Essay on Global Warming and Climate Change | Geography

The atmosphere absorbs part of the solar beam while reflecting rest back into space. The capacity to absorb solar energy by the atmospheric gases determines the average temperature of the atmosphere. Some of the gases, such as carbon dioxide can absorb infrared or heat energy portion of solar beam and by this process can increase the atmospheric temperature. Although present in small quantity, the variation in the amount of carbon dioxide can cause differences in the atmospheric temperature.

Scientist throughout the last two centuries found enough evidence that some of the gases in our atmosphere allow sunlight but absorb the solar heat. Eight decades ago, it was George S. Callendar, who attributed the rise in global temperature due to carbon dioxide formed by burning of fossil fuels.

However, several decades afterwards, it was Charles David Keeling who finally established the correlation of global warming with the increase in carbon-dioxide in the atmosphere. He accomplished this through collection of remarkably consistent and accurate data on the continued increase in carbon dioxide, a major greenhouse gas, for a prolonged period of time. Temperature being an integral part of climate, global warming can lead to climate changes.

The Earth’s climate changes in response to external forces, including greenhouse gases, variations in its orbit around the Sun, changes in solar luminosity, and volcanic eruptions. There are also Earth’s own variations in temperatures, for which UNFCCC uses the term climate variability.

However, the climate change due to excessive emissions from industries, known as, anthropogenic climate change depends mainly on the extent of man-made greenhouse gas emissions to the atmosphere. The major source of greenhouse gas is fossil fuel burning, while the forest remains a major sink.

In a 2001 report, an intergovernmental panel of experts on climate change (the IPCC) concluded that the net effect of feedbacks from global warming “is always to increase projected atmospheric CO₂ concentrations”. The mechanisms other than the greenhouse effect, such as, volcanic activity and changes in the sun’s brightness cannot explain the temperature increase of the past 100 years.

Global Warming and Heat Absorbing Atmospheric Gases:

George Callendar (1936) based on the data on temperatures taken at weather stations and on shipboards for decades, concluded that the world was gradually warming. Callendar attributed the rise in global temperature due to carbon dioxide formed by burning of fossil fuels. He was much ahead of his time.

Several decades after George Calendar’s observation of global temperature rise due to carbon dioxide, it was Charles David Keeling who finally established the correlation of global warming with the increase in carbon-dioxide in the atmosphere. He accomplished this with his collection of remarkably consistent data for a prolonged period of time.

Gas Absorbing Capacity of Ocean:

Scientists felt that the ocean being a sink for carbon dioxide, would absorb the extra carbon dioxide. However, Scripps Institute of Oceanography found that the carbon dioxide absorption capacity of sea water is limited. In addition to salt, the sea water is a complex mixture of chemicals.

These chemicals create a peculiar buffering mechanism that stabilizes the acidity of sea water. The mechanism had been known for decades, but Reveille’s works indicate that sea water surface layer has a limited capability of absorbing carbon dioxide, barely one-tenth of the calculated buffering capacity.

Gas Absorbing Capacity of Forests:

Deforestation has led to decrease in the capacities for absorbing greenhouse gases by the forests. The increasing quantities of carbon dioxide formation due to rapid industrialization and growing energy- requirements coupled with the decreasing absorption capacities of the ocean and forest have resulted in continuous increase in carbon dioxide concentration in the atmosphere.

Charles David Keeling and Keeling Curves:

The data on the increase in quantities of carbon dioxide annually in the atmosphere over several decades were collected for the first time by Charles David Keeling (1928-2005), an US Scientist, who is considered as the father of global warming issues. The dedicated scientist spent decades in collecting these data at Mauna Loa observatory at Hawaii, before making the famous Keeling curve. The Mauna Loa record shows a continuous increase in the annual concentration of carbon dioxide, an important greenhouse gas, thus establishing the role of human contribution to global climate change.

Keeling’s pioneering work is remarkable because of the following reasons:

i. Developed a device to measure carbon dioxide accurately in the atmosphere at parts per million (ppm) levels:

The current figure for carbon dioxide content in the atmosphere is approximately 0.038%, which in absolute quantity is 0.00038 or 380 parts per million. Hence it was absolutely essential to have measurement accuracy at ppm level and beyond, if the co-relation between increasing carbon dioxide and global warming was to be established. Average annual increase in Keeling’s measurement in 1959- 60 periods was 0.92 ppm, less than 1 ppm and thus conforms to measurement accuracy.

