Scientists analysed sea surface temperatures over the last 150 years, which have risen because of global heating. They found that extreme temperatures occurring just 2% of the time a century ago have occurred at least 50% of the time across the global ocean since 2014.
In some hotspots, extreme temperatures occur 90% of the time, severely affecting wildlife. More than 90% of the heat trapped by greenhouse gases is absorbed by the ocean, which plays a critical role in maintaining a stable climate.
“By using this measure of extremes, we’ve shown that climate change is not something that is uncertain and may happen in the distant future – it’s something that is a historical fact and has occurred already,” said Kyle Van Houtan, at the Monterey Bay Aquarium, US, and one of the research team. “Extreme climate change is here, it’s in the ocean, and the ocean underpins all life on Earth.”
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The heat content of the top 2,000 metres of the ocean set a new record in 2021, the sixth in a row. Prof John Abraham at the University of St Thomas in Minnesota, one of the team behind the assessment, said ocean heat content was the most relevant to global climate, while surface temperatures were most relevant to weather patterns, as well as many ecosystems.
“Oceans are critical to understanding climate change. They cover about 70% of the planet’s surface and absorb more than 90% of global warming heat,” Abraham said. “The new study is helpful because the researchers look at the surface temperatures. It finds there has been a big increase in extreme heat at the ocean’s surface and that the extremes are increasing over time.”
17 projects with a combined 25gw potential have been approved in a £700 million sale.
Greta Thunberg, Nicola Sturgeon and Vanessa Nakate at Cop26
The Scottish Government expects to secure at least £1 billion of investment in the Scottish supply chain for every gigawatt of power. Sturgeon says the workforce is “superbly placed with transferable skills to capitalise on the transition to new energy sources” and “people working right now in the oil and gas sector in the North East of Scotland can be confident of opportunities for their future”.
She went on: “While it is not yet possible to say with certainty what the scale of development will ultimately be, there is no doubt that the scale of this opportunity is transformational – both for our environment and the economy.”
Funds raised will be channelled to the Scottish Government and First Minister Nicola Sturgeon has said the “scale of opportunity here is truly historic”.
She said: “ScotWind puts Scotland at the forefront of the global development of offshore wind, represents a massive step forward in our transition to net zero, and will help deliver the supply chain investments and high quality jobs that will make the climate transition a fair one.”
The Scottish Government expects to secure at least £1 billion of investment in the Scottish supply chain for every gigawatt of power. Sturgeon says the workforce is “superbly placed with transferable skills to capitalise on the transition to new energy sources” and “people working right now in the oil and gas sector in the North East of Scotland can be confident of opportunities for their future”.
She went on: “While it is not yet possible to say with certainty what the scale of development will ultimately be, there is no doubt that the scale of this opportunity is transformational – both for our environment and the economy.”
National plans to cut carbon fall far short of what’s needed to avert dangerous climate change, according to the UN Environment Programme.
Their Emissions Gap report says country pledges will fail to keep the global temperature under 1.5C this century.
The Unep analysis suggests the world is on course to warm around 2.7C with hugely destructive impacts.
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Just a few days before COP26 opens in Glasgow and another scientific report on climate change is “another thundering wake-up call”, according to the UN Secretary General, Antonio Guterres.
If you’ve ever been seasick, “stable” may be the last word you associate with the ocean. But as global temperatures rise, the world’s oceans are technically becoming more stable.
When scientists talk about ocean stability, they refer to how much the different layers of the sea mix with each other. A recent study analysed over a million samples and found that, over the past five decades, the stability of the ocean increased at a rate that was six times faster than scientists were anticipating.
Ocean stability is an important regulator of the global climate and the productivity of marine ecosystems which feed a substantial portion of the world’s people. It controls how heat, carbon, nutrients and dissolved gases are exchanged between the upper and lower layers of the ocean.
So while a more stable ocean might sound idyllic, the reality is less comforting. It could mean the upper layer trapping more heat, and containing less nutrients, with a big impact on ocean life and the climate.
