Ocean heat puts pressure on poorest fisheries

Warm water Red Mullet catches in the UK have increased as sea temperatures have warmed, which William Cheung has linked to global warming. Credit: Nate Gray: A Culinary (Photo) Journal via Flickr Creative Commons License

Since 1970, our warming seas have driven fish across the world into cooler, deeper waters, potentially threatening fishing in Earth’s hottest seas. By analysing worldwide fish catches, Canadian and Australian scientists have found that the proportion of warmer-water fish caught has steadily grown. And in future, the warmest waters are set to become too hot for some of the fish that might previously have been caught there.

“Tropical fisheries are likely to be most impacted by ocean warming,” William Cheung from the University of British Columbia in Vancouver, Canada, told me. “We expect that the current trend would continue, and will reduce the catch for tropical fisheries. Many tropical fishing communities are in developing countries with limited socio-economic scope to deal with changes in resource abundance. Thus, these communities are most vulnerable to ocean warming.”

Like all living creatures, fish have a range of temperatures that they can comfortably live in. Sea temperatures are rising, with the US coast from North Carolina to Maine reaching the warmest level in 150 years last year, for example. Changing climate has already been linked to fish catches in some places, with William previously suggesting it’s behind rapid increases in warm-water red mullet catches around the UK. “However, there was no study that assessed the linkages between ocean warming and fisheries changes in the global scale,” he said.

So William and his teammates set about bringing together fish catch information from 52 ecosystems, including most of the world’s fisheries. That included data on 990 species, which the scientists analysed using a new measure, the ‘mean temperature of the catch’ or MTC, which William also calls a ‘fish thermometer’. To find the MTC, the scientists start by working out the preferred temperature of each species, based on the sea water temperatures in the areas that they used to live in. “For example, fishes that live in colder area, such as cod, will have a lower preferred temperature than a tropical fish, such as a tropical grouper,” William explained.

Probabilities reveal shape of climate change

Planners looking to prepare for floods, like this one in Venice, Italy, would like better local information on climate change – and now David Stainforth and his colleagues are helping deliver it. Image courtesy http://www.WorldIslandInfo.com, Allison Lince-Bentley, used under Flickr Creative Commons license.

If you want to plan for the future, or even for the present, knowing that our climate is changing, what’s the best way to do it? That’s a question that David Stainforth from the London School of Economics, Sandra Chapman from the University of Warwick and Nicholas Watkins from the British Antarctic Survey have puzzled over. And while David is co-founder of the climateprediction.net project that borrows spare time on peoples’ computers to run climate models, he doesn’t feel that models are always the best source of information.

“It’s clear to me that the detailed local information on how climate is changing, and what it will be like in 2050, can’t be had from climate models today,” David told me. “They’re just not that good. And yet I work a lot with the adaptation and impacts community, who are interested in what’s happening ‘here’, on a very local basis.” So together David, Sandra and Nicholas have turned to measured data, devising a simple way to pick the most important local climate changes from it.

Weather stations around the world monitor daily conditions, and combine to create a record containing occasional extremes, lots of ordinary days, and everything in between. Knowing how common these conditions are is important for people who want to prepare for future climate change. “For flood risks, you’re worried about going over certain rainfall amounts in a given time,” David explained. “Managers of overheating buildings are worried about what proportion of the time temperatures pass certain levels.”

Alternate histories back unique modern warmth claims

Tree rings have a light-colored band, or earlywood, that forms in the spring and a dark-colored band, or latewood, that forms in the summer. The width of the band tells how much the tree grew during that period and therefore can be used as a proxy for the climate during that season. That approach has some uncertainties, but Martin Tingley and Peter Huybers have reduced their impact on telling if any year is the warmest. Credit: thaths via Flickr Creative Commons license

If you build a temperature record going back in time to judge modern warming against, how certain can you be of your answer? That’s a big question for scientists making such records from effects temperatures have had on the natural world. And figuring out if today’s heat is unique is too great a challenge for the methods scientists normally use to calculate uncertainty, according to Harvard University’s Martin Tingley.

