Atlantic depths may hold key to heat hiatus

Atlantic depths may hold key to heat hiatus

Researchers analysing millions of oceanographic measurements believe they may finally have got to the bottom of the conundrum about why there is a slowdown in global warming despite greenhouse gas emissions rising.

LONDON, 22 August, 2014 − For years, researchers have puzzled over the temperature rises that haven’t happened – but scientists in China and the US believe they have cracked the mystery of the missing heat.

While calculations indicate that global average temperatures should be rising predictably, the planetary thermometers tell a different story.

But now Xianyao Chen, an oceanographer at the Ocean University of China in Qingdao, and Ka-Kit Tung, an atmospheric scientist at the University of Washington in Seattle, report in Science journal that they think they know where the notional extra heat has gone. It is at the bottom of the Atlantic Ocean.

And this time their conclusion isn’t based only on mathematical models and computer simulations. In their research − funded by the US National Science Foundation and the National Natural Science Foundation of China – they analysed millions of measurements of temperature and salinity taken by oceanographic instruments since 1970, and tracked the pathways that the heat must have taken since the beginning of the 21st century.

High temperatures

But first, a restatement of the conundrum. For more than a century, climate scientists have known that higher levels of carbon dioxide in the atmosphere mean higher atmospheric temperatures. For more than 30 years, every investigation has confirmed this link. And for the last 30 years of the 20th century, as greenhouse gas emissions increased, so did average temperatures.

This rise has continued, with 13 of the 14 warmest years ever recorded all falling in the 21st century, but the rate of increase unexpectedly slowed.

Researchers had expected that there would be some sort of heat hiatus, but not during the first years of the century, and they have been scratching their heads and examining the data again.

Some think that the measurements may be incomplete, or that natural cycles, such as the Pacific cooling event called La Niña, may be at play. Some have suggested that the pattern of trade winds may have a role in taking the warmth into the deep ocean, and some have suspected all along that the heat could be found far below the oceanic surface.

In the same week as the publication in Science, Reto  Knutti, a climate physicist at the federal technology institute ETH Zurich, and his colleague, Markus Huber, reported in Nature Geoscience that the apparent slowdown could be attributed to a cocktail of causes: a longer period of weaker solar irradiance – the sun has its own cycles of intensity − and to the cycle of El Niño and La Niña weather phenomena in the Pacific, and also to incompletely measured data.

“Many of the earlier papers had focused on
symptoms at the surface of the Earth”

But the Science report authors think they have an in-depth solution. “Every week, there’s a new explanation of the hiatus,” said Ka-Kit Tung. “Many of the earlier papers had focused on symptoms at the surface of the Earth, where we see many different and related phenomena. We looked at observations in the ocean to try to find an underlying cause.”

The oceans cover 70% of the planet, and are capable of storing 90% of the planet’s heat content. So the two Science report authors argue that a sudden shift in ocean salinity that corresponded with the slowdown of global warming could have triggered the movement of the heat to much deeper waters.

Saltier water is denser, sinks faster, and takes surface heat with it. As the two scientists see it, the depths of the North and South Atlantic have absorbed more heat in the last 14 years than the rest of the global ocean system put together.

This does not mean that global warming is not a problem: heat in the deep oceans is likely to come back to the surface, and to the atmosphere, sooner or later.

Natural cycle

The changes in the Atlantic ocean circulation system are part of a natural cycle that seems to date back many centuries. The surprise discovery by Chen and Tung is that the heat is tucked away in the Atlantic and Southern Oceans, rather than the Pacific − the suspected hiding place until now.

The argument is a complex one, and the latest research probably hasn’t settled the matter.

“All these analyses of ocean heat content are interpreting small changes in ocean temperature, and it will need to be picked over and repeated by others before being fully accepted,” said Professor Andrew Watson, head of the Marine and Atmospheric Science group at the University of Exeter, UK.

And Piers Forster, professor of climate change at the University of Leeds in the UK, said: “Most importantly, this paper is another nail in the coffin of the idea that the hiatus is evidence that our projections of long-term climate change need revising down.

