Arguably, the biggest climate news so far in 2018 is the International Maritime Organization, or IMO, finally adopting a global climate framework for international shipping. In doing so, it joined its sister agency, the International Civil Aviation Organization (ICAO) in establishing a plan to cut emissions in their respective sectors. These two sisters, who weren’t specifically mentioned in the Paris agreement, were in competition to be the next agency to formulate a strategy. ICAO beat IMO to the punch by adopting its own global deal on greenhouse gases (GHGs) in 2016. Now that both are in place, how do they compare?
Let’s start with IMO’s agreement, which we analyzed in detail here. The centerpiece of IMO’s GHG strategy is to halve total CO2 emissions from international shipping from 2008 levels by 2050, followed by complete decarbonization no later than 2100. The plan implies 60 to 70% cuts in greenhouse gas (GHG) emissions this century, which will require aggressive investments in low- and zero-carbon technologies. The next step is for IMO to flesh out a set of mandatory short-, mid-, and long-term measures to support this goal, with a particular focus on tightening energy efficiency standards for new vessels and speed management policies for the in-service fleet.
Contrast this to ICAO’s agreement, which was finalized in October 2016. Two goals were included: capping net CO2 emissions from international aviation at 2020 levels – carbon neutral growth, in ICAO parlance – plus a 2% annual fleetwide fuel efficiency goal, aspirational from 2020. ICAO developed two mandatory measures to support these goals: the Carbon Offsetting and Reduction Scheme for International Aviation (CORSIA), and a fuel efficiency (CO2) standard for new aircraft. Neither measure is expected rein in aircraft emissions growth in the foreseeable future: CORSIA because the offsetting approach sets near-term carbon prices too low to change airline behavior, and the CO2 standard because it does not require additional investments in fuel efficiency beyond those already in the works by manufacturers.
So how do the emissions targets in each sisters’ framework compare? We should start by noting a key philosophical difference in the two approaches. ICAO, arguing that aviation faces unique challenges to decarbonize, is prioritizing carbon offsets and the development of alternative jet fuels. Both measures aim to compensate for, rather than directly reduce, emissions from the aircraft. For example, by relying on fuel providers to reduce emissions upstream, the current fleet is allowed to continue to operate as-is.
IMO plots a different course, hoping that its 2050 absolute target and vision to completely phase out fossil fuels will drive new investments in the low- and zero-carbon technologies that are ultimately needed to decarbonize shipping. Notably, IMO considered, but ultimately rejected, a near-term cap on shipping emissions that might have favored offsetting.
With that, the numbers. The figure below compares projected CO2 emissions from international shipping (black solid and dotted lines, corresponding to the possible ranges of ambition under by IMO’s GHG strategy) to emissions from international aviation with and without CORSIA offsetting (blue surfaces). Shipping emission projections come from our summary of IMO’s recent agreement, aviation emissions from ICAO’s 2016 Environmental Report (base demand case, with an annual 1.4% improvement in fleetwide fuel efficiency), while CORSIA offsets are estimated using ICCT’s internal market-based measure calculator.
As shown, international aviation CO2 emissions are expected to grow from about 500 million metric tons (Mt) in 2015 to 1760 Mt (absolute) and 880 Mt (net minus offsets) in 2050, and approximately double again through 2075 assuming extrapolated growth. Shipping emissions will fall by at least 50% by 2050, meaning that aviation is likely to exceed shipping as the largest international source of CO2 beginning in 2035 (absolute emissions) and sometime before 2045 (net). A key source of uncertainty in this analysis is the degree to which offsets might be double counted across the Paris and ICAO climate frameworks, which would undermine their effectiveness in mitigating in-sector emissions. Note that this analysis doesn’t include CO2 emissions from domestic emissions (roughly one third of the aviation total), nor short-lived climate pollutants like black carbon, nitrogen oxides, or aviation-induced cloudiness.
The figure below shows the share of a Paris Agreement-compatible carbon budget claimed by international aviation, as represented by the International Energy Agency’s Beyond 2°C Scenario (B2DS). Here, cumulative emissions starting in 2015 are shown, with the black bars representing net emissions and the hatched bars portraying offsetting under the CORSIA agreement. Assuming business as usual growth, international aviation will exceed its proportional share (1.42%) of a Paris compatible carbon budget around 2030, with or without offsetting. Aviation would double its share of a B2DS carbon budget (roughly equivalent to IMO’s goal) starting in 2040 in absolute terms, and around 2045 on a net basis counting offsets.
Under its GHG strategy, IMO is laying claim to roughly double its proportional share of a carbon budget consistent with the Paris agreement – emissions would rise from about 2.3% of global CO2 today to between 3.8 and 5.8% of the total B2DS scenario. Aviation, in contrast, would increase its share of emissions much more, from 1.4% today to between 7% and 14% of the global carbon budget by 2075. To make matters worse, ICAO’s share would continue to grow even after 2075 unless rapid decarbonization is achieved.
ICAO is clearly the underperforming sister here. How might this be changed? A modest proposal for ICAO is to adopt its own long-term goal at its 40th Assembly next year. Indeed, the aviation industry has already proposed something close to that through its aspirational goal to cut net emissions by 50% compared to 2005 levels. However, the term “net” signals a continued reliance upon offsetting to meet that target, rather than true decarbonization. The risks of relaying upon offsetting emissions, especially without adequate safeguards on vintage and quality, are beyond the scope of this work but are described here, and here, and here. ICAO could adopt industry’s goal but strengthen it by targeting absolute, rather than net, emissions. That would go a long way to keeping this constructive sibling rivalry alive and well.