In the debate over global warming, many a time, there is an attempt to indicate that human contribution to the Greenhouse effect is on a very minuscule scale and is negligible when compared to the scale at which GHGs as a whole work.

However, this document suggests that in such discussions, Water Vapour has been excluded as a factor in the analysis of Earth's GHGs. The document argues how many 'facts and figures' regarding global warming completely ignore the powerful effects of water vapour in the greenhouse system. This point is so crucial to the debate over global warming that how water vapor is or isn't factored into an analysis of Earth's greenhouse gases makes the difference between describing a significant human contribution to the greenhouse effect, or a negligible one.

What are Greenhouse gases?

The Earth is surrounded by a thin layer of chemically distinct gases and particulate matter. These atmospheric gases are often divided into the constant components and the highly variable components. The variable components have a much greater influence on the short term weather and long term climate.

Among the variable components, the major greenhouse gas is Water Vapour. This is not influenced directly on a large scale by human activity, except in regional and local concentrations. It is largely a result of natural processes. Other naturally occurring GHGs are Carbon dioxide, Methane and Ozone. But, these are also produced by human activity, and are the root cause of human induced global warming.

We all know from our school days that human beings emit CO2 when they exhale. But this is not on a scale to influence global warming, and if we have to curtail our breathing, is there any point in discussing the issue of global warming? Global warming, after all, is not a crisis for the Earth; it is a crisis for human beings – for the survival of the human species, and for the survival of many other living beings that are part of the natural cycle and food chain, so crucial to the survival of human beings.

Carbon dioxide is removed - "sequestered" - from the atmosphere. Plants absorb Carbon dioxide as part of the biological Carbon cycle. The oceans also have a natural Carbon sequestration function.

Another set of gases are the synthetic gases – fluorinated gases like Hydrofluorocarbons, Perfluorocarbons and Chlorofluorocarbons - . they are not naturally occurring. They are solely created by human beings and are emitted by human activity alone.

Two other gases Nitrogen (N2) and Oxygen (O2) are major constituents of the atmosphere but they are not GHGs. N2 and O2 do not absorb nor emit Infrared radiation. So, the GHGs mainly responsible for human induced Global Warming are.

Carbon Dioxide (CO2): Burning fossil fuels like coal, oil, and natural gas, as well as burning trees, wood products and solid wastes results in the emission of CO2. Other major chemical reactions also result in the emission of CO2, for instance the manufacture of cement.

Methane (CH4): Methane is emitted during the production and transport of coal, natural gas, and oil. Methane emissions also result from livestock and other agricultural practices and by the decay of organic waste in municipal solid waste landfills.

Nitrous Oxide (N2O): Nitrous oxide is emitted during agricultural and industrial activities, as well as during combustion of fossil fuels and solid waste.

Fluorinated gases: Hydrofluorocarbons, Perfluorocarbons, and Sulfurhexafluoride are synthetic, powerful GHGs that are emitted from a variety of industrial processes. Fluorinated gases are sometimes used as substitutes for Ozone-depleting substances (i.e., CFCs, HCFCs, and Halons). These gases are typically emitted in smaller quantities, but because they are potent GHGs, they are sometimes referred to as High Global Warming Potential gases (High GWP gases).

What is the Greenhouse effect?

The Greenhouse effect is a natural process – a kind of thermostatic process, a natural temperature control system that enables the Earth to sustain average surface temperatures in the region of 15oC [15 degree celisius]. This is what sustains life – makes the Earth inhabitable.

The earth's surface gets warm due to the visible and near-visible component of solar radiation, which passes through the transparent medium – the earth's atmosphere. This radiation consists of shorter wavelengths of light, visible light, which is to a large extent absorbed by land, vegetation, the sea and oceans, and other water bodies– as much as two thirds of the radiation that reaches land and sea is absorbed. Ice sheets (the Arctic and Antarctic polar caps) reflect most of this radiation back. The atmosphere absorbs the least of this solar radiation. But it absorbs the shorter wavelength (ultra violet) and longer wavelength (infra red) components of solar radiation. The absorption capacity of different types of surfaces is termed as albedo.

As the Earth's surface becomes warm, it also emits infrared radiation, the longer wavelengths of invisible radiation. Some of this radiation is trapped in the atmosphere, and results in its warming. This is called the Greenhouse Effect.

