Tag Archives: climate change

Eastern Mediterranean Drought The Worst To Hit The Region In 900 Years

Modeling the historic droughts that have hit the Mediterranean basin, scientists have found that the region’s latestdry period was the worst drought to have hit the area in the past 900 years. The study, published in the Journal of Geophysical Research, highlights the concerns that climate change may be contributing to observed drying trends, and that those impacts might already be being felt.

The researchers looked back at the records of droughts documented in tree rings from all around the Mediterranean, sampling trees from North Africa, Greece, Lebanon, Jordan, Syria, and Turkey, as well as using existing tree ring data from Spain, France and Italy. They found that the growth of the trees matched up with historical records written at the time of droughts to have hit the region between 1100 CE and 2012 CE. Although the variability between wet and dry periods was quite large, the most recent 1998-2012 drought was still found to be about 50 percent drier than the driest period in the last 500 years, and over 10 percent drier than any in the past 900.

For January 2012, brown shades show the decrease in water storage from the 2002-2015 average in the Mediterranean region. NASA

The scale of the project also allowed the researchers to look at how droughts affected different regions of the Mediterranean. They found that if the east was experiencing a dry period, then it was likely that the west was going through a similar spell. This is important,because it has all sorts of implications for food and water security withinthe region as a whole if everyone is experiencing a drought at the same time, and could help predict where conflict over these resources might arise.

But interestingly, when the researchers then looked at how dry periods affected the north and south of the region, they found an opposite relationship. When Greece, Italy, France and Spain were in drought, the eastern areas of North Africa tended to be wet. The differences between what happens in the east and west of the region when compared to the north-south are thought to be due to airflow patterns that move the weather systems around the Med.

Having such a longterm data set will be invaluable for any future events, as it in effect provides a baseline for comparison. This means that any variability can be checkedto see if drying conditions could be seen as a natural cycle, or iscaused by man-made climate change.

The magnitude and significance of human climate change requires us to really understand the full range of natural climate variability, explains Ben Cook, from NASA’s Goddard Institute for Space Studies and who led the research. If we look at recent events and we start to see anomalies that are outside this range of natural variability, then we can say with some confidence that it looks like this particular event or this series of events had some kind of human-caused climate change contribution.

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Read more: http://www.iflscience.com/environment/eastern-mediterranean-drought-worst-hit-region-900-years

How Myths And Tabloids Feed On Anomalies In Science

UNDERSTANDING RESEARCH: What do we actually mean by research and how does it help inform our understanding of things? What if research throws up a result that calls for a new way of thinking? How do we handle that?

There are many misconceptions about science, including how science advances. One half-truth is that unexpected research findings produce crises, leading to new theories that overturn previous scientific knowledge.

Sometimes science progresses in this neat tidy fashion. But not very often. Assuming science is always so simple fuels misunderstanding of science, and provides ammunition to those who attack science, from cosmology to climate change.

Contrary to the myth, most anomalous findings have modest consequences. The vast majority of peculiar findings are usually the result of errors in data, methodology or misunderstanding the implications of existing theories.

Even when anomalies do prompt radical change, it is rare for them to completely upend large swathes of scientific knowledge.

Strange forces and Pioneers
In the 1970s, NASA’s Pioneer 10 and 11 spacecraft flew by Jupiter and Saturn before speeding towards interstellar space. As they coasted away from the sun, a strange “Pioneer Anomaly” was observed to be gently slowing the Pioneers. What was going on?

The Pioneer Anomaly has led to hundreds of papers, with many speculating on modified forms of gravity and relativity.

An artist’s impression of Pioneer 10 racing from the Solar System. NASA Ames/Donald Davis

In principle the Pioneers could measure tiny accelerations, as they cruised through space. But they were never designed for precision tests of relativity, nor were they tested (prior to launch) to see if the spacecraft themselves produced tiny accelerations.

After decades of study, it appears the Pioneer anomaly had nothing to do with new physics. The Pioneers generate heat, and thus infrared light (photons), which were subtly pushing on the spacecraft (including via reflections). The Pioneer anomaly, rather than provoking a crisis and new physics, is a triumph of century old physics.

Other anomalies have appeared and disappeared in a similar fashion. But despite this history, media reporting of anomalous results often emphasises how the laws of physics could be overturned, rather than the likelihood of anomalous results disappearing. “Einstein Wrong!” works as click-bait for headlines, but is usually not true.

