The Impact of Climate Change on Ocean Conditions - Ocean Central

As global temperatures rise, these shifts are reshaping the ocean, impacting ecosystems and human livelihoods in increasingly significant ways.

Warming Seas: A Steady Climb

As the atmosphere warms, so too does the upper ocean. The ocean has absorbed more than 90% of the excess heat derived from the increase in atmospheric greenhouse gas concentration. As a result, global surface temperatures show a steady rise in ocean temperatures since 1880, with a sharper increase in recent years. “Ocean warming has been accelerating to match the extent of atmospheric warming,” says Carlos Duarte, chief scientist for Ocean Central and author of “Ocean: The Secret of Planet Earth.”

This warming trend is causing significant changes in the marine environment. For instance, warmer oceans can lead to more frequent coral bleaching, where stressed corals expel the algae they rely on for nutrients and color. This affects entire coral ecosystems and a wide variety of marine species that depend on them for food and shelter. The Great Barrier Reef, for instance, is home to 400 species of coral and 1,500 species of fish.

Recent heat stress has led to widespread bleaching, or what scientists call “mass coral bleaching events.” Mass bleaching has been increasing in frequency as the ocean continues to warm. In fact, from the start of 2023 to mid-2024, mass bleaching occurred in at least 70 countries and territories worldwide, according to NOAA.

Melting Ice and Rising Seas

Higher temperatures are melting ice in the polar regions at an alarming rate. Greenland and Antarctica are losing hundreds of gigatons of ice per year, which directly contributes to rising sea levels. Greenland’s melting ice sheet is one of the largest contributors to global sea level rise, according to a study in Nature. In addition to the release of freshwater from melting ice caps, the ocean is also expanding due to warming, as warmer water is less dense and therefore occupies a larger volume for the same mass. This is known as thermal expansion.

Sea level rise is unevenly distributed across the globe. Some areas, like the western Pacific and Indian Oceans, are experiencing greater increases. This puts coastal regions, especially in low-lying areas, at higher risk of flooding and storm surges, endangering ecosystems and millions of people, particularly where resources to mitigate these impacts are limited.

The risks of fooding and salinization of aquifers derived from sea level rise are further aggravated in many coastal areas worldwide by subsidence, where the ground level sinks due to compaction when groundwater is extracted.

How Climate Change Alters Ocean Circulation

The ocean’s response to rising temperatures goes far beyond coastal communities and marine life — it is a global issue that affects weather patterns, food security, and human livelihoods around the world.

Changes in ocean currents can disrupt climate systems and even affect agricultural productivity. Understanding these interconnected dynamics is crucial for addressing the broader implications of climate change.

A system known as the Atlantic Meridional Overturning Circulation (AMOC), often described as the ocean’s “conveyor belt,” helps regulate global climate by moving warm water from the tropics to the North Atlantic.

Changes in this circulation pattern are not only relevant to the ocean environment and coastal communities but they also influence our climate on land and everyday weather patterns through the seasons. Increased freshwater from melting ice and more intense rainfall are weakening and changing this circulation. AMOC redistributes heat from tropical regions to high latitude regions. For this reason, a weaker AMOC is expected to lead to colder winters in Europe and warmer tropics, shifts in tropical rainfall patterns, and more severe hurricanes, impacting weather in towns around the world and showing just how connected our climate systems are.

How Climate Change Affects Ocean Chemistry

Climate change is largely driven by carbon dioxide emissions. The ocean, acting as a fluid in balance with the atmosphere, absorbs excess heat and CO2, having taken up about a third of the CO2 released by human activity. While this helps buffer climate warming, the added CO2 changes ocean chemistry by lowering pH levels and reducing carbonate ions. 

These changes make it harder for many marine organisms to form shells and skeletons. Additionally, oxygen levels in the ocean are dropping due to warmer water holding less oxygen and marine organisms using more of it as their respiration rates increase with temperature. This gradual loss of oxygen adds further stress to marine ecosystems.

Summary

The changes we see in the ocean reflect broader climate impacts. Warmer and more acidic ocean water affects marine life, fisheries, and global food security. As ocean conditions shift, fish populations migrate, disrupting fishing industries and the communities that depend on them. Melting ice also opens new shipping routes and access to resources, with significant geopolitical implications.

The data paints a clear picture: our oceans are warming, ice is melting, sea levels are rising, and vital ocean currents are slowing. These changes impact not only the physical landscape of our planet but also marine ecosystems and coastal communities. 

To address these challenges, we need urgent action and innovation to mitigate climate change and support ocean regeneration. By taking steps to reduce greenhouse gas emissions and investing in blue tech solutions, we can begin to rebuild the ocean’s health and resilience, paving the way for a sustainable future.

References

• Delworth, T. L., Cooke, W. F., Naik, V., Paynter, D., & Zhang, L. (2022). A weakened AMOC may prolong greenhouse gas–induced Mediterranean drying even with significant and rapid climate change mitigation. Proceedings of the National Academy of Sciences, 119(35), e2116655119. 
• GISTEMP Team, 2024: GISS Surface Temperature Analysis (GISTEMP), version 4. NASA Goddard Institute for Space Studies. Dataset accessed 2024-09-23 at https://data.giss.nasa.gov/gistemp/.
• Global Carbon Budget (2023) – with major processing by Our World in Data. “Cumulative CO₂ emissions – GCB” [dataset]. Global Carbon Project, “Global Carbon Budget” [original data]. Retrieved October 28, 2024 from https://ourworldindata.org/grapher/cumulative-co-emissions
• NASA. (2024). GRACE and GRACE-FO polar ice mass loss. Retrieved October 28, 2024, from https://svs.gsfc.nasa.gov/31166/
• Willis, J.K., Hamlington, B.D., and Fournier, S., Global Mean Sea Level Time Series, Trajectory and Extrapolation. Dataset access [2024-09-01] at 10.5281/zenodo.7702315.; GSFC. 2021. Global Mean Sea Level Trend from Integrated Multi-Mission Ocean Altimeters TOPEX/Poseidon, Jason-1, OSTM/Jason-2, and Jason-3 Version 5.1. Ver. 5.1 PO.DAAC, CA, USA. Dataset accessed [2024-09-01] at https://doi.org/10.5067/GMSLM-TJ151

Credits

• Data analysis by Peter Sherman
• Scientific contributions by Marcius Extavour