Bruce Melton PE, Climate Change Now Initiative
Science is slow. It has been slower than climate change for decades and as that science has warned, if we did not act promptly and appropriately, the speed of climate change would increase further and dangerously. We now find this future time upon us. Tipping responses, or earth systems collapses, have been active since about 2018. What were just a few publication in the 20-teens, have now emerged as an avalanche of peer review.
Four very important tipping papers have been published in the last six weeks. A “marked” and “dramatic” paper on the unexpected and significant drop in Antarctic sea ice extents, findings that 1.2 degrees C warming above normal will create meters of sea level rise from the Greenland and Antarctic ice sheets, creating challenges to sea level rise adaptation with warming, and one that states that, “up to 60% of the global subsurface ocean (down to 200 m) has crossed a critical ocean acidity boundary,” and an article that suggests that the two largest forests systems on Earth, tropical and boreal, are at risk of unavoidable impacts with a temperature of 1.5 degrees C above normal.
The meaning of these and the spate of other tipping papers that have been published since 2019, cannot be taken lightly. Tipping activation means tipping completion unless we restore our climate back to within its former natural variability before the point of no return where the systems are so degraded they cannot be stabilized. Time is critical. Irreversible collapse of our Earth systems means natural greenhouse gas emissions that dwarf humankind’s. The Sierra Club approved of a new climate policy in 2020 that stated that the Club “supports geoengineering research in case emergency cooling is needed.” With time frames to the point of no return being in the mid-century range, restoration actions cannot be delayed. Radical action is now indicated. Risks of tipping element responses are dramatically and markedly greater than not implementing emergency cooling to stabilize these collapses.
Antarctic Sea Ice
Antarctic sea ice coverage has taken a “markedly” strong, and “dramatic” downturn in coverage, plausibly indicating a new state is developing that significantly amplifies global warming with feedback effects to the Antarctic Ice Sheet. See –
Silvano et al., Rising surface salinity and declining sea ice, A new Southern Ocean state revealed by satellites, PNAS, June 30, 2025.
https://www.pnas.org/doi/10.1073/pnas.2500440122
Note: This is happening while Arctic sea ice extents is at a new record low.
Antarctic and Greenland Ice Sheets
Ice loss from Greenland and Antarctica has quadrupled since 199. These findings conclude that we passed the tipping point of these two system with warming of about 1 degree C above normal, where we are 1.5 degrees C above normal today. The authors state, “Here we synthesise multiple lines of evidence to show that +1.5 °C is too high and that even current climate forcing (+1.2 °C), if sustained, is likely to generate several metres of sea-level rise over the coming centuries, causing extensive loss and damage to coastal populations and challenging the implementation of adaptation measures. To avoid this requires a global mean temperature that is cooler than present and which we hypothesize to be closer to +1 °C above pre-industrial, possibly even lower, but further work is urgently required to more precisely determine a ‘safe limit’ for ice sheets.”
Stokes and DeConto, Warming of +1.5 degrees C is too high for polar ice sheets, Nature Communications, Earth and Environment, May 20, 2025.
https://www.nature.com/articles/s43247-025-02299-w
Ocean Acidification
The authors’ abstract states, “by 2020, the average global ocean conditions had already crossed into the uncertainty range of the ocean acidification boundary… Up to 60% of the global subsurface ocean (down to 200 m) has crossed a critical ocean acidity boundary.” The authors continue, “Large portions of the subsurface have already changed significantly from pre-industrial conditions.” The study finds impacts are already occurring, that “Loss of ecosystem function or suitable habitats can lead to fragmentation, the breaking up the continuous distribution of a species into smaller, isolated patches. This fragmentation directly reduces population connectivity, as individuals within the fragmented habitats have reduced opportunities for interaction, mating and dispersal.”
Findlay et al., Ocean Acidification – Another Planetary Boundary Crossed, Global Change Biology, June 9, 2025.
https://onlinelibrary.wiley.com/doi/10.1111/gcb.70238
Tropical and Boreal Forests
The authors show that our commonly understood 1.5 degree C warming target, which is our current level of warming, risks unavoidable impacts, meaning that warming of 1.5 C is to high for our forests with risks of foregone collapse or tipping. (Abstract) “With global warming heading for 1.5 °C, understanding the risks of exceeding this threshold is increasingly urgent. Impacts on human and natural systems are expected to increase with further warming and some may be irreversible. Yet impacts under policy-relevant stabilization or overshoot pathways have not been well quantified. Here we report the risks
of irreversible impacts on forest ecosystems, such as Amazon forest loss and high-latitude woody encroachment, under three scenarios that explore low levels of exceedance and overshoot beyond 1.5 °C. Long-term forest loss is mitigated by reducing global temperatures below 1.5 °C. The proximity of dieback risk thresholds to the bounds of the Paris Agreement global warming levels underscores the need for urgent action to mitigate climate change—and the risks of irreversible loss of an important ecosystem.”
Munday et al., Risks of unavoidable impacts on forests at 1.5 degrees C with and without overshoot, Nature Climate Change, May 12, 2025.
https://www.nature.com/articles/s41558-025-02327-9
Photo: An iceberg in the discharge of the Jakobshavn Glacier (Greenlandic: Sermeq Kujalleq), the largest ice stream draining the Greenland Ice Sheet, at the Ilulissat Icefjord World Heritage Site, Ilulissat, Greenland. Bruce Melton, https://ClimateDiscovery.org, https://ClimateChangePhoto.org
