Various evidence from observatories and satellites data display climate global warming trend. Since the mid-twentieth century, anthropogenic activity prompts temperature and water vapor increase, ozone reduction, enhancement of greenhouse gases (GHGs) and aerosols emission in the atmosphere, and positive climate feedback. This essay examines the reasons why global warming is occurring and discusses current mitigation strategies and potential solutions.
Most of climate changes have taken place during past centuries or even decades. It becomes the crucial evidence that not only natural forces but rather human-induced activity prompts warming effect. The Intergovernmental Panel on Climate Change (IPCC) report argues that with the 90% probability the pollution of heat-trapping gases caused by human activities has caused most of global average temperatures rises since the mid-twentieth century. The deforestation process, fossil fuel oxidation and other anthropogenic activities sharply increased the concentration of CO2, methane, nitrous oxide, and other GHGs around 1950 and again after 2000. Although the ocean and terrestrial biosphere absorb over half of anthropogenic emissions of the carbon dioxide, the other half remains in the atmosphere. Additionally, Earth Models of Intermediate Complexity shows a net positive reinforcing carbon cycle feedback, which might accelerate increasing of atmospheric CO2 by concentration by 20-30% till 2100 (Eby, Zickfeld, Montenegro, Archer, Meissner, and Weaver, 2009). Water vapor strengthens the greenhouse effect with an amplifying impact of other greenhouse gases. Climate models that simulate human-induced climate change show a sharp increase in globally averaged water vapor in recent decades.
Since 1978, solar irradiance output has not grown. Therefore, one cannot attribute the climate change to increase in solar activity during the past thirty years. Climate models that investigate the Sun’s and volcano activity as factors of climate alterations show that cannot reproduce such fast warming.
In recent decades, the tropopause has raised upward the cooler altitudes. The stratosphere cools rising gases, but heat-trapping aerosols and gases accumulated in tropopause conversely block heat from getting into there. It could not be possible if the sun was the only climate force, as a variation of solar activity would have warmed both the stratosphere and the troposphere (Peter, Tett, Jones, Allen, Mitchell, & Jenkins, 2000).
Moreover, IPCC and coupled ocean-atmosphere general circulation models reported that natural climate forces such as volcanic eruptions, heat-trapping gases in the atmosphere and sun intensity alterations cannot prompt the observed warming solely. With included human-induced climate impacts, models accurately embrace recent temperature rise in the oceans and atmosphere. In a comparison to natural, human-induced climate drivers through anthropogenic emissions of carbon are considerably larger climate warming forces during the past half century.
When the models compare all the natural and human-induced climate drivers, the carbon from anthropogenic emissions is considered the largest climate change factor over the past fifty years.
Here one can exemplify three lines of evidence regarding significant climate warming on the Earth’s surface and atmosphere. The first is atmospheric composition change. The Kyoto Protocol reported increasing atmospheric overload with the well-mixed greenhouse gases by 9% from 2005 to 2011. In 2011, the excess of CO2 acquired 390.5 ppm and nitrous oxide amounted 324.2 ppb. Consequently, since 1750 their portion has risen by 40% and 20% respectively. As well in 2011, methane reached 1803.2 ppb and this was 150% greater than in 1750. Montreal Protocol on Substances That Deplete the Ozone Layer also represented continuing increase of ozone exhausting gases, namely of HCFC (hydrochlorofluorocarbon). It is clear that global ozone layer has weakened about 3.5% below the 1964–1980 level; however, it remains almost constant now. There is 66–100% certainty that since 2000 ozone in eastern North America and Western Europe started to decline after short increasing trend. And since the 1990s the ozone precursor gas NO(mono-nitrogen oxides) has lowered by 30 to 50% in the same regions.
The second line of evidence refers to the temperature change. The Earth’s surface temperature has risen since the late nineteenth century. The overall increases show a warming of about 0.85°C during 1880–2012 and about 0.72°C during 1951–2012. The temperature has risen over last thirty years more than all throughout the prior decades. Furthermore, the first decade of the twenty-first century was the warmest. The station and satellite data brought strong arguments that sea, land surface and air temperatures have increased. Moreover, since 1950 the global diurnal temperature range shows rise in maximum and minimum average temperatures with the 50% level of confidence. Since 1950, the numbers of cold nights and days with the 90-100% likelihood have decreased and the numbers of warm nights and days has increased globally. And with 66-100% of confidence the heat wave frequency has risen during this period in large parts of Eurasia and Australia.
