This past week, a friend and I went on a cruise for spring break, a 5 day adventure on the Carnival Valor in the Gulf of Mexico. The trip was a lot of fun, but I’m very curious about the environmental impacts of a diesel powered ship with seemingly unlimited food, drink, and overall consumption.
The 2016 Cruise Ship Report Card from Friends of the Earth ranked 17 cruise lines with respect to four factors: sewage treatment, air pollution reduction, water quality compliance, and transparency. Of the 17, Carnival ended up in the middle of the pack with an overall final grade of D. Carnival’s individual scores broke down as follows:
- Sewage treatment: F
- Air pollution reduction: C-
- Water quality compliance: A
- Transparency: F
Several webpages and blogs already detail the various environmental affects and concerns regarding these four factors (and more), and I won’t re-iterate all of that information here. Instead, I will specifically examine the carbon footprint associate with my spring break cruise
One carbon calculator for cruises estimates a 1.1 ton CO2 footprint for one passenger on my 5 day cruise. Let’s investigate a little further to understand where this number comes from, and how accurate it may be, beginning with emissions related to fuel consumption.
Method 1: Reported Scope 1 and 2 Emissions
Carnival’s 2015 Sustainability Report provides some information on total CO2eq emissions, including scope 1 and scope 2 emissions. Understandably, most of the emissions come from burning fuel on the ship. Exact numbers were not provided in the report, but I estimated from a graph that in 2015 (the most recent year), Carnival had an overall carbon intensity of 250 g CO2eq/ALB-km (ALB = Available Lower Berth). If the Valor traveled approximately 1800 miles (2900 km) round-trip for the cruise, this amounts to 725 kg CO2 for the trip – just about 65% of the estimated 1.1 tonne footprint from the calculator.
Method 2: Direct Calculation
In an attempt to double check this number, I directly calculated the carbon emissions based on a second set of data. According to Carnival’s 2008 Environmental Management Report, their ship emits 0.33 kg CO2/ALB-km (ALB = Available Lower Berth). It’s not explicit whether this number accounts for the time in which ships are docked at port and still burning diesel to power the boat, but since Carnival calculated the number directly from the amount of fuel consumed, I will assume it does. If the Valor traveled approximately 1800 miles (2900 km) round-trip for the cruise, this amounts to 956 kg CO2 for the trip, or almost one tonne.
However, burning diesel does emit other greenhouse gases which are not incorporated into the 0.33 kg CO2/ALB-km because the amounts emitted are small in comparison to the amount of CO2 emitted. However, from a global warming perspective these emissions are indeed significant, since their impact can be hundred of times that of CO2 alone. The same Carnival Environmental Management Report indicates emissions of 2.3 kg SOx/ALBD and 3.5 kg NOx/ALBD (ALBD = Available Lower Berth Day). For a 5 day cruise with 100 year Global Warming Potentials of 32 for Sox and 282 for NOx, this adds another 5294 kg CO2eq for the entire trip, or 5.5 times the impact of CO2 alone.
In sum, the impact of moving the boat to Mexico and back alone is 6.25 tonnes CO2eq, well exceeding the estimate from the first method. Even with an estimated 23% reduction in carbon intensity between 2008 and 2015 (again estimated from the graph in the 2015 Sustainability Report) to account for presumably increasing efficiency, this number is still at 4.8 tonnes, again well above the result from the first method.
Essentially, three different approaches yielded three different estimates for the carbon footprint associated with my spring break cruise:
- Carbon calculator: 1.1 tonnes (components included are unclear)
- 2015 Sustainability Report: 0.8 tonnes (scope 1 and 2)
- 2008 Environmental Management Report: 4.8 tonnes (fuel only)
I’ll need to look more into these to assess which is the most accurate, but for now, it’s clear that the cruise had a significant impact on my carbon footprint.