In 1958 C.D. Keeling, while working at the University of California in San Diego introduced a new technique for the accurate measurement of atmospheric CO₂. Keeling used cryogenic condensation of air samples, followed by NDIR spectroscopic analysis against a reference gas, using manometric calibration.

Subsequently, this technique was adopted as an analytical standard for CO₂ determination throughout the world, including the World Meteorological Association (WMO). Keeling’s data on atmospheric concentration of carbon dioxide at Mauna Loa, from 1959 to 1995 are indicated in tab. 4.1.

ii. Collected data at different locations:

CO₂ measuring stations are distributed across the globe. Most, however, are located in coastal or island areas in order to obtain air without contamination from vegetation, organisms and industrial activity, i.e. to establish the so-called background level of CO₂.

In considering such measurements, account should be taken of the established fact that land-derived air flowing seawards loses about 10 ppm of its carbon dioxide to dissolution in the oceans, and even more in colder waters (Henry’s Law). Mauna Loa has an active volcano.

However, Keeling and his team made measurements on the incoming ocean breeze and above the thermal inversion layer to minimize local contamination from volcanic vents. In addition, the data are normalized to negate any influence from local contamination.

Measurements at many other isolated sites have confirmed the long-term trend shown by the Keeling Curve, though no sites have a record as long as Mauna Loa. Due in part to the significance of Keeling’s findings the NOAA began monitoring CO₂ levels worldwide in the 1970s. Today, CO₂ levels are monitored at about 100 sites around the globe.

iii. Collected data for every month of the year:

Keeling collected data on carbon dioxide variation for every month of the year to establish seasonal variation in emission and absorption by plants. The variations in monthly data are related to seasonal carbon dioxide levels in relation to global plant cycle. Carbon dioxide was high in winter, falling in spring, low in summer, and rising again in fall. In spring and summer, the plants require carbon dioxide for growing leaves, flowers, and fruits. Tab.4.1 shows Keeling’s data of 5-years interval, but measured and recorded every year.

iv. Collected data over a long period:

The measurements of carbon dioxide concentrations in the atmosphere by Keeling and his team were made over a long period of 36years (1959-1995).

In 1959, the highest CO₂ level was in the month of May at 318.13 ppmv an increase of 2.71 ppmv from January figure of 315.42ppmv (tab. 4.1). At the end of the year, in December, the CO₂ content in the atmosphere was 315.43ppmv, showing an almost complete carbon balance in that year and place.

The carbon dioxide data showed an increase in average value from 315.83 ppmv in 1959 to 324.52 ppmv in 1970,followed by 338.52 ppmv (1980) and 354.04 ppmv (1990)(tab. 4.1). The results indicate a increase in carbon dioxide in every decade and at higher rates than the preceding decade. The increase in the period, 1959 to 1970 is 9.69 ppmv, in the following decade, 1970-1980, is 10.00ppmv, and in the next decade. 1980-1990 is 15.52 ppmv.

Keeling Curves:

The results of the extensive data collection were graphically presented in the famous Keeling curves (Fig. 4.2). Beginning in 1955, Keeling collected air samples to measure their carbon dioxide content. His measurements over the decades that followed showed that carbon dioxide levels were steadily rising — a finding that shattered the conventional wisdom that Earth could soak up rising fossil fuel emissions without harm.

The measurements at Mauna Loa, extended to 2006, (Fig. 4.2) show a steady increase in average CO₂ concentration in atmosphere from about 315 parts per million by volume (ppmv) in 1958 to over 380 ppmv by the year 2006. That is 65 ppmv in last 40 years, 15.96 ppmv over the decade 1990-2000, and 10 ppmv over six years’ period from 2000-2006. The more recent data also indicates the same trend of increasing quantities of CO₂ in the atmosphere per year at a higher rate every year than the preceding one.

This increase in atmospheric CO₂ at an accelerated rate in recent year is considered to be largely due to increasing quantities of combustion of fossil fuels, to cater to the growing energy need. This is supported by measurements of carbon dioxide concentration in ancient ‘air bubbles’ trapped in polar ‘ice cores’, which show that mean atmospheric CO₂ concentration was between 275 and 285 ppmv for several thousand years but started rising sharply at the beginning of the nineteenth century.