A personal tale of dark matters

I measure how galaxies grow, and at the end of the 20th century something seemed very wrong with galaxy growth research.

Simulations predicted the biggest galaxies should grow rapidly, as their vast gravity dragged in gas and neighbouring galaxies. In contrast, many observational studies found massive galaxies weren’t growing at all. What happened to all that gravity?

Some speculated that the dark matter paradigm was in trouble. Perhaps galaxies were less massive than people imagined. But instead of prompting radical change, this “crisis” has slowly faded away.

In 2007, I used a vast sample of distant galaxies to detect the slow growth of massive galaxies, and others have mitigated errors that have hampered observational studies of galaxy growth. Observational evidence for dark matter also improved, including cosmic microwave background measurements and the mass distribution within colliding clusters.

As computing power improved and simulations incorporated more complicated astrophysics, including supernovae and black-holes, the growth of simulated galaxies slowed down. So the gulf between simulation and observation closed.

Not so fast big guy! The biggest galaxies don’t grow as quickly as astronomers originally expected. Sloan Digital Sky Survey/Michael Brown

The demise of this anomaly wasn’t as clean as that of the Pioneer anomaly. There were gradual improvements in both simulation and observation, and no single study tied up all the loose ends.

This gradual identification and resolution of anomalous results doesn’t always generate headlines, but it is often how science advances.

The scope for radical change

While most anomalous results fizzle and die, some do spark radical change.

The understanding of the world has been upended when scientific observations and theory have replaced pre-scientific ideas. For example, Galileo’s observations of planets resulted in heliocentric (sun-centred) models of the solar system replacing geocentric (Earth-centred) models.

Truly radical change can also happen when very limited data supports the previous hypothesis. Barry Marshall and Robin Warren won the 2005 Nobel Prize for Medicine for establishing that most stomach ulcers are caused by bacteria, not stress. While the stress causing ulcers had been widely accepted for decades, that hypothesis actually hadn’t been systematically tested.

Einstein’s theories had huge implications for physics, but didn’t upend all previous scientific knowledge. NASA

As a science becomes more mature, with a wealth of supporting data, the implications of anomalous results become more limited. An example of this is Einstein’s general theory of relatively, which was (in part) motivated by odd measurements of the speed of light and the behaviour of Mercury’s orbit.

While general relatively has had huge implications for physics, it didn’t completely upend all previous physics. Maxwell’s equations for electromagnetism are still in use and Newtonian mechanics provides a good approximation of how satellites orbit the Earth.

The apple may have fallen on Newton’s head, but Einstein didn’t make the apple fly away.

Icy anomalies and the tabloids

While anomalous scientific results may seem a curiosity, they are central to public debates about science. To see why, go south!

Temperatures have increased over the past century as a result of increasing atmospheric CO2. The evidence includes (but is not limited to) lab measurements of CO2, measurements of atmospheric CO2, the spectrum of light radiated the Earth, planetary temperatures, and the pattern of temperature increase across the globe.

Increasing sea ice around Antarctica has less implications for global warming that some imagine. Brocken Inaglory/Wikimedia Commons

As a consequence, Arctic sea ice is decreasing, Antarctica and Greenland are losing land ice and sea levels are rising, and yet sea ice area around Antarctica has increased.

The increase in Antarctic sea ice area has been the subject of numerous articles by Andrew Bolt in the Herald-Sun and David Rose in the Daily Mail, among others. Some journalists believe this increase in sea ice is a fundamental flaw in global warming. But what can we conclude from this anomalous result?

The world isn’t getting any colder, so that doesn’t explain the increase in Antarctic sea ice. While simulations didn’t predict the increase in Antarctic sea ice area, they also didn’t predict the unexpectedly rapid decrease in Arctic sea ice either.

Sea ice area depends on air temperature, winds, ocean temperatures and currents, complicating the modelling of sea ice area. A simulation correctly modelling the greenhouse effect can fail to predict sea ice area if it doesn’t correctly model polar winds and oceans. While scientists are aware of this, such nuance is often absent from the tabloid media and blogsphere.

The tabloid media and blogsphere too often falls back on the simplicity of the myth, assuming the anomalous results will upend well-established science. This approach makes for good headlines and political point scoring, but the history tells us that science is very rarely upended in the manner some are wishing for.

This article is part of a series on Understanding Research.

