Fidelity of El Niño Models and Simulations Matter for Predicting Future Climate

A new study led by University of Hawai’i at Mānoa researchers and recently published in the Nature Communications journal revealed that correctly simulating ocean current variations hundreds of feet below the ocean surface – the so-called Pacific Equatorial Undercurrent – during El Niño events is key in reducing the uncertainty of predictions of future warming in the eastern tropical Pacific.

The issue of prediction is not so much one of timing, but of degree or severity.

Trade winds and the temperatures in the tropical Pacific Ocean experience large changes from year to year due to the El Niño-Southern Oscillation, or ENSO, affecting weather patterns across the globe. For instance, if the tropical Pacific is warmer and trade winds are weaker than usual – an El Niño event – flooding in California typically occurs and monsoon failures in India and East Asia are detrimental to local rice production. In contrast, during a La Niña the global weather patterns reverse with cooler temperatures and stronger trade winds in the tropical Pacific.

These natural climate swings affect ecosystems, fisheries, agriculture, and many other aspects of human society. Changes to pink shrimp production and the location of market squid on the West Coast are frequently related to El Ninos.

Computer models that are used for projecting future climate correctly predict global warming due to increasing greenhouse gas emissions as well as short-term year-to-year natural climate variations associated with El Niño and La Niña.

“There is, however, some model discrepancy on how much the tropical Pacific will warm,” Malte Stuecker, co-author and assistant professor in the Department of Oceanography and International Pacific Research Center at UH Mānoa said in a press release. “The largest differences are seen in the eastern part of the tropical Pacific, a region that is home to sensitive ecosystems such as the Galapagos Islands. How much the eastern tropical Pacific warms in the future will not only affect fish and wildlife locally but also future weather patterns in other parts of the world.”

Researchers have been working for decades to reduce the persistent model uncertainties in tropical Pacific warming projections.

Many climate models simulate El Niño and La Niña events of similar intensity. In nature, however, the warming associated with El Niño events tends to be stronger than the cooling associated with La Niña. In other words, while in most models El Niño and La Niña are symmetric, they are asymmetric in nature.

In this new study, the scientists analyzed observational data and numerous climate model simulations and found that when the models simulate the subsurface ocean current variations more accurately, the simulated asymmetry between El Niño and La Niña increases–becoming more like what is seen in nature.

“Identifying the models that simulate these processes associated with El Niño and La Niña correctly in the current climate can help us reduce the uncertainty of future climate projections,” corresponding lead author Michiya Hayashi, a research associate at the National Institute for Environmental Studies, Japan, and a former postdoctoral researcher at UH Mānoa said in the release. “Only one-third of all climate models can reproduce the strength of the subsurface current and associated ocean temperature variations realistically.”

“Remarkably, in these models we see a very close relationship between the change of future El Niño and La Niña intensity and the projected tropical warming pattern due to greenhouse warming,” Stuecker noted.

That is, the models within the group that simulate a future increase of El Niño and La Niña intensity also show an enhanced warming trend in the eastern tropical Pacific due to greenhouse warming. In contrast, the models that simulate a future decrease of El Niño and La Niña intensity show less greenhouse gas-induced warming in the eastern part of the basin. The presence of that relationship indicates those models are capturing a mechanism known to impact climate. In turn, that signifies those models are more reliable. This relationship totally disappears in the two-thirds of climate models that cannot simulate the subsurface ocean current variations correctly.

“Correctly simulating El Niño and La Niña is crucial for projecting climate change in the tropics and beyond. More research needs to be conducted to reduce the biases in the interactions between wind and ocean so that climate models can generate El Niño-La Niña asymmetry realistically,” added Fei-Fei Jin, co-author and professor in the Department of Atmospheric Sciences at UH Mānoa.

“The high uncertainty in the intensity change of El Niño and La Niña in response to greenhouse warming is another remaining issue,” said Stuecker. “A better understanding of Earth’s natural climate swings such as El Niño and La Niña will result in reducing uncertainty in future climate change in the tropics and beyond.”

Graphic: Future increase of El Nino and La Nina intensity leads to enhanced warming in the Eastern Tropical Pacific, left. Future decrease of El Nino and La Nina Intensity leads to less warming in the eastern tropical Pacific, right. Credit: Data from NOAA.

Posted with permission of Seafood News

Susan Chambers
SeafoodNews.com
1-541-297-2875

Warming of Oceans Due to Climate Change is Unstoppable, Say US Scientists

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The warming of the oceans due to climate change is now unstoppable after record temperatures last year, bringing additional sea-level rise, and raising the risks of severe storms, US government climate scientists said on Thursday.

The annual State of the Climate in 2014 report, based on research from 413 scientists from 58 countries, found record warming on the surface and upper levels of the oceans, especially in the North Pacific, in line with earlier findings of 2014 as the hottest year on record.

Global sea-level also reached a record high, with the expansion of those warming waters, keeping pace with the 3.2 ± 0.4 mm per year trend in sea level growth over the past two decades, the report said.

Scientists said the consequences of those warmer ocean temperatures would be felt for centuries to come – even if there were immediate efforts to cut the carbon emissions fuelling changes in the oceans.

