Enhanced fingerprinting strengthens evidence for human warming role

Microwave sounding units, like the AMSU units on the Aqua satellite, shown here, can be used to take temperature measurements from different layers in the atmosphere. Ben Santer and his colleagues use this information to find a 'fingerprint' of human impact on recent climate changes. Credit: NASA

Microwave sounding units, like the AMSU units on the Aqua satellite, shown here, can be used to take temperature measurements from different layers in the atmosphere. Ben Santer and his colleagues use this information to find a ‘fingerprint’ of human impact on recent climate changes. Credit: NASA

We have left a clear climate change ‘fingerprint’ in the atmosphere, through CO2 emissions that have made air near the Earth’s surface warmer and caused cooling higher up. That’s according to Ben Santer from Lawrence Livermore National Laboratory (LLNL) in California, who started studying this fingerprint in the mid-1990s, and his expert team. They have strengthened the case by comparing satellite-recorded temperature data against the latest climate models including natural variations within Earth’s climate system, and from the sun and volcanic eruptions. Ben hopes that in the process their results will finally answer ill-tempered criticism his earlier work attracted, and lingering doubts over what causes global warming.

“There are folks out there even today that posit that the entire observed surface warming since 1950 is due to a slight uptick in the Sun’s energy output,” Ben told me. “That’s a testable hypothesis.  In this paper we look at whether changes in the sun plausibly explain the observed changes that we’ve monitored from space since 1979. The very clear answer is that they cannot. Natural influences alone, the sun, volcanoes, internal variability, either individually or in combination, cannot explain this very distinctive pattern of warming.”

That pattern emerged when scientists in the 1960s did some of the first computer modelling experiments looking at what would happen on an Earth with higher CO2 levels in the air. “They got back this very curious warming in the lower atmosphere and cooling of the upper levels of the atmosphere,” Ben explained. The effect happens because most of the gas molecules in the atmosphere, including CO2, sit relatively near to Earth’s surface. CO2’s greenhouse effect lets heat energy from the Sun reach the Earth, but interrupts some of it getting back to the upper atmosphere and outer space. Adding more CO2 by burning fossil fuels therefore warms the lower atmosphere, or troposphere, and cools the stratosphere, 6-30 miles above the Earth’s surface.  Read the rest of this entry »

Continuing the fight for CO2 monitoring

  • This is part two of a two-part post. Read part one here.
Dave Keeling had to balance his work measuring CO2's rise in the air and tracking its movements through the Earth's systems with fighting to get the money to fund his work. Credit: Scripps Institution of Oceanography

Dave Keeling had to balance his work measuring CO2’s rise in the air and tracking its movements through the Earth’s systems with fighting to get the money to fund his work. Credit: Scripps Institution of Oceanography

By 1963, having directly measured a steady increase in CO2 levels over five years, Dave Keeling felt he had clearly shown the value of such non-stop monitoring. But that message hadn’t reached government decision makers. And so Dave swung into the first battle in the war to continue tracking the key greenhouse gas that has flared up repeatedly in the following decades.

Thanks to four new instruments called spectrophotometers, Dave had been able to use the same molecular movements that allow CO2 to absorb heat to measure it. Though his most famous site was at Mauna Loa in Hawaii, one was also installed in Antarctica. Another sailed on a ship and the final one stayed at Dave’s lab at Scripps Institution of Oceanography analysing samples collected in vacuum-filled five litre flasks from aircraft and elsewhere. Thanks to funds from 1957-1958’s International Geophysical Year a team of scientists was busy collecting a “snapshot” of CO2 data that Dave’s boss at Scripps, Roger Revelle, wanted.

So in 1961, Dave moved his family to Sweden for a year to work out exactly what the measurements were showing. He took a fellowship at the Meteorological Institute, University of Stockholm working with its new director Bert Bolin, who had earlier worked on the first computerised weather forecast. With measurements ongoing, annual ‘breathing’ cycles of rising and falling CO2 and the increasing trend underlying them became ever clearer.

Together, Dave and Bert found CO2 concentrations were going up by 0.06 ppm per month on average. Bert also undertook a series of complex calculations by hand to work out CO2 movement and cycles in its levels. In doing so he was showing how oceans, plants on land, and human fossil fuel burning contributed to the patterns that would later need computer models for fuller analysis. This, Dave felt, clearly showed why non-stop CO2 monitoring was needed rather than just snapshots. But by 1963 the shipboard spectrophotometer had come home, and Dave had also called back the one in Antarctica. And with funding cuts biting at the Weather Bureau, now part of the National Oceanic and Atmospheric Administration (NOAA), the staff at Mauna Loa fell from eight to three. And soon afterwards, a problem with Dave’s equipment proved too much for the overstretched team to fix.

“Suddenly there were no precise measurements being made of atmospheric CO2 anywhere,” he recalled. “I had seen the budget cut coming early in 1963 and had tried to prevent its terminating the CO2 program at Mauna Loa Observatory. I even went to Washington to plead for supplemental funding. This had no tangible effect, however, until the cessation of measurements actually occurred. The National Science Foundation (NSF) then found funds to pay for an additional technician at Mauna Loa. I learned a lesson that environmental time-series programs have no particular priority in the funding world, even if their main value lies in maintaining long-term continuity of measurements.” Read the rest of this entry »

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 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 21st 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. Read the rest of this entry »

Temperature cuts swathe through Australian seaweed

A mixed seaweed canopy in Western Australia, including Scytothalia dorycarpa (far right), which was completely killed along 100km of the Australian coast by a heatwave in 2011. Credit: Dan Smale

A mixed seaweed canopy in Western Australia, including Scytothalia dorycarpa (far right), which was completely killed along 100km of the Australian coast by a heatwave in 2011. Credit: Dan Smale

A record-breaking heat wave in 2011 killed a seaweed species that many fish and other creatures call home along a 100 km stretch of the Western Australian coast. That underlines the threat from climate change, which is driving more regular ‘extreme events’ like heatwaves, according to Dan Smale of the University of Western Australia (UWA). “Extreme events can wipe out species at their range edge incredibly quickly, which may have wide ranging implications for whole communities of associated plants and animals,” he said.

