The draft Paris Agreement acknowledges the need to limit warming to well below 2 degrees C (3.6 degrees F) above pre-industrial levels and the need to try to limit the temperature increase to 1.5 degrees C to avoid the worst climate impacts. However, these temperature goals do not give obvious guidance to investors and policymakers on what changes they need to make and how fast they need to make them. So COP21 negotiators added a complementary, operational long-term goal to help work toward the temperature target and measure progress. The long-term goal is critical to catalyze climate actions and shift to low-carbon investment patterns.Negotiators have wrestled with the language for the long-term goal. In the climate conference’s last days, a new proposal surfaced for greenhouse gas (GHG) emissions neutrality in the second half of the century, on the basis of equity and guided by science in the context of sustainable development and poverty eradication.Here are five key questions and answers about this critical concept:What is GHG emissions neutrality?Greenhouse gas (GHG) emissions neutrality should be interpreted to mean net zero anthropogenic GHG emissions from all sectors. It is achieved first and foremost by reducing total GHG emissions to as close to zero as possible. Any remaining GHGs would be balanced with an equivalent amount of removals (such as enhanced sequestration in the land sector) or negative emissions (possibly using future technologies like bioenergy combined with carbon capture and sequestration, although these remain unproven at scale).How is that different from carbon neutrality?GHG neutrality covers all greenhouse gas emissions, which means emissions from carbon dioxide as well as other greenhouse gases like methane. All of these gases would reach net zero in a GHG neutral scenario. In contrast, carbon neutrality deals only with carbon dioxide emissions. In 2012, 23% of emissions were non-CO2 greenhouse gases.When do we need to achieve GHG emissions neutrality?There are two different temperature goals in the current agreement text, with Parties acknowledging the need to limit warming below 2 degrees C and try to limit it to 1.5 degrees C. Depending on the temperature goal, the total amount of emissions – or carbon budget – that we can emit, as well as the timing of those emissions to ensure plausible rates of emissions decline, changes.To have a likely chance of limiting warming to below 2 degrees C, we need to reduce GHG emissions according to the following timeframe:Carbon dioxide emissions have to drop to net zero between 2060 and 2075Total GHG emissions need to decline to net zero between 2080 and 2090To achieve GHG neutrality with a likely chance of limiting warming to below 1.5 degrees C, we need to reduce GHG emissions according to the following timeframe:Carbon dioxide emissions have to drop to net zero between 2045 and 2050Total GHG emission need to decline to net zero between 2060 and 2080What kind of transformation does GHG emissions neutrality require?With a long-term goal of GHG emissions neutrality, the world would make a commitment to pursue zero-carbon transformation across various systems and sectors. For example, according to the IPCC, in the majority of stringent mitigation scenarios with a likely chance of limiting warming to 2 degrees C, the electricity sector increases its share of low-carbon energy from the current level of 30 percent to more than 80 percent by 2050. Fossil-based electricity generation without CCS would be phased out by the end of the century. Transformation of other sectors and enhanced carbon storage like that achieved by increased landscape restoration would also be required.Why is getting to GHG neutrality so important?Climate negotiators recognize the need to avoid the most extreme impacts of a warming world by limiting temperature rise to 1.5 or 2 degrees C. To chart a course on that path, a goal of GHG neutral emissions is essential. While some earlier drafts of the agreement were more specific about the necessary scale and rate of GHG emissions reduction, it is clear that to reach GHG emissions neutrality with a likely chance of limiting warming to 1.5 or 2 degrees C, we must phase out emissions altogether well before the year 2100. Unabated fossil-fuel use must cease this century. The long-term goal of GHG emissions neutrality, coupled with the goal to limit warming to below 2 degrees C or 1.5 degrees C, commits governments around the world to ending high-emitting behavior. It will also require ramping up efforts to reach net zero GHG emissions in time to limit the worst consequences of climate change.