Further reading:
Why research beats anecdote in our search for knowledge
Clearing up confusion between correlation and causation
Where’s the proof in science? There is none
Positives in negative results: when finding ‘nothing’ means something
The risks of blowing your own trumpet too soon on research
How to find the knowns and unknowns in any research
The 10 stuff-ups we all make when interpreting research

The ConversationMichael J. I. Brown receives research funding from the Australian Research Council and Monash University, and has developed space-related titles for Monash University’s MWorld educational app.

The Conversation

Read more: http://www.iflscience.com/editors-blog/how-myths-and-tabloids-feed-anomalies-science

The latest report from the IPCC: scientists are 95% certain that humans are the “dominant cause” of global warming since the 1950s

The United Nations panel known as the Intergovernmental Panel on Climate Change meet once every six years, reviewing the latest independent analysese of climate change using direct observations of Earth’s climate, palaeoclimate archives, theoretical studies of climate processes and simulations using climate models. The 95 percent certainty that humans have caused most of the warming of the planet’s surface is an increase in certainty from the 90 percent certainty in the last assessment report, which came out in 2007. 

The Summary for Policymakers of the IPCC’s Fifth Assessment Report was released September 27, and warns that a pause in warming over the past 15 years is too short to reflect long-term trends. Present-day carbon dioxide levels are at an “unprecedented” level which has not been seen for at least the last 800,000 years. Continued emissions of greenhouse gases like carbon dioxide will cause further warming and changes in all aspects of the climate system. Containing these changes will require sustained reductions of greenhouse gas emissions.

Sea level is also set to continue to rise at a faster rate than over the past 40 years, with water levels expected to rise between 26 cm at the low end and 82 cm at the high end. Over the last twenty years the Greenland and Antarctic ice sheets have been melting, glaciers have receded in most parts of the world, and Arctic sea ice has continued to shrink in terms of extent.

The Arctic has lost 75 percent of its summer sea ice volume

Last year’s Arctic sea ice minimum exceeded the previous record low, with the ice declining the previous two years as well; this year there has been a short-term ‘recovery’. The Arctic has lost 75 percent of its summer sea ice volume over the past three decades and climatologists are not just concerned about the extent of the sea ice, but also its thickness, which has been in constant decline. Each year the Arctic sea ice reaches its minimum in September. Arctic sea ice extent reached its lowest point this year on September 13, 2013 when sea ice extent dropped to 5.10 million square kilometres. September averaged an ice extent of 5.35 million square kilometres, placing 2013 as the sixth lowest ice extent, both for the daily minimum extent and the monthly average. September ice extent was 1.17 million square kilometres below the 1981 to 2010 average.

Sea ice in Antarctica reached a winter maximum extent of 19.47 million square kilometres this year. Antarctic sea ice extent for August 2013 averaged 6.09 million square kilometres, which was 1.03 million square kilometres below the 1981 to 2010 average for August, but above the level recorded last year. 2012 had the lowest September ice extent in the satellite record. In any given year the weather can act to either preserve more or melt more sea ice at both poles.

The Arctic ice cap grows each winter as the sun sets for several months and shrinks each summer as the sun rises higher in the northern sky. Each year the Arctic sea ice reaches its annual minimum extent in September. It hit a new record low in 2012. This summer’s low ice extent continued the downward trend seen over the last thirty-four years. Scientists attribute this trend in large part to warming temperatures caused by climate change. Since 1979, September Arctic sea ice extent has declined by 13.7 percent per decade. Summer sea ice extent is important because, among other things, it reflects sunlight, keeping the Arctic region cool and moderating global climate.

Each of the last three decades has been warmer at the Earth’s surface, warmer than any period since 1850, and most likely warmer than any time in the past 1,400 years. Model simulations indicate that the change in the global surface temperature by the end of the 21st Century is likely to exceed 1.5 degrees Celsius, relative to 1850.

The new report alters one figure from the 2007 report: the temperature range given for a doubling of CO2 in the atmosphere was 2.0C – 4.5C in the 2007 report and this range has been changed to 1.5C – 4.5C.