How the oceans circulate heat
Sea surface temperatures get colder the further you travel from the equator towards the poles. It’s a simple point, but it has enormous implications. Because temperature, along with salinity and pressure, controls the density of seawater, this means that the ocean surface also becomes denser as you move away from the tropics.
Seawater density increases with depth too, because the sunlight that warms the ocean is absorbed at the surface, whereas the deep ocean is full of cold water. The change in density with depth is referred to by oceanographers as stability. The faster density increases with depth, the more stable the ocean is said to be.
Our series on the global ocean opened with five in-depth profiles. Look out for new articles on the state of our oceans in the lead up to the UN’s next climate conference, COP26. The series is brought to you by The Conversation’s international network.
It helps to think of the ocean as divided into two layers, each with different levels of stability.
The surface mixed layer occupies the upper (roughly) 100 metres of the ocean and is where heat, freshwater, carbon and dissolved gases are exchanged with the atmosphere. Turbulence whipped up by the wind and waves at the sea surface mixes all the water together.
The lowest layer is called the abyss, which extends from a few hundred metres depth to the seafloor. It’s cold and dark, with weak currents slowly circulating water around the planet that remains isolated from the surface for decades or even centuries.
Dividing the abyss and the surface mixed layer is something called the pycnocline. We can think of it like a layer of cling film (or Saran Wrap). It’s invisible and flexible, but it stops water moving through it. When the film is ripped into shreds, which happens in the ocean when turbulence effectively pulls the pycnocline apart, water can leak through in both directions. But as global temperatures rise and the ocean’s surface layer absorbs more heat, the pycnocline is becoming more stable, making it harder for water at the ocean’s surface and in the abyss to mix.
Why is that a problem? Well, there’s an invisible conveyor belt of seawater which moves warm water from the equator to the poles, where it’s cooled and becomes more dense and so sinks, returning back to the equator at depth. During this journey, the heat absorbed at the ocean’s surface is moved to the abyss, helping redistribute the ocean’s heat burden, accumulated from an atmosphere that’s rapidly warming due to our greenhouse gas emissions.
If a stabler pycnocline traps more heat in the surface of the ocean, it could disrupt how effectively the ocean absorbs excess heat and pile pressure on sensitive shallow-water ecosystems like coral reefs.
Increasing stability causes a nutrient drought
And just as the ocean surface contains heat that must be mixed downwards, the abyss contains an enormous reservoir of nutrients that need to be mixed upwards.
The building blocks of most marine ecosystems are phytoplankton: microscopic algae which use photosynthesis to make their own food and absorb vast quantities of CO₂ from the atmosphere, as well as produce most of the world’s oxygen.
Phytoplankton can only grow when there is enough light and nutrients. During spring, sunshine, longer days and lighter winds allow a seasonal pycnocline to form near the surface. Any available nutrients trapped above this pycnocline are quickly used up by the phytoplankton as they grow in what is called the spring bloom.
For phytoplankton at the surface to keep growing, the nutrients from the abyss must cross the pycnocline. And so another problem emerges. If phytoplankton are starved of nutrients thanks to a strengthened pycnocline then there’s less food for the vast majority of ocean life, starting with the tiny microscopic animals which eat the algae and the small fish which eat them, and moving all the way up the food chain to sharks and whales.
Just as a more stable ocean is less effective at shifting heat into the deep sea and regulating the climate, it’s also worse at sustaining the vibrant food webs at the sunlit surface which society depends on for nourishment.
Should we be worried?
Ocean circulation is constantly evolving with natural variations and human-induced changes. The increasing stability of the pycnocline is just one part of an extremely complex puzzle that oceanographers are striving to solve.
To predict future changes in our climate, we use numerical models of the ocean and atmosphere that must include all of the physical processes responsible for changing them. We simply don’t have computers powerful enough to include the effects of small-scale, turbulent processes within a model that simulates conditions over a global scale.
We do know that human activity is having a greater than expected impact on fundamental aspects of our planet’s systems though. And we may not like the consequences.
