What is net zero?

First introduced by the United Nations Framework Convention on Climate Change in Paris in 2015, the goal of “net zero” has since influenced public policy worldwide. More than 194 countries are party to the resultant Paris Agreement. As of January, the United States has officially left the treaty, but it still affects American climate policy and public opinion.

Technically, what does net zero mean? Burning fuel puts molecules with carbon, especially carbon dioxide, back in the atmosphere. Climatologists call these molecules carbon emissions and say they’re responsible for the atmosphere’s warming temperatures.

Net zero means a country has reduced carbon emissions to a low enough point that they can be naturally absorbed from the atmosphere into “carbon sinks” like forests or oceans. It’s hard to change how much carbon dioxide a country can reabsorb, so achieving net zero means significantly reducing human-generated carbon emissions to limit climate change. One way is to replace burning fuel with energy sources like wind and solar.

Who is pushing for net zero? The UN has said carbon neutrality is essential to keep global warming to less than 1.5 degrees Celsius above preindustrial levels. If temperatures rise more than that, the UN claims, Earth will no longer be livable. In 2020, the World Economic Forum warned of dangerous sea level rise and extreme weather if temperatures continue to rise. More recently, in light of better evidence, some climate activists, including billionaire Bill Gates, have walked back such dire predictions.

Have any countries hit their net zero targets? Only eight countries—mostly small, forested, and nonindustrial—have reportedly reached net zero, while only a few European countries claim to be on track for the 2050 target.

What exactly did countries agree to in the 2015 Paris Agreement? As part of the Paris Agreement, each country agreed to submit individual national goals in an effort to reduce carbon emissions. Those goals are called Nationally Determined Contributions (NDC) and are meant to be renewed and increased every five years. Because each nation sets its own goals, NDCs vary widely from country to country regarding targets for emission reduction and timelines to achieve them.

How legally binding is the agreement? Member countries have a legal requirement to submit NDCs, but not to keep them. A few countries have passed their NDC into domestic law.

How on earth are emissions measured? Emissions measurements follow internationally agreed guidelines and are actually estimates made by combining data on types and amounts of activity in a country with emissions typically produced by those activities.

What do critics say? Critics say it’s unfair for developing economies to take on net zero targets before they are fully industrialized. They also say that in developed countries, the cost of meeting these goals risks crippling economies. The Institute for Energy Research estimated the U.S. economy at the halfway point to net zero would have 1.2 million job losses, a $7.7 trillion drop in GDP, and an $840 uptick in household electric bills.