Metre-plus tall strands of Scytothalia dorycarpa seaweed sway around cool water rocky reefs in southern Australia, forming a playground for other species. It is thought to have evolved in cool conditions, and therefore to be sensitive to warmth. For that reason, in 2006, Dan and his UWA colleague Thomas Wernberg started tracking it in two main locations, Jurien Bay and Hamelin Bay, and 27 other sites. “We suggested that by monitoring its abundance and distribution, we could detect ecologically-significant climate change impacts over periods of years to decades,” Dan said. “We did not realise, however, that the highest-magnitude seawater warming event on record was just around the corner, and we did not expect to see such sudden and extensive shifts in its distribution.”

That extreme was reached in 2011 during the cooler ‘La Niña’ phase of the El Niño Southern Oscillation climate cycle. By contrast to the current Australian heatwave, temperatures rose thanks to an especially strong La Niña increasing the flow of warm water from the tropics. In March 2011 Thomas and Dan measured sea surface temperatures up to 4°C higher than the average for 2006-2010. The heatwave temperatures stayed more than 2°C above the 2006-2010 level for around 10 weeks in both bays. Read the rest of this entry »

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

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 22nd 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.” Read the rest of this entry »

Butterfly effect limits climate models

National Center for Atmospheric Research's Clara Deser. Credit: NCAR

National Center for Atmospheric Research’s Clara Deser. Credit: NCAR

Natural chaos in our climate system creates uncertainty in predictions that can’t be removed, no matter how good scientists’ models get. Clara Deser from the US National Center for Atmospheric Research (NCAR) in Boulder, Colorado and her colleagues have shown these effects can be as strong as human-caused warming. “Over multiple decades intrinsic climate variability on a local and regional scale can be on a par with climate change due to greenhouse gas emissions,” she told me. “You’re not going to just see the result of the greenhouse gas increases – you’re going to see both. This simple message has been missing from the climate change literature.”

Climate scientists are working hard to improve the accuracy of their models’ predictions – perhaps so hard they haven’t yet looked at what their limits are. “We’ve been focussed on identifying how greenhouse gas changes and the like can affect the climate system,” Clara said.  “The uncertainties in climate projections have all been lumped together. There hasn’t been a set of runs that were designed the way that we have done them to really address this point.”

Anyone who’s had to run outside to rescue drying clothes from a rain shower knows that weather can be variable from day to day. Climate patterns also vary from year-to-year, like El Niño or the North Atlantic Oscillation, and some chaotic climate processes work over decades. Wanting to reduce model uncertainty, Clara previously tried to answer a series of detailed questions about these kinds of natural variability. Her team’s answers showed that they accounted for at least half of the disagreement between different climate model predictions. When she told this to two fellow climate scientists, Reto Knutti, from the Swiss Federal Institute of Technology, Zurich and Massachusetts Institute of Technology’s Susan Solomon, they were surprised. “They said, ‘Something very simple and illustrative is needed to get this important message across,’” Clara recalled.
Read the rest of this entry »

Climate provides weak power to predict African violence

Two boys from the Local Defence Unit (LDU) in Kitgum, Northern Uganda, whose job is to protect the people at a refugee camp from attacks and kidnappings by the Lord's Resistance Army, which has been responsible for much violence in East Africa in recent years. Credit: John & Mel Kots/Flickr

Two boys from the Local Defence Unit (LDU) in Kitgum, Northern Uganda, whose job is to protect the people at a refugee camp from attacks and kidnappings by the Lord’s Resistance Army, which has been responsible for much violence in East Africa in recent years. Credit: John & Mel Kots/Flickr

Rainfall and temperature changes are linked to conflict in East Africa, but have less power to predict violence than links to political, economic and geographical factors. That’s according to one of the most detailed studies into climate-violence relationships yet, done by John O’Loughlin from the University of Colorado, Boulder, and his team-mates. “Fears of climate wars across Africa are exaggerated,” John told me. “Any effect of climate change will likely be localized and subject to other conditions.”

One political argument made about our changing climate is that it will bring more violence, particularly in Africa. For example, in 2009, US President Barack Obama told the United Nations that a warming world represents an “urgent, serious, and growing threat” because “more frequent drought and crop failures breed hunger and conflict”. But, with a background of looking in detail at where violence happens and having studied African conflicts before the 1990s, John was concerned that the evidence didn’t back such statements. That’s even though other researchers have reported statistical links between climate and conflict. “I believe that previous studies were limited by data problems and also that the policy discussions were not connected to the research findings,” John explained.

John’s team described how they fixed this in a paper published in the research journal Proceedings of the National Academy of Sciences of the USA on Monday. Previous attempts to study climate-violence have either lacked detail, looking at data per country, per year, or have been too narrowly focussed to allow generalisations, they wrote. John added that this type of work needs detailed data on both conflicts and all the factors that might predict it. Collecting the information needed on conflicts as well as political, health, location and other possibly predictive data was the biggest challenge in the work, he said.
Read the rest of this entry »

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