Climate change caused by human activity

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Climate change caused by human activity

Have the mechanisms that govern climate change been properly identified?

The mechanisms that govern climate change being known for almost two centuries, thanks to the work done by Joseph Fourier in 1824. The intensity of solar radiation (irradiance) reaching the Earth is 1.3 kW per m² on a surface perpendicular towards the sun’s rays. About one-third with this radiation is reflected back into space by the atmosphere additionally the ground, whilst the remaining two-thirds are mainly absorbed by the Earth’s landmasses and oceans. The Earth’s surface thus absorbs solar energy day after day; it can only stop heating up indefinitely if an amount of energy that is equal to the absorbed energy is released into space. This can be achieved by emitting waves of the same nature as the light waves of the sun, but which have a longer wavelength given the lower temperature of the Earth’s surface. These waves correspond to the color infrared, and are invisible towards the human eye. This infrared radiation has to first pass through the atmosphere, where the greater the quantity of absorbing gases, the ratio of energy emitted from the Earth’s surface to energy released into space. The clear presence of such gases therefore tends to increase the temperature of the Earth. These gases are said to produce a greenhouse effect by analogy with one of many phenomena that occur in gardeners’ greenhouses.

The Earth’s atmosphere contains naturally occurring water vapor and carbon dioxide gas (CO2), both of which are greenhouse gases. Without their presence, the ground temperature is around 30 degrees not as much as what it actually is. It really is thus the greenhouse effect that includes made life possible. Other planets are governed by the same laws of physics. This is why the dense atmosphere of Venus, made up essentially of CO2, results in a very significant greenhouse effect and temperatures of 450°C.

Figure 1: Diagram of the energy balance at the surface of the Earth. The greenhouse effect can be as follows: a fraction of the infrared radiation passes through the atmosphere, but most of it is absorbed and reemitted in all directions by greenhouse gas molecules and clouds. This results in the warming of the Earth’s surface additionally the lower layers of the atmosphere.(Source for this picture and the following ones : Intergovernmental Panel on Climate Change,

Does the climate evolve naturally?

The position of the continents additionally the composition of the atmosphere have evolved significantly within the geological ages. The Earth’s climate has thus inevitably been greatly afflicted with these major changes. More recently, throughout the last million years, the climate is rolling out in a fairly well-known way. This has occurred under the influence of natural causes that have always existed and that will continue to are likely involved in the next several millennia.

– Firstly, the orbit of the Earth round the sun undergoes variations because of the attraction of the moon additionally the other planets. These variations occur slowly over intervals which can be measured in tens of thousands of years. They result in changes in the angles at which the sun’s rays strike our planet and are at the origin of the large glacial and interglacial cycles with amplitudes of around 6°C for a period of 100,000 years. We have been now 10,000 years into an interglacial and thus warm period.

– the sun’s rays is itself subject to variability, as revealed by the presence of sunspots that vary over a period of 11 years. Nonetheless, this 11-year sunspot cycle affects the solar radiation mainly into the ultraviolet range. It thus has an impact on the behavior of the highest layers of the Earth’s atmosphere: the ionosphere (altitudes of 100 km and above) and, to a lesser extent, the stratosphere (altitudes of approximately 30 km, start to see the ozone page). It has a very slight effect on the total energy radiated and although its influence on climatic phenomena was detected, it is very small.

– Another factor that affects the outer lining temperature of the Earth is volcanic activity. During powerful volcanic eruptions, volcanic dust reaches the stratosphere (above 15 km) that will remain truth be told there for starters or two years before falling back to the ground. These particles, essentially made up of sulfur oxides, act as a screen towards the incident solar flux (radiation), which has a cooling effect on the outer lining for a year or two.

Can human activity modify climate?

Since the beginning of the manufacturing era, real human activities have added new resources of variation to the above natural causes, which result in atmospheric change.

Systematic observation of the atmosphere has indisputably shown an increase—for a little over a century—in the level of greenhouse gases such as CO2, methane, and nitrous oxide.

Figure 2: the existing concentrations of the main greenhouse gases and their rate of increase are unprecedented. Origin: EPA (Updated in 2016)

Looking at the important of them, CO2, we can see that how many CO2 molecules found in one million molecules of air has risen from 280 in 1850—before the manufacturing era—to over 380 today. Here, we reference 280 or 380 parts per million, or ppm. The annual increase in the concentration of CO2 is about 50 % of what it will be if the atmosphere had retained all the CO2 that humanity created by burning coal, oil, and natural gas. The other half is absorbed by the oceans and the biosphere. Additionally, we can also observe a very small decrease, in relative value, of the concentration of oxygen—oxygen that is necessary to produce additional CO2 that is taken from the atmosphere. Finally, measurements of isotopic composition of atmospheric carbon complete the body of arguments that enable us to attribute, without the doubt, the changes in atmospheric CO2 concentrations to real human activities.

Have we recently observed change in climate?