“Variability in the ocean will not affect long-term climate trends, but may mean we have a period of accelerated warming to look forward to.” – Climate News Network

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Climate change heralds end of civilisations

Climate change heralds end of civilisations

New research supports the growing body of evidence that many past civilisations have collapsed because of climate change. So is history repeating itself?

LONDON, 13 August, 2014 –  Scientists looking at what is known as the “Fertile Crescent” of ancient Mesopotamia have found new evidence that drought caused by climate change brings an end to civilisations.

It is the latest study that confirms the threat posed to present civilisations in Africa, Asia and parts of the United States by changes in rainfall pattern that could lead to the abandonment of once-fertile areas − and the cities that once were fed by them.

The focus of research by a team from Tübingen University, Germany, is the area currently part of Iraq and the Persian Gulf where the development of ancient agriculture led to the rise of large cities.

Evidence from grain samples up to 12,000 years old shows that while the weather was good, the soil fertile and the irrigation system well managed, civilisation grew and prospered. When the climate changed and rainfall became intermittent, agriculture collapsed and the cities were abandoned.

Analysed grains

Dr Simone Riehl, of the Institute for Archaeological Sciences and the Senckenberg Center for Human Evolution and Palaeoenvironment at Tübingen University, analysed grains of barley up to 12,000 years old from 33 locations across the Fertile Crescent to find out if they had had enough water while growing and ripening.

The 1,037 ancient samples were between 12,000 and 2,500 years old. They were compared with modern samples from 13 locations in the former Fertile Crescent.

Dr. Riehl and her team measured the grains’ content of two stable carbon isotopes.

When barley grass gets insufficient water while growing, the proportion of heavier carbon isotopes deposited in its cells will be higher than normal. The two isotopes 12C and 13C remain stable for thousands of years and can be measured precisely – giving Riehl and her colleagues reliable information on the availability of water while the plants were growing.

They found that many settlements were affected by drought linked to major climate fluctuations. “Geographic factors and technologies introduced by humans played a big role and influenced societies’ options for development, as well as their particular ways of dealing with drought,” Riehl says.

Her findings indicate that harvests in coastal regions of the northern Levant, at the eastern end of the Mediterranean Sea, were little affected by drought. But further inland, drought led to the need for irrigation or, in extreme cases, abandonment of the settlement.

The findings give archaeologists clues as to how early agricultural societies dealt with climate fluctuations and differing local environments. “They can also help evaluate current conditions in regions with a high risk of crop failures,” Riehl adds.

The study is part of a project, backed by the German Research Foundation, looking into the conditions under which Ancient Near Eastern societies rose and fell.

Scientists carrying out similar research in the Indus Valley, in present Pakistan and north-west India, home to the Harappan Civilisation, also believe that drought was the cause of the civilisation’s demise.

It was characterised by large, well-planned cities with advanced municipal sanitation systems and a script that has never been deciphered. But the Harappans seemed to slowly lose their urban cohesion, and their cities were gradually abandoned.

Cities abandoned

According to an article in Nature in March, a 200-year drought, caused by the failure of the monsoon, led to the abandonment of the cities and the end of the civilisation.

Across the Atlantic, another puzzle was the loss of the Mayan cities and culture in Central America. This was a people that had the time, money and manpower to build massive temples and cities for a population estimated at 13 million.

Many theories have been put forward as to why, over a period of about 200 years from 750 to 950AD, the Mayans abandoned their way of life. Research on the subject by Sigma Xi, The Scientific Research Society, says that a series of droughts caused by local climate change was the cause.

With the latest report of the Intergovernmental Panel on Climate Change predicting a faltering of the monsoon that is vital for the Indian sub-continent’s ability to feed itself, it seems as though history could repeat itself. Certainly, some people in India believe it could happen unless action to curb climate change is taken.