This video depicts a scenario in which carbon dioxide concentrations reach 670 parts per million by 2100, up from around 400 ppm today: http://bit.ly/1h8zPg9


The IPCC Summary for Policymakers: http://bit.ly/15UJlPg

IPCC: http://bit.ly/1a3HJUm

National Snow and Ice Data Center: http://bit.ly/15OwqE2

NASA: http://1.usa.gov/GFWHZr; http://1.usa.gov/198nQu6

Read more: http://www.iflscience.com/environment/latest-report-ipcc-scientists-are-95-certain-humans-are-dominant-cause-global-warming

New Analysis Suggests Sixth Mass Extinction Could Occur By 2200

We’ve already been warned that our planet faces a sixth mass extinction, and some even believe that we are already in the early stages of such an event. Now, the harsh reality of the impending situation has been highlighted by the scientific journal Nature, with a special report detailing the threats that major animal groups face. According to the analysis, those predicted to take the greatest hit are amphibians, with an alarming 41% of species within this group facing extinction. But mammals and birds won’t get off lightly, with 26% and 13% of species similarly threatened, respectively.

Among the known critically endangered species are numerous different primates, such as the snub-nosed monkey, black rhinos, the yangtzee river dolphin, western gorillas and the Amur leopard. But many species that are currently only listed as endangered also face being wiped out, such as bonobos and loggerhead turtles.

The primary driver? Humans. According to the Living Planet Index, exploitation—such as hunting and fishing—is playing a major role in triggering the decline in animal species. Other human activities that are helping obliterate populations include agriculture and urbanization, whereby large areas of wild habitats are destroyed to make way for buildings, infrastructure, livestock and crops.

Climate change, which is primarily due to humans, is also threatening many sensitive animals, such as polar bears and corals, and will probably accelerate extinctions in ways that are currently unknown. Increasing CO2 emissions are not only warming our planet and seas, but they are acidifying our oceans, making them a more hostile environment for marine organisms. It’s estimated that 10% of all Earth’s coral reefs are already degraded beyond recovery, and if current pressures continue, 60% could be dead by 2050.

While we know that the situation is not good for many organisms on Earth, attempting to predict how quickly species are likely to disappear is extremely difficult, which only exacerbates the problem. Much of the uncertainty comes from the fact that we only know about a fraction of our planet’s biodiversity, and many unknown groups often reside in small areas that are already being demolished by humans and may never be assessed.

When scientists attempt to assess the number of species of animals, plants and fungi alive today, estimates are wildly varied, ranging from around two million to more than 50 million. Not only that, but approximations of the rate of extinction also vary, ranging from 0.01% to 0.7%, meaning the number of species disappearing is somewhere between 500 and 36,000 a year. If we use the upper rate, a mass extinction—or loss of 75% of species—could occur within the next few hundred years. At the lower rate, however, it may not arrive for thousands of years.

Five mass extinction events have occurred before, all of which were triggered by either natural planetary transformations or asteroid strikes. But the impending 6th event will be the work of humans, who have been gradually wiping out animals since mammoths and mastodons during prehistoric times.

So what can we do? According to the report, it’s of fundamental importance that countries start extending protected areas and devoting more resources to counting and evaluating stocks of life on Earth before they disappear.

[Via Nature, Nature, The Guardian and The Independent]

Read more: http://www.iflscience.com/plants-and-animals/new-analysis-suggests-sixth-mass-extinction-could-occur-2200

Climate Change Killed The Last Ichthyosaurs

Ichthyosaurs became extinct in the Late Cretaceous about 90 million years ago thats roughly 28 million years before the mass extinction event that wiped out all non-avian dinosaurs at the end of the Cretaceous. According to a new Nature Communications study published this week, the extinction of these dolphin-shaped marine reptiles occurred in two phases driven by climate instability and reduced evolutionary rates.

Researchers have previously proposed that the earlier demise of ichthyosaurs after their 157-million-year reign was because of an increase in competition with other marine reptiles or a drop in their food resources, soft cephalopods in particular. But recent studies suggested that ichthyosaurs were richly diverse up to just a few million years before their extinction, so the overall cause of their disappearance is still a mystery.

To investigate, a team led by University of Oxfords Valentin Fischer estimated ichthyosaur diversity over time by studying their evolutionary relationships. They assembled this so-called phylogenetic dataset using 88 characters from 36 ichthyosaur groups, including three-fourths of all known species from the Late Jurassic and Cretaceous. The team also estimated ecological diversity in terms of diet using a series of measurements on skulls and teeth, and they examined the wide range of differences in ichthyosaur body shapes and forms. They then correlated these results with environmental data ranging from ocean chemistry to sea level change.

