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.”

Can we trust climate models?

Scientists use models like the Community Climate System Model (CCSM, shown here) to increase their understanding of the world’s climate patterns and learn how they may affect regions around the globe. Credit: PNNL

Computers crash, freeze, corrupt documents, and otherwise make us swear at them every day. At such moments I briefly blow my own fuse, and my computer becomes my enemy – until I remember it’s revolutionised how I work, communicate and access information. But knowing how easily they can go wrong – and how easily a small, overlooked, mistake in a piece of software can cause unexpected problems later – makes me cautious. That extends to writing this blog, when I often wonder just how much we can rely on the computer models used so widely by scientists studying global warming. So this year I’ve been asking researchers questions like: Why even use models? How can we trust that they’re accurate? How should we understand what they come up with?

These questions go deep into how science works, using evidence from what people see, or experiments we conduct, to build or knock down ideas. The best evidence is directly measured, in as much detail as possible. Today that’s available in some cases, but not all, and we can’t go back in time to get data over the long time periods that might be ideal. For example, this previously limited our understanding of global warming’s effect on tropical cyclones, Bruno Chatenoux from the Global Change and Vulnerability Unit at the United Nations Environment Program in Geneva, Switzerland told me in February. “Formal detection of trends in the existing records is challenged by data quality issues and record length,” he told me. “Model projections suffer less from this, but have other challenges, such as whether they are accurately representing all of the relevant physical processes.”

And while there are a lot of processes to represent, researchers have worked hard to establish them, underlined Xuefeng Cui from Beijing Normal University, China, in July. “Climate models have been developed by groups of scientists to include atmosphere, oceanography, land, biology, chemistry, physics, computing science for about 40 years,” he said. “They have a solid scientific foundation and model the climate system in reasonable resolution.”

CO2 casts off shackles to power up Atlantic hurricanes

NOAA’s GOES-13 satellite captured this visible image of Hurricane Sandy battering the U.S. East coast on Monday, Oct. 29 at 9:10 am EDT. Sandy’s center was about 310 miles south-southeast of New York City. Tropical Storm force winds are about 1,000 miles in diameter, and are set to intensify in the 21st century. Credit: NASA GOES Project

Changes in greenhouse gases and other air pollution will likely make Atlantic storms that could hit the Caribbean and Eastern US more intense through this century. That’s according to research from Gabriel Vecchi at the US National Oceanographic and Atmospheric Administration (NOAA) in Princeton, New Jersey, and Gabriele Villarini at the University of Iowa. They’ve found that more greenhouse gases strengthen these storms but other pollutants known as aerosols or particulates, which include soot, do the opposite. Increases in both types of pollution through the 20^th century therefore cancelled each other out. But with more recent efforts to limit aerosol pollution succeeding, Atlantic storms now look set to become more destructive. “Both reductions in particulate pollution and increases in greenhouse gases are going to co-operate, we think, to give us more intense hurricanes in the Atlantic,” Gabriel said.

Gabriel has long studied Atlantic storms, and together with Gabriele recently found that how often they happen will likely only increase during the first half of the 21^st century. “The number of storms in a season is only part of the story,” Gabriel told me. “A big question for society is the intensity.” So it was natural, he added, to follow on by looking at how strong and long-lasting they are. Scientists have already looked at their intensity for narrow “time-slices”, for example from 1985-2005 and then predicting from 2080 to 2100. “People haven’t explored how we go from the late 20^th century to the late 21^st century,” Gabriel said.” That’s because to do this research they need complex and very detailed ‘high resolution dynamical’ climate models, which use up scarce time on the world’s most powerful computers. For the same reason, previous studies only look at a few possible scenarios for how much of the greenhouse gas CO2 humans will produce by burning fossil fuels.

Monsoon instability raises food questions for India

A street in Calcutta floods during monsoon season. After some decades of increasing rainfall, climate change could bring drier monsoons, said Jacob Schewe from the Potsdam Institute for Climate Impact Research. Credit: Mark E Dyer/Flickr

Monsoon rains in India may fail more frequently as climate change proceeds into the 22^nd century, German researchers said this week. That danger could be critical for farming in what is set to become the world’s most highly populated country by 2030, and would follow an already expected wetter period. “Previous studies showed that Indian monsoon rainfall would increase more or less linearly with global warming over the next century,” said Jacob Schewe from the Potsdam Institute for Climate Impact Research. “The monsoon can respond to climate change in a more complicated way. We’ve seen that it matters to look further into the future.”