The carbon dioxide absorbs most of the infra-red energy thus making significant contribution in heating up the atmosphere. The atmosphere around the globe shall absorb more heat with the increase in concentration of carbon dioxide with every passing year. The ‘global warming’ would occur at an accelerated rate in conformity with the increased volume of CO₂ accumulating in the atmosphere, every year.

Monitoring Weather:

Monitoring our planet’s weather, oceans and land masses is of paramount importance to understand, forecast, and possibly manage Earth’s ecological goods and services in the face of global warming. This is being done by satellites dedicated to provide such information. Both the Global Earth Observation System of Systems (GEOSS) and the European Space Agency push to marshal science-based satellite constellations for a concerted focus on climate change.

On February 16, 2005, member countries of the Group on Earth Observations agreed to a 10-year implementation plan for a Global Earth Observation System of Systems (GEOSS). The GEOSS project will help all nations involved produce and manage their information in a way that benefits the environment as well as humanity by taking a pulse of the planet.

EPA-ORD represented the U.S. at GEO III Plenary in Bonn, Germany (2006). UN agencies on Global Warming include, UNFCCC (United Nations Framework Convention on Climate Change) and IPCC (Inter­governmental Panel on Climate Change) are tasked to co-ordinate the activities around the world on global warming.

Global Warming Projection:

Global warming has been observed to increase in the average of the Earth’s near-surface air temperature, which rose by 0.74 °C (1.3 °F) during the last century. Natural cycles of formation and absorption of carbon dioxide leads to seasonal climate changes by absorbing different quantum of heat by the amount of carbon dioxide available in the atmosphere at that period.

However, the enhanced concentration of greenhouse gases (GHGs) from anthropogenic sources in atmosphere can induce a global average temperature rise of over 2°C as early as 2035. Various agencies have shown an increase in temperature from 2°C to 5°C in 2100 AD (Fig.4.3). The increase in global temperature at these levels shall have great impact on the climate across the world. In the longer term, there would be more than a 50% chance that the temperature rise would exceed 5°C.

This rise would be equivalent to the change in average temperatures from the last ice age to today. To avoid the worst effects of global warming the mean global temperature rise must be kept below 2° C (3.6° F). In a decade or two, if the trend is not reversed then there would be irreversible changes leading to worst impacts of climate changes.

Natural processes of climate change:

The natural climate change includes processes, such as albedo, cloud forcing, glaciations, ocean variability, orbital variations, global forcing, radiative forcing, solar variation, and volcanization.

Some of these processes are discussed briefly in the following paragraphs:

i. Albedo:

This is the ability of a surface to reflect light that falls upon it. Snow, ice and white surfaces reflect 100% of sunshine from the surface thus having cent per cent albedo. Black bodies absorb 100% light and consequently have zero Albedo. Ice sheets reflect light fully and thus grow bigger with increasing snow fall. As an insulator, ice keeps the earth beneath it warmer. This causes the insulator to lose its grip on the land, and slide into the sea thereby continuing the process.

ii. Cloud forcing:

The term “cloud radiative forcing” refers to the effects clouds on both sunlight and heat in the atmosphere. Cloud radiative forcing measures how much clouds modify the net radiation of the earth, at wavelengths ranging from 0.3 to 100 micrometers. Cloud forcing (sometimes described as cloud radiative forcing) is the difference between the radiation budget components for average cloud conditions and cloud-free conditions.

Much of the interest in cloud forcing relates to its role as a feedback process in the present period of global warming. All global warming models, used for climate change projections, include the effects of water vapor and cloud forcing. Water vapor alone contributes between 36-70% of the greenhouse effect, and when combined with clouds the total contribution increases to 66-85%.

Trapping of the long-wave radiation due to the presence of clouds, reduces the radiative forcing of the greenhouse gases, when compared to the clear-sky forcing. However, the magnitude of the effect due to clouds varies for different greenhouse gases.

Relative to clear skies, clouds reduce the global mean radiative forcing due to GHGs, such as:

(i) CO₂ by 15%,

(ii) CH₄ & N₂O by 20%, and

(iii) Halocarbons by 30%.

