Halons Contain Halogens Which Are Highly Reactive With Oxygen

No, ozone depletion is not the principal cause of global climate change. Ozone depletion and global climatic change are linked because both ozone-depleting substances and their substitutes are greenhouse gases. Ozone is also a greenhouse gas, so stratospheric ozone depletion leads to surface cooling. Conversely, increases in tropospheric ozone and other greenhouse gases atomic number 82 to surface warming. The cooling from ozone depletion is minor compared to the warming from the greenhouse gases responsible for observed global climate modify. The Antarctic ozone hole has contributed to changes in Southern Hemisphere surface climate through effects on the atmospheric circulation.

While stratospheric ozone depletion is non the principal cause of climatic change, aspects of ozone depletion and climatic change are closely linked. Both processes involve gases released to the atmosphere by human activities. The links are all-time understood past examining the contribution to climate change of the gases involved: ozone; ozone-depleting substances (or halogen source gases) and their substitutes; and other leading greenhouse gases.

Greenhouse gases and the radiative forcing of climate. The warming of World by the Sun is enhanced by the presence of greenhouse gases (GHGs). The natural abundances of GHGs in Earth’s atmosphere absorb outgoing infrared radiation, trapping estrus in the atmosphere and warming the surface. The nearly important natural GHG is h2o vapor. Without this natural greenhouse outcome, Earth’s surface would exist much colder than current weather. Man activities have led to significant increases in the atmospheric abundances of a number of long-lived and brusk-lived GHGs since 1750, the start of the Industrial Era, leading to warming of Earth’due south surface and associated climate changes. This grouping includes carbon dioxide (COii), marsh gas (CH4), nitrous oxide (N2O), tropospheric ozone, and halocarbons. Ozone-depleting substances (ODSs) and their substitutes make upwardly a large fraction of the halocarbons in today’s temper. Increases in the abundances of these gases from homo activities cause more approachable infrared radiation to be absorbed and reemitted back to the surface, further warming the atmosphere and surface. This change in Earth’s free energy balance caused by human activities is called a
radiative forcing of climate
or, more simply, a climate forcing. The magnitude of this energy imbalance is usually evaluated at the top of the troposphere (tropopause) and is expressed using units of watts per square meter (W/m2). The potential for climatic change rises as this radiative forcing increases.

A summary of radiative forcings of climate in 2011 resulting from the increases in the main long-lived and curt-lived GHGs from human activities since 1750 is shown in
Figure Q17-ane. Positive forcings generally pb to
and negative forcings pb to
of Earth’s surface. Climate forcings also lead to other changes, for example reductions in glacier and sea-ice extent, variations in precipitation patterns, and more extreme weather events. International climate assessments conclude that much of the observed surface warming and changes in other climate parameters over the final several decades are due to increases in the atmospheric abundances of CO2
and other GHGs, which consequence from a variety of man activities.

Carbon dioxide, marsh gas, and nitrous oxide. All three of these GHGs have both human and natural sources. The accumulation of CO2
since 1750 represents the largest climate forcing caused by man activities. Carbon dioxide concentrations go on to increase in the atmosphere primarily as the result of burning fossil fuels (coal, oil, and natural gas) for energy and transportation, also as from cement manufacturing. The global mean atmospheric abundance of CO2
at present exceeds 400 parts per million (ppm), which is more than 40% larger than the abundance of CO2
present in 1750. Carbon dioxide is considered a
gas, since a significant fraction remains in the atmosphere 100– 1000 years after emission.

Methyl hydride is a
climate gas (atmospheric lifetime of about 12 years). Sources related to human activities include livestock, fossil fuel extraction and use, rice agriculture, and landfills. Natural sources include wetlands, termites, and oceans. The global mean atmospheric abundance of CH4
has more than than doubled since 1750.

Nitrous oxide is a
climate gas (atmospheric lifetime of about 120 years). The largest source related to homo activities is agriculture, especially the use of fertilizer. Microbial processes in soils that are part of natural biogeochemical cycles correspond the largest natural source. In the stratosphere, nitrous oxide is the primary source of reactive nitrogen species that participate in ozone devastation cycles (see Q8). The global mean atmospheric abundance of nitrous oxide has increased by virtually 20% since 1750.

