Environmental Science

LESSON 36. GLOBAL WARMING

The Intergovernmental Panel on Climate Change (IPCC) is a scientific body tasked to evaluate the risk of climate change caused by human activity. The panel was established in 1988 by the World Meteorological Organization (WMO) and the United Nations Environment Programme (UNEP), two organizations of the United Nations. The IPCC shared the 2007 Nobel Peace Prize with former Vice President of the United States Al Gore. The IPCC does not carry out research, nor does it monitor climate or related phenomena. A main activity of the IPCC is publishing special reports on topics relevant to the implementation of the UN Framework Convention on Climate Change (UNFCCC), an international treaty that acknowledges the possibility of harmful climate change; implementation of the UNFCCC led eventually to the Kyoto Protocol. The IPCC bases its assessment mainly on peer reviewed and published scientific literature.  The IPCC is only open to member states of the WMO and UNEP. IPCC reports are widely cited in almost any debate related to climate change. National and international responses to climate change generally regard the UN climate panel as authoritative. . The  Intergovernmental Panel on Climate Change (IPCC) an international body of over 3000 experts, concludes that most of the observed temperature increase since the middle of the 20th century was very likely caused by increasing concentrations of greenhouse gases resulting from burning of fossil fuels for transportation, generation of electricity, production of cement, steel, plastics and other materials and household cooking and deforestation releases carbon dioxide, which is one of the key gases causing global warming.

Global surface temperature increased 0.74 ± 0.18 °C (1.33 ± 0.32 °F) between the start and the end of the 20th century. Most of the warming (of more than 0.1 ⁰C per decade) observed over the last 50 years, is very likely due to human activities. The IPCC projects that the global mean temperature may increase between 1.8 to 4 ⁰C by 2100. The IPCC also concludes that variations in natural phenomena such as solar the radiation and volcanic eruptions had a small cooling effect after 1950. As per report of  UN’s IPCC (2013) the rate of warming over the past 15 years at 0.05 degree Celsius per decade is smaller than the trend over 1951 to 2012 which stands at 0.12 degree Celsius. The report predicts that by the turn of this century, the temperatures are likely to exceed 1.5 degree above pre-industrial era. The chance that the temperatures will go beyond 2 degree above the pre-industrial

Greenhouse Gases and Global Warming:

Many greenhouse gases occur naturally, such as water vapor, carbon dioxide, methane, nitrous oxide, and ozone. Others such as chloroflorocarbons, hydrofluorocarbons (HFCs), perfluorocarbons (PFCs), and sulfur hexafluoride (SF6) result exclusively from human industrial processes. The United Nation’s IPCC in its latest report warns that a large part of the changes that occur on the planet cannot be reversed even after the next few centuries unless carbon dioxide emissions are brought down fast, substantially and kept extremely low for a very long time. The summary notes, “it is very likely that more than 20 % emitted carbon dioxide will remain in the atmosphere longer than 1000 years after anthropogenic emissions have stopped. Carbon dioxide induced warming is projected to remain approximately constant for many centuries following a complete cessation of emissions.” This will have long lasting impact on the environment.

While many greenhouse gases occur naturally and are needed to create the greenhouse effect that keeps the Earth warm enough to support life, human use of fossil fuels is the main source of excess greenhouse gases. By driving cars, using electricity from coal-fired power plants, or heating our homes with oil or natural gas, we release carbon dioxide and other heat-trapping gases into the atmosphere. Deforestation is another significant source of greenhouse gases, because fewer trees mean less carbon dioxide conversion to oxygen. Warming drives sea level to rise through thermal expansion of sea water and widespread loss of land ice. Sea level rise will continue for many centuries because of the warming of the oceans and temperatures will continue to rise until 2200.

During the 150 years of the industrial age, the atmospheric concentration of carbon dioxide has increased by 31 percent. Over the same period, the level of atmospheric methane has risen by 151 percent, mostly from agricultural activities such as raising cattle and growing rice.

