This year, besides having the potential of being the hottest on record, marks the start of our new “400 parts per million (ppm)” world. Carbon dioxide monitoring station on Hawaii’s Mauna Loa reached a critical milestone three years ago, when for the first time, CO2 concentrations exceeded the benchmark of 400 ppm and now, they may never go back down.

Emissions from human activities are largely responsible for the irrevocable increase in CO2 concentrations in the atmosphere. These CO2 levels begin to drop toward their annual minimum in the spring as plants absorb it while during the fall, those plants lose their leaves which eventually decompose and release the stored carbon dioxide back into the atmosphere. While the world’s plants need CO2 to function, they can only soak a certain amount, leaving behind an excess each year.

Furthermore, besides Mauna Loa, the Cape Grim station in remote northwestern Tasmania saw its first measurements above 400 ppm this year. This is particularly significant because Cape Grim, having a less pronounced seasonal cycle due to less landmass and plant life than the Northern Hemisphere, was not supposed to reach this mark yet.

Fossil fuel burning and other industrial activities have already raised global temperatures by an average of 10C since the 1800s, pushing sea levels up more than 8 inches. Island leaders worry that 20C of warming will make their nations uninhabitable or entirely sunk. This is particularly alarming to me as I come from a small island and if the climate somehow does not improve, my country might soon disappear.

Our planet reaching new highs, in terms of ppm and temperatures, indicates that we are in a different time, the Anthropocene. It is critical that urgent action be taken as we are moving away from the climate humans know and thrive in to something unsure.