We’ve in fact observed an increase in the average temperature of the Earth of an estimated 0.8°C (plus or minus 0.2°C), for a little over a century. The average global temperature is not directly measurable and can only be expected by compiling all the limited observations of local temperatures available around the world. This estimation is a parameter whose changes reflect, in summarized form, the general trend of temperature variations observed within the whole Earth. Several other indicators, apart from global temperatures, also confirm global warming: the melting of glaciers in all the continents and at all latitudes, the decrease in the snow cover in the Northern Hemisphere; the rise in sea level (3 mm per year), due in part towards the thermal expansion of water additionally the addition of water towards the oceans from the melting of continental ice sheets; and changes in the physical and biological systems consistent with local increases in temperature.

This warming just isn’t uniformly distributed. Oceans, by their very nature, heat up less than land because of their well-known regulatory effect on temperatures. Continents are thus warmer compared to the average earth temperature. Also, it is observed that the rise in temperatures is especially significant into the northernmost elements of America, Europe, and Asia.

Precipitation is also afflicted with climate change with some regions getting more rain among others less.

We sometimes come across the following statement: ‘Temperature has stopped rising since the beginning of the century.’ In fact, the unpredictable variations from twelve months to another location do not allow any conclusions becoming drawn based on a few years of study alone. Only the averages spread over several decades provide any real insight. The most recent study regarding the evolution of temperature, published in January 2010 by the U.S. National Aeronautics and Space Administration (NASA), concludes that the final decade was the hottest ever recorded; in terms of individual years, last year (2009) came in third destination, after 2005 and 1998.

What is mathematical modeling of the climate?

Climatic models numerically simulate well-known physical processes that govern the dynamics and thermodynamics of the oceans additionally the atmosphere as well as the energy exchanges between infrared radiation and the molecules of certain gases (Laboratory experiments and quantum mechanics have enabled the precise determination of the corresponding absorption spectra.) Computers are indispensable tools for describing these complex phenomena that obey non-linear equations in a non-homogenous milieu that is stratified vertically and is horizontally variable. At the same time, their use might be seen as a potential source of doubt. Nonetheless, computers are not responsible for the success or failure of a mathematical model. What matters is good knowledge of the phenomena this 1 proposes to replicate numerically. The results of climate modeling are nevertheless afflicted with uncertainties, mostly related to the practical impossibility of simulating phenomena spread over small spatial scales (below 100 km), in realistic computing intervals. One has to therefore introduce parameters that describe them empirically. The uncertainty of results is evaluated by researching the outputs of models for different possible parameterizations. It really is in this way that the increase in average global temperatures caused by way of a doubling of greenhouse gas concentrations was expected to be in the range of 1.5°C to 4.5°C. The credibility of climatic models is based on their ability to recreate large geographical structures and past climatic developments.

Models have sometimes been criticized for neglecting the role of water vapor, considered essential. This criticism is very unfounded. It is true that water vapor is the most effective greenhouse gas present in the atmosphere. Nonetheless, the introduction of water vapor into the atmosphere has no lasting effect on its concentration into the atmosphere, insofar as its atmospheric lifetime is only one or two weeks. This injection therefore does not modify climate. Yet, the atmospheric lifetime of CO2 is multiple century as well as its concentration is altered permanently by human waste, which has the capacity to result in a change in the climate. Even though water vapor might not be directly responsible for climate change, it nevertheless plays a part. The increase in temperature causes an increase in the concentration of water vapor into the atmosphere. This in turn causes a complementary warming and thereby creates a feedback loop with an amplifier effect, which is taken into account by models. This increase in atmospheric water vapor has in fact been observed throughout the last twenty years.

Do mathematical models replicate recent observations?

Thanks to mathematical climate simulation models, it is possible to assess whether or not the warming that is actually observed is quantitatively consistent with the models’ results. When these models take into account the totality of known phenomena—of either natural or human origin—their results match up satisfactorily with observations. This holds true when dealing with average global temperatures, average land temperatures, or average ocean temperatures. Even though the potential for error increases when you focus on more localized regions, the agreement remains significant for individual continents.

Nonetheless, the discrepancy involving the observations additionally the modeling results is glaring when models deliberately ignore changes in the concentration of greenhouse gases. Put simply, natural phenomena usually do not explain the recent observations.

In particular, variations of total solar radiation, observed by satellite, are insufficient to explain the perceived warming into the absence of an amplification phenomenon that includes yet becoming specified. Objections towards the thesis of a preponderant role for the sun are threefold. Firstly, the greenhouse effect related to the change in atmospheric composition is enough to quantitatively explain the climatic observations; if the sun experienced a greater impact, it would cause more warming than it actually does. Secondly, the 11-year sun cycle is more important compared to the variations that occur over several decades and should therefore translate into a periodicity marked by 11 years in climate variations. Finally, the rise observed in temperature decreases with altitude and in actual fact begins to decrease at the degree of the stratosphere. This variation in altitude cannot be explained by way of a variation in solar radiation. Yet, it really is predicted by the models that simulate the modification of the transfer of radiation caused by an increase in gases absorbing infrared radiation.

Can we estimate the climate changes that will take place during the course of the 21st Century?

