What does it mean to make a climate action plan “Paris compliant”? You may have heard this phrase, but do you really know what it means? “Paris” refers to the Paris Climate Agreement of 2015, which every nation in the world except the United States is committed to. “Compliant” refers to the goals set in the agreement to keep global temperature increase to well below 2 degrees Celsius, and attempt to limit warming to 1.5 degrees, compared to pre-industrial temperatures. So, what does that mean for a city wanting to do its fair share to avert climate crisis?
1.5 vs. 2 Degrees Celsius
The Paris Climate Agreement names two goals, but which one should we focus on – limiting warming to 1.5 or to 2 degrees Celsius? Half of a degree might not sound like much, but, as NASA puts it, it’s a “big deal.” That’s because the temperature increase won’t be spread out evenly over the area of the Earth or evenly throughout the year or time of day. Some places and times will see much greater increases, resulting in more extreme weather. Heat-waves would be longer, rainstorms more intense, sea levels would rise further, tropical coral reefs would be totally destroyed, and agriculture would be hit harder.
There’s also a strong equity argument to be made for the 1.5 degree Celsius goal. The Alliance of Small Island States (AOSIS) advocated for this more protective goal during the Paris Climate Agreement negotiations because their very existence is threatened by climate change. Rising sea levels are already making some low-lying coastal areas uninhabitable, and a 2 degree increase would completely inundate many of the 44 low-lying AOSIS member countries.
Beyond the clear and present threat to low-lying nations, warming has been and will continue to be most pronounced in the tropics, which includes many poorer nations. And poor people around the world will be most negatively impacted by climate change because the poor often live in more marginal areas – in flood plains or in drought-prone regions – and because the poor lack the resources to cope with extreme weather.
Global temperatures have already increased by about 1 degree Celsius and climate change is causing health problems. As this trend continues, those without access to medical care or living in flood plains will struggle to cope.
Global Carbon Budget
Understanding the concept of the global carbon budget (which is really a greenhouse gas budget) is important. Fundamentally, limiting warming requires limiting the total quantity of greenhouse gases released into the atmosphere, with emissions accumulating in the atmosphere year after year.
Determining an exact number is challenging and various climate models yield different results. Some models indicate that the carbon budget for limiting warming to 1.5 degrees Celsius has already been exceeded. The Intergovernmental Panel on Climate Change (IPCC) recognizes the need for additional analysis of the carbon budget to meet the 1.5 degree goal and is working on a report focused on this topic.
In the meantime, the carbon budget values provided in the IPCC 2013 AR5 Synthesis Report are the most comprehensive source of guidance because they include all GHGs from all sources, identify pathways to likely (defined as a two-in-three chance) meet the 1.5 and 2 degree Celsius goals, and are based on modeling out to 2100. Using the IPCC budget for the 1.5 degree goal, and accounting for emissions since that report was released, the remaining carbon budget at the start of 2017 was 162.02 gigatonnes. Limiting emissions to this amount would give us a 66% chance of limiting warming to 1.5 degrees Celsius.
A 66% chance of success also translates to a 34% chance of failure. Failure to preserve a livable climate. Ideally, we would aim to keep cumulative GHG emissions well below this budget to increase our chances of keeping to 1.5 degrees Celsius of warming.
Negative Emissions
Past inaction to reduce GHG emissions now makes negative emissions, or carbon sequestration, necessary to meet the goal of limiting warming to 1.5 degrees Celsius and likely even to meet the 2 degree goal, but the assumed scale of such efforts can easily be overestimated. The vast majority of the climate models relied on by the IPCC – and therefore, the underlying Paris Climate Agreement – assume massive negative emissions. While there are existing technologies and techniques for achieving negative emissions, all face significant challenges, including cost, other impacts on the environment, and use of land needed to feed the growing world population. Recent research suggests that negative emissions technologies are more limited than climate scientists have assumed in their modeling.
GHG Emissions Reductions Goals for U.S. Cities
The realities of the carbon budget and limits of negative emissions technologies makes a rapid reduction in greenhouse gas emissions necessary to avert climate crisis. While meeting the goals set in the Paris Climate Agreement is still possible, there is no time to waste on inaction. Net zero global GHG emissions must be reached by around 2050, and substantial near-term emissions reductions are critical.
C40 has developed a roadmap, called Deadline 2020, for how cities can translate these global goals and carbon budgets to local goals and actions. The emissions reduction curve for a given city depends on how much greenhouse gases the city emits and how much wealth the city has. Compared to the global average, U.S. cities are high emitters and have high wealth (defined as greater than $15,000 per capita gross regional product per year). The Deadline 2020 roadmap calls for such cities to get on a “steep decline” GHG emissions trajectory, with emissions reaching zero before 2050. The roadmap makes it clear that wealthy, high emitting cities, such as those in the U.S. must take significant action prior to 2020 to make it possible to achieve the 1.5 degree goal.
The good news is that more and more cities are engaging in climate planning. In Texas, that includes Austin, San Antonio, Houston, and hopefully soon Dallas. While each city has its own challenges and opportunities, the C40 Deadline 2020 roadmap can and should be used to set fair, science-based goals.
