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      Introduction

      This report is a survey of research and analysis performed into the subject of small-scale impact on global warming, and into what can be done about it by an individual or small organisation. It processes information from diverse sources: collecting it into one place, and explaining thoroughly and in layperson’s terms the various dilemmas and solutions surrounding the subject of global warming.

      Central to this report is the concept of a carbon offset. This report’s major aim is to investigate the effectiveness of various approaches to cutting carbon dioxide emissions, and to suggest a course of action for the individual or small organisation wishing to become carbon neutral or ‘carbon negative’. Approaches are evaluated both in terms of their actual effectiveness as a carbon offset and in terms of cost, to give the offsetter the freedom to make an informed judgement about how to cut their carbon.

      In specific terms, this report investigates both conventional and less conventional approaches to this problem. The costs and benefits of purchasing carbon credits as an offset are explored. Building improvements such as micro-generation and insulation are considered and costed. Additionally, it is recognised that some approaches such as micro-sequestration may occur to the layperson, but they choose not to take this forward, because they have no specific information. This report explores such common-sense solutions, giving them equal weight to more conventional options, and so it allows the layperson to explore the appeal of their own ideas in practice.

      Global Warming and Carbon Footprint

      This section gives an overview of two sorts. Firstly, to remind the reader, in layperson’s terms, of how the greenhouse effect works. This includes a short discussion of how greenhouse gases affect the Earth’s temperature, and information on the nature of the human effect on this process. Secondly, to describe the nature of an individual’s or organisation’s contribution to emissions (their ‘carbon footprint’), and to explain the process of calculating this.

      Greenhouse Effect

      Figure 1. The Greenhouse Effect.

      Fig. 1 is a familiar diagram of the greenhouse effect: the basic mechanism through which global warming is taking place. When light from the Sun hits the Earth, some of it is reflected back as infra-red radiation. This reflected radiation comes into contact with gases in the atmosphere. Some gases – ‘greenhouse gases’ – reflect some of that radiation back down to Earth again. This means some heat, which would otherwise have left the atmosphere, is sent back to Earth and warms the surface further.

      Greenhouse gases make up much less than 1% of the atmosphere, and human activity is responsible only for a tiny fraction of that: nearly all of the greenhouse effect is perfectly natural. If there were no greenhouse gases in the atmosphere at all, the surface of the Earth would be at a temperature around -18 C [Ref. 1]. By comparison, human beings are having only a tiny effect, but what we are adding is enough to increase the temperature of the Earth by anything between 1.1 to 6.4 C over the 21st Century [Ref. 2]. Immediate consequences of this are well known: retreating glaciers causing rising sea levels, extinction of many species, expanding deserts and reduced agricultural capacity causing food shortages.

      Greenhouse Gases

      Water Vapour

      By far the most common greenhouse gas is water vapour: water in the atmosphere contributes 66% to 85% of the overall greenhouse effect [Ref. 3]. The amount of water vapour in the atmosphere (humidity) varies by location, and is almost entirely part of the natural water cycle. While human activities such as burning fossil fuels do emit water vapour, they do not significantly alter its concentration in the atmosphere.

      Gases Emitted by Human Activity

      Figure 2. Greenhouse Gases Emitted by Human Activity [Ref. 2].

      The Kyoto protocol identifies the six major gases emitted by human activity that contribute to global warming: carbon dioxide, methane, nitrous oxide, hydrofluo-rocarbons (HFCs), perfluorocarbons (PFCs) and sulphur hexafluoride [Ref. 4]. Fig. 2 shows the relative concentration of these gases, and Fig. 3 breaks down the sources of the most significant of these gases by sector.

      Figure 3. Human Sources of Greenhouse Gases [Ref. 5].

      Global Warming Potential

      Table 1. Global Warming Potential of Greenhouse Gases.

      These gases do not contribute equally to the greenhouse effect: a tonne of carbon dioxide creates a much weaker greenhouse effect than a tonne of methane. These different strengths of gases are called their ‘global warming potential’ (GWP). Carbon dioxide is by far the weakest of the six Kyoto gases, and is considered the most significant simply because we produce so much of it: by weight alone, carbon dioxide accounts for 99% of human greenhouse gas emissions. Figs. 2 and 3 break down the gases by their mass multiplied by their GWP, to demonstrate their actual contribution to man-made climate change. Table 1 [Ref. 6] shows the GWP of the six Kyoto gases. GWP is defined in terms of carbon dioxide: a GWP of 12 would mean a gas was twelve times more potent a greenhouse gas than carbon dioxide.

      This leads to the basic unit of measurement for greenhouse gas emissions: carbon dioxide equivalent, or CO2e. In calculating your carbon footprint, you would give one tonne of methane emitted as 25 tonnes CO2e, because of methane’s strength as a greenhouse gas. Because HFC and PFC are general terms for a range of gases they have a range of GWP values. Their GWP is generally large but they are emitted in relatively small quantities. In terms of individual scale emissions, they are generally not significant: fridges and air conditioners are likely to be the only appliances producing them. Even then, they generally represent only 10% of that appliance’s impact, with the other 90% coming from the electricity used [Ref. 7]. As such, most small-scale carbon footprint calculations don’t take them into account.

      Individual Scale Emissions

      Non-Transport Emissions

      Table 2. Non-Transport Sources of Emissions.

      On an individual scale, most greenhouse gas emissions are likely to be from the use of fuel: electricity, heat and transport. Because much of this tends to come from common sources in the UK - the national grid, the rail network - the impact of an individual in these ways can be calculated relatively easily. Tables 2 and 3 [Ref. 8] give the rate (in CO2e) at which common sources emit greenhouse gases. The figure for waste is based on a percentage of the overall emissions for a typical landfill, so any landfill waste can be modelled in this way. Transport emissions are given per passenger per kilometre (p.km). Emissions from water usage are virtually negligible [Ref. 11] and so are not included.

      Transport Emissions

      Table 3. Transport Emissions.

      More complicated to model are emissions from car and aeroplane travel. Car emissions vary according to make and model. Tables of emissions can be found online containing emissions of CO2 and NOx, usually given in grams per kilometre. NOx is a blanket

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