Environmental refugees in Africa are also seen as victims of changing weather patterns, and California is suffering a three-year drought that is badly affecting water supplies in this most prosperous of American states. – Climate News Network

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Data adds to confusion over polar sea ice

Data adds to confusion over polar sea ice

Possible errors in the interpretation of satellite data may help to explain scientists’ puzzlement over indications that sea ice cover is apparently increasing in the Antarctic, but is shrinking visibly in the Arctic.

LONDON, 26 July, 2014 − Scientists believe they may have found explanations for two inconsistencies in their understanding of global warming.

One cause for head scratching is in the Antarctic, where the sea ice seems to be getting bigger when it ought to be shrinking, and another has been the apparent slowdown overall in the rate of global warming for the last decade.

Climate scientists around the world have been picking away at both puzzles, and not just because climate sceptics and energy industry lobbyists use them as ammunition to argue that global warming is not a problem at all. Scientists are naturally unhappy when data doesn’t match their predictions − and they want to know the reason why.

The Antarctic problem is hard to miss. The Arctic Ocean sea ice is shrinking visibly, and the entire sea could be ice-free most summers in a few decades. But even though there is clear evidence from separate sources that West Antarctica is responding to climate change, the southern hemisphere ice cover, overall, has been increasing.

Or has it? Ian Eisenman, a climatologist at the Scripps Institution of Oceanography at the University of California San Diego, begs to differ. He and colleagues report, in The Cryosphere journal, that it could be due to an error in the way satellite data is processed.

Spliced together

Scientists have been using satellite data to check sea ice cover for 35 years. But the data does not come from one instrument on just one satellite: observations transmitted from a series of satellites have been spliced together.

One report from the Intergovernmental Panel on Climate Change said the sea ice cover was more or less constant, but a later report said it had grown by 16,500 square kilometers a year between 1979 and 2012.

“When we looked at how the numbers reported for the trend had changed, and we looked at the time series of Antarctic sea ice, it didn’t look right,” Dr Eisenman said.

The researchers think that the difference between the two datasets might be linked to a change in satellite sensors in 1991, and the way the data collected by the two instruments was calibrated. What the Scripps team has done is identify a source of possible error, but it hasn’t settled the question one way or the other.

Since the Arctic and Antarctic are very different places, it would be unrealistic to expect the patterns of melting to be the same. And it may still be that southern hemisphere sea ice is growing.

However, while that question remains open, there is less doubt about the long slowdown in the rate of average global warming during the 21st century.

Missing heat

Separate teams of researchers have proposed a series of possible explanations for the failure of the climate to keep up with the projections of the climate scientists. These have included the suggestion that the missing heat may be “concealed” in the deep oceans, and that a pause in warming was going to happen anyway, but it just happened earlier than anyone expected.

Shaun Lovejoy, professor of physics at McGill University in Canada, reports in Geophysical Research Letters that there is yet another explanation. He argues, from statistical analysis, that coincidentally with the increase in man-made emissions of greenhouse gases, there has been a natural cycle at work, and that the most recent human impact on climate has been damped down by a cooling phase.

He had already ruled out with 99% certainty the possibility that natural variation could explain all the ups and downs of global average temperatures since 1800. This time he used the same statistical approach to the data for the 15 years from 1998 to the present.

His research suggests that there has been a natural cooling of 0.28°C to 0.37°C since 1998, which is in line with natural variations that occur every 20 to 50 years. “The pause has a convincing statistical explanation,” Lovejoy says. – Climate News Network

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How nature affects the carbon cycle

How nature affects the carbon cycle

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In Australia and the Arctic, scientists say, they have found unexpected ways in which natural processes are helping to compensate for global warming.

LONDON, 1 June – The great drylands of the planet – and they cover almost half of the terrestrial surface – may be bigger players in the carbon cycle than anyone had suspected. The world’s semi-arid regions may absorb huge volumes of carbon dioxide from the atmosphere whenever it rains enough.

Benjamin Poulter of Montana State University and colleagues report in Nature that they used a mix of computer-driven accounting methods to work out where the carbon goes after fossil fuel burning emits extra carbon dioxide into the atmosphere. Decades of meticulous measurement confirm that, overall, carbon dioxide levels are increasing inexorably, and the world is warming accordingly.