But Martin and Peter Huybers have shown the precise chances that northern areas of the world are warmer than any time in rebuilt records reaching back to the year 1400. They have worked out that there’s less than one chance in 20 that 2005, 2007, 2010 and 2011’s northern summers weren’t the warmest in that time. They also find that summer 2010 has a 99% chance of being the warmest western Russia has seen. There have already been lots of claims made over the unusualness of recent warmth, Martin pointed out, but his and Peter’s are the most robust yet. “We put these estimates on a much sounder statistical footing,” he told me.

Saying one year’s summer is uniquely warm across a long period is difficult for subtle reasons that Martin explained through his height. “I’m a tall guy, 6 foot 4 inches,” he said. “I’ve never met you, but I’m going to bet I’m taller than you. What’s the intuition behind my bet? We have a sense of the distribution of heights. I’m aware I fall pretty far out on the tail, so the chances are if I meet an average person they don’t fall further out than I do. What if I’m in a room with 1,000 people I’ve never met before? Am I still likely to be the tallest in the room? Probably not.”

Temperature patterns produce perplexing Pliocene puzzle

Lafayette College’s Kira Lawrence and her teammates have used ocean bed sediment cores, like this one, to produce a 5 million year climate record. © Intergrated Ocean Drilling Program

US, UK and Hong Kong Researchers have produce a unique ‘movie’ of climate reaching back 5 million years, by bringing together data drilled from ocean beds. It reveals three important temperature patterns during the warm early part of the Pliocene period that they couldn’t recreate together in climate models using existing explanations. That’s important because scientists hope the Pliocene could help us know what the future of a warmer Earth might be like. And having uncovered another layer to the Pliocene puzzle, team member Kira Lawrence from Lafayette College in Easton, Pennsylvania, underlined the value of finding its solution.

“Our community of scientists think of the Pliocene as though it was about 3°C warmer than modern temperatures with CO2 concentration about where we are right now,” Kira told me. “But we haven’t recognised before that the pattern of temperature was a lot different. If that’s where we’re headed in the not too distant future, if the temperature and precipitation patterns change in that way, we should have some significant things to think about.”

The Pliocene period started 5.3 million years ago, during which primates made important evolutionary steps towards humanity. Since 2000, there has been a climate data explosion reaching back through this era. Around the world, international drilling expeditions have pierced ocean beds kilometres below sea level, reaching hundreds of metres into sediment to bring back ‘core’ samples. Tiny fossils within that rock and mud can tell scientists temperatures through history, which can give climate scientists real data to test their models against.

Diving deep into ocean data uncovers ‘missing heat’ treasure

A new ocean reanalysis called ORAS4, here showing the difference between September 2012 sea temperatures and the average for 1989-2009 (not part of the latest study), has helped show that extra heat trapped in the atmosphere by CO2 humans are emitting is buried in the deep ocean. Credit: ECMWF

A newly-made picture of ocean history has backed a theory that the missing piece of a climate puzzle at the edge of space lies deep in Earth’s waters. The puzzle comes because the amount of heat energy our planet has absorbed should have warmed it more than it seems to have done. But now, using an ocean reanalysis assembled from data gathered from many sources, UK and US researchers have shown especially strong recent warming in oceans below 700m. “We have found some energy buried at depths,” Kevin Trenberth from the National Center for Atmospheric Research (NCAR) in Boulder, Colorado. “We also have a plausible explanation for it related to changes in winds.”

In 2010, Kevin went public over his worries about a budget that didn’t balance. But rather than money, that budget tallies heat energy from the Sun entering the top of the atmosphere against energy the Earth radiates back out into space. Satellite measurements show more energy coming in than leaving, which is what causes global warming. But Kevin noticed that existing measurements showed the world hadn’t warmed as much since 2003 as this budget would suggest.

With over nine-tenths of the surplus energy coming into the Earth going into the sea, the deep ocean has always looked the likeliest hiding place for the missing heat. However, temperature data from those depths is scarce, making the theory hard to prove. Yet, in the years since Kevin pointed out the problem, scientists have gathered some clues to back that explanation. For example, some used a model that includes the complex links between the atmosphere, land, oceans, and sea ice to run five simulations of the 21^st century. They found warming slowdowns on the Earth’s surface similar to what has happened in the 2000s, with the heat going into the deep oceans. But even this just underlined the importance of using measurements to see the effect directly.