It is similar to the effect of greenhouses that enable us to stabilize temperatures artificially, to grow plants that would not survive in local climatic conditions. But the processes are different, and therefore the analogy is actually incorrect! The Greenhouses in which plants are grown are heated directly by solar radiation – the sun's heat. Whereas the Greenhouse Effect we are referring to, which heats the Earth's atmosphere, is a result of the infrared radiation emitted by the heated earth's surface

The naturally occurring gases that trap infrared radiation include water vapour, carbon dioxide, ozone, methane and nitrous oxide. These are called Greenhouse Gases (GHGs).

The Earth has the right thickness of atmosphere, and the right mix of these gases to heat the atmosphere to pleasant levels. This makes life as we know it possible on Earth. Else the Earth would heat up by day, and cool down by night.

Venus is too hot, Mars too cold, the Earth just right – until recently. As the concentration levels of GHGs in the atmosphere change, the lower atmospheric temperature also changes. This is a natural cycle of warming and cooling over long periods of time and is a natural process of Climate Change.

National GHG emissions data

The page on Greenhouse Gas Inventory data provides access to most recent data on national GHG emissions and removals such as:

GHG data - UNFCCC: this page is an entry to the UNFCCC GHG data interface which provides access to the most recent GHG data reported by countries that are Parties to the Climate Change Convention.

KP data - UNFCCC: this is a page with GHG data relating specifically to the Kyoto Protocol; the data are as reported by countries that are Parties to the Kyoto Protocol.

GHG data - Non-UNFCCC: this page provides links to the web sites of various organizations that also collect, estimate and/or disseminate data on GHG emissions/removals.

Online help: the help page contains extensive explanatory information to assist the use in finding the right GHG data

The UNFCCC secretariat has released an update of its GHG Data Interface in May 2008. This update provides access to activity data and implied emission factors for all Annex I Parties and for a few non-Annex I Parties; to population (provided by the Population Division, UN DESA) and GDP (as provided by the World Bank and used in the UN Statistics) data for all Parties; and to base year data under the Kyoto Protocol for Annex I Parties with targets under the Kyoto Protocol (Annex B Parties).

GHG emissons across the world

This flow chart from the Earth Trends, World Resources Institute site shows the sources and activities across the global economies that produce greenhouse gas emissions.

This diagram shows GHGs at the global level. However,  the type of GHGs is much different in developed and developing countries. In developing countries, land-use change and agriculture contribute much greater shares of emissions than those shown here. In industrialized countries agriculture is usually a much smaller share--6% in the United States for example--and land-use change is often a sink.

The flowchart indicates that energy consumption is the major contributor of GHGs (61%). Within energy consumption, 40% is electricity and heat generation, another 20% is transportation and the remainder is building heat and industry. 

Land-use change is the second largest contributor globally. Land-use change includes deforestation, reforestation (replanting in existing forested areas) and afforestation (creating new forested areas). Together, the activities under land-use change can be either a source or a sink of greenhouse gases; they can either contribute GHGs to or remove them from the atmosphere.Agriculture is another significant GHG source.

Country-wise GHG emissions

This document on the CarbonPlanet website includes a table that provides information on the Green House Gas (GHG) emissions by country. 

Carbon Planet has been working with businesses around the world, helping them quantify the risks and explore the opportunities emerging in the carbon constrained economy.

An analysis of greenhouse gas intensity targets - World Resources Institute

This report published on the World Resources Institute site looks specifically at intensity targets and explores their underlying indicators, rationales, real-world applications, and implementation issues. It finds that although intensity targets are often dismissed as being environmentally lax or deceptive, they nonetheless could be useful policy instruments, when properly used, for furthering significant and real commitments to reducing greenhouse gases.

Navigating the numbers - Greenhouse gas data and international climate policy

This report by the World Resources Institute aims to convey the wide range of greenhouse gas (GHG) emissions data in digestible form, with the hope of increasing knowledge and awareness within the climate change policy community. In addition, the report offers a set of policy-relevant insights and observations that flow from the data. In some cases, an understanding of GHG emissions and related trends can help illuminate particular national circumstances faced by countries and inform policy responses of the international community.

Data in this report are drawn primarily, though not exclusively, from the Climate Analysis Indicators Tool (CAIT) developed by the World Resources Institute. Using CAIT and other databases, WRI has organized data relevant to climate change policy, and extract the most relevant details and findings. The hope is that sound information will contribute to a better-informed debate among stakeholders and, ultimately, improved decision-making.

Read more

• Diagrams: What is The Greenhouse effect? - Click here
• This website provides basic reading material on Greenhouse effect with a simple diagram - Click here
• A quick animated explanation of Global warming and the Greenhouse effect - Click here
• This website is an eBook on physical geography and the chapter on Atmosphere has a detailed write-up on the Greenhouse Effect, with a lot of links to technical terms - Click here