The day many thought would never arrive just has. The US and China, the world’s two most prolific greenhouse gas emitters, have officially ratified the groundbreaking Paris agreement. Although the two nations disagree on a vast array of other issues, and in many instances are in direct conflict with each other, both have come to realize that man-made climate change is the most pertinent threat to us all.

President Barack Obama and Xi Jinping, the Chinese president, confirmed the ratification at the start of the G20 summit in Hangzhou, China. According to The Independent, Obama told an audience that this was “the moment we finally decided to save our planet”.

“Our response to climate change bears on the future of our people and the well-being of mankind,” Xi added, as reported by the Guardian.

In order for the Paris agreement to be officially enacted, 55 countries representing 55 percent of global greenhouse gas emissions must ratify the deal. The US and China’s ratification brings the total to 26 countries now out of 195, representing 39 percent of emissions. And it removes arguably the biggest stumbling block to achieving this monumental goal, namely getting these two large countries officially on board. Climate campaigners now expect a “surge” of ratifications, particularly from other major emitters like Brazil and perhaps India.

Humanity has been changing the climate for around 7,000 years, ever since widespread agriculture began pumping methane into the atmosphere. Today, carbon dioxide is the primary greenhouse gas emission, and it is altering the global climate in unprecedented ways. On average, the world is warming 10 times faster than would be expected after a glacial maximum.

By the end of this century, if radical action isn’t taken, then the Arctic will have disintegrated. Our crops will not be able to keep up with the pace of global warming, and forests will dramatically shrink. The economy will suffer, there will be an apocalyptic refugee crisis, sea level rise will consume islands and cities, and floods, wildfires and hurricanes will become more potent.

Disproportionately so, the US and China are responsible for these changes, producing roughly 38 percent of greenhouse gas emissions. As of 2014, China produces 9.7 billion tonnes of CO₂ per annum, with the US second at 5.6 billion tonnes. Together, they produce more every year than Europe, the Middle East, Africa, and South America combined.

^{The declaration was made at the start of the G20 summit in Hangzhou, China. Zhao jian kang/Shutterstock}

Although everyone needs to act, it’s clear that without the help of China and the US, the Paris agreement would fail. Unfortunately, as a recent study revealed, this doctrine simply doesn’t go far enough. Even with the support of all 195 signatories, the entire carbon budget for keeping to the 2°C (3.6°F) may be emitted as soon as 2030, 70 years ahead of schedule.

The 1.5°C (2.7°F) limit requested by many low-income nations, particularly those vulnerable to sea level rise, may be impossible to achieve in just five years, according to NASA. The most likely scenario is that global temperatures will actually rise by 2.6°C to 3.1°C (4.7°F to 5.6°F) by 2100 – a devastating future, then, awaits.

Strong action needs to be taken, and it’s certainly possible to stick to the 2°C limit. Evidence shows that the adoption of nuclear power and renewables, along with eschewing fossil fuels, could dramatically militate against climate change, particularly in Europe, the US, and even China. So although the Paris agreement is a good start, it needs to be strengthened and added to over time.

In fact, the greatest threat to it right now is the current Republican nominee in the race for the White House. If the anti-science, climate denialist Trump is elected, the agreement will be vetoed by the US, and all hope of saving the world from a scorched future will disappear.

^{Wildfires will become far more common if nothing's done to reduce greenhouse gas emissions. macknimal/Shutterstock}