Climate change set to bring Western Europe more hurricanes

In January 2009 a cyclone called Klaus, which is shown here and boasted hurricane-force winds, hit France, Spain and Italy. Such conditions could become much more common in Europe by the end of the 21st century, according to Rein Haarsma and his KNMI team. Credit: H de C via Flickr Creative Commons license

Current once-in-a-century hurricane-force winds may become as much as 25 times as likely in parts of Western Europe at the end of the 21^st century. That’s what Rein Haarsma and a team from the Royal Netherlands Meteorological Institute (KNMI) have shown using one of the highest-resolution climate models around today. Their findings spring from a change in where hurricanes will develop that could also affect western North America, though more research is needed to study this. “The statement that the wind climate in Western Europe will not change significantly is questionable,” Rein told me. “Significant changes in wind climate will have consequences for agriculture – the increased winds are during the autumn – infrastructure and coastal defence.”

With Europe so far from the tropical regions where warmth and unstable atmosphere spawns hurricanes, it rarely sees them today. But when hurricane conditions do happen, like the ‘Great Storm’ in 1987, or Hurricane Floyd in 1993, they live long in the memory. The hurricane remnants that sometimes reach Western Europe usually bring a lot of rain, Rein noted, and only occasionally hurricane-force winds.

The warming Arctic is reducing ocean temperature differences that help create Europe’s traditional storms, meaning they pose less of a threat. But recently findings have shown that a warmer atmosphere raises hurricane risks. “Many model simulations suggest that the strength of hurricanes will increase due to climate change,” Rein explains. “The area where hurricanes develop appears to move poleward and the moisture content in a warmer atmosphere will increase. These factors might alter the possibility that these remnants of hurricanes are still strong enough to produce hurricane-force winds.”

How cold hearts and ice ages kindled the science of warming

Svante Arrhenius, who won the Nobel Prize for chemistry, and also was the first to show that while water plays the largest role in the greenhouse effect, the smaller but forcing effect from CO2 can be important. Image via Wikimedia Commons, PD-US

In 1896, Swedish scientist Svante Arrhenius took off into the atmosphere. Or at least into an immense calculation about the atmosphere that might distract him from having divorced his wife Sofia, who had taken custody of their baby son Olof. He looked to the skies to settle a key argument: How can landscapes around the world show evidence of ice scraping over it?

At the time, the idea of an ice age was controversial, and the world’s great minds struggled to explain the mile-thick sheets clues suggested had existed. For months Svante laboured by hand to calculate how tiny reductions in a gas called carbon dioxide – CO2 – could team up with water vapour to cool down the world. He didn’t produce an immediate answer to the riddle of the ice age, and he may or may not have escaped the woes of his personal life. But Svante Arrhenius did lay a foundation that climate science still rests upon today.

The tools that Svante used had recently been forged in the furnace of scientific progress that was the 19^th century. Until then, even an effect as seemingly basic as heat had been poorly understood. Only slowly had the idea that it was a kind of fluid or gas been replaced by the modern understanding that it’s a flow of energy. In the 1820s French mathematician Joseph Fourier helped drive that shift. He also mused on why, when the Sun heats the Earth, doesn’t the Earth get as hot as the Sun?

Projected warming set to exceed civilisation’s experience

Oregon State University’s Shaun Marcott has built a climate record reaching back 11,300 years, showing that today’s temperatures are warmer than at least 70% of that period. Credit: Shaun Marcott

The world is headed for average surface temperatures warmer than it has seen in at least 11,300 years. That’s one conclusion US researchers have reached after bringing together 73 studies of ancient climate from across the world into a single global record. Their work supports previous records for the past 2,000 years built mainly from tree ring data, explained Shaun Marcott from Oregon State University, and gives a much broader view.

“We can put today’s global temperature into context against the entire Holocene period,” Shaun told me. “That’s when human civilisation was born, developed and progressed to today.” Modern temperatures are higher than in around three-quarters of that period, which reaches back to the end of the last ice age. And their comparison against forecasts for 2100 made in models used by the Intergovernmental Panel on Climate Change (IPCC) is even starker. “If those scenarios come to fruition, we’ll be well outside anything human civilisation has seen,” Shaun warned. “We won’t have even have been close.”