Ichthyosaurs were highly diverse throughout the Early Cretaceous, but they were evolving slowly. These findings support climate change as a main driver of changes in marine ecosystems, and they fit with the hypothesis that ichthyosaurs were outcompeted by other marine reptiles and fishes. Additionally, the team identified an earlier extinction event that occurred about 100 million years ago. The earlier event eliminated most of their ecological diversity, and a second event about 94 million years ago finished them off, Fischer explains to IFLScience.

Ichthyosaurs faced an abrupt two-phase extinction linked to reduced evolutionary rates and environmental volatility. The beginning of the Late Cretaceous was a peculiar period of numerous climatic and oceanic disturbances, the authors write, with no polar ice, extremely high sea levels, unique sedimentation, strong anoxia, and high temperatures and carbon dioxide concentrations.

Read more: http://www.iflscience.com/plants-and-animals/climate-change-killed-last-ichthyosaurs

Deep Ancient Water Is Stopping The Antarctic Ocean From Warming

The waters around the Antarctic may be one of the last places on Earth to feel the effects of man-made climate change. According to researchers at the University of Washington (UW) and the Massachusetts Institute of Technology (MIT), ancient seawater upwelling from the depths explainwhy the sea surface has remained roughly the same temperature while most of the planet has experienced temperature rises.

Using a combination of observations from floating ocean current trackers and cutting-edge computer simulations, the new Nature Geoscience study shows that this centuries-old seawater hasnt been to the surface since the dawn of the Industrial Revolution. Although the cooler waters around the Antarctic were previously blamed on ocean currents drawing sea surface heat down to the depths, it appears that cold water yet to experience the newly-warmed atmosphere is currently rising up to the surface.

With rising carbon dioxide you would expect more warming at both poles, but we only see it at one of the poles, so something else must be going on, the studys lead author Kyle Armour, a UW assistant professor of oceanography and of atmospheric sciences, said in a statement. We show that it’s for really simple reasons, andocean currentsare the hero here.

Observed warming over the past 50 years, as measured in degrees Celsius per decade. Its clear that the Southern Ocean has warmed by only a fraction, and it appears ocean currents are to blame for this unusual refrigeration mechanism. Kyle Armour/UW

Seawater from the deepest depths of the worlds oceans upwell at different times, and they do so when they become less dense than the water above them. This can happen for many reasons, including a reduction in salt concentrationor an influx of heat at depth, both of which make them more buoyant. On occasion, there can be a mechanical driver of seawater upwelling, such as persistent winds.

This is whats happening in the Southern Ocean, where extremely powerful westerly winds keep pushing warming surface water northwards; this gives the deeper, older water space to upwell into. The novel aspect of the waters here is that they have to upwell from depths of several thousand meters, far beyond the depths that most other oceanic currents reach. This means that it takes them an incredibly long time to reach the surface and interact with the atmosphere.

According to the models run by the team, the water only just beginning to reach the surface off the coast of Antarctica last experienced the Earths atmosphere centuries ago in the North Atlantic, before any serious man-made climate change had the chance to significantly heat it up. In fact, their simulations show that the oceanic currents that have experienced the most warming appear to be gathering at the North Pole, which also partly explains why Arctic sea ice is disintegrating so rapidly.

When we hear the term ‘global warming,’ we think of warming everywhere at the same rate, Armour added. We are moving away from this idea and more toward the idea of regional patterns of warming, which are strongly shaped by ocean currents.

The fact that Antarctic sea ice has been growing just as the Arctics has been disintegrating has baffled scientists for some time; irritatingly, this discrepancy is often cited by climate change deniers as proof that climatologists dont know what theyre talking about. It was only a matter of time before several explanations emerged, and this new study represents one of two corroborating theories helping to explain why the sea ice around Antarctica has been unexpectedly growing.

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Read more: http://www.iflscience.com/environment/deep-ancient-water-stopping-antarctic-ocean-warming

NASA Satellites Capture Superstorm Jonas From The Skies

While the inches upon inches of snow caused joy, inconvenience and tragedy to millions of people on the East Coast, NASAs satellites were up above and taking full advantage of their front-row view.

NASAs Landsat 8 satellite captured to these natural-color images shown above and below of Virginia, Maryland, and Washington, D.C. in the early afternoon on January 24, 2016.

Image credit: NASA

Thisimage and video,below, were caught on NASAsAquasatellite at around the same time at1:30 p.m. EST on January 24, 2016.

AsNASA explains on itsEarth Observatory site, It is possible that the strength of the storm was amplified by global warming and the record warm temperatures this year.

