The new international Paris Agreement on climate change aims to keep global warming to well below 2 degrees C (3.6 degrees F) above pre-industrial levels and to try to limit the temperature increase to 1.5 degrees C (2.7 degrees F) to avoid the worst climate impacts. This temperature goal is critical, since the hotter it gets, the more severe the climate impacts. However, it is difficult to communicate what needs to happen across various sectors to achieve this temperature goal. As a result, the Agreement also has a complementary long-term goal that gives concrete guidance to investors and policymakers on what they need to do and by when.

Negotiators have wrestled with the language for this complementary long-term goal in the months leading up to the December 12 adoption of the Agreement. The final text on the long-term goal sets out the need to: “achieve a balance between anthropogenic emissions by sources and removals by sinks of greenhouse gases in the second half of this century, on the basis of equity, and in the context of sustainable development and efforts to eradicate poverty.” These terms require a bit of explaining to understand this balancing act.

What Kind of Balance?

Where the Agreement says it aims “to achieve a balance” between anthropogenic emissions and removals by sinks, we should interpret this to mean cancelling out anthropogenic greenhouse gas (GHG) emissions with removals of GHG emissions from the atmosphere by enhanced action to sequester it in carbon sinks (e.g. increase afforestation to sequester more carbon dioxide in vegetation). First and foremost, human-caused GHG emissions – like those from fossil-fueled vehicles and factories -- should be reduced to as close to zero as possible. Any remaining GHGs would be balanced with an equivalent amount of sustainable GHG removal, such as restoration of forests. Any removal strategies should be sustainable and not have adverse impacts on biodiversity and food. This is a concept akin to net zero GHG emissions, where anthropogenic GHG emissions are reduced as much as possible and enhanced removals of those gases make up the remainder to achieve net zero emissions.

Which GHG Emissions? Which GHG Removals?

It’s important to understand that the Agreement’s long-term goal includes GHGs beyond carbon dioxide. These non-carbon dioxide gases accounted for almost a quarter of GHG emissions in 2012.

The phrase “anthropogenic emissions by sources and removals by sinks of greenhouse gas emissions” has been used before by the UNFCCC (the UN Framework Convention on Climate Change) in the context of national inventories. Therefore it could be viewed as pertaining to those anthropogenic GHG emissions and anthropogenic removals that are covered by national inventories, i.e. the six/seven GHGs and a set of activities linked to land-use, land-use change and forestry. As scientist Malte Meinsausen states, given how the term has been used in the Convention, “the adjective ‘anthropogenic’ refers to both ‘emissions’ and ‘sinks.’” Accordingly, emissions will be sequestered by removals that occur as a result of human activities that enhance sinks, as opposed to natural sinks. Furthermore, geoengineering technologies that simply alter the energy balance but do not reduce emissions or enhance sinks – such as solar radiation management – would not be viable for meeting such a balance.

When Specifically Is “In the Second Half of the Century”?

The text refers to balancing anthropogenic emissions and removals in the second half of the century, which is a stronger signal than just “by 2100” which is a reference in the IPCC. Coupled with the temperature goal to limit warming to well below 2 degrees C and trying to limit it to 1.5 degrees C, scientists have established when during the second half of the century this needs to occur. Coupling the temperature goal with the long-term goal of balancing anthropogenic emission and removals provides clearer signals for the exact timing of emissions reductions.

To have a likely chance of keeping warming to below 2 degrees C, here’s when we need to achieve net zero emissions:

  • Carbon dioxide emissions have to drop to net zero between 2060 and 2075
  • Total GHG emissions need to decline to net zero between 2080 and 2090

For a likely chance of limiting warming to below 1.5 degrees C, we need to achieve net zero emissions by:

  • Carbon dioxide emissions have to drop to net zero between 2045 and 2050
  • Total GHG emissions need to decline to net zero between 2060 and 2080

A recently published paper in Nature Climate Change suggests that to limit warming to either 1.5 degrees C or 2 degrees C, carbon dioxide emissions from electricity are brought close to zero by 2050. Furthermore, around 25 percent of energy required for transportation will also come from electricity, up from the current share of less than 1 percent.

How does the final language for the long-term goal help get us to the temperature goal?

While some of the terms that existed in earlier drafts of the agreement were clearer and more specific about the amount of greenhouse gas emissions that had to be reduced and by when, the final language does send a signal that net zero greenhouse gas emissions need to be reached in the second half of the century. To get there, according to the IPCC, unabated fossil-fuel power generation must cease this century.

Balancing anthropogenic emissions and removals -- coupled with the goal to limit warming to well below 2 degrees C and trying for 1.5 degrees C -- commits governments around the world to ending high-emitting behavior and ramping up efforts to reach net zero GHG emissions in time to limit the worst consequences of climate change.

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