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AAAS: Climate risks irreversible change

March 18, 2014 in AAAS, Child Malnutrition, Climate risk, Coastal Threats, Extreme weather, Flooding, Food security, IPCC, Weather


By Alex Kirby

In a highly unusual intervention in the debate over climate policy, US scientists say the evidence that the world is warming is as conclusive as that which links smoking and lung cancer.

LONDON, 18 March – The American Association for the Advancement of Science (AAAS) says there is a “small but real” chance that a warming climate will cause sudden and possibly unalterable changes to the planet.

This echoes the words used in its 2007 report by the Intergovernmental Panel on Climate Change (IPCC), which said climate change might bring “abrupt and irreversible” impacts.

A child with kwasiorkor, caused by evere protein deficiency: Child malnutrition may rise by about a fifth Image: Dr Lyle Conrad via Wikimedia Commons

A child with kwashiorkor, caused by evere protein deficiency: Child malnutrition may rise by about a fifth
Image: Dr Lyle Conrad, Centers for Disease Control and Prevention, via Wikimedia Commons

In a report, What We Know, the AAAS makes an infrequent foray into the climate debate. The report’s significance lies not in what it says, which covers familiar ground, but in who is saying it: the world’s largest general scientific body, and one of its most knowledgeable.

The AAAS says: “The evidence is overwhelming: levels of greenhouse gases in the atmosphere are rising. Temperatures are going up. Springs are arriving earlier. Ice sheets are melting. Sea level is rising. The patterns of rainfall and drought are changing. Heat waves are getting worse, as is extreme precipitation. The oceans are acidifying.

“The science linking human activities to climate change is analogous to the science linking smoking to lung and cardiovascular diseases. Physicians, cardiovascular scientists, public health experts and others all agree smoking causes cancer.

Few dissenters

“And this consensus among the health community has convinced most Americans that the health risks from smoking are real. A similar consensus now exists among climate scientists, a consensus that maintains climate change is happening, and human activity is the cause.”

The report’s headline messages are unambiguous. It says climate change is occurring here and now: “Based on well-established evidence, about 97% of climate scientists have concluded that human-caused climate change is happening.

“This agreement is documented not just by a single study, but by a converging stream of evidence over the past two decades from surveys of scientists, content analyses of peer-reviewed studies, and public statements issued by virtually every membership organization of experts in this field.

“We are at risk of pushing our climate system toward abrupt, unpredictable, and potentially irreversible changes with highly damaging impacts…Disturbingly, scientists do not know how much warming is required to trigger such changes to the climate system.

Expensive to delay

“The sooner we act, the lower the risk and cost. And there is much we can do…as emissions continue and warming increases, the risk increases”.

The AAAS says there is scarcely any precedent for the speed at which this is happening: “The rate of climate change now may be as fast as any extended warming period over the past 65 million years, and it is projected to accelerate in the coming decades.”

Historically rare extreme weather like once-in-a-century floods, droughts and heat waves could become almost annual occurrences, it says, and there could be large-scale collapses of the Antarctic and Greenland ice sheets, and of part of the Gulf Stream, loss of the Amazon rain forest, die-off of coral reefs, and mass extinctions.

The authors acknowledge that what the AAAS is doing is unusual: “As scientists, it is not our role to tell people what they should do or must believe about the rising threat of climate change.

“But we consider it to be our responsibility as professionals to ensure, to the best of our ability, that people understand what we know: human-caused climate change is happening…”

More child malnutrition

At the end of March the IPCC, the UN’s voice on climate science, is due to release a summary of the report of its Working Group II, on impacts, adaptation and vulnerability to climate change.

The London daily The Independent, which says it has seen a draft of the report’s final version, says it will spell out a prospect of “enormous strain, forcing mass migration, especially in Asia, and increasing the risk of violent conflict.”

The newspaper says the report predicts that climate change “will reduce median crop yields by 2% per decade for the rest of the century”, against a backdrop of rising demand set to increase by 14% per decade until 2050. “This will in turn push up malnutrition in children by about a fifth”, it adds.