Clouds play a significant role in our world’s energy balance — they exert both a cooling effect on the surface by reflecting sunlight back into space, and a warming effect by trapping heat emitted from the surface The magnitude of cloud radiative forcing (in Watts/m ²) for a given month can be positive or negative.

The positive and negative effects in the magnitude of cloud radiative forcing varies between (-) 280 to (+) 280 W/m² in different regions. Regions of positive cloud radiative forcing indicate areas where clouds act to increase net energy into the Earth system (i.e., regions of deep tropical convection). Whereas areas of negative cloud radiative forcing, signifies regions where clouds act to decrease net energy into the Earth system (such as areas of stratus clouds off the coast of California).

Clouds remain one of the largest uncertainties in future projections of climate change by global climate models. This is due to the physical complexity of cloud processes, and the small scale of individual clouds relative to the size of the model computational grid.

iii. Glaciation:

Glacier is a large, slow moving river of ice, formed from compacted layers of snow, that slowly deforms and flows by gravity. The process of glacier formation and growth is called glaciation. Glacier ice is the largest reservoir of “fresh water” on Earth, and second only to oceans as the reservoir of total water. Glaciers cover large areas of Polar Regions, and also form on the highest mountains in the tropics.

A large quantity of precipitation gets trapped in glaciers; instead of flowing immediately back to the oceans. This causes the sea level to drop, and greatly modifies the hydrology of streams, and the Earth’s hydrologic cycle. Prolonged glaciations may cause a reduction in shallow seas, which is the most productive regions of marine products, leading to strains in marine environment.

iv. Ocean variability:

By using ocean simulations, from a twenty-year time series, scientists are trying to understand the causes of the variability in global ocean circulation patterns. They are also trying to determine if this variability can be predicted. The ocean’s circulation can be predicted through the use of satellite-measured SSH (sea surface height), and it has been found that sea level at one location influences the variability downstream. Ocean variability leads to natural disasters like El Nino.

v. Orbital variation:

The Earth spins around an axis that is not perpendicular to the plane in which the Earth orbits the Sun. This tilt results in seasons. At the height of the Northern Hemisphere winter, the North Pole is tilted away from the Sun. While in the summer, it is tilted toward the Sun. The angle of the tilt varies between 22° and 24.5° on a cycle of 41,000 years.

When the tilt angle is high, the Polar Regions receive less solar radiation than normal in winter and more in summer. As the Earth spins around its axis and orbits around the Sun, several quasi-periodic variations occur. Although the curves have a large number of sinusoidal components, a few components are dominant.

Milankovitch studied changes in the eccentricity, obliquity, and precession of Earth’s movements. Such changes in movement and orientation alter the amount and location of solar radiation reaching the Earth. This is known as solar forcing (an example of radiative forcing). Changes near the north polar area are considered important due to the large amount of land, which reacts to such changes more quickly than the oceans do.

vi. Radiative forcing:

RF is the relative effectiveness of greenhouse gases to restrict long-wave radiation from escaping back into space. For a particular greenhouse gas, radiative forcing is measured as the change in average net radiation (in watts per square meter) at the top of the troposphere, and depends on the wavelength at which the gas absorbs the radiation, the strength of absorption per molecule, and the concentration of the gas.

Greenhouse gases have a positive radiative forcing because they absorb and emit heat. Radiative forcing is a measure of greenhouse effect (global warming) and it is proportional to the concentration of these gases in the atmosphere.

Radiative forcing energy (W/m²) for a greenhouse gas, such as CO₂, in terms of relative radiative transfer in atmosphere, i.e. ÄF as a function of changing concentration, can be calculated from the simplified expression:

ΔF = 5.35 × In C/C₀

Where C = CO₂ concentration in parts per million by volume and C₀ = reference concentration. The above equation shows logarithmic relation between CO₂ concentration and radiative forcing. Therefore the increased concentrations have a progressively smaller warming effect.

Formulas for other greenhouse gases such as methane, nitrous oxide, or CFCs are given in the IPCC reports.

Radiative forcing can be used to estimate a subsequent equilibrium surface temperature change, arising from that forcing with the following equation:

δTs = λRF

where λ = climate sensitivity in K/(W/m²). A typical value of λ = 0.8, which gives a warming of 3K for doubling of CO₂.

