Overheating a Water Planet: Warmed Oceans Will Not Be Ignored

For those of us on land, it’s easy to overlook that the Earth is predominantly a water planet, with over 70% of its surface covered by oceans. Yet, a time is approaching—or rather, we have ushered in an era—where ignoring this fact will no longer be possible. Climate change is causing the seas to rise and, just as crucially, to warm. This gradual warming is reaching a point where it can significantly alter life on land. Such changes are already observable, with many unfolding this year and others poised to have long-lasting impacts.

Equally astonishing as the magnitude of these shifts are efforts by the Trump administration to dismantle the scientific tools that help us comprehend them. We’ll address that shortly. However, first, let’s delve into our planet to understand the implications of overheating the oceans and forcing them to absorb the excess heat.

Earth, despite the name, is a water planet

Here’s a brief overview of Earth’s oceans. How did we acquire all this water?

Following Earth’s molten formation 4.6 billion years ago, it gradually cooled below water’s boiling point. Volcanic steam led to rain that lasted for thousands of years, filling the planet’s low-lying areas. Icy asteroids added significant volumes of water, leading to the formation of a water planet almost entirely covered by a giant ocean. Tectonic activity eventually created large land masses, and over time, plate movements and global temperature changes have reshaped both ocean and land. Despite a few global ice ages, liquid oceans have always been the dominant feature of Earth’s surface, making it a “blue planet” and a water planet.

Water manages heat—and thus life—on Earth

Water is the cradle of life on Earth and is considered the origin of carbon-based life anywhere, which is why scientists search for it in other solar systems. It took at least 500 million years for the first life to form in the ocean (~4.1 billion years ago). Life remained simple and aquatic for most of Earth’s history. Fungi, plants, and animals took significant evolutionary strides to leave the ocean, and even today, nearly 80% of Earth’s animal life (by biomass) is found in the oceans. The ocean continues to exert immense influence on terrestrial life by managing Earth’s heat and making large regions habitable.

One primary way the ocean does this is by absorbing solar radiation in tropical areas and transporting that heat via extensive ocean currents to cooler parts of the world. These currents then return cooled water from the poles to the equator. Without this process, equatorial regions would be unbearably hot, and life would struggle elsewhere. Thus, oceans act as climate regulators, moderating extremes and fostering favorable conditions worldwide.

The oceans are also the primary source of moisture and precipitation, essentially shaping weather patterns on land. As the sun heats ocean surfaces, water evaporates, forming humid air that’s moved by winds and Earth’s rotation, delivering precipitation essential for terrestrial life.

If the ocean’s role in regulating Earth’s temperature is crucial for life, what happens when we overheat it?

The ocean: an unfathomably huge heat buffer

The ocean is believed to have absorbed 91% of the excess heat trapped in Earth’s atmosphere, mainly due to fossil fuel combustion. This heat storage is possible because of the ocean’s specific heat capacity, meaning water requires more energy to warm than land or air. Direct sunlight absorption, the primary way the ocean absorbs heat, depends on albedo levels; darker surfaces like ocean water absorb more solar energy than lighter ones like ice caps. Other mechanisms, like heat exchange with the atmosphere, also warm the ocean.

Without this heat absorption and storage over recent decades, life on land would have faced chaos from soaring temperatures. According to one study, the heat absorbed by the ocean’s upper layer between 1955 and 2010 could have raised atmospheric temperatures by 36 degrees C. This underscores the ocean’s climate-regulating role, highlighting our struggle to limit warming to 1.5 or 2 degrees C, given that the ocean has shielded us from the full impact of our fossil fuel consumption.

The buffer is getting thin

The ocean’s vastness requires significant inputs to affect change. The excess heat trapped by carbon emissions since the Industrial Revolution is one such input. Recent research highlights this scale, as described by study author John Abraham: the heat absorbed by the ocean in 2025 equals “12 Hiroshima bombs being detonated each second, every minute, hour, and day for the entire year.”

This heat absorption has steadily increased ocean temperatures, now reaching levels that drive impacts, including on land, that are unavoidable.

Overall, the ocean has set average temperature records annually for nine consecutive years. Surface temperatures have risen approximately 0.8C between 1901 and 2020, recently breaking new high monthly records for thirteen months in a row, starting in mid-2023. Deeper layers are also warming. The chart below shows ocean heat content at different depths, and about 20% of total warming is happening below 700 meters, despite slow ocean circulation limiting heat movement to great depths.