Other predictions in the draft, The Independent says, include possible global aggregate economic losses of between 0.2 and 2.0%; more competition for fresh water; and by 2100 hundreds of millions of people affected by coastal flooding and displaced by land loss, mainly in Asia. – Climate News Network

Old Greek plays record halcyon days

March 8, 2014 in Climate, Europe, History, Weather


The theatre at Epiidaurus, where many of the leading dramatists' plays were performed Image: plusgood via Wikimedia Commons

The theatre at Epiidaurus, where many of the leading dramatists’ plays were performed
Image: plusgood via Wikimedia Commons

By Tim Radford

History and literature provide evidence of consistently mild mid-winter weather in ancient Greece, helping climate scientists to reconstruct the past and so understand the future.

LONDON, 8 March – In fifth century Athens, in January at least, the skies were clear and the rain stayed away. The days, to use a classical reference, were halcyon.

Two Greek researchers have combed the great plays of Aeschylus, Sophocles and Euripides and the bawdy comedies of Aristophanes to deliver a long-term weather report for mid-winter days from 458 BC to 401 BC. They report in the Royal Meteorological Society’s journal Weather that, clearly, the city was a good place to hold open-air stage productions in mid-winter. Sophocles, in his masterpiece Oedipus at Colonus, actually says so:

“A distant music, pure and clear rises from green secluded vales. The constant trill of nightingales deep in their haunts of tangled vine, of sacred ivy, dark as wine, thick is the god’s inviolate wood; rich in berries and rich in fruit, the sun is curtained; the wind is mute, in winter.”

To understand the climate of the future, scientists must reconstruct the patterns of the past, long before the first formal weather records. They do this by examining pollens in lake beds, growth rings in ancient trees, ice cores and ocean muds to deliver circumstantial evidence of bygone seasons.

Balmy mid-winter

But there are also indirect references in human records: in naval log books, in medieval tax records, in monastic manuscripts, and in chronicles from Baghdad in the golden age of Islamic scholarship.

Christina Chronopoulou of the National and Kapodistrian University of Athens, and a colleague from Panteion University in the same city, decided to comb 43 surviving works performed during the Lenaia celebrations in mid-winter. They found seven clear direct and indirect references to the beneficial halcyon days of mid-winter.

The halcyon days are now a cliché but once referred to the myth of Alcyone, the grieving widow who was turned into a kingfisher by the gods, and who nested on the beach at midwinter.

But the fact the ancient Greeks routinely watched and expected to watch drama in open amphitheatres during the Attic month of Gamelion, which ran from 15 January to 15 February, provides indirect confirmation of good weather. Halcyon days, say the authors, are “atypical winter-time weather periods characterized by sunny and calm conditions” and the result of a stagnant high-pressure system that dominates the area at such a time of year.

Observant dramatists

And, as they worked through some of the great plays, they found enduring references to clear skies: in Agamemnon, by Aeschylus, in 458 BC a character spends his nights on the roof “to know thoroughly the throng of stars…” Aristophanes in The Birds in 414 BC describes a wedding.  Attic weddings lasted for three days and were performed in the open air, another indicator of mellow conditions. The Birds also contains references to a “skiadeion”, a parasol, an umbrella to provide shade from the sun, rather than shelter from the rain.

Euripides in Medea in 431 BC mentions “the temperate and sweet breezes” while Aristophanes in The Frogs in 405 BC actually addresses “you halcyons who chatter by the ever-flowing waves.”

“Combining the fact that dramatic contests were held in mid-winter without any indication of postponement, and references from the drama about clear weather and mild winters, we can assume that those particular days of almost every January were summery in the 5th and maybe the 4th centuries BC,” said Dr Chronopoulou. – Climate News Network

Penguins feel climate change’s impacts

February 1, 2014 in Antarctic, Climate, Extreme weather, Marine ecology, Rainfall, South America, Weather, Wildlife


Adélie penguin chicks chase an adult in the hope of finding food Image: Liam Quinn from Canada via Wikimedia Commons

Adélie penguin chicks chase an adult in the hope of finding food
Image: Liam Quinn from Canada via Wikimedia Commons

By Tim Radford

Scientists have identified climate change as the direct cause of rising mortality among penguin chicks hatched in Argentina.

LONDON, 1 February – Climate change is bad for penguin chicks. If rain doesn’t soak their feathers and kill them with cold, then extremes of heat could finish them off with hyperthermia.

