In February 2000, Paul Krutzen went up to speak at the International Geosphere-Biosphere Program in Mexico. And when he spoke, people paid attention. At the time, he was one of the world’s most cited scientists, a Nobel Prize winner, working on large-scale problems such as the ozone hole and the consequences of nuclear winter.

So it’s no surprise that the word he improvised has become adopted and popularized: the Anthropocene, a proposed new geological epoch representing an Earth transformed by industrialized humanity.

The idea of ​​a completely new man-made geological era is a serious scenario in the context of the current UN climate summit COP28. The impact of the decisions taken at this and similar conferences will be felt not only beyond our own lives and the lives of our children, but perhaps beyond the lives of human society as we know it.

The Anthropocene is now widely accepted, but when Crutzen first spoke it was still a new hypothesis. Crutzen listed many planetary symptoms to support his new discovery: massive deforestation, the growth of dams on the world’s major rivers, overfishing, the overload of the planet’s nitrogen cycle due to fertilizer use, and the rapid growth of greenhouse gases.

When it comes to climate change, the bells are certainly ringing. Global average surface temperature has increased by about half a degree since the mid-20th century. But they were still within the normal range for the interglacial phase of the ice ages. Among the many issues that arose, it seemed, was the climate of the future.

A little over twenty years have passed and the future has arrived. By 2022, global temperatures will rise by another half degree, making the last nine years the hottest in history. In 2023, climate records were not just broken, they were broken.

As of September, there had been 38 days when global average temperatures exceeded pre-industrial temperatures by 1.5°C, the safe limit for warming set by the United Nations Framework Convention on Climate Change (UNFCCC) in the Paris Agreement. In previous years this was a rare occurrence and until 2000 this milestone had never been recorded. With this increase in temperatures came record heat waves, wildfires and floods, exacerbated by other local human activities. During the Anthropocene, climate came to the fore on Earth.

Why is there such an increase in temperature? This is partly due to the relentless increase in greenhouse gas emissions as fossil fuels continue to dominate human energy consumption. When Crutzen spoke in Mexico, atmospheric carbon dioxide levels were around 370 parts per million (ppm), already above the pre-industrial level of 280 parts per million. They currently stand at about 420 parts per million and are increasing at a rate of about 2 parts per million per year.

Some of the warming is a result of clearer skies both on land and sea in the past few years, thanks to new regulations that phase out old power plants and dirty, sulfur-rich fuels. As the industrial smog clears, more solar energy penetrates the atmosphere and reaches the ground, and global warming begins in full force.

Some of our planet’s heat-reflecting mirrors are rapidly shrinking as sea ice melts, first in the Arctic and, in the last two years, around Antarctica. It looks like climate feedback is starting to work, too. A sharp new increase in atmospheric methane (a greenhouse gas much more potent than carbon dioxide) since 2006 appears to be the source of the increase in decaying vegetation in tropical swamps in a warming world.

This final warming step brought the Earth to a level of warmer climate not seen in about 120,000 years, the level of the last interglacial phase that was slightly warmer than the current period. Warming is expected to increase further in the coming centuries as various feedbacks come into play.

A recent study on the effects of this warming on Antarctic ice suggests that “policymakers should be prepared for sea level rise of several meters in the coming centuries” as the heat wave spreads into the oceans, weakening the large polar ice sheets.

This is true even in the most optimistic scenario in which carbon dioxide emissions decrease rapidly. However, emissions continue to increase rapidly, deepening climate impacts.

Controls are being redefined

To see how this plays out on a geological time scale, we need to look through the lens of the Anthropocene. The delicately balanced planetary mechanism, consisting of thousands of years of regular oscillations in Earth’s rotation and orbit, has tightly controlled patterns of hot and cold over millions of years.

Now, suddenly, this control machine has shut down due to trillions of tons of carbon dioxide released into the atmosphere over more than a century.

Modeling the effects of this impact on the Earth system shows that this new, suddenly disrupted climate pattern has been around for at least 50,000 years, and probably much longer. This is a big part of how our planet has changed so fundamentally and irreversibly that it can be compared to some of the major climate change events in Earth’s deep history.

So will this special session of the COP, with strong representation from fossil fuel interests, make a difference? Ultimately, achieving and stabilizing net zero carbon emissions is only an important first step. In order to restore an optimal climate for humanity and life in general, negative emissions are needed to remove carbon from the atmosphere and ocean system and return it to the subsurface. A lot is at stake for future generations.