Greenhouse Effect:

The greenhouse effect is a natural process by which some of the radiant heat from the Sun is captured in the lower atmosphere of the Earth, thus maintaining the temperature of the Earth's surface. The gases that help capture the heat, called “greenhouse gases” . The energy from the sun that reaches Earth's surface is mostly "shortwave" radiation - mostly visible light. This energy passes freely through the atmosphere and is absorbed by Earth’s surface. The surface warms from the energy input, and some of its heat projects back to the atmosphere as infrared radiation. The greenhouse gases in the atmosphere absorb 95% of the energy in infrared radiation, allowing only 5% to pass into space. When greenhouse gases absorb energy, heat is released in all directions, including back towards Earth. As the concentration of greenhouse gases increases, this “insulating blanket” thickens, further warming the Earth.

CAUSES OF GLOBAL WARMING :

Global warming is primarily a problem of too much carbon dioxide (CO₂) in the atmosphere—which acts as a blanket, trapping heat and warming the planet. As we burn fossil fuels like coal, oil and natural gas for energy or cut down and burn forests to create pastures and plantations, carbon accumulates and overloads our atmosphere. Certain waste management and agricultural practices aggravate the problem by releasing other potent global warming gases, such as methane and nitrous oxide. See the pie chart for a breakdown of heat-trapping global warming emissions by economic sector.

 

Source: IPCC Fourth Assessment Report: Climate Change 2007, Working Group III

The table below outlines the major sources of greenhouses gases:

Gas:	Source:	Use:	Way it increases global warming:
Water vapour	Oceans, lakes, rivers, reservoirs. Humans have little impact upon levels.	Absorbs limited outgoing radiation.	Water vapour and clouds are responsible for nearly 98% of the natural greenhouse effect.
Carbon dioxide	Burning of fossil fuels, and forests, breathing animals, less produced by southern hemisphere (less land).	Absorption of long wave radiation.	Approximately 50%.
Methane (CH4)	Much from break down of organic matter by bacteria (rice paddy fields) cows, swamps marshes.	As above.	Approximately 18%.
Ozone	Naturally from some oxygen atoms. Ozone in the troposphere is due to chemical reactions between sunlight and agents of pollution.	Filters short wave UV radiation.	Difficult to estimate.
CFCs	Fridges and aerosols.		25%, but increasing due to ability to survive within the atmosphere for 100 years.
Nitrous oxide	Nitrate fertilisers, transport and power stations (combustion).	Absorption of long wave radiation.	Approximately 6%.

 

The global warming potential of six major greenhouse gases:

The final report of IPCC (2013) notes that carbon dioxide emissions accumulating in the atmosphere since 1750 make the largest contribution to the net radiative forcing (in other words caused the greatest warming of the planet). Scientists have assessed that cumulative carbon dioxide emissions in the atmosphere should not accede 1000 PgC (pentagrams of Carbon). Of this, the IPCC report notes, 460 to 630 PgC of carbon space has already been filled up. But the emissions of another, much more potent but short-lived gas methane have increased by 150 percent as compared to carbon dioxide emissions that rose by 40 percent between 1750-2011. The panel of scientists have concluded that the impact of methane on the climate is much higher that had been assessed when IPCC put out its last report in 2007. The impact of aerosols on climate change remains the least understood.

India’s per capita emissions are one of the lowest among the large economies while that of other emerging economies have raced to or already past the levels achieved by the OECD countries. India will require greater carbon space (and therefore time to let its emissions peak) than other developed or emerging economies to cater to the energy needs of a growing nation.

The Properties of Greenhouse Gases:

Greenhouse gases vary in their ability to absorb and hold heat in the atmosphere, a phenomenon known as the "greenhouse effect." HFCs and PFCs are the most heat-absorbent, but there are also wide differences between naturally occurring gases. For example, nitrous oxide absorbs 270 times more heat per molecule than carbon dioxide, and methane absorbs 21 times more heat per molecule than carbon dioxide.

Human influence on climate is caused by tiny particles called “aerosols” (not to be confused with aerosol spray cans). For example, the burning of coal produces emissions of sulphur-containing compounds. These compounds form “sulphate aerosol” particles, which reflect some of the incoming sunlight away from the Earth, causing a cooling influence at the surface. Sulphate aerosols also tend to make clouds more efficient at reflecting sun light, causing an additional indirect cooling effect.  Another type of aerosol, often referred to as soot or black carbon, absorbs incoming sunlight and traps heat in the atmosphere. Thus, depending on their type, aerosols can either mask or increase the warming caused by increased levels of greenhouse  gases.