But inside this big picture is a lot of seasonal and inter-annual variation. So climate scientists, when they try to work out what all this means for future climates, need to understand the carbon cycle better.

The assumption has always been that the most important terrestrial consumers of carbon dioxide were the tropical rainforests. But the match of terrestrial biogeochemical and atmospheric carbon dioxide and global carbon budget accounting models by 13 scientists from the US, Europe and Australia has revealed a different story.

In 2011 more than half of the terrestrial world’s carbon uptake was in the southern hemisphere – which is unexpected because most of the planet’s land surface is in the northern hemisphere – and 60% of this was in Australia.

Natural brake

That is, after a procession of unusually rainy years, and catastrophic flooding, the vegetation burst forth and the normally empty arid centre of Australia bloomed. Vegetation cover expanded by 6%.

Human activity now puts 10 billion tonnes of carbon into the atmosphere annually, and vegetation in 2011 mopped up 4.1 billion tonnes of that, mostly in Australia.

There remains a great deal of uncertainty about the carbon cycle and how the soils and the trees manage the extra carbon. Nobody knows what will happen to this extra carbon now in the hot dry landscapes of Australia: will it be tucked away in the soil? Will it be returned to the atmosphere by subsequent bushfires? As scientists are fond of saying, more research is necessary.

But this is an example of negative feedback: as carbon dioxide levels and temperatures rise, the green things respond, and slow the acceleration of both. This is quite different from the positive feedback that follows when Arctic ice – which reflects sunlight – melts and gives way to blue water which absorbs solar energy, thus accelerating the melting.

But even the slow disaster of the polar regions could be accompanied by an ameliorating process. British researchers report in Nature Communications that the ice sheet meltwaters may be rich in iron. A boost of iron would stimulate phytoplankton growth, which means more carbon dioxide could accordingly be absorbed from the atmosphere.

Feeding the oceans

The scientists collected meltwater from a Greenland glacier in the summer of 2012, and then tested it to discover significant quantities of what geochemists call “bio-available” iron.

So, in another example of those cycles of the elements that make the world go round, ice that scrapes over rock also delivers vital nutrients to the sea, for marine plants to take up yet more carbon dioxide and flourish more vigorously in the oceans and keep the planet a little cooler.

The Greenland research gives scientists a chance to estimate more accurately the delivery of this dietary supplement to the oceans: they reckon somewhere between 400,000 and 2.5 million tonnes a year in Greenland and somewhere between 60,000 and 100,000 tonnes in Antarctica. Or, to put it more graphically, it would be like dropping 3,000 fully-laden Boeing 747s into the ocean each year.

“The Greenland and Antarctic ice sheets cover around 10% of the global land surface,” said Jon Hawkings, of the University of Bristol, UK. “Our finding that there is also significant iron discharged in runoff from large ice sheet catchments is new. This means that relatively high concentrations are released from the ice sheet all summer, providing a continuous source of iron to the coastal ocean.” – Climate News Network

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Borneo’s mystery trees guzzle carbon

Borneo’s mystery trees guzzle carbon

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Scientists discover that the unique and mysterious trees of  Borneo’s tropical rainforest − being felled at an alarming rate − soak up even more carbon than those in Amazonia and have a vital role to play in slowing down global warming

LONDON,  11 May −  If there was just one place in the world where it would make sense to protect trees, maintain the rainforest and damp down global warming, scientists have confirmed that it would be the island of Borneo.

A new research report published in the Journal of Ecology says that while the Amazon rainforest might be the biggest and most important area of green canopy on the planet,  Borneo soaks up, tree for tree, more carbon from the atmosphere.

Lindsay Banin, an ecologist at the UK-based Centre for Ecology and Hydrology (CEU), and colleagues from Malaysia, Brunei, the US, Brazil, Taiwan, Peru and Ecuador investigated what is called above-ground wood production  – the most visible, tangible indicator of carbon uptake – to see how forests in Amazonia and Indonesia measured up as consumers of atmospheric carbon.

