World leaders are concluding COP30, the United Nations climate meeting in Brazil, with discussions focused on global warming mitigation and climate adaptation funding.
For the past eight years, a primary objective of these annual negotiations has been to limit global warming to 1.5 degrees Celsius above late-1800s temperatures. This target was established following a significant international scientific report outlining the potential consequences of exceeding this warming level.
Scientists now state that achieving the 1.5 degrees Celsius goal is no longer considered plausible. A recent United Nations report indicates that global planet-warming pollution has not been reduced sufficiently, and the planet is projected to surpass 1.5 degrees Celsius of warming, likely within the next decade.
Despite this, scientists suggest that if countries reduce overall greenhouse gas emissions by half by 2035, global temperatures could subsequently decrease to lower warming levels. U.N. climate chief Simon Stiell emphasized the necessity for faster progress in both emissions reductions and resilience strengthening. Current national policies are projected to achieve only a 12% reduction in emissions by 2035. Stiell affirmed that scientific consensus supports the possibility of returning temperatures to 1.5 degrees Celsius after a temporary overshoot.
Latest estimates, based on current emissions reduction commitments, project Earth's temperature to stabilize around 2.5 degrees Celsius of warming this century. The World Meteorological Organization reports the planet has already warmed approximately 1.3 degrees Celsius, leading to observed increases in storm intensity, flooding, and heatwaves in various communities.
Beyond 1.5 degrees Celsius of warming, scientists indicate that substantial, self-reinforcing changes, often termed climate tipping points, could be initiated. These changes are typically not abrupt, unfolding over decades or centuries, and some may be partially reversible. However, they are projected to have significant and lasting implications for Earth's ecosystems and human populations. A new report by 160 international climate researchers highlights that each additional tenth of a degree of warming increases the likelihood of these tipping points.
Key Climate Tipping Points
1. Coral Reef Degradation
The degradation of coral reefs may represent an early climate tipping point. Widespread coral die-offs have been documented globally due to increasing ocean temperatures. Coral reefs, while occupying a small oceanic area, form a foundational ecosystem supporting an estimated 25% of all marine species.
Corals are highly sensitive to heat. Marine heatwaves induce stress, causing corals to expel the symbiotic algae essential for their survival, resulting in a white coloration. While corals can recover given sufficient time, repeated heatwaves, such as those observed at Australia's Great Barrier Reef and off Florida's coast, can lead to reef mortality and ecosystem collapse.
Ocean acidification, resulting from the absorption of atmospheric carbon dioxide, also stresses corals, impeding their ability to construct skeletons. A global coral bleaching event occurred in 2023-24, the second in a decade. Projections indicate that if global heating exceeds 2 degrees Celsius, an estimated 99% of the world's coral reefs could be lost. This damage is occurring at a faster rate than previously anticipated. A recent study from the University of Hawai'i at Mānoa suggests that by 2035, half of all reefs worldwide will experience uninhabitable conditions, exacerbated by pollution and human development.
Erik Franklin, a professor at the Hawaii Institute of Marine Biology, noted that the coming decades are expected to bring substantial changes for reef systems and humanity. An estimated half a billion people globally rely on coral reefs for food, income, and livelihoods. The loss of reefs could lead to societal and economic challenges, particularly in equatorial and tropical regions, and poses extinction risks for reef-dependent marine life. Scientific efforts include identifying potential 'refuges' for corals and selectively breeding heat-resistant corals in locations such as Florida and Australia, aiming to sustain them until greenhouse gas emissions are reduced.
2. Ice Sheet Instability in Greenland and West Antarctica
Ice sheets covering Greenland and Antarctica contain approximately two-thirds of Earth's freshwater. Climate change is already causing their melting and contributing to global sea-level rise. Sustained global warming at or above 2 degrees Celsius is projected to accelerate this melting, potentially leading to the disintegration of parts of these ice sheets and substantial contributions to ocean volume.
Glaciologists, such as Ian Joughin from the University of Washington, explain that ice sheet disintegration occurs over decades or centuries, rather than abruptly. Greenland has experienced a net ice loss for 29 consecutive years. In 2021, rainfall, rather than snow, was observed at the ice sheet's highest point, indicating warming-induced melting. As temperatures rise, Greenland's two-mile-thick ice sheet is experiencing a mass imbalance, with melt rates exceeding accumulation rates, initiating a process that is difficult to halt.
Research suggests that the West Antarctic ice sheet's disintegration may be ongoing. A large glacier in this region, comparable in size to the state of Washington, is melting rapidly and could fracture into the ocean within decades. If this glacier melts completely, it is projected to contribute approximately 2 feet to global sea levels. The complete melting of the West Antarctic ice sheet is estimated to raise sea levels by about 12 feet.
Due to their vast scale, ice sheets possess significant inertia. Once melting processes commence, they become self-accelerating and challenging to stop. While the most extreme effects of this melting are projected to manifest over several centuries (200 to 1,000 years), reducing the pace of global warming could decelerate ice melt, providing populations in coastal areas more time for adaptation.
3. Permafrost Thawing in the Arctic
Climate change is causing permafrost, the permanently frozen ground in the Arctic, to thaw. As Earth's warming approaches 2 degrees Celsius, this thawing is expected to generate both localized and global impacts.
Locally, permafrost thawing results in the melting and drainage of ground ice. Merritt Turetsky, a permafrost researcher at the University of Colorado Boulder, notes that this can lead to significant consequences such as rapid lake drainage and localized ecosystem desiccation, as previously contained surface water is released. For the millions inhabiting the Arctic, thawing permafrost causes land subsidence, damaging building foundations, infrastructure like roads and runways, and pipelines; these effects are projected to intensify with further warming.
Globally, permafrost serves as a substantial reservoir for millennia of accumulated organic matter. Ted Schuur, a permafrost expert at Northern Arizona University, explains that thawing permafrost enables microbial decomposition of this carbon-rich soil, releasing planet-warming methane and carbon dioxide into the atmosphere. This constitutes a self-reinforcing feedback loop: human emissions cause warming, which thaws permafrost, subsequently releasing additional emissions.
Recent advancements in Arctic data collection have improved the accuracy of greenhouse gas emissions measurements from permafrost, confirming that this process is currently underway. The extent of future carbon release from Arctic permafrost is contingent upon human actions regarding global decarbonization. Turetsky emphasizes that a faster societal decarbonization effort can help retain more permafrost carbon in the Arctic ground. Schuur underscores the significance of each increment of temperature change and the cumulative impact of all mitigation actions.