Over a 27-year research project in the world’s largest colony of Magellanic penguins, on the arid Argentine coast, researchers have seen a greater number of deaths directly attributable to climate change.

“We’re going to see years where almost no chicks survive if climate change makes storms bigger and more frequent during vulnerable times of the breeding season”, says Ginger Rebstock, who, with Dee Boersma, reports on the state of penguin survival in the Public Library of Science journal PLOS One.

The two scientists, biologists from the University of Washington, Seattle in the US, believe starvation and weather are going to make life harder for the offspring of the 200,000 pairs of penguins that breed each year at Punta Tombo, on Argentina’s Atlantic coast.

The number of storms during the first two weeks of December – when all the chicks are less than 25 days old and their downy coats are not yet waterproof – has increased between 1983 and 2010.

Every new chick is at hazard: over the span of study, the researchers calculate that 65% of chicks do not survive, 40% of them die by starvation. But climate change has begun to offer new dangers.

A Magellanic chick, still too young to have an adult's waterproofing, in the rain Image: D Boersma/University of Washington

A Magellanic chick, still too young to have an adult’s waterproofing, in the rain
Image: D Boersma/University of Washington

Some years up to half of all chicks die because of the weather. Punta Tombo is historically an arid region. In the last 50 years, the scientists report, rainfall has increased. The number of wet days has increased, the number of consecutive wet days has increased and the level of rainfall during those days has continued to increase.

Air temperatures changed too. The minimum temperatures decreased by up to 3°C and the number of these colder days increased. Storms, too, make it more difficult for foraging parents to gather enough food to feed their chicks.

Sea ice changes

“Starving chicks are more likely to die in a storm”, says Prof Boersma. “There may not be much we can do to mitigate climate change, but steps could be taken to make sure the Earth’s largest colony of Magellanic penguins have enough to eat by creating a marine protected reserve, with regulations on fishing, where penguins forage while raising small chicks.”

Further south, extreme weather is beginning to make life difficult for the Adélie penguins of Ross Island in Antarctica. Amélie Lescroël from the CNRS in France and colleagues report in the same edition of PLOS One that abnormal sea ice conditions reduce access to food.

Antarctic penguins are of course adapted to sea ice: it is their preferred habitat. But they must respond to short and long term changes in ice levels. For 13 years, scientists have monitored the feeding success of the Ross Island colony and observed that the birds could cope in those seasons when there was less sea ice.

But climate change in Antarctica, too, creates new problems for the birds and limits their foraging efficiency.

“Our work shows that Adélie penguins could cope with less sea ice around their summer breeding grounds”, said Dr Lescroël. “However, we also showed that extreme environmental events, such as the calving of giant icebergs, can dramatically modify the relationship between Adélie penguins and sea ice.”

If the frequency of such extreme events increases, then it will become hard to predict how penguin populations will get by, she thinks. – Climate News Network

2013 was fourth warmest year recorded

January 22, 2014 in Climate deniers, El Niño, NOAA, Rainfall, Temperature Increase, Warming slowdown, Weather


Drought in Ethiopia, one of the countries which experienced record warmth in 2013 Image: By USAID Africa Bureau via Wikimedia Commons

Drought in Ethiopia, one of the countries which experienced record warmth in 2013
Image: By USAID Africa Bureau via Wikimedia Commons

By Alex Kirby

Arguments that global warming has slowed or even stopped since the turn of the century are undermined by US data which show that 2013 maintained the warming trend of recent decades.

LONDON, 22 JanuaryPeople who argue that global warming has stopped and the Earth’s average temperature has not risen this century should perhaps read no further. US scientists say 2013 was the fourth warmest year globally since records began in 1880.

The National Climatic Data Center (NCDC), part of the US National Oceanic and Atmospheric Administration, says in its Global Analysis of the last year that 2013 ties with 2003 as globally the fourth warmest year on record.

The annual global combined land and ocean surface temperature was 0.62°C above the 20th century average of 13.9°C, marking the 37th consecutive year (since 1976) that the yearly global temperature was above average.

The warmest year on record is 2010, which was 0.66°C above average. Including 2013, nine of the 10 warmest years in the 134-year period recorded have occurred in the 21st century. Only one year during the 20th century – 1998 – was warmer than 2013.

