Frequently Asked Questions

A greenhouse is a structure, usually made of glass, in which temperature and humidity can be controlled for the cultivation or protection of plants. A greenhouse is designed to trap heat from the sun's rays inside and acts to keep the plants inside warm, even when it is cold outside. Although the Earth does not have a layer of clear material over it, certain molecules in our atmosphere absorb the Earth's heat, basically trapping some of that energy. This is called the greenhouse effect, and the molecules that trap the heat are called greenhouse gases.

Even though greenhouse gases don't make a hard surface like the glass of a greenhouse, but because they have a similar effect in keeping our planet warm, the term "Greenhouse Effect" is a good description. The greenhouse effect keeps the temperatures on our planet mild and suitable for living things.

Greenhouse gases (GHG) include carbon dioxide, water vapor, methane, ozone, nitrous oxide and fluorinated gases. These molecules in our atmosphere are called greenhouse gases because they absorb heat. There may not be much of some of these gases in our atmosphere, but they can have a big impact. These molecules eventually release the heat energy and it is often absorbed by another greenhouse gas molecule.

More technically: Greenhouse gases effectively absorb thermal infrared radiation, emitted by the Earth's surface, by the atmosphere itself due to the same gases, and by clouds. Atmospheric radiation is emitted to all sides, including downward to the Earth's surface. Thus, greenhouse gases trap heat within the surface-troposphere system. This is called the greenhouse effect. (Definition courtesy of IPCC AR4.)

Without its atmosphere and the greenhouse effect, the average temperature at the surface of the Earth would be zero degrees Fahrenheit. However, too many greenhouse gases can cause the temperature to increase out of control. Such is the case on Venus where greenhouse gases are abundant and the average temperature at the surface is more than 855 degrees Fahrenheit (457 degrees Celsius).

You might hear people talking about the greenhouse effect as if it is a bad thing. It is not a bad thing, but people are concerned because Earth's 'greenhouse' is warming up very rapidly. This is happening because we are currently adding more greenhouse gases to our atmosphere, causing an increased greenhouse effect. The increased greenhouse effect is causing changes in our planet that can affect our lives.

The major Greenhouse Gas, carbon dioxide, emitted naturally and by the burning of fossil fuels, stays in the atmosphere for a long time. Its warming effect occurs even when the sky is clear and dry. Climate scientists are so concerned about carbon dioxide because the more carbon dioxide in the atmosphere, the hotter the earth will become, changing the Earth's climate. The result is called Global Warming because on average, the Earth and our oceans are warming up, and the climate is changing as the carbon dioxide and other greenhouse gases in the atmosphere continue to build up.

Scientists have known and understood this for over 100 years, and it has been confirmed by measurements and in laboratory experiments. There is no doubt about the basic science behind global warming.

Greenhouse gases are most frequently measured and described in terms of the most common greenhouse gas, Carbon Dioxide (CO2), often called Carbon Dioxide Equivalents (COe2). The amount of greenhouse gases that each one of us is responsible for emitting each year is described as our Carbon Footprint. Our modern way of life relies heavily on the emission of carbon. When we think about this, we often limit ourselves to considering the use of automobiles and trucks and a few industrial processes. We understand that when we burn the gasoline in our engines, we are oxidizing the fuel and creating carbon dioxide.

However, there are other activities in our life that also contribute to COe2 emissions even though we do not see the oxidation. When we use electricity, we are also emitting carbon dioxide. The majority of the electricity created in the U.S. is derived from burning natural gas or coal. We also emit CO2 when we heat our homes since this requires the use of electricity or the burning of natural gas, propane, heating oil, or wood.

The processes involved in growing the food we eat, and transporting it to our stores and then to our homes, also produce CO2 and other greenhouse gas emissions. Even our creation of waste and garbage results in greenhouse gas emissions. If this garbage is put into a landfill, it decays and puts CO2 and methane (CH4) back into the atmosphere. If it is burned in an incinerator, it emits CO2 as a product of combustion. If it is recycled, the energy of some form will be used to accomplish this, emitting COe2 in the process.

(Much of the above information on greenhouse gases and carbon dioxide emissions is courtesy of National Center for Atmospheric Research webpages)

To answer this question of how much carbon dioxide is emitted to the atmosphere through your activities, you can calculate your carbon footprint by using an online Carbon Footprint Calculator (see below for description and examples). These calculators add up the carbon dioxide produced by your different personal activities and provide you with an estimate of your annual carbon dioxide emissions.

Carbon calculators will first ask where you live, because certain emissions are related to where you live - particularly in terms of what mix of fossil fuels are used to generate your electricity. There are two major ways that carbon calculators make the calculation of your carbon footprint, either:

1. They ask for very specific information (so you need to gather some data) - such as on how much electricity and gas/oil/wood/coal you use, how many miles you drive, how often you eat meat, how much you travel, and by what means, etc.; or
2. They ask what kind of dwelling you live in (single family home, apartment, etc. to make estimates from geographic averages); how many and what type of car you drive, how often you take public transportation and for how many miles; and ask about some of your habits. Many of the calculators that use averages are asking about behaviors or habits that would either increase your 'footprint' above the average or decrease it below the average.