So, where are we today?

The NOAA sea surface temperature (SST) data in the chart below indicates that 2026 SSTs are rising to match the record-breaking levels of 2024. This is influenced by the formation of a Super El Niño. Forecasts suggest new record high ocean temperatures this year, potentially making 2027 the hottest year on record for Earth.

Climate change is the evident cause here. Tools like Climate Central’s Climate Shift Index (CSI) now allow us to identify climate change’s role in daily sea surface temperatures, and consequently in marine heat waves and other anomalies. According to the CSI, this week, both the significant warmth in the Indian Ocean and that in the Equatorial Pacific (where the El Niño is forming) are considerably more likely due to climate change.

Symptoms of the ocean’s fever

These elevated temperatures are manifesting in global impacts, indicating accelerated change. Future blogs will explore these symptoms in detail, but here are some key issues:

Warmer water accelerates the melting of “ocean-terminating” ice sheets (land-based ice connected to the ocean), contributing to sea level rise. It creates a warming feedback loop by shrinking sea ice and enhancing the ocean-warming albedo effect; it increases ocean stratification, where warmer surface waters fail to mix with cooler deep waters, disrupting heat distribution. This can lead to hypoxia, depriving deeper waters of oxygen; it can slow major ocean currents (thermohaline circulation), driven by density changes, in turn driven by water temperature and salinity, and can intensify storm systems, from tropical cyclones to Nor’easters, causing stronger, rapidly intensifying storms.

Acute heat also manifests in marine heat waves, now a chronic and widespread condition in oceans worldwide. In 2023, an estimated 96% of the ocean by area experienced a marine heatwave. The most significant heat waves (all recent) have disrupted marine food webs and caused major ecological damage, leading to widespread, prolonged coral reef bleaching, large-scale wildlife deaths, and damaged commercial fisheries.

Given the ocean’s crucial role in shaping significant terrestrial climate patterns, like the Asian Monsoon, ocean overheating has implications for human systems that rely on these patterns, including water supply, agriculture and food security, energy production, and more. We will continue to monitor ocean temperatures, report on developments, and explore these implications in future blogs.

An age of consequence for warming a water planet

The ocean’s immense capacity to store heat has delayed the visible consequences of warming our planet. Now, it means that a vast amount of excess heat energy resides in the oceans, to be gradually released to other Earth systems, manifesting as atmospheric heat, ice melting, and sea-surface heat fueling tropical cyclones, among others.

Additionally, releasing this heat, slowing ocean warming, and eventually cooling the ocean cannot be achieved within practical human timescales, but rather over hundreds to thousands of years. We have created an era of ocean heat consequences and must now find ways to adapt to it while working to correct it.

Our need to understand our changing planet meets the Trump administration

An essential requirement for addressing the era of ocean heat is a better understanding of how our oceans and climate are changing, supported by global ocean and climate monitoring infrastructure. In the US, the Trump administration is attempting—through staff cuts, budget reductions, data and information elimination (such as datasets and websites being taken down), and dismantling our monitoring infrastructure—to make it harder to track ocean, land, and atmospheric changes.

Recently, the administration ordered the “descoping” of the National Science Foundation’s Ocean Observing Infrastructure Project, a network of sensing and data gathering infrastructure in the North Atlantic and Pacific. Information about this dismantling is sparse; the process lacks transparency. What’s evident is that, at a time when ocean heat, the slowing of the Gulf Stream, and other major changes are causing shock waves through scientific and decision-making circles, we require a deeper understanding of our challenges, not self-imposed blind spots. Sending taxpayer-funded ships on taxpayer-funded missions to essentially unplug functional taxpayer-funded ocean monitoring systems is perplexing. Given the fossil fuel industry’s influence on the Trump agenda, it might appear as a massive attempted cover-up, except that the issue—planetary warming—is ongoing, and there’s no hiding the changing climate because we inhabit it.

The ocean has become easy for wealthier individuals to ignore: a place for resource extraction and waste disposal. But this giant is now awakening, becoming more of a central force than a backdrop. It’s difficult to imagine a greater failure than overheating a water planet and leaving it for future generations. History will not be kind to leaders who disregard science and clear signals. Let it be recorded that they were compelled by their people, in time frames that mattered, to phase out fossil fuels and invest in a secure and just climate future for all on this unique water planet.