The tropical rainforests cover only a tenth of the planet’s land surface, but they account for about a third of the terrestrial primary production – that is, about a third of the conversion of sunlight into greenery happens in the tropical forests – and they soak up about half of all terrestrial carbon.

Vigorous consumers

However, it turns out that some tropical forests are more vigorous consumers than others. The Amazon and the Borneo forests have similarities – for example, neither has an annual dry season, and each has a range of soil types. So if there is a difference, it must be in the trees.

The researchers examined data from 17 plots in Amazonia and 11 in Borneo, with a total of 12,000 trees − all of which have been monitored for more than  two decades.

They found that the woody growth in north Borneo was almost half as much again (49%) as in the north-west Amazon. South-east Asian trees of a given diameter were taller than Amazon trees, which meant they amassed a greater volume of wood. On average, the south-east Asian plots grew 3.2 tons of wood per hectare more than the South American plots.

The research matters because climate scientists still have an uncertain picture of the carbon cycle. Simulations of future temperatures depend on what happens to carbon dioxide emissions, and how vigorously the natural world responds to all that extra potential fertility.

There has been recent concern that higher temperatures and changes in rainfall pattern could drastically alter the rainforests in the Congo and in the Amazon rainforests.

But there is also evidence that mature forests, with a high population of elderly giant trees, can still soak up surprising quantities of carbon dioxide.

Alarming rate of loss

On the debit side, Borneo has been losing its primal forest cover at an alarming rate. More than half of the lowland forests of Kalimantan – the equivalent of an area the size of Belgium − were felled for timber between 1985 and 2001.

If trees in Borneo grow faster than anywhere else in the tropics, then any loss of those trees is likely to accelerate global warming.

The next step in the research is to try to figure out what Borneo has that Amazonia hasn’t.

The difference can be linked to local evolutionary history and the types of trees that flourish in each region.

“In Borneo, dipterocarps – a family of large trees with winged seeds – produce wood more quickly than their neighbours,” said Dr Banin, lead author of the CEU report. “This means that they have evolved something special and unique – and what this is exactly remains a mystery.

“Dipterocarps are known to make special relationships with fungi in the soil, so they may be able to tap into scarce nutrient resources. Or they may be trading off growth of other plant parts.” – Climate News Network

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Climate costs ‘may prove much higher’

Climate costs 'may prove much higher'

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There may be a higher price for our descendants to pay for the greenhouse gas build-up, researchers say, as the real costs are updated.

LONDON, 16 April – Economists and scientists may have seriously underestimated the “social cost” of carbon emissions to future generations, according to a warning in Nature.

Social cost is a calculation in US dollars of the future damage that might be done by the emission of one metric ton of carbon dioxide as greenhouse gas levels soar and climates change, sea levels rise and temperature records are broken in future decades.

How much would society save if it didn’t emit that tonne of CO2? One recent US estimate is $37. Such a measure helps civil servants, businessmen and ministers to calculate the impact of steps that might be taken.

On the other hand, say Richard Revesz of New York University School of Law and US and Swedish colleagues, assumptions of cost per tonne – and these range from $12 to $64 according to various calculations – are based on models that need to be improved and extended. The cost of climate change could be higher, for four reasons.

Flawed assumptions

The impact of historic temperature variation suggests societies and economies may be more vulnerable than the models predict, and in this case weather variability is more important than average weather – because crop yields are vulnerable to extremes of temperature.

Then the models omit the damage to productivity, and to the value of capital stock, because of lower growth rates: as these lower growth rates compound each other, human welfare will begin to decline. And that’s without factoring in climate-induced wars, coups or societal collapse.

Third, the models assume that the value people attach to ecosystems (and water is an ecosystem service) remains constant. But, they point out, as commodities become scarce, value increases, so the costs of ecosystem damage will rise faster than models predict.

Finally, the models assume that a constant discount rate can translate future harms into today’s dollars. But discount rates of the future may not be constant.