“I think of it more like a fly wheel or a freight train. It takes a big push to get it going but it is moving now and will contiue to move long after we continue to pushing it,” Greg Johnson, an oceanographer at Noaa’s Pacific Marine Environmental Laboratory, told a conference call with reporters.

“Even if we were to freeze greenhouse gases at current levels, the sea would actually continue to warm for centuries and millennia, and as they continue to warm and expand the sea levels will continue to rise,” Johnson said.

On the west coast of the US, freakishly warm temperatures in the Pacific – 4 or 5F above normal – were already producing warmer winters, as well as worsening drought conditions by melting the snowpack, he said.

The extra heat in the oceans was also contributing to more intense storms, Tom Karl, director of Noaa’s National Centers for Environmental Information, said.

The report underlined 2014 as a banner year for the climate, setting record or near record levels for temperature extremes, and loss of glaciers and sea ice, and reinforcing decades-old pattern to changes to the climate system.

Four independent data sets confirmed 2014 as the hottest year on record, with much of that heat driven by the warming of the oceans.

Globally 90% of the excess heat caused by the rise in greenhouse gas emissions is absorbed by the oceans.

More than 20 countries in Europe set new heat records, with Africa, Asia and Australia also experiencing near-record heat. The east coast of North America was the only region to experience cooler than average conditions.

Alaska experienced temperatures 18F warmer than average. Spring break-up came to the Arctic 20-30 days earlier than the 20th century average.

“The prognosis is to expect a continuation of what we have seen,” Karl said.

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Sardines swim into northern waters to keep cool

Sardines, mackerel, anchovies and other staples of the Mediterranean diet are moving north – to as far as the Baltic Sea – to escape warming ocean temperatures. The commercial fishery is suffering. Above, a purse seiner off the coast of Italy hauls in a net full of fish. Photo courtesy Prigalla/flickr.

A staple of the Mediterranean diet is migrating north to escape warming seas – leaving fishermen with empty nets.

LONDON – Several important fish species that for centuries have been a staple of the Mediterranean diet are abandoning sub-tropical seas because the water is too warm.

Sardines, for generations have been the most abundant commercial fish species in Portugal, are moving North. They are now established in the North Sea and are being caught in the Baltic – a sea that until recently was normally frozen over in the winter.

Sardines, anchovies and mackerel – three important species in the diet of many southern European and North African countries – have been studied by scientists trying to discover how climate change and warming seas are affecting their distribution.

Crucial for the food chain

As well as the affect on the fishing industry, the abundance or disappearance of these species is crucial for many other marine species that rely on them for food.

A pioneering study, published in Global Change Biology, analyzed 57,000 fish censuses conducted over 40 years and has tracked the movement of these fish during this period.

It confirms that the continued increase in water temperature has altered the structure and functioning of marine ecosystems across the world. But it also shows that the effect has been greater in the North Atlantic, with increases of up to 1.3 degrees Celsius in the average temperature over the last 30 years.

This variation in temperature directly affects the frequency and range of pelagic fish, which live in the middle of the water column and are directly influenced by temperature rather than habitat. It includes the sardine (Sardina pilchardus), anchovy (Engraulis encrasicolus), horse mackerel (Trachurus trachurus) and mackerel (Scomber scombrus), among others.

They feed off phytoplankton and zooplankton and are themselves the staple diet of large predators, such as cetaceans, large fish and marine birds. These fish occur off the shores of many coastal countries in the world and are important sources of protein.

Response to changing temperatures

Scientists have known that fish were moving to new areas, but they did not know whether it was in response to their main food supply plankton moving first or whether it was a simple response to changing temperatures.

The new study has developed statistical models for the North Sea area, and confirms the great importance of sea temperatures.

“Time series of zooplankton and sea surface temperature data have been included to determine the factor causing these patterns,” Ignasi Montero-Serra, lead author of the study and researcher in the department of Ecology at the University of Barcelona, explains to the Scientific Information and News Service.

To demonstrate the consequences of the warming of the seas, the research team analyzed fish censuses from commercial fishing performed independently along the European continental shelf between 1965 and 2012, extracted from data provided by the International Council for the Exploration of the Sea.

Rapid ocean warming

The study, the first to be carried out on such a large timescale and area, allows for the dynamics of this species to be understood in relation to the rapid warming of the oceans observed since the 1980s.

The results reveal that sardines and other fish with fast life cycles, planktonic larval stage and low habitat dependence are highly vulnerable to changes in ocean temperature, and therefore represent, Montero-Serra says, “an exceptional bio-indicator to measure the direction and speed of climate change expected in the near future.”

Montero-Serra says that accelerated increase in temperature of the continental seas has resulted in sardines and anchovies – with a typically subtropical distribution – increasing their presence in the North Sea and “even venturing into the Baltic Sea.” And the presence of species with a more northern distribution, such as the herring and the sprat, has decreased.

A clear sign

The analysis is therefore a clear sign that species in the North Sea and Baltic Sea are “becoming subtropical.”

This is due to the pelagic fish being highly dependent on environmental temperatures at different stages of their life cycle – from reproductive migrations and egg-laying, to development and survival of larvae.

According to the researchers, the changes in such an important ecological group “will have an effect on the structure and functioning of the whole ecosystem,” although they still do not know the scale of the socio-economic and ecological repercussions.

Read the original post: DailyClimate.org