The World Just Hit This Disturbing Climate Change Metric by Katie Fehrenbacher @FortuneMagazine September 28, 2016, 12:38 PM EDT E-mail Tweet Facebook Linkedin Share icons Earth has seemingly passed a worrisome threshold for the changing climate this week, according to scientists. The last week in September is often the time of the year when the planet’s carbon emissions are at their lowest as summer turns to fall and plants and leaves start to decay, releasing carbon. However, this year the amount of carbon emissions in the atmosphere this week has remained above 400 parts per million, reports Climate Central. That means that even with the fluctuating of the seasons, which pushes the levels of carbon emissions up and down, the planet is likely now officially at 400 parts per million for the foreseeable future. While that could change decades into the future—if society worked hard to reverse the carbon emissions in the atmosphere or if there was a large catastrophic climate event—but the metric for now is likely here to stay. With four hundred parts of carbon emissions in the Earth’s atmosphere, the climate is changing including rising global temperatures, rising sea levels, ocean acidification and increased intensity of storms. Global temperatures have already risen by almost 1.5 degrees Celsius compared to about a century ago, and world leaders are trying to enact commitments and policies to keep rising temperatures under two degrees Celsius. This disturbing data point is the backdrop to the current U.S. political environment. This week, climate change was only brought up briefly during the first Presidential debate. Republican candidate Donald Trump denied calling climate change a hoax perpetuated by the Chinese (but he actually did do that) and also bizarrely referred to solar company Solyndra, which went bankrupt five years ago and lost a loan from the U.S. government. Meanwhile, the U.S. Court of Appeals for the District of Columbia Circuit heard oral arguments on Tuesday for President Obama’s Clean Power Plan, which seeks to push power plant companies to lower greenhouse gas emissions. If the policy stands, mostly it would accelerate shutting down old coal plants and adding in new natural gas plants, as well as solar and wind farms. Get Data Sheet, Fortune’s technology newsletter. But if the Clean Power Plan is shot down, the U.S. will lose its chief way to meet its commitments to lower carbon emissions and meet the pledges to the international Paris climate agreement. For the first time in history, the U.S. and China ratified the Paris agreement this weekend. Perhaps billionaire entrepreneur Elon Musk has the best strategy. On Tuesday, he showed off how his space company SpaceX plans to get human beings off of Earth and onto Mars in an effort to enable humans to be an “interplanetary species.” For more on the U.S. and China ratifying the Paris agreement, watch: Humans will inevitably face an extinction event, said Musk at a astronautical conference on Tuesday in Mexico. Perhaps this week the Earth hit that metric which will put start it on a path to meet that fate.