Third evidence concerns the hydrological cycle. After 1951, the precipitation level raised over the mid-latitude land areas of the Northern Hemisphere. Since the 1970s, the global near surface and tropospheric air specific humidity has also increased with the 66-90% certainty. However, during recent years, the near surface humidification over land has lowered. With the 90–100% likelihood, the frequency or intensity of heavy precipitation has grown in central North America and Europe since about 1950. From the other side, the AR4 (IPCC Fourth Assessment Report) updated studies indicated an increase in frequency and intensity of drought in the Mediterranean region and West Africa. Conversely, the drought rate reduction in central North America and north-west Australia since 1950 was noted (Hartmann et al., 2013).
Following the carbon sequestration with relevance to the Kyoto Protocol is assessed as a strategy aimed at reducing industrialized nations’ fossil fuel emission by 5% below the 1990 level. As an example, according to the Protocol, the US was required to lessen its emissions by 7%. However, the US emissions of CO2 have increased by 18% since 1990 making decrease unattainable. After 2001 Kyoto Protocol revision, the US headed for increasing of carbon stored and sank through land use changes and soil management within a strong conservation title in the Farm Bill (14 February 2002). Recommended management practices, which encompass aggregation, humification, translocation of soil carbon sequestration, and formation of secondary carbonates enhance the retention of recalcitrant soil organic carbon (SOC) fractions. The RM practice restores degraded soils, cleans ground and surface waters, and diminishes the rate of atmospheric carbon emissions of fossil fuel. The global benefit of its sequestration ranges from 50 to 1000 kg/ha per year and during 25-50 years this process can cumulate 30-60 Pg of soil carbon (Lal, 2004). It is also important to identify and implement policy instruments that facilitate realization of these practices. Clean Development Mechanism, emission trading, or associated implementation activities of the Kyoto Protocol may further the soil carbon sequestration.
Following the use of carbon taxes and permits is considered as the economically-effective strategy in achieving emissions mitigation with regard to Annex B countries. Although price elasticity of demand and supply remains uncertain, a carbon tax provides a greater certainty about the plausible costs of complying with the emission reduction. However, it has some drawbacks. Namely, concerning the distributive impacts of carbon taxes, in developing countries they are generally evaluated to be regressive. The reason for this lies in the critical role of a relation of the carbon taxes to the international price of permits. Results of the empirical studies show that countries with lower tax rates in comparison to the permit price receive substantial tax revenues. Conversely, the use of higher permits price instead of tax payments improves efficiency, but it puts the governments at risk of decrease in revenues. High revenues from carbon taxes also might restrict the degree to which permits can be implemented to protect these revenues. As a result, Annex B countries should better orient on compliance requirements of the Kyoto Protocol. Excess emissions tax must be used as a penalty for uncovered emissions. This domestic compliance mechanism acts as an effective deterrent for non-compliance (Zhang, Baranzini, 2004).
Based on developed countries experience, Annex B and developing countries are recommended to complement an implementation of carbon taxes with a general reform of the fiscal system, in particular, the three following aspects. Firstly, remove energy subsidies which are still widespread in many countries. Secondly, eliminate provisions that may increase environmentally damaging activities such as reductions or release from value added tax for energy using. Thirdly, recycle the carbon tax revenues to the economy and citizens by decreasing other taxes, for example, on personal and corporate income, and/or social changes. It results in economic dividends in terms of increased employment and economic growth, in addition to emissions reductions (Baranzini, Goldemberg, & Speck, 2000). Finally, it is necessary to establish real or implicit carbon prices of 20 to 50 US$/tCO2-eq. It could help to lower GHG emissions by 2050 and make many mitigation opportunities in the end-use sectors economically.
The objective climate quality data indicates the significant alterations in the surface and atmosphere with regard to warming. The changes are considerable and they take place during last centuries or even decades. Intensive usage of fossil fuels, deforestation, fossil fuel oxidation and other human activity sharply increased the concentration of CO2, methane, nitrous oxide, and other heat-trapping greenhouse gases around 1950 and again after 2000. Thereby, it appears as the main evidence that human-induced activity prompts warming effect. Changes in the atmospheric composition, temperature and hydrological cycle are the main proofs of a global warming. The sequestration of soil carbon and carbon taxes have a global potential to reduce fossil carbon emission, and these mitigation strategies are economically cost-effective. Proposed changes in domestic fiscal policy concerning modifications in taxes on energy use, carbon tax revenues, and international carbon prices may have an impact on economic growth and emissions reductions reciprocally.