The 2013 global average ocean temperature (0.48°C) was the highest since 2010, the last time El Niño conditions were present in the central and eastern equatorial Pacific. El Niño is a periodic weather disruption in the eastern Pacific which affects conditions over thousands of miles.

The NCDC says global annual temperature has increased at an average rate of 0.06°C per decade since 1880 and at 0.16°C per decade since 1970.

“…For 2013 as a whole, most regions across the globe were warmer than average”

Regionally, it says, most of the world experienced above-average annual temperatures in 2013. Over land, parts of central Asia, western Ethiopia, eastern Tanzania, and much of southern and western Australia experienced record warmth. Only part of the central United States was cooler than average over land.

Parts of the Arctic Ocean, a large swathe of the south-western Pacific Ocean and parts of the central Pacific, and an area of the central Indian Ocean also set new records for warmth.  Small regions scattered across the eastern Pacific and an area in the Southern Ocean south of South America were cooler than average. No part of the world experienced record cold in 2013.

Perhaps surprisingly for anyone who thinks of the last twelve months as memorable chiefly for the amount of rain that fell, the NCDC says precipitation measured at land-based stations around the globe was near average on balance for 2013, at just 0.31 mm above the long-term average.

However, it adds prudently: “As is typical, precipitation varied greatly from region to region. This is the second consecutive year with near-average global precipitation at land-based stations.”

Taking 2013 as a whole, it acknowledges that some regions were cooler than usual. But it says: “In summary for 2013 as a whole, most regions across the globe were warmer than average.

“Notably, Australia observed its warmest year since national records began in 1910, at 1.20°C above average and 0.17°C higher than the previous record warmest such period in 2005. New Zealand recorded its third warmest year since its national records began in 1909.” – Climate News Network

How weather shapes our climate ideas

January 12, 2014 in Public Awareness, USA, Warming, Weather

EMBARGOED until 1800 GMT on Sunday 12 January

Very hot days can dispose us to accept that climate change is happening, while cold days do the opposite Image: Craig Shaw SnowMonkeyJapan via Wikimedia Commons

Very hot days can dispose us to accept that climate change is happening, while cold days may do the opposite
Image: Craig Shaw SnowMonkeyJapan via Wikimedia Commons

By Alex Kirby

Researchers in the US say most people’s convictions about climate change are largely shaped by the weather outside – because that’s the most immediate data we can find.

LONDON, 12 January – It’s by now a no-brainer to say that what we think about climate change is often influenced by what we know of weather change. On a cold day many of us are much less ready to agree that the climate is changing than we are on a warm one.

But now researchers have gone a stage further, trying to establish just why we react to these topical prompts rather than to the evidence of long-term change. And In a series of surveys, they have found that we often respond to the most accessible and immediate information – whether on temperature or something else – that we can find.

The research, published in Nature Climate Change, was completed by the Center for Research on Environmental Decisions (CRED) at Columbia University’s Earth Institute.

One survey examined several possible influences on perceptions of the climate, for example testing 686 people on whether individual words could alter their reactions on a very warm day. But the researchers found that speaking of “global warming” rather than “climate change” made little difference.

Experience beats memory

Another survey gave around 330 respondents information on the scientific distinction between local temperature and global climate change, while a control group – a different set of respondents, used to draw comparisons – received information unconnected to climate. Yet greater knowledge about how climate works made very little difference to how that day’s weather affected the respondents’ views on climate.

Then the researchers wanted to see whether more accessible information – like the current day’s temperature – simply took over from less accessible information, such as scientific explanations of global climate change.

So as well as asking about the current temperature they asked 300 participants to do a word puzzle which included several heat-related terms. This “priming” with extra “accessible” information did increase levels of belief in climate change.

In another test they asked 251 people about the previous day’s temperature (which was by then a memory), and found it did not influence their beliefs about climate change in the same way that the current day’s temperature did: that was a matter of immediate experience.

One cold day

In a final survey of 270 people, asking what they recalled of warmer-than-usual events, the researchers found that one unusually warm day could prompt memories of other similar days and could lead people to overestimate the frequency of such exceptionally warm days.

