The world's biggest climate agreement goes into effect tomorrow - here's what it actually means

The Intergovernmental Panel on Climate Change, an international body of scientists created in 1988, assesses data about the climate and gives policymakers recommendations about how to address rising temperatures.

The panel concluded that if the overall average temperature of the earth increases more than 2 degrees Celsius above what it was before the Industrial Revolution (when we started burning large quantities of fossil fuels), the planet could face severe consequences. Those impacts would include rising seas, which would lead to increased flooding and more severe storms, harsher droughts, more fires, and the extinction of many species.

Even a 2-degree temperature rise will have noticeable impacts on the planet. A study recently published in the journal Science suggests that any temperature rise about 1.5 degrees will cause southern Spain and Sicily to become deserts by the end of the century. Low estimates suggest that a 2-degree increase will still eventually cause the sea level to rise 20 feet above the current high tide line. And many animal populations are already declining — an Australian rodent called the Bramble Cay has already disappeared due to rising sea levels.

That’s why the Paris Agreement aims to keep the earth’s temperature well below the 2-degree threshold, and suggests 1.5 degrees as an ideal target based on the current concentration of carbon dioxide in our atmosphere.

When ratifying the agreement, each country had to submit what the UN calls nationally determined contributions that it will pursue. The agreement states that the countries will take stock of those efforts in 2018 to see how much progress has been made toward the goals. After that, there will be peer review and reporting sessions every five years to take stock of the efforts made.

The US set a target of reducing its greenhouse gas emissions by 26-28% below 2005 levels by 2025. India, which expects its electricity demand to increase by more than three times by 2030, pledged to reduce the emissions intensity of its GDP by 20-25% over 2005 levels by 2020. And all the European Union’s member states committed to a 40% reduction of their greenhouse gas emissions by 2030 compared to 1990 levels.

Each country’s national contributions are recorded in a public registry, which is accessible online.

Besides a set of transparency requirements and the periodic assessments stipulated by the agreement, there aren’t any concrete mechanisms for enforcement. It’s up to each individual nation to figure out how to meet the targets they’ve set for their emissions, and they won’t have to pay fines or face other consequences if they don’t hit those goals. They’ll just have to disclose data about their performance every two years (a requirement that doesn’t even apply to some developing countries).

Because regulations and policies have to be confirmed by a country’s legislature or governing body, it is easy to imagine a scenario in which differing positions on how to protect the environment and lower emissions prevent new initiatives from being realized. However, UN Secretary General Ban Ki Moon has said he is hopeful that the forced transparency will be enough of an incentive for nations to make good on their pledges.

“We are not going too shame, but everybody knows which country is doing what and how much they are doing. Everybody has an interest to fully comply,” he told the Wall Street Journal in April.

After the initial Paris Agreement was established in December 2015, Hillary Clinton expressed her support for the deal, hailing it as “an historic step forward in meeting one of the greatest challenges of the 21st century.” Her platform includes upholding the agreement, and she has pledged to make combatting climate change a top priority.

Donald Trump, however, opposes the deal. After it was ratified in October, Trump’s campaign released a statement saying that “Hillary Clinton and other supporters of this global political agreement ignore the reality that it will cost the American economy trillions of dollars.” In May, Trump suggested he would cancel the deal if elected president — but since there aren’t any mechanisms to force the US to enact emissions-reducing policies, he wouldn’t even have to do that.

China, a country that has historically been one of the world’s major carbon emitters, recently chided Trump for that position. On November 1, the country’s top climate change negotiator, Xie Zhenhua, told reporters that “a wise political leader should take policy stances that conform with global trends,” and that backing out of the agreement would affect economic and social progress in the US. China is planning to launch a national carbon trading policy in 2017, a strategy the US has not yet embraced.

Even if every country does their individual goals, the temperature will still likely rise more than 2 degrees. The UN Environment Programme suggests that in order to stay below 2 degrees, global greenhouse gas emissions have to be cut from 54 billion tons per year (where we are now) to about 42 billion tons by the year 2030. The current Paris Agreement pledges, however, are only anticipated to keep those emissions flat over the next 14 years. That’s better than the amount emissions would have increased without the agreement, but not quite enough.

A study released in September suggested that even if every country does reach the goal of its nationally determined contribution, the 2-degree rise could still happen by 2050. Robert Watson, a British-American atmospheric scientist, told Reuters that if governments really intent to stay below a 2-degree rise, they should really double or triple the pledges they made in the Paris Agreement.

And James Hansen, a climate scientist at Columbia University, recently published a paper suggesting that limiting global warming to 1.5 degrees Celsius would require negative emissions, which would mean capturing carbon and taking it out of the atmosphere. If emissions are scaled down quickly, the study says, we could achieve that by making improvements to agricultural and forestry practices. Otherwise, the study suggests, we’d have to develop new technologies that could capture and store CO2.

Though individual countries’ targets might not be ambitious enough to accomplish the agreement’s goal, it has unified the world on a path towards climate action. The treaty sends a message to governments, corporations, and organizations around the globe that controlling temperature rise is a high priority, and it sets expectations about future regulations that will be needed to lower emissions.

The agreement also set a new precedent for international environmental accords that was quickly followed by two other groundbreaking deals. More than 170 countries agreed to a worldwide ban on hydrofluorocarbons, a chemical compound that causes the temperature to rise. And the UN overwhelmingly ratified a pact to limit carbon emissions from airlines.

So although questions still linger about whether the agreement will effectively protect the planet from climate change, and how much it will actually lead countries to decrease their emissions, Friday is a big day nonetheless.