Radiative Forcing of Climate

Figure Q17-one. Radiative forcing of greenhouse gases and ozone depletion.
Human activities since the offset of the Industrial Era (around 1750) take caused increases in the atmospheric abundance of greenhouse gases (GHGs). Rise levels of GHGs lead to an increase in the radiative forcing of climate (RF) by trapping infrared radiations released by World’s surface. Hither, values of RF are for the fourth dimension period from 1750 to 2011 and are expressed in units of watts per square meter (W/grand2); black whiskers on each bar show uncertainties. Positive values of RF (shown in cherry-red) contribute to climate warming and negative values (shown in blue) contribute to climate cooling. The largest positive RFs are due to carbon dioxide (COtwo), methane (CH4), tropospheric ozone (O3), halocarbons, and nitrous oxide (N2O). Halocarbons include all ozone-depleting substances, hydrofluorocarbons, and a few other gases (see Effigy Q17-2). The RF due to ozone is shown as the separate response to changes in ozone within 2 layers of the atmosphere: the troposphere and stratosphere. Tropospheric ozone increases result from the emission of air pollutants and lead to surface warming whereas stratospheric ozone depletion results in a small forcing that most probable cools the surface.

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Halocarbons. Halocarbons in the atmosphere contribute to both ozone depletion and climate change. The halocarbons considered in Figures Q17-i and Q17-2 are gases containing chlorine, bromine, or fluorine atoms that are either controlled under the Montreal Protocol or are GHGs that fall under the auspices of the United Nations Framework Convention on Climate Change (UNFCCC). Historically, ODSs were the simply halocarbons controlled under the Montreal Protocol. In 2016, the Kigali Amendment to the Montreal Protocol established controls on the hereafter product and consumption of sure hydrofluorocarbon (HFC) substitute gases. Perfluorocarbons (PFCs) and sulfur hexafluoride (SF6) are in the UNFCCC group of GHGs that now fall nether the Paris Agreement. Perfluorocarbons are compounds that incorporate simply carbon and fluorine atoms, such as carbon tetrafluoride (CF4) and perfluoroethane (C2F6). Technically, SF6
is not a halocarbon since information technology lacks carbon. Yet, the ecology effects of SF6
are commonly examined with those of halocarbon gases since all of these compounds contain at least one halogen atom.

In 2011, the halocarbon contribution to the radiative forcing of climate was 0.36 W/m2, which is the fourth largest GHG forcing following carbon dioxide, marsh gas, and tropospheric ozone (see Figure Q17-1). The contributions of individual halocarbon gases are highlighted in
Figure Q17-2. Within the halocarbons, CFCs contribute the largest percentage (71%) to 2011 climate forcing. The intermediate-term ODS substitutes, hydrochlorofluorocarbons (HCFCs), make the next largest contribution (14%). The long-term ODS substitutes, HFCs, contribute five% and, finally, PFCs and SF6
contribute some other 3%.

Radiative Forcing of Climate past Halocarbons

Figure Q17-2. Halocarbons and radiative forcing of climate.
Halocarbon gases in the temper represent an important contribution to the radiative forcing (RF) of climate since the start of the Industrial Era (see Effigy Q17-1). Halocarbons are gases containing chlorine, bromine, or fluorine atoms, with at to the lowest degree one carbon atom, that contribute to RF by trapping infrared radiation released by Globe’southward surface. The ascent in RF between 1750 and 2011 is shown for all halocarbons controlled either under the Montreal Protocol (cherry-red) or included in the Paris Agreement (bluish) forth with the RF due to the rising in SF6. Notation that while SFsix
is technically not a halocarbon because information technology lacks any carbon atoms, it is an of import halogen-containing gas in the atmosphere. Divide contributions to RF of each gas or group of gases are indicated every bit estimated using atmospheric abundance histories and the radiative efficiency specific to each compound. The gases listed in the right-mitt labels brainstorm with the largest contribution in each grouping and proceed in descending order, except for the entry for small CFCs and halons, which are shown as one total value. The private RF terms add to form the bottom bar, representing the total RF due to halocarbons and SFsix. The RFs of CFC-11 and CFC-12, the largest halocarbon contributors, are decreasing and volition go along to decline as CFCs are gradually removed from the atmosphere (meet Figure Q15-1). In contrast, the total RF of HCFCs, the intermediate-term ODS substitute gases, is projected to grow for about another one to two decades before decreasing. HFCs are the long-term ODS substitute gases. With the Oct 2016 Kigali Amendment, the Montreal Protocol now controls time to come product and consumption of important HFCs. As a result, nearly all of the RF due to element of group vii-containing GHGs is now controlled by the Montreal Protocol (lesser bar). The future RF of climate due to HFCs is expected to peak in nigh ii decades under the provisions of the Kigali Amendment (see Q19).

The big contribution of the CFCs has been gradually decreasing following the decline in their atmospheric affluence and is expected to farther subtract (run into Figure Q15-ane). Based on their long lifetimes, CFCs volition even so make a pregnant contribution, and about likely the largest contribution from ODSs, to halocarbon climate forcing at the finish of this century. Fifty-fifty with adherence to the provisions of the Kigali Amendment to the Montreal Protocol, the radiative forcing from HFCs is projected to increment for another ii to three decades before starting to slowly decline (see Figure Q19-2).