Only mathematical models simulating real phenomena allow an estimation of the potential effect of anthropic emissions on global climate into the decades to come. They therefore have to be based on assumptions about the evolution of those emissions. Greenhouse gas emissions depend on human elements which can be by nature unpredictable, such as for example demography, rate of economic development, the nature of exchanges, behavior, etc. We have been therefore led to develop scenarios which can be likely to occur within the realm of the possible.

What will the evolution of the climate be in the absence of pro-active policies?

The first family of scenarios that was used is based on the absence of pro-active measures taken to reduce the magnitude of climate change. Present trends show a rapid increase in emissions—especially in terms of CO2—given that 80% of the commercialized energy comes from fossil fuel. We have been therefore led to believe that CO2 concentrations will reach 1,000 ppm in 2100, which represents more than 3.5 times the pre-industrial concentrations.

The expected concentrations of CO2 during the 21st century are two to four times those of the pre-industrial era.

The inherent uncertainty associated with models adds to the difficulty of choosing the correct scenario for the evolution of emissions. The result is an increase in global temperatures in 2100 ranging from 1 to 6°C. These numerical values can take place becoming small when compared to variations observed on a daily basis. To measure the extent of those changes, we need to remember that these are global averages and that the Earth’s temperature—even in the last glacial period when 3 km of ice covered northern Europe—differed from present-day average temperatures by only 6°C.

Average temperature is clearly not enough to characterize climate. This is exactly why important geographical variations are simulated. The increase in continental temperature is double the average and triple the average of northern regions.

Additionally, precipitation is affected. All models simulate an increase in precipitation in northern Europe and a decrease in areas surrounding the Mediterranean, especially in summer for both regions.

Can we start thinking about limiting emissions to reduce the extent of climate change?

Reducing emissions to put a ceiling on greenhouse gases into the atmosphere and restricting the extent of climate change is an objective that is explicitly mentioned in Article 2 of this United Nations Framework Convention on Climate Change, signed at the Earth Summit in Rio de Janeiro, Brazil in 1992. The Convention—prepared by 28 heads of state and taken cognizance of at the Copenhagen summit in December 2009—specified this objective more plainly by giving a value of 2°C as the maximum permissible rise in average global temperature. The declaration does not, however, involve any concrete commitment on limiting emissions that would make this result achievable.

The latest report of the Intergovernmental Panel on Climate Change (IPCC) has provided the range of average global temperatures that the planet could reach for a maximum CO2 equivalent concentration ranging from 450 to 1,000 ppm. This idea of CO2 equivalent concentration involves expressing the average warming potential of all greenhouse gases during the years to come in terms of the change in concentration of CO2 ( the main greenhouse gas) alone that would result in the same warming. It’s important to specify how many years considered, since all gases would not have the same life. Conventionally, into the absence of any other indication, time frame of 100 years was fixed.

For a concentration of 450 ppm equivalent ( close to the current values with A co2 concentration alone of more than 380 ppm), the rise in temperature would be 1.5°C to 3°C and for 1000 ppm 4°C to 8°C. To limit this concentration to around 500 ppm equivalent, it will be necessary to halve the total global emissions from now to 2050. Since French emissions per inhabitant are double the world average, these emissions would have to be divided by way of a factor of four—if we admit that each inhabitant of the planet has the right to emit the same quantity of CO2 equivalent.

Reducing emissions in such vast proportions is a formidable challenge specially since 80% of commercialized global energy comes from fossil fuels. The various approaches to scale back emissions involve, first of all, a reduction in the number of energy required for a given service. This means, for example, better thermal insulation of buildings or an improvement into the efficiency of motors and processes. a second possibility involves the production of energy with little or no greenhouse gas emissions. A good way of attaining this objective is through skin tightening and capture and storage. This involves recovering the gases emitted by the combustion of coal, oil, or natural gas—when how big the facility allows it—and preventing their release into the atmosphere by storing them in suitable underground structures. Another way is to rely upon the production of energy that does not release greenhouse gases such as for example hydroelectricity, nuclear energy (fission and fusion), and renewable energies.

Will the global depletion of fossil fuels be enough to prevent a climatic upheaval?

This is a fact that underground resources are finite. Estimates concerning oil and natural gas lead towards the conclusion that these two fossil fuels should start becoming very scarce in a few decades. Coal, on the other hand, is more abundant and will probably not be exhausted before the next two or three centuries. Since coal produces more CO2 per unit of energy than oil or natural gas, the exploitation of all coal deposits would lead to a variation in atmospheric composition. This might result in a climate change that is greater than that which separates glacial periods (during the last of which northern Europe was covered with a 3 km-thick ice layer additionally the sea level was 120 m not as much as it really is today). While it is true that global warming caused by anthropogenic emissions would make us move even further away than the glacial era, this comparison with natural climatic cycles allows us to imagine the extent to which the climate would change. We can particularly fear a rise in sea level of several meters, resulting in dramatic consequences.

Nonetheless, in a few centuries, when all fossil fuels will likely be exhausted and will no longer be able to supply us with cheap resources of energy, we will need certainly to learn to do without them in a situation of stress. Learning gradually to live without them from now on will allow us to prevent an energy crisis in a few decades. It will also save yourself us from the disadvantages of a brutal change in the very climate that made our development possible.

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