In South Asia, summer monsoon rains fall as winds blow from the southwest Indian Ocean over the continent between June and September. They end when the wind direction reverses in September or October. What Indian monsoon rain seasons will do as the world warms is an important and difficult question that many researchers are trying to answer. Though more rainfall has been predicted, recent years haven’t matched that expectation. While factors like pollution have an effect, changes climate scientists already know a major climate pattern plays a very important part in monsoons.

“There is a coupling between the El Niño Southern Oscillation and the monsoon that’s been observed for a long time,” Jacob told me. In years when El Niño occurs, an air movement pattern called the Walker circulation pattern gets shifted eastward. That brings high pressure over India and weakens the monsoon. While some changes in El Niño are already happening, the Walker circulation is expected to weaken, but not for some time yet. That could mean scientists’ climate models don’t pick up its effects. “People have looked at monsoon changes but not many studies have looked beyond 2100,” Jacob said. “You really have to consider longer timescales – beyond 2100 – to assess the full range of consequences for the monsoon.”

Warming cost estimates cheat our children

Economic calculations saying future generations are at least as important as we are make a strong argument for replacing fossil fuel electricity generation with renewable energy sources like wind. Credit: Caveman Chuck Coker/Flickr

The financial benefits of reducing CO2 emissions, and avoiding the climate change they would bring, is at least 2.6 times larger than the US government estimates. And, according to Laurie Johnson of the Natural Resources Defense Council in Washington, DC, and Chris Hope at the University of Cambridge, UK, they could be much higher. Undervaluing the damages, which play a part in how the US government makes decisions about climate issues, borders on insanity, Laurie told me. “What we have to ask ourselves is what our children are going to think of us,” she said. “We’re being very self-destructive, but also deeply unethical. We’re not even trying to minimise how much worse it’s going to get. They’ll look back at all this science and how everything is changing, and see how we treated the damages so trivially and did so little.”

In 2010 some of the top departments in the US government got together to publish the first estimates of the money value of benefits from CO2 cuts. The benefits come from avoiding losses through damage caused by climate change. Called the social cost of carbon (SCC), this value is important because it affects rules on CO2 emissions, such as those from cars and power stations. Using three models that linked climate and economics, the government departments decided that the SCC was $21 per metric tonne of CO2*. Thanks to its importance for future climate rules, Laurie had watched the value being calculated closely – and was worried about what she saw.

“One of the models includes infectious disease damage estimates that are highly questionable,” she told me. “The models also estimate net gains from agriculture from now up to 2300 globally. By contrast the insurance industries appear to be estimating $25 billion dollars for crop losses in the US this year. That’s just one year for one country, and their calculation is for more than two hundred years, all countries. It also estimates a couple of billion in extreme weather damages globally over that period. Last year, in the US alone, there was over $50 billion dollars’ worth of extreme weather damage. Overall, it’s a very problematic estimate.” While the faults are plain, correcting any of these areas with more accurate values is a big problem itself. So Laurie and Chris looked at two other areas that they also felt had been worked out badly, but were simpler to tackle.

Warming brings more frequent and fickle European heatwaves

Heatwaves prompt creative ways to stay cool, as these children in Paris showed during the 2003 heatwave, and can lead to deadly consequences if people don’t stay cool enough, especially amongst the elderly. Credit: Christophe Becker/Flickr

Our changing climate will make future European summer heatwaves like the one in 2003, blamed for killing 35,000, more likely but harder to forecast a season in advance. That’s what research done by Benjamin Quesada from the Laboratoire des Sciences du Climat et de l’Environnement (LSCE) in Gif-sur-Yvette, France, suggests. Together with fellow climatologists, he has found that water trapped in Southern European soil during wet winters and springs keeps the continent reliably cool in summer. “Under global warming, climate models almost all agree about drier soils in Southern Europe and more frequent and long lasting summer heatwaves,” Benjamin told Simple Climate. Losing that cooling influence currently makes the weather less predictable but with a higher chance of being hot – though Benjamin hopes his findings will eventually bring more accurate forecasts.