More warming

“What now?” they ask. “Modellers, scientists and environmental economists must continue to step outside their silos and work together to identify research gaps and modelling limitations.”

They hint at an even deeper problem: the basis of the social harm costs dates from calculations more than 20 years old, and is predicated on an average global warming of less than 3°C. Yet without mitigation, the Intergovernmental Panel on Climate Change projects a warming of 4°C by the end of the century.

“If warming continues unchecked into the twenty-second century, it could render parts of the planet effectively uninhabitable during the hottest days of summer, with consequences that would be challenging to monetize,” they write.

Economic harm may not be the only thing underestimated. Michael Mann, a meteorologist at Penn State University in the US, reports in Geophysical Research Letters that the so-called “slowdown” in global warming during this decade  could be because of an underestimate of the impact of a meteorological monster called the Atlantic Multidecadal Oscillation (AMO), an oceanographic cycle of warming and cooling that delivers natural change in northern hemisphere weather patterns.

More methane

A misreading of this cycle – probably because scientists have not known about it for long – could account for this apparent slowdown. “Some researchers in the past attributed a portion of Northern Hemispheric warming to a warm phase of the AMO,” said Professor Mann.

“The true AMO signal, instead, appears likely to have been in a cooling phase in recent decades, offsetting some of the anthropogenic warming temporarily.” And when the rate of warming rises again, there’s yet more alarming evidence of possible acceleration, according to new research.

The thawing of the Arctic sea ice is also accompanied by a softening and warming of the Arctic permafrost, and changes in the chemistry of the preserved peat, that could release ever larger amounts of methane. Methane is a greenhouse gas, present in smaller quantities than carbon dioxide, but 34 times more potent as a warming agent over 100 years.

If the permafrost melts entirely, that would put five times the present levels of carbon into the atmosphere, US researchers report in the journal Proceedings of the National Academy of Sciences.

“The world is getting warmer, and the additional release of gas would only add to our problems,” said Jeff Chanton of Florida State University, a co-author. – Climate News Network

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Hotter extremes belie warming ‘pause’

Hotter extremes belie warming 'pause'

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Increasing and more frequent extremes of heat affecting wider regions, scientists say, are evidence that it is misleading to claim that climate change has paused.

LONDON, 1 March – If global warming has paused, nobody told the thermometer. Although global average temperature rises have not kept pace with greenhouse gas emissions in the last decade, the mercury has been higher than ever for longer than ever over increasingly larger areas of land, according to a new study in Nature Climate Change.

Sonia Seneviratne from the Swiss Federal Institute of Technology in Zurich and colleagues in Australia and Canada chose not to look at averages but at extremes of temperature. The scientists examined daytime extremes from 1979 onwards, and compared the temperatures of any particular day anywhere to an average of daily temperatures between 1979 and 2012, to identify the hottest 10%. Any region might normally expect 36.5 hottest days in a year; that is, hotter than the average.

Then they looked more closely at temperatures from 1997 to 2012. Regions that experienced 10, 30 or 50 extremely hot days above this average saw the greatest upward trends in extreme hot days over time – and over area. That is, not only were people experiencing greater heat extremes, but they were experiencing them over more days and over more extended regions.

And this consistent upward trend persisted right through the so-called “hiatus” of 1998 to 2012. The year 1998, at the time the hottest ever, coincided with a major El Niño event, the peak of a natural cycle of warmth and cooling in the Pacific.

Extreme extremes change most

Thereafter, although 13 of the 14 warmest-ever years have occurred this century, the rate of increase in warming as a global average has fallen. Climate sceptics used the trend to argue that global warming was an illusion, or part of a natural cycle. Dr Seneviratne and her colleagues do not see it that way.

“It quickly became clear the so-called ‘hiatus’ in global average temperatures did not stop the rise in the number, intensity and area of extremely hot days,” said Lisa Alexander of Australia’s Centre of Excellence for Climate System Science.

“Our research has found a steep upward tendency in the temperatures and number of extremely hot days over land and the area they impact, despite the complete absence of a strong El Niño.”