The lead author of the study, Lisa Zaval, a graduate student in psychology at Columbia University working with CRED, said the survey’s findings about warm weather events could apply to cold ones, too. “Our data suggest that perceiving today’s local temperature to be colder than usual can lead to decreased belief in and reduced concern about global warming”, she said.

“Strengthening the association between… cold weather, or extreme weather fluctuations, and climate change in people’s minds might be a good step.”

Her team’s report sounds a similar note: “If the United States is to take a stronger stance against climate change, forecasters may be well advised to make increasing warming abnormalities more cognitively available to the general public.” In other words: in a warming world, prepare for all sorts of surprises. – Climate News Network

Florida’s mangroves head northwards

December 30, 2013 in Adaptation, Vegetation changes, Warming, Weather, Wetlands



Florida's mangroves are moving north as very frosty days become less frequent Image: Wilen Bill, US Fish & Wildlife Service, via Wikimedia Commons

Florida’s mangroves are moving north as very frosty days become less frequent
Image: Wilen Bill, US Fish & Wildlife Service, via Wikimedia Commons

By Tim Radford

Mangroves are colonising new areas in northern Florida, moving up the coast because the frequency of very frosty days is falling.

LONDON, 31 December – The mangroves of Florida are on the move. Mangrove forests in the north of the state have doubled in area in the last 28 years, thanks not to global warming as such, but because the number of sharply frosty days has dropped.

The discovery is in itself not a surprise – mangrove growth is limited by temperature – but once again it confirms a pattern of climate change and species migration in response to man-made global warming.

Kyle Cavanaugh and colleagues report in the Proceedings of the National Academy of Sciences that they examined 28 years of satellite imagery over one particular stretch of an important ecosystem on the coast of northern Florida between 1984 and 2011. All the increase occurred north of Palm Beach County, and growth in the area between Cape Canaveral National Seashore and St Augustine doubled.

“Before this work there had been some scattered anecdotal accounts and observations of mangroves appearing in areas where people had not seen them, but they were very local”, said Dr Cavanaugh, a researcher at the Smithsonian Institution in the US.

Simple pattern

“One unique aspect of this work is that we were able to use this incredible time series of large-scale satellite imagery to show that the expansion is a regional phenomenon. It’s a very large-scale change.”

The other important aspect of the research was that it eliminated some of the other possible causes behind the expansion of mangroves into the salt marshes a little to the north.

The pattern of change over the 28-year period, in which the area colonised by mangroves grew by another 1,240 hectares, was not a consequence of a shift in average temperatures, or of the change in management patterns, or an altered pattern of precipitation, or changes in the tidal regimes, or even altered rates of nutrient flow and sedimentation.

What emerged from the painstaking match of seasonal weather and mangrove advance was quite simple. With a decline in the number of days in the year in which a sharp frost occurred, and in which the temperatures fell to minus 4°C or below, the mangrove reach began to extend.

Salt marsh loses

It was not the overall warmth, but the change in the frequency of severe events that mattered most. And this change in frequency was surprisingly slight: just 1.4 fewer frosty days a year at Daytona Beach seemed to be enough to account for the expansion.

In the region overall, the scientists write, minimum temperatures have been rising faster than either the daily mean temperature, or the daily maximum. The implication is that stands of the mangrove genus Avicennia will go on colonising new habitat.

Mangroves are important ecosystems for both wildlife and for coastal citizens, and worldwide, mangrove forests have been under threat. But even a welcome change may not be entirely for the good.

“The expansion isn’t happening in a vacuum”, said Dr Cavanaugh. “The mangroves are expanding into and invading salt marsh, which also provides an important habitat for a variety of species.” – Climate News Network

Arctic melting ‘affects temperate zones’

December 18, 2013 in Arctic, Extreme weather, Polar ice, Weather, Weather Systems


Bear on the ice near Svalbard: Arctic warming appears to be having effects far to the south Image: Hannes Grobe via Wikimedia Commons

Bear on the ice near Svalbard: Arctic warming appears to be having effects far to the south
Image: Hannes Grobe via Wikimedia Commons

By Tim Radford

Weather extremes in temperate countries may be the consequence of the melting of Arctic snow and ice, according to Chinese and American scientists.