The dramatic heatwaves in 2003 and 2010 took Europe by surprise. That has motivated the continent’s scientists to try to understand them and therefore predict them better. The role that water absorbed in soil plays has been one area that they’ve looked at. Their research shows a vicious “feedback” cycle where drier soils mean that less water reaches the atmosphere to create clouds. In turn, more heat from the sun reaches the ground and dries it out yet more. “Soil moisture can be seen as a buffer,” Benjamin said. “On dry soil, solar energy will directly heat soil, and isn’t ‘wasted’ first in evaporation as in wet soil.” Usually an escape from this cycle can come thanks to factors like winds circling the planet and carrying clouds with them, he added.

Thick ice decline could advance watery Arctic summers

NASA's shipborne ICESCAPE mission cuts a path through multiyear Arctic ice last year. This thicker form of ice is declining fastest, NASA's Joey Comiso has shown in a separate study. Credit: NASA/Kathryn Hansen

The oldest and thickest ice in the Arctic is vanishing the fastest, data studied by NASA scientist Joey Comiso and published last month have shown. “This is alarming since it is usually the thick component that would survive the long summer melt period,” Joey told Simple Climate. “Since the thick component is declining more rapidly, the Arctic summer ice cover is more vulnerable to further decline. Assuming that the surface temperature continues to warm up as it has in the last several decades, this makes it more likely that we will have very little or no sea ice cover in the summer sooner than we previously expected.” And when the Arctic is ice-free in summer, dramatic environmental changes could follow that would speed warming further and limit the supply of fish for food.

Having long studied Arctic sea ice cover, Joey previously showed that 2007′s record smallest summer area was around one quarter smaller than the previous minimum in 2005. That “has been regarded as the event that could trigger an irreversible change in the Arctic sea ice cover”, Joey wrote in this latest research paper in the Journal of Climate. But after that low the area of thickest ice that can survive the summer melts, known as perennial ice, recovered slightly before dipping again this winter.

Intrigued by that recovery, Joey wanted to understand it. He therefore turned to data collected by tools called microwave radiometers that have been flying over the Arctic on satellites since 1979. These can collect information on the ability of different objects to emit microwave energy, or their microwave emissivity. Salt content, or salinity, influences this emissivity. As sea ice is initially around one-third as saline as sea water, microwave emissivity can be used to tell one from the other. It can also separate multiyear ice, which has survived at least two summer melt seasons, from thinner second year ice that has only survived one summer.

Shrinking Arctic ice area is just the tip of the iceberg

Like icebergs, much of the mass of Arctic ice lies under the surface, making studying its thickness important, as well as the area it covers. Credit: Florida State University

A sheer white glacial mountain apparently floating on the sea emerges from the freezing mists. A lone lookout cries “Iceberg!”, stirring the crew into panic, before the stomach-churning sound of ripping metal sends them to the lifeboats. It’s a familiar scene from the TV and movies, and one where the main threat comes because eight-ninths of a typical iceberg lies below the waterline. While sea ice formed from ocean water is much thinner than such glacier ice, its thickness also lies mostly beneath the surface. Consequently, knowing that thickness is “perhaps the most basic measure of how the ice is responding to climate change”, according to the University of Colorado’s James Maslanik. Although it’s possible to track the area that the Arctic ice cap covers from space, knowing the depth it reaches is harder. “While the European Space Agency has just launched Cryosat-2 to measure thickness, the US no longer has a satellite operating that is capable of directly measuring ice thickness from space,” the scientist explained.

To tackle this problem, Maslanik and Colorado colleagues Julienne Stroeve, Charles Fowler, and William Emery have turned to assessing how many summer melt periods the ice is surviving. Maslanik says not only is this closely linked to ice thickness, it also reflects the influence of many climate- and weather-related factors. Ice that survives one summer melt is called “multi-year ice”. In a Geophysical Research Letters paper soon to be published, they find that multi-year ice makes up 45 per cent of the total Arctic ice cover in 2011, down from about 75 per cent in the mid 1980s. The proportion of ice older than five years fell from 50 per cent of all ice that has survived more than one summer to 10 per cent in the same period.

“The work of our Colorado group and other researchers clearly shows extreme decreases in the area of the Arctic Ocean covered by the oldest and thickest sea ice types,” Maslanik told Simple Climate. “This loss has accelerated in recent years, and while we continue to search for factors such as natural variability that could account for the changes, the effects of large-scale warming in the Arctic, including changes in the Arctic Ocean itself, are the most likely drivers for the loss in the old sea ice.”