Knowing climate’s history helps understand its present, and so researchers have puzzled out temperatures on the Earth’s surface from proxy, or indirect, records for the last 2,000 years. In particular, bringing together measurements from tree rings, ice and coral has showed a sharp recent temperature rise often referred to as the ‘hockey stick’. Meanwhile, studies scattered across the world had reached back across the 11,300 years since the beginning of the Holocene. But they can be influenced by regional effects, and no one had pieced them into a global view that would overcome that.

Evidence rethink puts CO2 and ancient warming back in sync

A thin layer of ice from an area of the Antarctic where ancient ice records are collected, in polarized light that reveals ice crystals. Rethinking how ice crystal formation affects ancient data collection is helping to solve an outstanding climate puzzle. © Frédéric Parrenin

A different way to dig up links between past levels of CO2 in the air and temperatures could solve a troubling question over the historical climate. Previously, data collected from long cylinders drilled from Antarctica’s ice sheet seemed to show temperatures rising hundreds of years before CO2 levels did. If ancient warming came before a CO2 rise, then the greenhouse gas seemingly couldn’t have caused the warming. Climate skeptics have used this to argue  that the CO2 we produce today isn’t causing global warming.

Now, Frédéric Parrenin at the French National Centre for Scientific Research in Grenoble and his teammates have used a different method on these cylindrical ice cores. They say that their approach shows CO2 and temperature rises happened together during the last ‘deglaciation’, when ice sheets retreated during an abrupt warming period 20,000-10,000 years ago. “This makes it possible that CO2 was actually a cause of warming corresponding to the last deglaciation,” Frédéric told me.

Scientists have been using Antarctic ice cores, and bubbles of air from the time the ice formed trapped inside, to study climate history for over 30 years. The time capsule-like bubbles show what chemicals were in the air. Meanwhile, the amounts of different forms, known as isotopes, of elements like hydrogen, carbon and oxygen in the ice reveals the temperature it formed at. And finally, scientists figure out how old the ice and bubbles are from how deep they are in the core – and that’s where Frédéric found problems.

Extra stations bolster warming-extreme rainfall link

The highest daily rainfall in a year is increasing by around 7% per 1°C warming. Credit: Andrew Ciscel via Flickr

The most comprehensive review of changes to extreme rainfall yet has confirmed the link between extreme rainfall intensity and global atmospheric temperature, with annual rainfall highs intensifying by around 7% per 1°C warming. University of Adelaide’s Seth Westra and his teammates called on 8326 weather stations across the Earth’s surface with over 30 years’ data from the period between 1900 and 2009. “The real innovation in this study is the strength of the data set we used,” Seth told me.

As a flood engineer, Seth has conducted numerous flood risk studies using highest daily rainfall amounts over a year period for planning. But when trying to understand how these rainfall amounts are changing, he found that many studies did not present their information so engineers could use it easily. He therefore wanted to do a statistical study that could produce more precise estimates. And when he found out that Lisa Alexander at the University of New South Wales, Australia was bringing together measurements of temperature and rainfall extremes, he saw his opportunity.

Lisa is part of a team that has collected data from 11391 weather stations worldwide, a much larger record than previous studies had used. That’s partly to contribute to the Intergovernmental Panel on Climate Change’s fifth assessment report on global warming, due out in stages in late 2013 and 2014. But it meant the massive task of collecting the measurements needed to do the kind of study Seth planned was already being done. “You can imagine the sheer amount of work in getting data from dozens of meteorological agencies from around the world,” he said. “Trying to feed them all into one single repository is a lot of effort.”

With this data in hand, Seth, Lisa and Francis Zwiers from the University of Victoria, Canada, first selected only the 8326 stations with over 30 years’ worth of data. They then used two statistical tests to look at the annual extreme rainfall highs, which they published online last year in a paper in the Journal of Climate. In the first, they simply looked at whether rainfall extremes increase or decrease at each station over time, Seth explained.