LONDON, 18 December – The shrinking Arctic sea ice – a loss of 8% per decade during the last 30 years – isn’t just bad news for polar bears. It could be bad news for citizens of Europe and the United States who like to think they live in a temperate zone.

Qiuhong Tang of the Chinese Academy of Sciences and colleagues from Beijing and the US report in Nature Climate Change that they have identified a link between declining snow and ice in the polar north, and catastrophic heat waves, droughts and floods in the mid-latitudes.

Recent years have been marked by devastating extremes of heat in Russia, Europe and the US, and by unprecedented floods in the UK and in East Asia. Over the same period, snow cover and sea ice in the Arctic have been in retreat.

The link, the scientists say, could be changes in atmospheric circulation triggered by the loss of snow cover.

There are perfectly good reasons to expect some impact on weather systems from a retreat of the snow line. In the first place, snow and ice are white – that is, they reflect sunlight, and its warmth – while ocean and forest and tundra are dark, and absorb heat.

Closer link established

Good snow fall means lots of soil moisture in the summer months while dry ground tends to be warmer. So temperatures change, overall. Air currents flow because of pressure differences, which are linked to temperature. So winds would inevitably be affected.

But the researchers went beyond this loose generalisation, to match satellite observations of the snow cover and sea ice extent in the Arctic with atmospheric data, to explore the effects further south.

They found a distinct set of patterns of circulation associated with the loss of snow and ice.

The upper atmospheric winds in the north become weaker, and the jet stream shifts northwards, which means that weather systems become more stable. The longer a weather system stays in one location, the greater the probability that the conditions will become extreme.

In 2012, in the continental United States, it was the hottest summer ever recorded and the second worst for floods, hurricanes and droughts. In September 2012, the Arctic sea ice fell to its lowest level ever. It could be just chance, it could be just two aspects of the same big picture, but Tang and colleagues think not.

Hotter future

They think the link is clear. They even see a closer link between the loss of sea ice and a change in circulation pattern, even though the area of sea ice lost is only half of the total area of snow lost in the months of May and June.

That could be because much of the northern hemisphere snow cover is over land which is forested anyway – that is, partly dark – whereas the Arctic sea can only be white or dark.

The link is not certain – they are putting the idea out there for others to challenge or confirm, which is the way science advances – but the three authors argue that their research builds on studies by others which spell out the same conclusion.

And they don’t see things getting better, either for polar bears who need the sea ice to hunt, or for farmers in the great plains of the US or city dwellers on floodplains and river estuaries in the temperate world.

“As greenhouse gases continue to accumulate in the atmosphere and all forms of Arctic ice continue to disappear, we expect to see further increases in summer heat extremes in the major population centres across much of North America and Eurasia where billions of people will be affected”, they conclude. – Climate News Network

Local climate predictions stay uncertain

December 6, 2013 in Agriculture, Butterfly Effect, Climate, Forecasting, Uncertainty, Vegetation changes, Weather


Florida's orange harvest is likely to be at risk of climate-induced damage Image: Benjamin D Esham via Wikimedia Commons

Florida’s orange harvest is likely to be at risk from climate-induced damage
Image: Benjamin D Esham via Wikimedia Commons

By Tim Radford

Uncertainty will continue to mark attempts to predict detailed, local climates, scientists say, though they are confident that widespread and significant changes are coming.

LONDON, 6 December – Prediction is very difficult, especially if it is about the future, the great physicist Niels Bohr once observed. Eric Fischer, a climate scientist at ETH-Zurich, has just arrived at much the same conclusion.

Fischer and colleagues reported in Nature Climate Change that their attempts to look at weather patterns even in the near future delivered very large uncertainties. This, they report, is a consequence of something sometimes called the butterfly’s wing effect and sometimes chaos theory.

Meteorologists are fond of saying that the flap of a butterfly’s wing in Brazil could set up a chain of air movements that might end with a tornado in Texas. Even the tiniest change in the initial starting conditions can produce wildly different outcomes later.

Fischer and his fellow researchers simply wanted to solve a puzzle for the farmers, decision-makers and civic authorities who must prepare for floods, heat waves and ice storms in the next decade or two, and who have already been urged to face up to the need to adapt to climate change.

