China: Extreme heat & climate change

In August last year (2022) CEN reported on heat wave conditions hitting China. Similar conditions since hit India and South East Asia.

Researchers at Tsinghua University and the Beijing Institute of Economics and Management said that this was no longer unusual, and stressed that “the world needs to adopt stronger climate change mitigation and adaptation measures, such as reducing the use of fossil fuels and increasing urban green spaces.”

Heat-related deaths in China have increased fourfold over the past 20 years, to reach 26,800 in 2019. From June 16 to July 9 last year, local governments issued 1,372 high-temperature “code reds,” indicating temperatures were expected to rise above 40 degrees Celsius within 24 hours.

To understand what causes such events, we publish the following.

The key key point to note is that increases in global temperatures are moderted by the planet’s oceans, and that the massive amount of heat stored in these has profound consequences for weather and terrestial environments.

The most immediate consequence of too much ocean heat will be more severe marine heat waves which are comparable to terrestrial wildfires of rainforests. These underwater fire-equivalents degrade/destroy underwater kelp forests (e.g., in the Pacific, West Coast Pacific kelp losses, and Great Barrier Reef coral bleaching) while also negatively altering key life-giving nutrients and oxygen needed for all sea life.

Ocean warming and permanent heatwaves

Until the 1970s, the constant flow of energy that Earth receives from the sun was offset by heat reflected back into space, so the planet’s overall energy level did not change very much over time. The amount of incoming solar energy has not changed, but rising concentrations of greenhouse gases are trapping ever more of the reflected heat, preventing it from leaving the atmosphere. Climate scientists call this Earth’s Energy Imbalance.

The excess energy is not distributed evenly through the Earth System. Although global warming is usually expressed as increased air temperatures, the ocean is actually much better at storing heat than the atmosphere — one degree of ocean warming stores over 1000 times as much heat energy as one degree of atmosphere warming — so it isn’t surprising that the ocean has taken up most of the excess solar energy. Just seven percent warms the air and land and melts snow and ice — 93 percent is absorbed by the ocean.

Since 1987 the ocean has warmed 4.5 times as fast as in the previous three decades. The Intergovernmental Panel on Climate Change (IPCC) projects that even if emissions are substantially reduced, by 2100 the ocean will heat 2 to 4 times as much as it has since 1970 — and if emissions are not cut, it will heat 5 to 7 times as much. Since 2010, the Atlantic ocean has been hotter than at any time in the past 2900 years, and the Arctic is warming two to three times as fast as the rest of the world. Summer sea ice may disappear entirely by 2035.

Scientist Lijing Cheng of China’s Institute of Atmospheric Physics calculates that “The amount of heat we [humanity] have put in the world’s oceans in the past 25 years equals to 3.6 billion Hiroshima atom-bomb explosions.”

The concept of marine heatwaves is new: the term itself first appeared in 2011, in a Australian report on “a major temperature anomaly” in which “water temperatures off the south-western coast of Australia rose to unprecedented levels.”

Marine heatwaves (MHWs) are usually defined as five or more consecutive days in which sea surface temperatures are in the top ten percent of the 30-year average for the region. Using an even stricter definition — temperatures in the top one percent — the IPCC recently concluded that since 1982, marine heatwaves “have doubled in frequency and have become longer lasting, more intense and more extensive. A marine “temperature anomaly” might encompass an area as large as Canada and last over two years. Ocean-based food webs that have sustained life for millennia have collapsed in unprecedented heat of MHWs.”

Article first published as China: Heat waves are more frequent, lasting longer, and getting hotter, in China Environment Net on Facebook, 20 Aug 2022.

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