Evaluation of Selected Ozone-Depleting Substances and Substitute Gases

Figure Q17-3. ODPs and GWPs.
The environmental impacts of ozone-depleting substances and their substitutes are usually compared based upon their Ozone Depletion Potentials (ODPs) and Global Warming Potentials (GWPs) (come across Table Q6-1). The ODPs and GWPs represent the magnitude of ozone depletion and climate forcing, respectively, of a given mass of gas emitted to the atmosphere, relative to that of Chlorofluorocarbon-eleven (for ODP) or CO2
(for GWP). Therefore, the ODP of CFC-11 and the GWP of COii
are assigned reference values of i. The GWPs shown here are evaluated for a 100-year time interval after emission. The CFCs, halons, and HCFCs are ozone-depleting substances (ODSs) since they contain either chlorine or bromine (run across Q6). HFCs, used as ODS substitutes, do not destroy ozone (ODPs equal zero) since they are mixtures of only hydrogen, fluorine, and carbon atoms. The ODPs of halons far exceed those of the CFCs, since all halons contain bromine. The GWPs of these gases bridge a wide range of values, from less than one (HFO-1234yf) to 12,690 (HFC-23).

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Stratospheric and tropospheric ozone. Ozone in both the stratosphere and the troposphere absorbs infrared radiation emitted from Globe’due south surface, trapping heat in the atmosphere. Ozone also significantly absorbs solar ultraviolet (UV) radiation. As a result, increases or decreases in stratospheric or tropospheric ozone induce a climate forcing and, therefore, represent directly links betwixt ozone and climate. Air pollution from a variety of man activities has led to increases in global tropospheric ozone (run into Q2), causing a
radiative forcing (warming) estimated to be +0.iv W/mii
over the 1750-2011 fourth dimension period, with a range of uncertainty spanning +0.2 to +0.6 Due west/thoutwo
(come across Figure Q17-1). The large doubt in the climate forcing due to release of air pollutants reflects our limited knowledge of changes in the abundance of tropospheric ozone between 1750 and the mid-1950s as well as the difficulty in modeling the complex chemical processes that control the production of tropospheric ozone.

On the other hand, rising abundances of ODSs in the atmosphere since the heart of the 20th century have led to decreases in stratospheric ozone, most likely causing a
radiative forcing of –0.05 W/one thousand2
(cooling) over the 1750-2011 fourth dimension menstruation, with a range of incertitude spanning –0.15 to +0.05 W/ m2 (see Figure Q17-1). The sign of the radiative forcing due to stratospheric ozone depletion is uncertain because this quantity is the difference between two terms of comparable magnitude, each of which has an associated doubtfulness. The first term represents the trapping past ozone of outgoing infrared radiation released past the surface and lower atmosphere: this is a cooling term because less ozone results in less trapping of estrus. The second term represents the absorption of solar UV radiation past ozone: this is a warming term considering less ozone results in greater penetration of solar UV radiations into the lower atmosphere (troposphere). The 2013 Intergovernmental Panel on Climate change (IPCC) climate assessment concluded that stratospheric ozone depletion nearly probable acquired a
slight cooling
of World’southward surface, every bit shown in Figure Q17-i. This radiative forcing due to stratospheric ozone depletion will diminish in the coming decades, every bit ODSs are gradually removed from the temper.

The 2013 IPCC climate assessment likewise evaluated the radiative furnishings due to changes in ozone induced solely by the release of ODSs and as well as changes in ozone caused but by air pollutants. They concluded that changes in atmospheric ozone over the 1750-2011 time period caused solely past the release of ODSs led to a cooling of –0.18 W/m2
with a range of uncertainty spanning –0.03 to –0.33 W/mii
and that changes in atmospheric ozone over the same time period caused only by release of air pollutants led to a warming of +0.fifty W/m2
with a range of dubiousness spanning +0.30 to +0.70 W/m2. The radiative forcings for ozone shown in Figure Q17-1 are based on estimates of the actual changes in the abundance of stratospheric ozone and tropospheric ozone, respectively. The values given in Effigy Q17-ane differ from those stated in this paragraph because some stratospheric air masses that feel loss of ozone due to human release of ODSs are transported to the troposphere, somewhat mitigating the radiative forcing of climate due to elevated amounts of tropospheric ozone acquired by air pollutants. Similarly, polluted tropospheric air inbound the stratosphere has led to changes in stratospheric composition that accept slightly commencement the turn down in ozone acquired solely by ozone-depleting substances.

Information technology is clear that stratospheric ozone depletion is non a principal crusade of present-day global warming. First, the climate forcing from ozone depletion is small and very likely acts to absurd Earth’south surface. Second, the total radiative forcing of climate from other GHGs such as carbon dioxide, marsh gas, halocarbons, and nitrous oxide is large and positive, leading to warming (see Figure Q17-1). The full forcing from these other GHGs is the principal crusade of the observed warming of Earth’s surface.