The Zurich team used a climate model to simulate extremes of temperature and precipitation between the periods 2016-2035 and 2041-2060. They matched the model with real, historical data from 1950 to 2005, they assumed that greenhouse gas emissions would be the same in all simulations, and they ran the model 21 times, each time making a tiny random variation in the global atmospheric temperature on the first day: 1 January 1950.

Big changes certain

This variation truly was tiny: no more than one hundred billionths of a degree Celsius. It was the thermal equivalent of the beat of a butterfly’s wing. And yet, each time, it produced huge variations in the predicted extremes for various spots of the globe: variations in the coldest temperatures of between -1°C and 7°C, for example.

This would not be much help to a farmer wondering what to plant on any particular farm, or a local authority wondering whether to economise on grit for icy roads.

“Our study reveals that we have to live with uncertainties in local, medium-term projections”, said Fischer. But although the chaotic outcomes meant that precision forecasting was impossible the results nevertheless confirmed that there would be big changes over very large areas.

Heat extremes will become significantly more intense on two-thirds of the land surface within the next three decades; rainfall will increase by 10% in one quarter of the land area and by less than 10% in the remaining three quarters.

South-east US at risk

In Europe, the USA, China and Australia, the intensity of heat waves will increase in the next 30 years, and heavy rainfall will increase in the next 50 years.

“The different models agree that changes in extreme weather events will occur and how strong they will be, but not where they will be strongest,” said Fischer. “This is largely determined by chaos.”

One area likely to experience dramatic change and devastating extremes, however, is the south-eastern United States, according to Keith Ingram of the University of Florida, who has just edited a new book intended to consider the possible consequences of climate change for Florida, North and South Carolina, Virginia, Tennessee, Kentucky, Arkansas, Mississippi, Alabama and Puerto Rico. More than one in four citizens of the US lives in these states.

“The Southeast already experiences extreme weather events including floods, droughts, heat waves, cold outbreaks, winter storms, severe thunderstorms, tornadoes and tropical cyclones”, said Ingram.

“In the future, these events are likely to become more frequent or more severe, causing damage to most of our region’s agriculture. The sooner we make preparations, the better off we will be.” – Climate News Network

Salt Lake City will dry as temperatures rise

December 2, 2013 in Climate, Drought, Forecasting, Rainfall, Water, Weather


Southwestern states in the US are likely to become arid as temperatures rise. Image: Al Jazeera English via  Wikimedia Commons

Southwestern states in the US are likely to become particularly arid as temperatures rise.
Image: Al Jazeera English via Wikimedia Commons

By Tim Radford

As climate change increases temperatures, parts of the American Southwest are likely to become increasingly arid.

LONDON, 2 December – It’s just one aspect of the future for just one city among hundreds: researchers have calculated that, for every extra notch on the temperature scale, Salt Lake City in the state of Utah, USA, will face a serious drop in the annual flow of fresh stream and river water to its people.

The fall in flow could be anything from 1.8 to 6.5%. The measure of temperature used by the Americans is Fahrenheit, and 1°F is the equivalent of five ninths of 1°C. But average temperatures in the region have risen 2°F in the last century and are expected to go on climbing.

By mid-century, according to Tim Bardsley from the University of Colorado at Boulder,  some of the streams that feed the city will dry up several weeks earlier each summer and autumn. Climate scientists have predicted that the American Southwest could become steadily more arid as the planet warms through a build-up of carbon dioxide in the atmosphere. But city planners need more than general warnings: they need a clear idea of what might happen in this or that environment.

“Because our research team included hydrologists, climate scientists and water utility experts, we could dig into the issues that mattered most to the operators responsible for making sure clean water flows through taps and sprinklers without interruption,” said Bardsley.

Snow is Salt Lake’s lifeblood

He and colleagues report in Earth Interactions that they used climate models to project temperature and rain and snowfall in the region, along with detailed historical analysis to confirm that more of the annual precipitation will fall as rain, rather than snow.

Salt Lake City was the base for the 2002 Winter Olympics: snow is important to the city in more ways than one. Since snow stays where it falls but rainwater runs off immediately, the flow downstream will end significantly earlier in the growing season, as temperatures rise.

In June, scientists forecast a detailed snowfall future for the City of Los Angeles. The Salt Lake City study is just another example of attempts by local authorities to confront a future of global climate change.