And her colleague Markus Donat added: “There has been no pause in the increase of warmest daily extremes over the land and the most extreme of the extreme conditions are showing the largest change.

“Another interesting aspect of our research was that those regions that normally saw 50 or more excessive hot days in a year saw the greatest increases in land area impact and the frequency of hot days. In short, the hottest extremes got hotter and the events happened more often.”

‘Illusory’ pause

However, perhaps because the world is mostly ocean, and the extremes have been measured over land, the average, year-on-year rises in temperatures have been lower in the last decade than in previous decades. There have been a number of inconclusive explanations for this phenomenon.

Cyclic changes in trade winds are one explanation; another is that the heat is there, but has been stored in the deep ocean, where measurements are not systematically taken. It’s there somewhere, waiting to be found.

And US scientists argue in the latest issue of the journal Science that the oceans may have an even bigger influence on climate than anybody foresaw, and that persistent cool conditions in the tropical Pacific may be behind what they call the “pause in global warming since 2000.”

But the latest Nature Climate Change paper puts the case that this pause or hiatus is illusory with – for a scientific paper – unusual clarity. “Based on existing observational evidence,” the authors say, “we highlight that the term pause, as applied to the recent evolution of global annual mean temperatures, is ill-chosen and even misleading in the context of climate change.

“Indeed, an apparently static global mean temperature can mask large trends in temperatures at both regional and seasonal scales.” – Climate News Network

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Trade winds draw ‘missing’ warmth to deep ocean

Trade winds draw 'missing' warmth to deep ocean

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Contrary to some reports, global warming hasn’t stopped or slowed at all, new research suggests. The trade winds have simply carried the heat into the Pacific Ocean – temporarily.

LONDON, 10 February – Australian and US scientists think they know where a lot of global warming has been concentrated: it has been tucked away below the surface waters of the western Pacific Ocean. And the agency that took the heat out of the atmosphere and transferred it into a liquid form could have been the equatorial trade winds.

Matthew England from the Australian Centre of Excellence for Climate System Science and colleagues report in Nature Climate Change that a dramatic acceleration in the winds has drawn heat from the atmosphere and transferred it to the ocean: cooler waters have risen to the surface to mask the transaction.

Climate sceptics – and some climate scientists – talk about a slowdown, or a pause, or a hiatus in global warming. In fact, temperatures have gone on rising and 13 of the 14 warmest years ever recorded have all occurred since 2000. But the rate of rise in global average temperatures since 2000 has not been as fast as the rate during the 1980s and 1990s.

Since greenhouse gas levels have continued to rise, and since scientists are sure of their atmospheric physics, then there was some “missing heat” to be accounted for.

Researchers have variously suggested that a puzzling increase in deep ocean temperatures could be one explanation or that perhaps the unevenness of temperature measurements around the planet might be another. But both suggestions were hypotheses: nobody had an answer that could be tested by any kind of experiment.

Slower rate

Professor England and colleagues worked with observed winds, surface air temperatures, and a set of ocean climate models to calculate what may have happened.

The global warming story has always been one of fits and starts: a warming that ought to have been observed 70 years ago stalled between 1940 and 1970, and when it resumed, did so in fits and starts. The overall trend continued upward, but the rate of rise slowed noticeably during the last decade.

Ocean circulation loops are driven by winds, and speed up as the winds intensify. Cool waters well up, warm waters descend. And intensify is just what the trade winds have done. They began strengthening during the 1990s, a process which continues today. Once the researchers added the trade winds to their calculations, the global average temperatures looked very like the observations during the hiatus.

They also found that four-fifths of the surface temperature cooling occurred after 2000, which confirmed that wind acceleration was the key contributor.

“Scientists have long suspected that extra ocean heat uptake has slowed the rise of global average temperatures, but the mechanism behind the hiatus remained unclear”, said Professor England.

Rapid rise on the way

“But the heat uptake is by no means permanent: when the trade wind strength returns to normal – as it inevitably will – our research suggests heat will quickly accumulate in the atmosphere. So global temperatures look set to rise rapidly out of the hiatus, returning to the levels projected within as little as a decade.”

