Understanding greenhouse gas reduction targets
As the largest city in the USA states its intention to achieve 80×50 status, sustainability consultant and urban planning expert Josh Margul explores the implications of this and other common carbon reduction targets
The recently-released New York City 1.5°C Climate Action Plan represents a major step forward in the city’s efforts to control its carbon emissions.
Having committed in 2014 to reducing its greenhouse gas (GHG) emissions 80% by 2050, New York City released its initial Roadmap to 80 x 50 in 2016. This year’s 1.5°C Climate Action Plan builds on the Roadmap by setting out an ambitious set of initiatives for city agencies to pursue, with the aim of achieving significant GHG reductions from buildings, waste and transportation.
As the pressure to address global warming mounts year on year, cities around the world are joining New York in the bid to reduce carbon emissions. Achieving 80×50 status is the target set out in the Paris Agreement of 2015, and the most commonly adopted, but there are other options for even more ambitious cities to pursue.
Carbon reduction targets
New York is one of 17 cities that has committed to achieving an 80% reduction in GHG emissions by 2050. This target stems from a 2007 Intergovernmental Panel on Climate Change (IPCC) report, which states that we must stabilise the concentration of heat-trapping GHGs in the atmosphere to ensure global warming doesn’t reach 2°C above preindustrial levels.
This figure is recognised worldwide as an ambitious but achievable target in the battle to safeguard the future of our planet. The concept of limiting global warming to this level is based on the assumption that, by keeping changes to the climate within the bounds experienced in the recent geological past, we can avoid catastrophically disrupting both human lives and natural ecosystems.
In 2015, 195 nations signed the Paris Agreement, pledging to work together to find ways for leading cities to reduce their emissions to an average 70-80% below levels recorded in 2000, to meet the 2°C target by 2050 and achieve 80×50 status.
Another target commonly referred to in GHG reduction discussions is ‘carbon neutral’. This is simply defined as being when ‘the net greenhouse gas emissions of a city is zero’, but the path to achieving it is less clear.
The guiding principle associated with the deep decarbonisation required to achieve carbon neutral status is the use of sustainable energy systems. One option is for a city to become fossil-fuel free, while another is establishing a 100% renewable energy supply. Some cities have adopted this goal only with reference to electricity generation, while others encompass all energy sources in their boundaries.
Due to physical and jurisdictional limitations – like a lack of available land to dedicate to renewable energy generation, or decisions affecting energy supply being taken at a state or national level – cities typically have to offset some remaining emissions in order to achieve carbon neutrality.
The Carbon Neutral Cities Alliance (CNCA) recommends several ways in which cities can do this. These include generating excess renewable energy and providing it to consumers outside the geographical boundary of the city, as seen in Copenhagen, or purchasing carbon offsets, like Melbourne.
This stringent target moves beyond carbon neutrality to attain net-negative carbon emissions, ie actively reducing levels of carbon in the atmosphere. In cities, this can only be achieved by providing excess renewable power to the grid, or excess heating/cooling energy to neighbouring developments.
In theory, a city could produce enough energy within its borders to supply other cities, but in reality few cities have the land resources required for this level of renewable energy generation. That is why cities with climate positive aspirations boast unique geographical features that provide opportunities to harness off-shore wind, hydropower, geothermal or local biomass resources.
Notably, C40 Cities’ Urban Planning & Development Initiative has created a certification process for buildings and district-level developments, so while a city at-large may find it difficult to become climate positive, the target is achievable at a smaller scale.
Choosing the right target
As all these efforts are laudable, it comes down to factors such as geography, availability of renewable resources, and the difficulties of implementation to determine which target is the most appropriate for each individual city.
Whichever target is adopted, deep decarbonisation requires substantial structural, economic and policy changes to drive increased energy efficiency, decreased use of fossil fuels, and reductions from other emissions sources such as waste.
Given this, most cities will have to consider offsetting a portion of their energy consumption with off-site renewable energy generation, or by purchasing certified offset credits, to achieve their chosen target.
The chart below provides a comparison of carbon reduction targets and timelines for 30 global cities, all of which are affiliated with C40 Cities, CNCA and/or the Global Covenant of Mayors (GCM).
Most of these cities have adopted 80×50 targets. Some, such as Seattle and Oslo, have aimed for a 100% reduction to achieve CNCA-defined carbon neutrality. Copenhagen, with its unique and vast offshore wind resources, stands alone in aiming to be climate positive by 2025.
To see if your city has committed to a carbon reduction target, visit: www.globalcovenantofmayors.org/cities. For more information on BuroHappold Engineering’s work in climate, environment and sustainability, visit: www.burohappold.com