“Water emanating from our local Wasatch Mountains is the lifeblood of the Salt Lake Valley and is vulnerable to the projected changes in climate, “ said the city’s mayor, Ralph Becker. “This study, along with other climate adaptation work Salt Lake City is doing, helps us plan to be a more resilient community in a time of climate change.”

The researchers confirmed that every increase of 1°F meant, on average, a 3.8% decrease in annual water flow from the city’s watersheds. The lower the altitude of a stream, the more sensitive it was to increasing temperatures, which means that planners have to store more water, or rely on streams from higher altitudes.

On the climate boundary

But events in Utah are hard to estimate. In a warming world, climate scientists expect the US south-west to become much more arid while nd the northern states will experience more precipitation. Utah is poised more or less at the climate change boundary.

The climate models suggest that there would be a more generous flow of water in the winter, but this is the period at which demand is likely to be lowest. To counteract a 5°F rise in local temperatures, the city would hope for at least 10% more precipitation. But a 5°F rise would also mean that peak water flow in the creeks would occur up to four weeks earlier than it does today, which is likely to be a problem for farmers who rely on irrigation. – Climate News Network

Geo-engineering ‘could upset rainfall’

December 1, 2013 in Adaptation, Geoengineering, Rainfall, Vegetation changes, Weather


The Asian monsoon, the source of life for hundreds of millions, could be at risk Image: Yann via Wikimedia Commons

The Asian monsoon, which ensures a harvest for hundreds of millions, could be at risk
Image: Yann via Wikimedia Commons

By Tim Radford

Geo-engineering may be able to lower global temperatures but could be damaging to seasonal rainfall patterns, a study says.

LONDON, December 1 – Geo-engineering – the confident technocrat’s last resort solution to catastrophic climate change – could create damaging conditions of its own, according to new research.

Simone Tilmes of the National Center for Atmospheric Research in Boulder, Colorado, in the US and an international team of colleagues report in Geophysical Research Letters: Atmospheres that at least one deliberate technological strategy to limit global warming could reduce seasonal rainfall, including the monsoons of Asia that provide a lifeline to hundreds of millions.

Senior scientists have in the last decade tentatively considered technological responses to climate change on the basis that economies, politicians and consumers show no sign of making the dramatic reductions in fossil fuel use that would cut the greenhouse gas emissions that fuel global warming.

Among these responses is a relatively simple one. If greenhouse gases go on increasing, then more solar heat will be trapped in the atmosphere. So, the world should think of a way to reduce solar radiation instead: spray sulphate particles into the stratosphere to block incoming sunlight, or even place arrays of mirrors into orbit to reflect a proportion of the sunlight away from the Earth.

So the scientists used 12 different climate models to simulate various possible futures, including one based on historical factors in which carbon dioxide did not just double, but reached four times the levels in the atmosphere during the American Revolution, and the Napoleonic wars that ravaged Europe at the dawn of the Industrial Revolution.

They found – not surprisingly – that a greenhouse world would be matched by a significant increase in rainfall in many places, along with prolonged droughts in others. That would happen because more warmth means more evaporation, greater saturation of the atmosphere and consequently more precipitation.

Harvests at risk

And then, still using the same climate models, they tested what would happen to rainfall if they artificially blocked some of the incoming sunlight, to lower the overall global temperatures. But they could not recreate the world as it had been before the alarming increase in carbon dioxide levels to the predictable climates on which agriculture and industry and different urban civilisations have come to depend.

The models predicted that instead of increasing with potentially disastrous outcomes, seasonal rains would diminish, with equally damaging consequences. A reduction in normal sunlight would mean less evaporation. Plants would on balance respond to increased carbon dioxide levels by closing their stomata, or pores, thus transpiring less water.

Monsoon rains in East Asia would fall by 6%, in South Africa by 5%, in North America by 7%, and in South America by 6%. These differences don’t sound huge – but many millions could starve as a result of the changes.

“Geo-engineering the planet doesn’t cure the problem. Even if one of these techniques could keep global temperatures approximately balanced, precipitation would not return to normal conditions,” said Dr Tilmes. “What we do know is that our climate is very complex, that human activity is making the planet warmer and that any technological fix we might try to shade the planet could have unforeseen consequences.” – Climate News Network