Ocean temperatures in the North Atlantic are unusually high this winter, providing a deep well of moisture that was drawn into the storm system. Warmer air masses can carry more water to fall as snow or rain, makingextreme snow eventsmore likely even thoughoverall annual snowfallhas been dropping in recent decades.

Image credit: NASA

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Read more: http://www.iflscience.com/environment/nasa-satellites-captures-superstorm-jonas-skies

Wreckage Of Sunken Whaling Ships Discovered Off Alaskan Coast

The sunken remains of two ill-fated whaling ships have been found off the coast of Alaska, 144 years after they became crushed by pack ice, forcing all crew members to abandon their vessels. Though all were later rescued, the event marks one of the greatest catastrophes in the history of U.S whaling, and resulted in the loss of an entire fleet of 33 ships.

Back in the 18th and 19th centuries, whale oil was used around the world for heating, candle wax, soap, and a number of other purposes. As such, whaling was pretty big business, and attracted fleets from across the world to the Arctic each summer, when the ice relented and several species of whales migrated northwards.

However, the conditions at the top of the world can be unpredictable, as this particular fleet discovered to their peril in September 1871, when their ships became trapped in ice before they had a chance to manoeuvre away. Since the disaster, various artefacts from the sunken vessels have been discovered floating in the sea or washed up on the shore. Andresearchers have now located two of the ships for the first time.

Using sonar and other submarine-sensing equipment, a team of archaeologists from the National Oceanic and Atmospheric Association (NOAA) surveyed the waters along a 48-kilometer (30-mile) stretch of coastline near Wainwright, Alaska. In doing so, they were able to plot the outline of two flattened hulls, along with other items such as anchors, ballast and blubber-boiling equipment.

The researchers found anchors, rigging equipment, and other structural features of the sunken ships. NOAA

Until now, attempts to uncover the downed fleet had been thwarted by the thick layer of pack ice that covers much of the Arctic for large periods of the year, although a steady decrease in the amount of ice present during the height of summer over the past four decades has opened up new opportunities for conducting the search. As a consequence, the team was finally able to locate the ships last September, when the Arctic sea ice reaches its yearly minimum.

Reacting to the exciting discovery, project co-director Bad Barr said in a statement: This exploration provides an opportunity to write the last chapter of this important story of American maritime heritage and also bear witness to some of the impacts of a warming climate on the regions environmental and cultural landscape, including diminishing sea ice and melting permafrost.

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Read more: http://www.iflscience.com/editors-blog/wreckage-sunken-whaling-ships-discovered-alaskan-coast

Why Arctic Melting Will Be Erratic In The Short Term


rctic sea ice melts each summer, reaching its minimum extent sometime in September, before refreezing through the winter. Over the past 35 years, the September sea ice extent has reduced by about 35% overall and this decline is projected to continue as global temperatures increase.

In 2007 and 2012 the summer ice extent was dramatically lower, causing some some media speculation that we would soon see a summer which was “ice-free” (meaning a year with less than 1 million km2 of sea-ice).

Most climate scientists were more cautious. The weather in 2007 and 2012 was warmer than usual and the winds were particularly favourable for melting sea ice. Although human influence on Arctic sea ice has been detected, there was no evidence that these weather patterns would continue each year.

In contrast, 2013 and 2014 had more sea ice than 2012, causing other speculation that a recovery was underway. Is this claim warranted?

The figure below shows Arctic sea ice extent (the black line) has undergone a long-term decrease, with the dashed line representing a linear trend. But there have also been shorter periods of rapid melt, no change, and apparent increases in extent during this decline – represented below by coloured trend lines for some deliberately chosen eight year periods.


Satellite observations of September Arctic sea ice extent. Ed Hawkins/University of Reading

The most recent eight-year period, starting from the extreme low of 2007, shows an upward trend. This does not mean that the Arctic sea ice is recovering. As with global temperature, these erratic changes are what we expect to see.

Bouncing Towards An Ice-Free Summer

Imagine a ball bouncing down a bumpy hill. Gravity will ensure that the ball will move downwards. But if the ball hits a bump at a certain angle it might move horizontally or even upwards for a time, before resuming its inevitable downward trajectory. This bouncing ball is an analogy for the changing Arctic sea ice.

The hill represents the long-term downward trend in Arctic sea ice due to increasing global temperatures and the bumps introduce changes from this smooth trajectory. These erratic bounces could be in either direction, causing an apparent acceleration or temporary reduction in melt rate. By only examining a small part of the trajectory you might conclude that the ball was moving against gravity. A longer term view would see it as a bounce.