The variety of calculators provides more or less accuracy depending on the detail they use and what they consider. One major difference in calculators is that some do not include activities that may have a large impact on your carbon footprint, such as eating habits (whether you eat much meat - the production of meat has a high carbon footprint) or whether you travel by airplane (traveling by plane has a high carbon footprint).

Here are several free internet-based carbon footprint calculators:

I. The Environmental Protection Agency has an explanation and a calculator from their webpage. View that calculator. EPA offers a calculation based on your own household data, so you need to do some up front data gathering. View how they begin on the Carbon Footprint Calculator page

1. To get the most accurate results, gather your recent electric, gas, and/or oil bills so you can use real numbers for your household's energy consumption. Remember that your energy bills vary by season, so use an average of winter and summer values if you can.

2. Allow yourself 10 to 15 minutes to enter the data.

3. After entering data, use the TAB key to continue moving through each section of the calculator. When you get to the end of a section, click "Next Section" to move on.

4. Visit the What You Can Do section of the climate change website to learn about other actions you can take to reduce your greenhouse gas emissions."

EPA's calculator does not ask about travel habits (such as flying) nor food and diet, which many other calculators use. EPAs webpages do provide some tips on things you can do to reduce your emissions.

II. An organization indicating it is the web's leading carbon footprint calculator can be found by visiting the Carbon Footprint website.

This calculator uses factors sourced from a diverse group of references including the UK Department for Environment, Food and Rural Affairs, UK Vehicle Certification Agency, World Resource Institute, U.S. Environmental Protection Agency, U.S. Department of Energy, Australia Green House Office, and Canada Standards Association GHG Registries.

Choosing your country allows you to compare your carbon footprint with the average person in your country, and also sets up the units used in the calculator. The accuracy of electricity generation emissions, and gas and electricity prices, depends on where you live.

This calculator uses your home heating and electricity data, air travel information, car, motorbike, bus, and rail travel habits, and includes a category for secondary information. The secondary information gives some insight into lifestyle choices that can make a difference including food preferences, furniture, fashion, packaging, recycling, recreation, car manufacture, and finance.

The results page for this website includes a comparison to world averages, an option to buy carbon offsets (see below for a description of carbon offsets) and a link to a webpage offering some tips to reduce your carbon footprint.

III. The Nature Conservancy (TNC) has a carbon footprint calculator that can be viewed on the Nature Conservancy website.

The Nature Conservancy carbon footprint calculator is one that is mainly based on averages. Questions include the number of people in your home, and information on: where you live and home energy, driving and flying, foot and diet, and recycling and waste habits. This is a very simple calculator that estimates your emissions. The Nature Conservancy also offers you the opportunity to buy offsets (see below for a description of carbon offsets)

TNC notes: "Inevitably, in going about our daily lives - commuting, sheltering our families, eating - each of us contributes to the greenhouse gas emissions that are causing climate change. Yet, there are many things each of us, as individuals, can do to reduce our carbon emissions. The choices we make in our homes, our travel, the food we eat, and what we buy and throw away all influence our carbon footprint and can help ensure a stable climate for future generations."

Carbon offsets are voluntary programs that consumers can buy into to help reduce the buildup of carbon pollution that is causing climate change. When you know how much you are contributing to greenhouse gas emissions (see carbon footprint above), you can opt to buy credits to offset those emissions. The major criticism of carbon offsets is that because carbon dioxide and greenhouse gases are so long-lived in the atmosphere, if you somehow pay for something that will offset your emissions, it must last at least 100 years.

Carbon Offset opportunities include renewable energy projects, forest carbon sequestration projects, projects that donate to efforts to reduce the use of fossil fuels or reduce the rate of deforestation, and the like. Such programs vary greatly in terms of their methodologies and offerings.

The Nature Conservancy (TNC) offers the following list of important considerations that they use for their offset program. TNC's program is forest-based but the principles include good considerations. Any project offered by TNC must address certain issues, including:

• Permanence - which, simply stated, is the life of the project. It wouldn't help to reduce climate change much if a tree were planted or saved one year only to be cut the next. The most desirable forest carbon projects are those where the restored and protected forests are likely to remain intact indefinitely.
• Additionality - refers to the amount of carbon dioxide captured, stored, or prevented from reaching the atmosphere compared to what would happen without the project. In other words, is this something that would have happened anyway?
• Leakage - occurs when emissions avoided within a site are not eliminated, but rather displaced to another location, or when carbon capture and storage at a site lead to land clearing elsewhere.
• Measurement and monitoring - which entails periodic field measurements of forest growth and associated capture and storage of carbon, as well as, in some cases, analysis of satellite imagery and models of forest growth and deforestation.
• Verification - of carbon benefits by an accredited independent third-party, which occurs periodically throughout the life of a project to ensure it meets its intended goals of carbon storage and that all additionality, measurement, leakage and permanence requirements are being met."

However, it is far better to do everything possible to reduce your emissions than to purchase carbon offsets in the hope that you can mitigate emissions that will persist a hundred years or more.

This information comes from the Nature Conservancy website.