Ozone Depletion Potentials and Global Warming Potentials. A useful manner of comparing the influence of private emissions of halocarbons on ozone depletion and climate change is to compare Ozone Depletion Potentials (ODPs) and Global Warming Potentials (GWPs). The ODP and GWP are the effectiveness of an emission of a gas in causing ozone depletion and climate forcing, respectively, relative to a reference gas (encounter Table Q6-i). The main halocarbon gases are contrasted with each other in
Effigy Q17-3. The ODP of CFC-11 and the GWP of carbon dioxide are assigned reference values of 1. The CFCs and carbon tetrachloride all have ODPs most 1, indicating comparable effectiveness in causing ozone depletion per mass emitted. The chief halons have ODPs greater than vii, making them the most effective ozone-depleting substances per mass emitted. All HFCs take ODPs of zero since they incorporate no chlorine and bromine, and therefore do not directly cause ozone depletion (meet Q6).

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All halocarbons have non-zero GWPs and, therefore, contribute to the radiative forcing of climate. The GWP does not stand for strongly with the ODP of a gas considering these quantities depend on different chemical and physical properties of the molecule. For instance, while HFC-143a does not destroy ozone (ODP equals zilch), each gram emitted is almost 5000 times more than effective than a gram of carbon dioxide in causing climate forcing. When HFCs are released to the atmosphere, their contribution to climate forcing depends on their GWPs, which vary over a wide range (less than 1 to 13,000).

Montreal Protocol regulations have led to reductions in Cfc emissions and increases in HCFC emissions (see Q15). As a result of these actions, the total radiative forcing from ODSs stopped increasing and is now slowly decreasing (see Q18). Overall halocarbon radiative forcing, even so, is slowly increasing because of growing contributions from non-ODS gases (HFCs, PFCs, and SF6). The growth in the HFC contribution will be limited by the provisions of the 2016 Kigali Subpoena (see Q19). It is important to note that despite having a GWP that is modest in comparison to many other halocarbons and other greenhouse gases, carbon dioxide is the most important greenhouse gas produced by human activities considering its emissions are big, its atmospheric lifetime is long, and its atmospheric affluence is far greater than those of all other greenhouse gases associated with man activities.

The Antarctic ozone pigsty and Southern Hemisphere climate. While stratospheric ozone depletion is not the principal crusade of global climate change, the reoccurring Antarctic ozone hole has contributed to observed changes in climate parameters in the temper and oceans of the Southern Hemisphere. These inquiry findings are explained in more detail in the box below.

The Antarctic Ozone Hole and Southern Hemisphere Surface Climate

Links betwixt stratospheric ozone depletion and changes in surface climate were beginning plant in research studies in the early 2000s, based on both observations and models. While increasing greenhouse gases (such as carbon dioxide, methyl hydride, and nitrous oxide) are the chief drivers of global climate alter, the Antarctic ozone hole, which has occurred every spring since the early 1980s, was shown to contribute to observed changes in Southern Hemisphere surface climate during summertime due to its effects on atmospheric circulation.

The severe springtime depletion of ozone over the Antarctic leads to a strong cooling of the polar lower stratosphere persisting into early on summer in the Southern Hemisphere. This cooling increases the temperature dissimilarity between the tropics and the polar region and strengthens stratospheric winds. As a outcome, in the Southern Hemisphere there has been a poleward shift of tropospheric circulation features including the tropical Hadley prison cell (which determines the location of the subtropical dry zones) and the midlatitude jet stream (which is associated with weather systems). There is show from both models and observations that subtropical and midlatitude summer precipitation patterns in the Southern Hemisphere take been affected by these changes. The observed air current changes over the Antarctic ocean have also likely driven significant changes in sea currents. Model studies indicate that fifty-fifty though long-lived greenhouse gases that cause climatic change exacerbate this shift in the summertime tropospheric circulation in the Southern Hemisphere, ozone depletion has been the dominant correspondent to the observed changes over the last few decades. Paleoclimate reconstructions suggest the current state of these climate features is unprecedented over the past 600 years.

During the 21st century, as the ozone hole recovers due to the decline of stratospheric halogens, the ozone-depletion related climate impacts discussed above will lessen (see Q20). Thus, ozone recovery will outset some of the hereafter Southern Hemisphere apportionment changes driven by ascent abundances of greenhouse gases. The extent of this offset depends on the greenhouse gas emissions assumed in futurity climate projections. The Southern Hemisphere surface climate response to ozone depletion in other seasons is weaker than the summer response. No such links between ozone depletion and regional climate change have been observed for the Northern Hemisphere.

Halons Contain Halogens Which Are Highly Reactive With Oxygen

Source: https://ozone.unep.org/20-questions-and-answers

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