Equity or inertia: how emissions sharing philosophies shape climate policy success

What is the best way for the global community to set greenhouse gas emission goals to stave off global temperature increases over the dreaded 2 degrees Celsius? This question framed the heart of negotiations between 190 countries during a UN-sponsored meeting in Lima earlier this year.¹As a result, countries agreed to create 'fair and ambitious' post-2020 emission standards tailored to each country's economic, environmental, and social circumstances.

Next, countries will declare their Intended Nationally Determined Contributions (INDC) at the Paris Climate Conference next month. Each INDC is a national pledge made by a country to reduce greenhouse gas emissions by a certain amount by a particular date, with the entirety of INDCs summed to meet UN reduction goals. The expectations for the conference are high: the declared goals will set the stage for post-2020 reductions and dictate the course of human civilization's combat against global warming.

This step toward global consensus is necessary and admirable. But what actually constitutes a 'fair and ambitious' standard? Also, when each INDC is made individually, how can we be sure that their sum will meet the global emissions goal of preventing a 2 C global temperature increase? The US, EU, and China - the primary emissions culprits - have already made pledges. Are they enough to meet global goals when taking into account the rest of the world?

To answer these questions, researchers in the US, Norway, and England have quantified ambitious and fair pathways to share CO2 emissions globally in an effort to keep global temperatures below 2 C.² In particular, they test whether current US, EU, and Chinese pledges are good enough to reduce emissions sufficiently by 2050 based on two measures of fairness. The results are not exactly hopeful but should spark an important discussion about realistic policy goals and how to prepare for a warmer future.

A world's ambition

The 'ambitious' component of climate policy must determine a global temperature limit and then quantify the necessary emissions reduction. Policymakers often consider 2 C warming as an important goal to minimize some of the more dangerous impacts of global warming, and the researchers here used this mark to quantify ambitious policy.

Based on the latest IPCC reports, an almost linear relationship exists between cumulative CO₂ emissions and global increases in temperature, which makes it easy to predict how future emissions will affect temperature. Assuming this relationship, we can emit about 765 gigatons of CO₂ (GtCO₂) through 2050 to keep global temperatures below 2 C with 66% likelihood. The probabilistic part comes from the fact that climate models are inherently uncertain, so we're never quite sure the exact amount of CO₂ that will lead to this 2 C increase (but we're close enough to sensibly inform policy!). To put these numbers in perspective, we have already contributed about 2750 GtCO₂since the 1870's through non-CO₂ gases, fossil fuel industrial emissions (FFI), and past land use change (LUC), as shown in the graph to the right.

Equity or inertia?

The 'fairness' policy component addresses how we share the emissions burden across countries to meet this 765 GtCO₂goal. The researchers determined two guiding philosophies on opposite sides of the fairness spectrum: equity and inertia. Equity suggests a democratic sharing based on country population. This type of policy would create the same per capita emissions limit across all countries that would be needed to reach the necessary global reduction.

The problem with the equity approach is that the US already has per capita emissions five times larger than non-EU countries not named China (EU and China are about twice as high). Dramatically reducing this may not be feasible (as we'll see below). To account for this, the inertia approach would create reduction standards based on historical emissions. So, the US would be allowed a higher per capita emissions than, say, Albania, because it's already emitting such a large amount. This would be the ufair but practical approach to emissions sharing.

In reality, policy will probably blend the two approaches, but these limits are great guideposts to see how each philosophy will lead to CO₂ emissions by 2050. And the equity approach will call out those countries already way over their limit (ahem...US, I'm looking at you) and possibly motivate them to enact more drastic interventions promoting low-carbon technology. We can always hope...

The Big Three must do more

The US, EU, and China have already set pledges for emission goals between 2030-2050, so the researchers projected these goals together with either the equity or inertia policy approaches to predict what would be demanded of the rest of the world to stop 2 C warming. The US INDC promises 27% reductions from 2005 levels by 2025 and the EU INDC shoots for a 40% reduction from 1990 levels by 2050. The China INDC is based on relative growth, hoping for a 60% reduction in emission intensity by 2030 compared to 2005.

So how do these emission goals compare with global sharing methods? The figure to the left plots colored lines projecting future emissions based on these INDCs, along with a shaded region bounded by emission requirements from the equity and inertia philosophies. In all cases, these are the trajectories that would be required in each case to limit warming below 2 C. There are a couple major conclusions from this:

Current US and EU pledges are generally close to the inertia sharing philosophy, indicating that per emission capita in these countries would continue to be higher compared to the rest of the global average. This policy approach puts the onus on many developing countries, who are trying to industrialize and electrify, to keep per capita emissions low when they would otherwise be increasing to catch up with the rest of the world.
China is nowhere close to meeting the necessary reductions for either the inertia or equity trajectories. The primary challenge for China is to overcome still-growing emissions, whereas the US and EU are already decarbonizing. China started running the industrial revolution race at just the wrong time when the world is telling them to slam on the brakes.
Notice that the US has the widest change in its inertia versus equity trajectory. This is because it has the largest per capita emissions by far, so the equity path would require the most significant shift in fossil fuel consumption. The US has the largest to lose from an equity approach; or, but another way, the greatest responsibility to change average lifestyle and consumption.

So the current pledges by the Big Three are a good start, but not enough to meet the ambitious 2 C warming goal. Indeed, based on these analyses, the world is actually heading for roughly 3 C warming with 66 percent likelihood. Even if the US and EU are close to the inertia policy goals, this would require developing countries to somehow jump the fossil fuel-fired economy and move directly into renewables and low-carbon sources. There hasn't really been a global examples of this type of transition yet (that I know of). The alternative is to allow developing countries to increase per capita emissions (equity) and count on remarkable advances in renewables and carbon sequestration in developed nations.

Both of these paths are extremely difficult: one requires a social jump and the other requires research advances at a pace never seen before. So this brings up the elephant in the room: is a 2 C warming limit realistic? We should probably still shoot for such an ambitious goal, but these results suggest we should also start thinking about how to adapt and prepare for a hotter world.

Good policy should plan for both possibilities. Finance and research renewable energy development and carbon sequestration technology to try to advance to a low-carbon economy as quickly as possible. But if this doesn't work out, let's be prepared with coastal migration strategies, organized disaster relief efforts, among other steps.

Christiana Figueres, the head of the UN Framework Convention on Climate Change, discussed emissions policy on Reddit's 'Ask Me Anything', during which she acknowledged that INDCs are a starting point and not a destination. This is a hopeful sign that officials also see the need to do more, but also understand that reasonable and credible goals will build momentum toward even stricter emission limits. The talks in Paris next month will advance this conversation, giving emission goals to build upon that some day may lead us to a 2 C warming path.

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