Our carbon footprint is driven by economic development. It is correlated with GDP and therefore shows a lot of variability across the world.
CO2 emissions amount to 77% of greenhouse gas emissions, and it is therefore the engine that drives climate change. Methane is 14% and nitrous oxide 8%. The remaining 1% is the contribution of other greenhouse gases.
The carbon footprint is often measured in “CO2 equivalent”. This is the amount of CO2 that is necessary to replicate the impact of all greenhouse gases. The current concentration of CO2 in the atmosphere is 385 ppm (parts per million), and the CO2 equivalent is 430 ppm.
The CO2 concentration in the pre-industrial era was 280 ppm. This is the bottom line from which to measure human contribution to global warming.
Carbon emissions are surrounded by myths. It is widely believed that aviation is responsible for much of it. However it accounts for 1.6% of emissions. On the other hand, deforestation is a topic that hasnt received the attention that it deserves. It is responsible for 18.3% of all emissions, a higher contribution than the combined electricity and heat emissions for household and commercial buildings.
The emissions for agriculture are 17.4% of the total and a slightly lower percentage for all transport (13.5%). Therefore the carbon footprint of food production is similar to that of transport.
If we add to these figures the cost of transporting food, the real carbon footprint of food consumption is very significant.
The current level of emissions increases the concentration of CO2 by 2.7 ppm per year. A continuation of this trend takes the concentration of CO2 beyond the threshold of irreversible global warming within the next decades.
The correlation of emissions with economic development raises the further concern that the carbon footprint will accelerate as emerging economies develop.
Road transport accounts for 10% of our carbon footprint. Cars are responsible for the bulk of these emissions.
Freight and road public transport account for a small fraction of this.
The carbon footprint of all car transport is comparable to that of residential buildings. In other words, cars create as much CO2 as the generation of electricity and heat for our households. This means that car engines are very inefficient in generating kinetic power relative to their emissions.
Driving causes a high visibility carbon footprint. To compare, the carbon footprint of deforestation is twice as big, but whereas this is not an everyday topic we all see cars everywhere in our cities. Due to congestion and traffic fumes, the 10% contribution of cars to our carbon footprint is the most visible contribution of all.
Excessive use of private cars results in congestion in major cities and motorways, and as a result the average driver spends more time in stationary traffic. Therefore the real amount of CO2 emitted per mile is on the increase. Drastic cuts in driving can result in a significant reduction in our carbon footprint.
Rail transport is the low-carbon footprint alternative to combustion cars. Also, it alleviates congestion and can be a valid substitute for many unnecessary car journeys.
Clearly the future of road transport is in electric vehicles. They are efficient and their carbon footprint is comparable to other household appliances. Electric cars do not have “visible” emissions but they have a share in the carbon footprint of power generation.
Electric vehicles are bound to create a lot of pressure in sourcing power. If all road transport is converted to electric in the next decades, as should be the case in order to mitigate dramatic climate change, the electricity consumption will increase enormously. This emphasises the importance of clean energy sources, and the role of nuclear energy in the short to medium term in parallel with renewable sources of energy.
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The carbon footprint from the generation of power is 25% of all emissions. This is the largest single contributor to global warming.
Out of this, the carbon footprint of residential households is 10%, industry 10% and commercial buildings 5%.
These CO2 emissions are created by burning fossil fuels, such as petroleum, coal and gas.
The energy that we consume in our households comes from a range of sources. Mostly of it is from fossil fuels, and a small fraction from nuclear and renewable sources such as wind and solar energy. Therefore our carbon footprint depends entirely on how the energy is sourced. How green is the energy we consume depends on governments and utility companies.
Energy consumption is correlated with economic development and the concern is that the growth in the demand of power is significant. The carbon footprint of energy generation has grown 2% per year, the largest growth of any single source of emissions. Emissions have grown much more rapidly in China, India and the Middle East.
The fast growth in the use of computers creates a strong pressure on demand. The IPCC estimates that by 2050 the carbon footprint of energy generation will increase four-fold, mainly due to gas and coal. It is a staggering prediction.
It is quite clear that a strategy of mitigation requires a low-carbon energy production strategy. Coal or any other fossil fuel is the antithesis of this.
In the long-term the answer is less about limited consumption and more about clean energy production. The best option are renewables and a significant effort must be made to move in that direction quickly.
In the medium to long term, the shortfall in energy must be met through other means. This need must be balanced with the urgency to cut emissions drastically in the shortest term possible. Nuclear energy is the only option capable of delivering such immediate needs. However the problem of waste disposal is serious and merits a lot of research funding to address rapid improvement.
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Commercial aviation accounts for 1.6% of our carbon footprint.
In relative terms it is a small fraction of the total. Emissions from cars are six times as much.
The comparison of road and air travel is interesting. There are about 850 million vehicles on the worlds roads, and a similar number of air passengers per year (840 million, as of 2008). Therefore on average the carbon footprint of one car is six times that of an air passenger.
The higher impact of road travel is easy to understand because air travel is more infrequent. Most of the 840 million passing through the worlds airports every year travel once a year or even less frequently. The carbon footprint for their journey is high but in contrast a car completes many journeys in a year (on average 33 miles per day).
Like cars, airplanes have a highly visible carbon footprint. In the major cities of the world air traffic is on the increase creating congestion and pressure on airports to expand.
Access to air travel is correlated to GDP and varies enormously in different regions of the world. With the availability of cheap air travel there is a growing trend to fly frequently that is no longer limited to the affluent. As a result, there are a significant number of people who are frequent flyers and whose carbon footprint is several orders of magnitude greater than the average.
The main concern is that emissions from aviation are the fastest growing of all forms of transport. The IPCC predicts a three-fold growth by 2050. The enormous growth in passenger numbers and frequency of travel emphasise the urgency of finding greener technologies for air travel.
In the short term it seems unlikely that technology will be able to address drastic emission cuts unless passenger numbers drop dramatically. In the absence of a solution, effective mitigation of climate change would require that all air travel is offset through carbon capture programmes (such as reforestation).
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The main greenhouse gases resulting from human activity are: carbon dioxide (CO2), methane and nitrous oxide.
In modern times, the concentrations of these gases have increased dramatically. Their effect is to contribute to the warming of the Earths atmosphere by trapping more heat from the Sun.
The increase in CO2 is mostly from fossil fuels, used in transport, energy generation and manufacture.
Deforestation is also a contributor to emissions (18% of the total). A further consequence of deforestation is that it reduces the Earths capacity to capture carbon.
Methane is the by-product of agricultural activity, waste management and natural gas production. Methane concentrations have actually decreased in the last decades.
Nitrous oxide is emitted through the use of fertilisers and fossil fuel burning. It is also released naturally in the oceans.
Water vapour is an abundant and important greenhouse gas. It is not the cause of global warming but it is affected by it. Human activity has an impact on the water cycle through global warming. It affects weather patterns and the movement of water vapour in the atmosphere.
The impact of greenhouse gases is in the disruption of the balance between the incoming radiation received from the Sun and the heat dissipated into outer space. Each greenhouse gas has a different capacity to retain extra heat and therefore impacts differently on global warming.
CO2 has the greatest effect, greater than all other greenhouse gases combined.
The total of all contributions of greenhouse gases and aerosols results in a steady accumulation of excess heat in the atmosphere.
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