Kategorie: News
Oceans as Heat Reservoirs and a Warning Sign for Climate Protection
The latest IGCC analysis shows that greenhouse gases are exacerbating the energy imbalance, leading to ocean heatwaves and rising sea levels. The Earth is increasingly losing its balance.
More solar energy is being trapped in the climate system because concentrations of greenhouse gases such as CO2, methane, and nitrous oxide continue to rise. This is the key finding of the fourth edition of the “Indicators of Global Climate Change” (IGCC) report, which researchers presented at the current UN Climate Change Conference in Bonn. Unlike the less frequently published IPCC reports, the IGCC provides annual interim assessments—and these reveal clear trends that are particularly relevant for marine conservation and climate policy.
Greenhouse Gases: More and More in the Air
Global greenhouse gas emissions have remained high recently: in 2024, they were equivalent to the effects of approximately 56.8 gigatons of CO₂, of which about 38.6 gigatons came from fossil fuels and industry. Measurement data through 2025 show that atmospheric concentrations continued to rise: according to the report, CO₂ stands at around 425.6 ppm, and methane at about 1,936 ppb. More greenhouse gases mean that the Earth captures more incoming radiant energy than it radiates back into space—the so-called energy imbalance is growing.
Oceans as Heat Reservoirs
The oceans absorb the lion’s share of the additional heat: Since the 1970s, the oceans have stored about 90 percent of the excess energy. Particularly concerning is the increase in warming at depths between 700 and 2,000 meters since the 1990s. Warmer oceans have far-reaching consequences: They alter ocean currents, reduce oxygen uptake, endanger ecosystems, and contribute to extreme events.
Ocean heatwaves are increasing sharply
A new metric in the IGCC is the frequency of ocean heatwaves—that is, periods of unusually high surface water temperatures. The number of such days more than tripled from 1991 to 2025; in 2025, monitoring stations recorded an average of about 60 heatwave days per location. Such events lead to coral bleaching, massive fish kills, shifts in habitats, and negative effects on coastal fisheries and marine biodiversity.
Accelerating Sea Level Rise
Ocean warming and the melting of land ice are also driving sea level rise. Between 1971 and 2018, the annual rise was approximately 2.33 mm; from 2018 to 2025, it has accelerated to about 3.84 mm per year. This means greater coastal risks: more frequent flooding, coastal erosion, and land loss in particularly vulnerable regions.
Climate Policy and Remaining CO2 Budgets
Although emissions are no longer growing as rapidly as they did in the 2000s, global greenhouse gas emissions continue to rise. According to IGCC calculations, only a limited CO2 budget remains for the Paris Agreement’s 1.5-degree target:
At current emission rates, this budget would be exhausted in about three years—with only a 50 percent probability of staying within the 1.5-degree limit. Even if the target were relaxed to 1.7 degrees, the remaining budget would be limited and would be exhausted in about twelve years. These figures make it clear: short-term action is needed to limit long-term risks.
Threats to Observation Systems
The IGCC analyses are based on over 40 datasets, including satellite observations, measurements from ships, buoys, and weather stations. Yet it is precisely this data foundation that is under threat: due to budget cuts, numerous satellite and ocean observation programs—particularly those in the U.S.—are at risk. Many ocean measurements have so far been funded by U.S. institutions; a reduction in this support would severely impair the monitoring of heat in the ocean and, consequently, our understanding of future climate and weather changes.
What does this mean for marine conservation and action?
Clear areas for action emerge for marine conservation and adaptation to climate change:
- Emissions reduction: Faster and more ambitious reductions in CO₂ and methane remain crucial to limiting further ocean warming.
- Strengthening observation: Sustainable funding for global measurement programs and satellites is essential to ensure early warning systems and the scientific basis for decision-making.
- Coastal protection and adaptation: Appropriate protective measures for coastal regions, sustainable fishing practices, and the restoration of marine ecosystems (e.g., seagrass beds, mangroves) mitigate damage and strengthen resilience.
- International cooperation: Climate protection and ocean monitoring are global challenges—solidarity-based financing and data sharing are necessary, especially for coastal states that are particularly affected.
Conclusion
The IGCC report delivers a stark warning: Earth’s systems are storing more and more heat, and the oceans are the main drivers of this process. The consequences for the oceans, coasts, and the global climate are already being felt and will worsen without rapid emissions reductions. This makes stable observation networks, ambitious climate action, and targeted measures to protect marine habitats all the more important.
Sources
- Indicators of Global Climate Change (IGCC):
- IGCC study and publication in Earth System Science Data
- Mercator Ocean International (Information on ocean observation)
- Article: “U.S. Scales Back Ocean Monitoring – Europe Expands Observation” (taucher.net)