Signs of the drastic—and in some cases irreversible—changes that humans have made to the climate are now impossible to ignore.

The Intergovernmental Panel on Climate Change (IPCC) does not mince its words when describing the disastrous effect that humans are having on the planet. “It is unequivocal that human influence has warmed the atmosphere, ocean, and land,” reads its latest report.

From heat waves and wildfires to downpours and flooding, 2023 has given us a taste of the impacts we can expect over the coming decades and centuries. In short, it’s not good news. Without very significant reductions in greenhouse gases—beginning immediately—it is very likely that global surface temperatures will exceed the 1.5 degrees Celsius threshold set in the 2015 Paris climate agreement.

1. There’s more carbon dioxide in our atmosphere than at any time in human history

The Mauna Loa observatory in Hawaii has been tracking Earth’s atmospheric concentration of CO2 since the late 1950s. In 2022, the global average concentration it recorded was 417.06 parts per million (ppm). Preindustrial levels were 278 ppm, which means that humans are halfway to doubling the concentration of CO2 in the atmosphere compared to the period between 1750 and 1800.

CO2 concentrations fluctuate with the seasons, while the speed at which they increase yearly is affected by human behavior. For example, the rising concentration of CO2 in the atmosphere slowed during the early stages of the pandemic when emissions fell, but then rose steeply in 2021 as the world reopened. The annual rise in emissions and atmospheric concentration of CO2 has since slowed down again.

The global average CO2 concentration for 2023 is predicted to be 419.2 ppm. The last time Earth’s atmosphere contained this much CO2 was more than 3 million years ago, when sea levels were several meters higher and trees grew at the south pole.