.

Effects of Greenhouse Gas Emissions on World Agriculture, Food Consumption, and Economic Welfare

Human action is causing an increase in global temperature. For that reason, the greenhouse effect, far from being our great ally as was the case in the past, is now a risk to our survival. The flooding of coastal cities, the desertification of fertile areas, the melting of glacial masses and the proliferation of devastating hurricanes are just some of the main consequences. Global warming is having a profound impact on the processes of soil degradation and is contributing to the desertification of the most arid areas on the planet. The increase in the global temperature of the planet produces a rise in the level of the sea, which will cause the disappearance of islands and coastal cities.

The effect is natural and not new. When sunlight hits the surface of the earth it is absorbed and the visible light short wave radiation is converted to heat infrared or long wave radiation Fig. Figure 1. Some gases in the atmosphere the so called greenhouse gases: such as carbon dioxide, water vapour, methane, etc. Eventually these molecules then emit heat back into the atmosphere as infrared radiation. Figure 2.

Not a MyNAP member yet? Register for a free account to start saving and receiving special member only perks. In simplest terms, "greenhouse gases" let sunlight through to the earth's surface while trapping "outbound" radiation. This alters the radiative balance of the earth see Figure A. The greenhouse gases in the atmosphere act in much the same way as the glass panels of a greenhouse, which allow sunlight through and trap heat inside.

changes due to anthropogenic greenhouse gases emission. Evaluating the temperature distribution in atmosphere. The adiabatic theory of greenhouse effect.


Of those gases, known as greenhouse gases , water vapour has the largest effect. The origins of the term greenhouse effect are unclear. Fourier, however, neither used the term greenhouse effect nor credited atmospheric gases with keeping Earth warm.

Because of many uncertainties, quantitative estimates of agriculturally related economic impacts of greenhouse gas emissions are often given low confidence. A major source of uncertainty is our inability to accurately project future changes in economic activity, emissions, and climate. This paper focuses on two issues. First, to what extent do variable projections of climate generate uncertainty in agriculturally related economic impacts? Second, to what extent do agriculturally related economic impacts of greenhouse gas emissions depend on economic conditions at the time of impacts?

Geneva, 23 November WMO - The industrial slowdown due to the COVID pandemic has not curbed record levels of greenhouse gases which are trapping heat in the atmosphere, increasing temperatures and driving more extreme weather, ice melt, sea-level rise and ocean acidification, according to the World Meteorological Organization WMO. The lockdown has cut emissions of many pollutants and greenhouse gases such as carbon dioxide. But any impact on CO2 concentrations - the result of cumulative past and current emissions - is in fact no bigger than the normal year to year fluctuations in the carbon cycle and the high natural variability in carbon sinks like vegetation. Carbon dioxide levels saw another growth spurt in and the annual global average breached the significant threshold of parts per million, according to the WMO Greenhouse Gas Bulletin.

Greenhouse Gases Factsheet

Synthetic greenhouse gases are man made chemicals. They are commonly used in refrigeration and air conditioning, fire extinguishing, foam production and in medical aerosols. When they are released, synthetic greenhouse gases trap heat in the atmosphere. Greenhouse gases are naturally occurring.

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