Sources of emissions
Long distance travel
Long distance travel on course trips, department business and journeys home releases more greenhouse gases than any other sector of activity at DUSP. Based on data from 2006-07, 577 MTCDE were emitted, with 412 MTCDE alone due to flights purchased through the department offices. Vehicle travel emissions are estimated at 2.1 MTCDE. An annual trip home by each student is also included in the long distance travel section, estimated at 163 MTCDE. The total impact of travel is likely to be higher, because the flight data are incomplete, and local travel is not included.1. Erroneous duplicated records were cleaned from the data. Most trips listed the destination city (e.g. New Orleans; Vienna; Hong Kong), these flights were assumed to originate and return to Boston. Each destination city's main airport was located using an online list of airport codes. Some assumptions were made, e.g. all flights to New York go to JFK. Each pair of airport codes (e.g. BOS to JFK) was then fed into an online flight distance calculator and the results recorded in a spreadsheet to allow cross-ref lookups. Finally, the total distance of each flight was doubld to represent a round trip. For 57 domestic and 18 international flights made by visitors to MIT, the destination was listed as 'Boston' and no origin was given. Using all other flights, average trip lengths were obtained: average domestic trip 1,780 km, average international trip 7,860 km.
Methodology for flight emissions
DUSP administration provided a list of all flights booked through the department between February 2006 and April 2007. These flight were taken by faculty, students and visitors to MIT, to destinations nationwide and international. In total, 444 flights were listed, with 220 domestic and 224 international. Total flight distance was calculated for each trip 1.
The greatest number of flights was to New Orleans (33 trips), followed by Mexico City (30), Beijing (30), Venice (26), Washington DC (22), New York (21) and Sao Paulo (19). These cities account for 40% of the total destinations. Four faculty flew over 60,000 km each. The top flier at DUSP travelled over 160,000 km in less than 14 months.
Greenhouse gas emissions for flights take place in two distinct phases: take off/landing, when fuel consumption and emissions are high, and cruising2 2. See Aircraft Emissions, IPCC National Greenhouse Gas Inventories Programme.. This means that short haul flights have a higher emission of GHG per km travelled than long haul flights once the take off/landing emissions are considered and other factor such as plane type and loading are included. For long distance flights, 0.11 kg of greenhouse gases are emitted per passenger km; for short haul, 0.16 kg GHG per passenger km. All flights over 500 km are considered long distance. 3 3. "Factors for a long haul flight refer to a 5,000 km journey on a typical 450 seat capacity aircraft used for these journeys, with a 70% load factor. Factors for a short haul flight refer to a 500 km journey on a typical 128 seat capacity aircraft used for these journeys, with a 65% load factor." UK Government Department for Environment, Farming and Rural Affairs (DEFRA), Guidelines for Company Reporting on Greenhouse Gas Emissions - Annexes, 2005..
Emissions from DUSP air travel
| Short haul (> 500 km) | Long distance | Total | |
|---|---|---|---|
| Total flights | 220 | 224 | 444 |
| Total km travelled | 24,314 | 4,281,282 | 4,305,596 |
| Emissions per km | 0.15 | 0.11 | - |
| Total emissions (MTCDE) | 3 | 471 | 474 |
| Total annual emissions (MTCDE) | 2.6 | 409 | 411 |
Methodology for vehicle and train travel emissions
DUSP does not collect data on train travel, car hire or vehicle distances in as accessible a format as the flights data. For a very rough estimate, 25 km of driving in an car was assumed as part of each trip, resulting in 9,646 km travelled and 2.1 MTCDE emitted4.4. Assuming 2.1 litres and above petrol vehicle emitting 0.22 kg GHG per passenger km. DEFRA ibid. This value is extremely approximate.
Methodology for annual trip home emissions
For each student, emissions from a single air trip home have been calculated, using the average domestic or international flight distance to provide emissions for the trip. The total is probably an underestimate, since students may travel home more than once each year. For many students from the US, the average US flight will be further than they travel, but since they may travel home more often by other means there may be some balancing. This measure is discussed in the Limitations section below.
Emissions from flights home
| Domestic | International | Total | |
|---|---|---|---|
| Number of students | 134 | 64 | 198 |
| Emissions per round trip (MTCDE) | 0.391 | 1.73 | - |
| Total emissions | 52 | 111 | 163 |
Limitations
Greenhouse gas emissions from flights are thought to be more damaging to the environment than other forms of emissions, because they are inserted directly into the upper atmosphere5. 5. For more information, see Rogers, H L et al. The impacts of radiation on the upper atmosphere, The Aeronautical Journal 2002. Further investigation could provide more accurate measures of the relative impacts of these emissions relative to others.
Flights for DUSP activities that were purchased through other routes are not counted (e.g. Dean's office, project sponsor). At least two classes this spring took flights that do not show up in the records, so these emissions are missing.
Train or bus travel is not included, though the low emissions from rail transport mean that this is probably not a large additional contribution.
No allowance is made for emissions due to ongoing projects within Boston or Massachusetts, e.g. Lawrence or Springfield. These collaborations involve frequent trips from campus on transit or in vehicles, though the overall level of emissions is far lower than the missing flights data.
Each DUSP student is allocated $250 per year to cover conference costs, which can be spent on travel. For students giving a presentation, $400 is provided. PhD students are able to make two trips. This means that there is at least one and possibly two trips per year per student taking place on DUSP funds that should be included (e.g. train travel).
"Trips home" is a contentious measure and should possibly be dropped from a revised version of the audit - if the purpose of the study is to highlight potential for change around the department, what should be inferred from the emissions due to students' personal travel? In addition to DUSP's evaluation of its greenhouse gas emissions, each student should be considering her own personal "footprint", which could include non-school trips to visit family.
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