This article is currently outdated. Best look for another source for calculating air freight carbon.
Updated Sep 2016
Updated Aug 2012.
With the Copenhagen climate conference starting today, it's useful to calculate the carbon emissions for production and shipping of specific products. As a next step, an offset could be provided.
Some initial research on basic carbon calculations for shipping:
Definitions
Anthropogenic = manmade, Defra = UK Department for Environment, Food and Rural Affairs, GHG = Greenhouse gas, GWP = Global warming potential, UN IPCC = UN Intergovernmental Panel on Climate Change
CO2e stands for Equivalent Carbon Dioxide. It defines the effects of all gases that have global warming potential under one term, or "currency". That currency is CO2e. It is defined as the flow into (not a given concentration in) the atmosphere. Some gases have a higher, others a lesser impact. This can be measured and compared by using the term of "equivalent CO2 value".
Source: http://en.wikipedia.org/wiki/Carbon_dioxide_equivalent Some sources use CO2e as a concentration of parts per million (i.e 350 ppm CO2e). According to the definition above, this might indicate incorrect usage.
Conversion
GHC Conversion factors - converting other gases to CO2e: Source: http://www.defra.gov.uk/environment/business/reporting/pdf/ghg-cf-guidelines-annexes2008.pdf
Price
The price of 1 tonne CO2e is said to be between 10-30 euro. On 7 Dec 2009 it stood at 14.86 euro. That makes it 0.01486 euro per kg (or about 1.5 eurocent/kg). A lower price is shown at the second source. Source: http://www.pointcarbon.com/trading/ 14.86 +0.58 euro on 7 Dec 2009, http://www.co2e.com/.
Update 2012: 1 EUA (European Union Allowance) is 6.81 euro on 11 April 2012, http://www.bloomberg.com/quote/EUETSSY1:IND (EUETSSY1 - Bloomberg spot price).
Air freight
Figures for short, medium and long-haul are different. Also different calculators come to different conclusions.
Air freight is calculated at 0.00189317 kg CO2e /km (avg 1.500 km assumed). Source: http://www.carbonneutral.com.au/calc/cncalcip.pdf (on p22+ and re air travel on p10+):
Dec 2009: Sending a small 3 kg air freight package from SEA to EUR (20.000 km) would then be 0.00189317 kg CO2e /km x 20.000 km = 113.59 kg CO2e. This 113.59 kg CO2e x 0.01486 euro/kg CO2e = 1.69 euro.
Update Apr 2012: with carbon price less than half the level of 2009, the current carbon cost is halved (approximately).
Summary result
The CO2e offset cost for 3 kg air freight shipping from Southeast Asia to Europe was 1.69 euro in Dec 2009 and about half that in Apr 2012.
Related
Exploring the market for voluntary carbon offsets - 2006 http://pubs.iied.org/pdfs/G00268.pdf
Spekboom soaks up co2 - 2008-06-24 http://www.urbansprout.co.za/spekboom_soaks_up_co2
Falling EU carbon prices reflect political doubts (opinion) - 2011-10-05 http://www.reuters.com/article/2011/10/05/climate-carbon-idUSL5E7L519Q20111005 (Reuters)
Carbon prices reach new low with bureaucratic delay and oversupply - 2012-07-20 http://www.climateactionprogramme.org/news/carbon_prices_reach_new_low_with_bureaucratic_delay_and_oversupply/
6 August 2012. The carbon price has declined further. I'll need to look into what is wrong with this carbon pricing system. Things to do.