Climate change in deep oceans could be seven times faster by middle of century, report says. Uneven heating could have major impact on marine wildlife, as species that rely on each other for survival are forced to move. By Graham Readfearn @readfearn Email 25 May 2020 in The Guardian
Climate worst-case scenarios may not go far enough, cloud data shows: Modelling suggests climate is considerably more sensitive to carbon emissions than thought, by Jonathan Watts 13 Jun 2020 in The Guardian
Worst-case global heating scenarios may need to be revised upwards in light of a better understanding of the role of clouds, scientists have said.
Recent modelling data suggests the climate is considerably more sensitive to carbon emissions than previously believed, and experts said the projections had the potential to be “incredibly alarming”, though they stressed further research would be needed to validate the new numbers.
Modelling results from more than 20 institutions are being compiled for the sixth assessment by the United Nations Intergovernmental Panel on Climate Change, which is due to be released next year.
Compared with the last assessment in 2014, 25% of them show a sharp upward shift from 3C to 5C in climate sensitivity – the amount of warming projected from a doubling of atmospheric carbon dioxide from the preindustrial level of 280 parts per million. This has shocked many veteran observers, because assumptions about climate sensitivity have been relatively unchanged since the 1980s.
“That is a very deep concern,” Johan Rockström, the director of the Potsdam Institute for Climate Impact Research, said. “Climate sensitivity is the holy grail of climate science. It is the prime indicator of climate risk. For 40 years, it has been around 3C. Now, we are suddenly starting to see big climate models on the best supercomputers showing things could be worse than we thought.”
He said climate sensitivity above 5C would reduce the scope for human action to reduce the worst impacts of global heating. “We would have no more space for a soft landing of 1.5C [above preindustrial levels]. The best we could aim for is 2C,” he said.
Worst-case projections in excess of 5C have been generated by several of the world’s leading climate research bodies, including the UK Met Office’s Hadley Centre and the EU’s Community Earth System Model.
Timothy Palmer, a professor in climate physics at Oxford University and a member of the Met Office’s advisory board, said the high figure initially made scientists nervous. “It was way outside previous estimates. People asked whether there was a bug in the code,” he said. “But it boiled down to relatively small changes in the way clouds are represented in the models.”
The role of clouds is one of the most uncertain areas in climate science because they are hard to measure and, depending on altitude, droplet temperature and other factors, can play either a warming or a cooling role. For decades, this has been the focus of fierce academic disputes.
Previous IPCC reports tended to assume that clouds would have a neutral impact because the warming and cooling feedbacks would cancel each other out. But in the past year and a half, a body of evidence has been growing showing that the net effect will be warming. This is based on finer resolution computer models and advanced cloud microphysics.
“Clouds will determine humanity’s fate – whether climate is an existential threat or an inconvenience that we will learn to live with,” said Palmer. “Most recent models suggest clouds will make matters worse.”
In a recent paper in the journal Nature, Palmer explains how the new Hadley Centre model that produced the 5+C figure on climate sensitivity was tested by assessing its accuracy in forecasting short-term weather. This testing technique had exposed flaws in previous models, but in the latest case, the results reinforced the estimates. “The results are not reassuring – they support the estimates,” he wrote. He is calling for other models to be tested in a similar way.
“It’s really important. The message to the government and public is, you have to take this high climate sensitivity seriously. [We] must get emissions down as quickly as we can,” he said.
The IPCC is expected to include the 5+C climate sensitivity figure in its next report on the range of possible outcomes. Scientists caution that this is a work in progress and that doubts remain because such a high figure does not fit with historical records.
Catherine Senior, head of understanding climate change at the Met Office Hadley Centre, said more studies and more data were needed to fully understand the role of clouds and aerosols.
“This figure has the potential to be incredibly alarming if it is right,” she said. “But as a scientist, my first response is: why has the model done that? We are still in the stage of evaluating the processes driving the different response.”
While acknowledging the continued uncertainty, Rockström said climate models might still be underestimating the problem because they did not fully take into account tipping points in the biosphere.
“The more we learn, the more fragile the Earth system seems to be and the faster we need to move,” he said. “It gives even stronger argument to step out of this Covid-19 crisis and move full speed towards decarbonising the economy.”
Rates of climate change in the world’s ocean depths could be seven times higher than current levels by the second half of this century even if emissions of greenhouse gases were cut dramatically, according to new research.
Different global heating at different depths could have major impacts on ocean wildlife, causing disconnects as species that rely on each other for survival are forced to move.
In the new research, scientists looked at a measure called climate velocity – the speed at which species would need to move to stay within their preferred temperature range as different ocean layers warm.
The study, published in the journal Nature Climate Change, found different parts of the ocean would change at different rates as the extra heat from increasing levels of greenhouse gases moved through the vast ocean depths.
By the second half of the century, the study found “a rapid acceleration of climate change exposure throughout the water column”.
The study used climate models to first estimate the current rates of climate velocity at different ocean depths, and then future rates under three scenarios – one where emissions started to fall from now; another where they began to fall by the middle of this century; and a third where emissions continued to rise up to 2100.
Prof Jorge García Molinos, a climate ecologist at Hokkaido University and a co-author of the study, said: “Our results suggest that deep sea biodiversity is likely to be at greater risk because they are adapted to much more stable thermal environments.”
At present, the world’s heating was already causing species to shift in all layers of the ocean from the surface to more than 4km down, but at different speeds.
But even under a highly optimistic scenario, where emissions fell sharply from now, the ocean’s mesopelagic layer – from 200m to 1km down – climate velocity would change from about 6km per decade to 50km by the second half of the century. But over the same period, climate velocity would halve at the surface.
Even at depths of between 1,000 and 4,000 metres, climate velocity would triple current rates, even if emissions dropped sharply.
Prof Anthony Richardson, of the University of Queensland and the CSIRO and one of the study’s 10 authors, told Guardian Australia: “What really concerns us is that as you move down through the ocean, climate velocity moves at different speeds.”
This could create a disconnect for species that rely on organisms in different layers.
For example, Richardson said tuna lived in the mesopelagic layer between 200 and 1,000 metres deep, but they relied on plankton species near the surface.
He said because the planet’s oceans were so large and stored so much heat, “warming already absorbed at the ocean surface will mix into deeper waters.”
“This means that marine life in the deep ocean will face escalating threats from ocean warming until the end of the century, no matter what we do now.”
Isaac Brito-Morales, the study’s lead author and a researcher at the University of Queensland, said: “Because the deep ocean has a more stable temperature, any small increase will have an impact on species – they’re more at risk than those at the surface.”
Richardson added it was “concerning” their results showed, as well as different rates of climate velocity at different depths, the direction that species would need to move wasn’t uniform either.
This could mean that marine park areas designed to protect different species or habitats could become compromised as species moved out of the protected areas into unprotected areas.