In the pre-industrialization periods, the radiative forcing was almost constant due to negligible variation in the concentrations of the green house gases in the atmosphere.

RF is an important tool in determining the effects of greenhouse gases, aerosols, and clouds on climate change. It is necessary, however, to state that RF does not depict the climate response in its entirety. There are several parameters related to climate change that exist, but they are greatly variable and complex. Since RF is easy to calculate, it provides a general estimate of how the climate will respond to changes in greenhouse gas concentrations and various other agents.

vii. Volcanization:

Normally volcanization leads to excess carbon dioxide in the atmosphere. However, some of the volcanic gases released from the Siberian trap flood basalts could have the opposite effect to the CO₂, cooling the climate instead of heating it.

Anthropogenic Heat:

Anthropogenic heat is the heat generated by humans and human activity. It is defined as the heat and/or greenhouse gases released to the atmosphere as a result of human activities, often involving combustion of fuels. Sources include industrial plants, space heating and cooling, human metabolism, and vehicle exhausts.

Anthropogenic heat becomes more significant in dense urban areas and has small influence on rural temperatures. It is the main contributor to urban heat islands.

Other human-caused effects (such as changes to albedo, or loss of evaporative cooling) that might contribute to urban heat islands are not considered to be anthropogenic heat by this definition. Anthropogenic heat is a much smaller contributor to global warming than are greenhouse gases. Anthropogenic waste heat flux can be significantly high in certain urban areas. For example, waste heat flux was +0.39 and +0.68 W/m² for the continental United States and Western Europe, respectively.

Anthropogenic heat accounts for only 1% of the energy flux created by anthropogenic greenhouse gases. Anthropogenic climate change is therefore due to excessive greenhouse gas emissions.

Anthropogenic GHGs and Radiative Forcing:

The net radiative forcing due to anthrpogenic components (fig.3.3) amounts to approximately (+) 1.82W/mm.sq.

The radiative forcing contribution (since 1750) from increasing concentrations of well-mixed greenhouse gases (including CO₂, CH₄, N₂O, CFCs, HCFCs, and fluorinated gases) is estimated to be +2.64 Watts per square meter, wherein more than half of the amount is due to increases in CO₂ (+1.66 Watts per square meter). Thus CO₂ makes major contribution to warming relative to other climate components.

According to NOAA’s (National Oceanic and Atmospheric Administration, USA) Annual Greenhouse Gas Index (AGGI), which tracks changes in radiative forcing from greenhouse gases over time, shows that radiative forcing from greenhouse gases has increased 21.5% since 1990 as of 2006. Much of the increase (63%) has resulted from the contribution of CO₂. Methane is more effective greenhouse gas than carbon dioxide, but its radiative forcing is 1/4^th of carbon dioxide due to presence of lower percentage.

The accumulation of excessive greenhouse gases in the atmosphere has resulted from:

i. Fossil fuel burning:

Most of the energy requirements are met by burning fossil fuels. Fossil fuel burning has produced about three-quarters of the increase in CO₂ from human activity over the past 20 years.

ii. Destruction of biomes:

Biomes, like forest and ocean, act like a buffer to maintain the global temperature at a nearly constant level. However, deforestation, land-use change, destruction of marine life, lead to imbalances in eco cycles, such as, carbon-cycle and hydrological cycle. The reduction in the capacity to act as a buffer, leads to excess carbon dioxide in the atmosphere, thereby causing more heat absorption and consequent warming.

An increasing number of groups worked up models that coupled climate changes with changes in soils, vegetation and the oceans. It was a matter of simple physics that as the oceans grew warmer; the sea water would absorb gases less readily. Tropical forests would show a similar effect for biological reasons.

The worst worry was the Amazon forest, sustained by rains that were largely water evaporated from the jungle itself. It appeared that warming would make it harder for the planet to take up carbon, and might even trigger increased emissions. If the tropical forests get dried they would start to emit massive amounts of CO₂, would turn from a net absorber to a major emitter of carbon, speeding up climate change.

Potential Effects of Anthropogenic Climate Change:

The anthropogenic climate change can have disastrous consequences, and can cause frequent occurrences of severe weather. Global warming shall make a vast change in the natural climate pattern with increasing frequencies of disasters.