Researchers involved in a new international assessment say feedback mechanisms within the climate system may interact in ways that trigger cascading effects across multiple regions, pushing global temperatures beyond levels compatible with modern civilisation.
The study, led by Professor William Ripple of Oregon State University and published in the journal One Earth, synthesises findings on climate feedback loops and 16 major tipping elements — large-scale Earth systems that may undergo abrupt and potentially irreversible change once key temperature thresholds are crossed.
According to the authors, if several of these tipping elements were activated in close succession, the combined effects could drive the planet onto a trajectory of sustained and severe warming. Such a pathway, they caution, would be extremely difficult to reverse within human timescales, even with deep and rapid emissions reductions.
"For thousands of years, Earth's climate remained relatively stable, allowing agriculture and complex societies to flourish," Ripple said. "We are now moving beyond that period of stability and into conditions humanity has never experienced."
The tipping elements identified in the report include the Greenland and Antarctic ice sheets, mountain glaciers, Arctic sea ice, boreal forests and permafrost regions, the Amazon rainforest, and the Atlantic Meridional Overturning Circulation (AMOC) — a system of ocean currents that plays a central role in regulating global climate patterns.
Nearly a decade after governments agreed under the Paris climate accord to limit long-term warming to 1.5C above pre-industrial levels, global average temperatures recently exceeded that threshold for 12 consecutive months. While official temperature targets are assessed over 20-year averages, climate simulations indicate that sustained short-term breaches may signal the world is already at or near the 1.5C benchmark.
Recent months have also seen intensifying wildfires, floods and other extreme weather events, underscoring what researchers describe as the growing volatility of the climate system.
Co-author Christopher Wolf said current global temperatures may rival or exceed those recorded during the last interglacial period around 125,000 years ago. He added that atmospheric carbon dioxide concentrations — now above 420 parts per million — are likely higher than at any point in at least two million years, roughly 50% above pre-industrial levels.
The report highlights the role of climate feedback loops — processes that can either amplify or dampen warming. In the current context, many feedbacks appear to be reinforcing change. Melting ice reduces the planet's reflectivity, allowing it to absorb more heat. Thawing permafrost can release additional greenhouse gases. Forest dieback and soil carbon loss further weaken natural carbon sinks.
"These amplifying feedbacks increase the risk of accelerated warming," Ripple said, noting that once certain processes begin, they can interact in complex and compounding ways.
The researchers argue that the uncertainty surrounding exact tipping thresholds should not be seen as reassurance, but rather as a reason for precaution. Even triggering a subset of these elements, they warn, could commit the planet to long-lasting and potentially irreversible shifts.
The study calls for urgent strengthening of mitigation and adaptation strategies, including a rapid expansion of renewable energy, stronger protection of ecosystems that store carbon, and a socially equitable phaseout of fossil fuels. It also recommends improved global monitoring systems to detect early warning signs of tipping behaviour and better frameworks for managing systemic risk.
Some tipping processes may already be underway. The Greenland and West Antarctic ice sheets are showing signs of accelerated loss, while boreal permafrost, mountain glaciers and the Amazon rainforest appear increasingly vulnerable.
Because Earth's climate system is tightly interconnected, disruption in one region can reverberate globally. Melting ice in Greenland, for example, can freshen the North Atlantic and weaken the AMOC. A slowdown of that current system could alter tropical rainfall patterns and heighten the risk of large-scale forest loss in the Amazon.
Scientists warn that such interactions could create feedback loops in which warming triggers forest dieback, releasing carbon that further accelerates global heating.
"The window to avoid the most dangerous outcomes is narrowing," Ripple said. "Preventing a hothouse trajectory is challenging, but far more achievable than attempting to reverse it once critical thresholds have been crossed."