The world witnessed record climate and weather disasters in 2021, destructive flash floods that swept mountain towns in Europe and flooded metro systems in china and United States, heat waves and forest fires. Typhoon Rai killed more than 400 people in the Philippines; Hurricane Ida caused approximately $74 billion in damages in the USA
Globally, it was the sixth warmest year on record for surface temperatures, according to data released by NASA and the National Oceanic and Atmospheric Administration in their annual global climate report on January 13, 2022. But below the surface, ocean temperatures set new heat records in 2021.
As a climatologist Kevin Trenberg explains, while the temperature on the Earth’s surface is what people feel day to day, the temperature in the upper ocean is a better indicator of how excess heat is building up on the planet.
The Conversation spoke with Trenberth, co-author of a study published on January 11, 2022 by 23 researchers from 14 institutes who tracking global warming in the world’s oceans.
Your latest research shows that ocean heat is reaching record highs. What does this tell us about global warming?
The world’s oceans are warmer than ever, and their heat has increased every decade since the 1960s. This relentless increase is a primary indicator of human-induced climate change.
As the oceans warm, their heat supercharges weather systems, creating more powerful storms and hurricanes, and more intense precipitation. This threatens human lives and livelihoods as well as marine life.
The oceans occupy about 93% more energy trapped by increasing greenhouse gases from human activities, especially the burning of fossil fuels. Because water contains more heat than land and the volumes involved are immense, the upper oceans are a primary memory of global warming. I explain this in more detail in my new book.The evolution of energy flow through the climate system.”
Our study provided the first analysis of ocean warming in 2021, and we were able to attribute the warming to human activities. Global warming is alive and well, unfortunately.
The global average surface temperature was the fifth Where sixth hottest on record in 2021 (record depends on dataset used), partly due to year the girl weather conditions, in which the cool conditions of the tropical Pacific influence weather patterns around the world.
There is much more natural variability in surface air temperatures than in ocean temperatures due to El Nino/La Nina and weather events. This natural variability over a warming ocean creates hotspots, sometimes called “marine heat waves,” that vary from year to year. These hot spots have profound influences on marine life, from tiny plankton to fish, marine mammals and birds. Other hotspots are responsible for more activity in the atmosphere, such as hurricanes.
While surface temperatures are both a consequence and a cause, the main source of the phenomena causing the extremes is linked to the heat of the oceans which energizes weather systems.
We found that all oceans are warming, with the greatest amounts of warming in the Atlantic Ocean and in the Southern Ocean surrounding Antarctica. This is a concern for the Antarctic ice – the heat in the Southern Ocean can crawl under the ice floes of Antarctica, thinning them and causing the calving of huge icebergs. The warming of the oceans is also a concern for sea level rise.
How does the extra ocean heat affect air temperature and humidity on land?
Global warming increases evaporation and drying on land, as well as rising temperatures, increasing the risk of heat waves and wildfires. We saw the impact in 2021, especially in western North America, but also in the midst of heat waves Russia, Greece, Italy and Turkey.
Warmer oceans also provide atmospheric rivers moisture in land areas, increasing the risk of flooding, as the West Coast of the United States has experienced.
The year 2021 has seen several destructive cyclones, including Hurricane Ida in the United States and Typhoon Rai in the Philippines. How does ocean temperature affect storms like these?
Warmer oceans provide additional humidity to the atmosphere. This extra moisture fuels storms, especially hurricanes. The result can be prodigious rainfall, as the United States has seen from Ida, and widespread flooding like that which has occurred in many places over the past year.
Storms can also become more intense, bigger and last longer. Several major floods occurred in Australia last year, as well as in New Zealand. Heavier snowfalls can also occur in winter provided temperatures remain below freezing because warmer air holds more moisture.
If greenhouse gas emissions slowed, would the ocean cool?
In the oceans, warm water sits on top of cooler, denser water. However, the oceans warm from top to bottom and as a result the ocean becomes more stratified. This inhibits the mixing between layers that would otherwise allow the ocean to warm at deeper levels and absorb carbon dioxide and oxygen. It therefore impacts all marine life.
We have found that the first 500 meters of ocean have clearly warmed up since 1980; depths of 500 to 1,000 meters have been warming since about 1990; depths of 1,000 to 1,500 meters since 1998; and below 1,500 meters since around 2005.
Slow downward heat penetration means the oceans will continue to warm and sea levels will continue to rise even after greenhouse gases stabilize.
The final area requiring attention is the need to increase the capacity of scientists to monitor changes in the oceans. One way to achieve this is to Argo board – currently around 3,900 profiling floats that return temperature and salinity data from the surface to around 2,000 meters deep, measured as they rise and then fall, in ocean basins around the world. These robotic, diving and drifting instruments require constant replenishment and their observations are invaluable.
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