There is no expectation that sea ice, or any other aspect of the climate, will change smoothly over time. The climate system simply does not work that way. Previous studies have suggested that natural climate variations (or “bounces”) play a key role in how sea ice evolves, and suggested that some of the rapid melt in the early 2000s was a temporary acceleration.


September minimum, 1984 and 2012. NASA

A new study I co-authored with a team of Canadian and American scientists, published in Nature Climate Change, highlights that the recent slower melt is a temporary, but not unexpected, deceleration. The complex climate models used to make projections of future climate also exhibit similar periods of little change and more rapid change in Arctic sea ice. The recent trends are well within the range of these expectations. We might even see a decade or more with little apparent change in sea ice.

The causes of these fluctuations in melt rate are still being explored. One suggestion is that slow variations in Atlantic sea surface temperatures are involved. More observations of the Arctic ocean, atmosphere and sea ice would help answer this question.

An Ice-Free Future?

When will the Arctic be ice-free – or equivalently, when will the ball reach the bottom of the hill? The IPCC concluded it was likely that the Arctic would be reliably ice-free in September by 2050, assuming high future greenhouse gas emissions (where “reliably ice-free” means five consecutive years with less than 1 million km2 of sea ice).

We expect the long-term decline in Arctic sea ice to continue as global temperatures rise. There will also be further bounces, both up and down. Individual years will be ice-free sometime in the 2020s, 2030s or 2040s, depending on both future greenhouse gas emissions and these natural fluctuations.

Even when it reaches the bottom of the hill the ball will continue to bounce. Similarly, not every future year will be ice-free in summer. But if global temperatures continue to increase the bounces will become smaller and the ice-free periods will spread from late summer into autumn and early summer.

Commercial Arctic shipping is already increasing to exploit shorter journey times from Europe to Asia, while oil, gas & mineral extraction possibilities are being explored and Arctic tourism is growing. Decisions about such activities need to assess both the risks and opportunities. The important role of natural sea ice fluctuations needs to be considered in such assessments.

The Conversation

Read more: http://www.iflscience.com/environment/why-arctic-melting-will-be-erratic-short-term

Greenland’s Ice Is Getting Darker, And That’s Very Bad News

Satellites have been collecting data on the Greenland ice sheet since 1981. But since the mid-’90s, scientists have noticed the sheet has become progressively darker.

The satellites have been measuring the albedo of the Greenland ice sheet, essentially how much sunlight is reflectedback from the surface towards space. The process is not viewable with the human eye, butthe level of albedo is detectablethrough satellite instruments. Researchers from Columbias Earth Institute have collected and analyzed the data in a study recently published in the journal The Cryosphere.

Their findings state that if the current trend of darkening continues, parts of the sheet will be 10 percent less reflective by the end of the 21st century than they are today.

So what exactly is going on?

The study said soot from wildfires in China, Siberia,and North Americagetting into the ice is no doubt contributing. However, using the Global Fire Emissions Database, they found there was no increase in the number of wildfiresfrom the mid-nineties, suggesting another culprit was at play.

They found that the real driver for the change was rising temperatures. From 1996 onwards, the ice began absorbing about 2 percent more solar radiation per decade. This is in line with the findings that the near-surface temperatures in Greenland have been increasing by0.74Cper decade.

The snowpack of the sheet undergoes a constant processof thawing and refreezing throughout the seasons. However, the warmer and brighter summers are producing a bigger thaw in the ice. With each of these refreezings, the grains of ice get larger and larger. The larger the grains get, the less reflective a surface they have, hence they become darker.

The real issue with this darkening is the vicious circle itcreates. As youll know if you touch the bonnet of a black car on a hot day, darker colors are less reflective so absorbmorelight and, importantly, heat. The darker the icegets, the more vulnerable it is to melting, so it gets darker, and the cycle continues.

“It’s a complex system of interaction between the atmosphere and the ice sheet surface. Rising temperatures are promoting more melting, and that melting is reducing albedo, which in turn is increasing melting,”lead author Professor Marco Tedesco, from the Columbia University’s Lamont-Doherty Earth Observatory and NASA, said in a statement.

“As warming continues, the feedback from declining albedo will add up. It’s a train running downhill, and the hill is getting steeper,” Tedesco added.

Read more: http://www.iflscience.com/environment/greenlands-ice-getting-darker-and-its-not-good-news