Oceans

    Just as warm air rises, so does warm water.  But warm water is already at the top of the ocean (usually).  This inhibits water's vertical mixing.  But saltier water, being denser, sinks.  This promotes vertical mixing.  So can winds.  The balance among them vaaries by space (regions of the world) and time (seasons, perhaps years).
    From 1961 to 1993, the atmosphere warmed ~50 times as fast as the ocean.  From 1993 to 2004, it warmed only 25 times as fast.  (See the bar graph, a ways below.  Oceans weigh more than 250 times as much as the atmosphere.  Moreover, water has ~4 x the heat capacity of air, gram for gram.)  So oceans hold 1,000 times as much heat as air.

     Warming in the air at the land surface is terribly sensitive to what % of Earth's net heat absorbed goes into the ocean.

The Great Decoupling - How Ocean Stratification is Boosting Global Warming 0326.rtf

     "As we look toward a potential 2026 El Niño, the “pre-conditioning” is unprecedented.

     "Despite 2025 being a neutral to weak La Niña year, ocean heat content set new records by a substantial margin.  Such a jump should have only been possible during an extreme La Niña, since colder equatorial surface water accelerates ocean heat uptake while the system loses less energy to space.  In the past, ocean heat uptake to greater depths slowed down surface warming.  This process appears to be stalling.  The ocean surface layers now absorb so much energy that is increasingly being trapped within the upper 300 [meters], accelerating surface warming and, through its connection with the atmosphere, air warming.

     "When the El Niño begins to return, part of the stored energy will start to be released into the atmosphere.  Potentially in late 2026, with peak values over the winter months.  We are likely to see global temperatures jump to +1.6°C or even +1.7°C during 2027.

     "A deadly principle seems to be emerging.  With each [0.1°] of warming, extreme events increase disproportionally.  Persistence of each jump in temperature - with no La Niña cooling phases - create a very worrying prognosis.  We have not experienced these temperatures before. [We] can only guess at the weather extremes, fire season, floods, droughts and crop disturbances that will now emerge.  Whatever does emerge is then unlikely to retreat, it's just the next step in the escalation of climate damage.

     "If an El Niño fails to develop in 2026, then unfortunately that won’t let us off the hook.  It would just mean that the oceans will increasingly accumulate even more heat (aided by the neutral to La Nina conditions), to produce an even larger temperature jump in a following year when a strong El Niño does eventually emerge.  The longer it takes, the stronger the force and worse the impacts.  Until then, stratification and MHWs will likely further intensify.

     "It happened during 2014-2016, then in 2023/24, so it will happen again...

     "A warning seems warranted.  We are in the process of triggering an ocean-atmosphere feedback that may well never have happened before in Earth’s history.  This is because it depends on the warming rate, rather than the pure temperature.  Previous spikes in emissions and warming, such as the PETM, have occurred over millennia rather than a century, allowing systems some time to gain balance.  This is not the case today.

"Conclusion: The End of the Buffer

     "We can no longer afford to prepare for “averages.”  The 2024 Valencia floods and the North Pacific’s “Super Heatwave” are not outliers; they are the early tremors of a system reaching a thermal breaking point.  Our global infrastructure—from drainage systems to food supply chains—was built for a linear world that no longer exists.

     "As the ocean surface continues to decouple from the deep, we are losing our greatest climate buffer, disrupting the “safe” storage of almost unimaginable amounts of energy.  The upcoming 2026/2027 El Niño will not simply be a repeat of the past; it will be a global ventilation event, dumping years of “trapped” energy into a fragile atmosphere.  We must monitor the ocean’s “pulse” with the same urgency we monitor the air.  The lid is popping and the climate no longer resets, it only moves forward.

     "Ocean stratification is emerging as a vitally important aspect of the changing climate with major global implications.  It is driven by a complex network of feedbacks but has the potential to disrupt the planet’s energy flows in hugely significant ways.  Over half of the energy accumulating as a result of our emissions is being stored in the top 700 [meters] of the oceans compared to just 2% in the atmosphere."

     Above in August, in the northern hemisphere, the Gulf of Mexico and the Caribbean Sea are much hotter in August than in April.  So is the Pacific from Taiwan and Japan to California and Washington.  And the North Atlantic Ocean and especially the Mediterranean Sea.

      Below in April, the reverse (warmer in April) is true for much of the southern hemisphere: for most of the Indian Ocean, the south Atlantic and east from Australia.  But not for the east Pacific and west coast of South America.

Below and also on Overviews page, 1961-2003 is in blue, 1993-2003 in magenta.  More than half the 42-year change was in the then-most recent 10 years.

Section Map: Heat