The same mechanism could explain the slowdown between 1940 and 1970. In 1938, the British scientist G S Callendar argued that rising carbon dioxide levels should mean global warming but the evidence proved elusive, perhaps because the trade winds accelerated during those decades.

Richard Allan, professor of climate science at the University of Reading in the UK, said the current slowdown was only a temporary reprieve.

“Measurements from satellites and ocean buoys show that the planet is absorbing more heat than it is radiating out to space and the heat is building up in the oceans.

“This new research suggests that when the trade winds weaken again, the planet can expect rapid warming of the surface to resume, as greenhouse gas concentrations continue to rise.” – Climate News Network

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There’s no warming standstill says WMO

There's no warming standstill says WMO

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The head of the World Meteorological Organization tells Climate News Network there is no standstill in global warming, which is on course to continue for generations to come.

LONDON, 5 February – The planet is continuing to warm, with implications for generations ahead, and temperatures are set to rise far into the future, the World Meteorological Organization (WMO) reports.

It says 2013 was among the ten warmest years since modern records began in 1850, equalling 2007 as the sixth warmest year, with a global land and ocean surface temperature 0.50°C above the 1961–1990 average and 0.03°C higher than the most recent 2001–2010 average.

Thirteen of the 14 warmest years on record have all occurred in this century. The warmest years on record are 2010 and 2005, with global temperatures about 0.55 °C above the long-term average, followed by 1998, which also had an exceptionally strong El Niño event.

El Niño events (which intensify warming) and cooling La Niñas are major drivers of natural climate variability. Neither occurred during 2013, which was warmer than 2011 or 2012, when La Niña exerted its cooling influence. 2013 was among the four warmest neutral years recorded, when neither El Niño nor La Niña affected temperatures.

“The global temperature for the year 2013 is consistent with the long-term warming trend”, said WMO Secretary-General Michel Jarraud. “The rate of warming is not uniform but the underlying trend is undeniable. Given the record amounts of greenhouse gases in our atmosphere, global temperatures will continue to rise for generations to come.

“Which standstill? The coldest year since 2001 is warmer than any year before 1998″

“Our action – or inaction – to curb emissions of carbon dioxide and other heat-trapping gases will shape the state of our planet for our children, grandchildren and great-grandchildren”, Mr Jarraud said.

Asked by Climate News Network how WMO regarded claims by some critics that there has been a “global warming standstill since 1997″, Mr Jarraud said: “Which standstill? The coldest year since 2001 is warmer than any year before 1998.

“Each decade is warmer than the previous one. There is global variability from year to year. You have to look at the longer period. If you do that, then the message is beyond any doubt…Despite the fact that there was no El Niño in 2013, it was still the sixth warmest year. This is significant.”

The WMO says surface temperature is just part of a much wider picture of climate change. “More than 90% of the excess heat being caused by human activities is being absorbed by the ocean“, it says.

It has released the temperature data in advance of its full Statement on the Status of the Climate in 2013, to be published in March. This will give more details of regional temperatures and other indicators.

Consistent findings

In contrast with 2012, when the US in particular experienced record high annual temperatures, the warmth in 2013 was most extreme in Australia, which had its hottest year on record.

WMO’s global temperature analysis is based mainly on three independent and complementary datasets. One is maintained by two UK centres, the Met Office Hadley Centre and the Climatic Research Unit at the University of East Anglia. The other two are based in the US: NOAA’s National Climatic Data Center, and the Goddard Institute for Space Studies (GISS), operated by NASA.

Each dataset uses slightly different methods of calculation and so each gave 2013 a different temperature ranking, but they were consistent on the year-by-year changes and the longer warming trends globally.

WMO also uses reanalysis-based data from the European Centre for Medium-Range Weather Forecasts (ECMWF), which showed annual global land and ocean temperature to be the fourth highest on record. – Climate News Network

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2013 was fourth warmest year recorded

2013 was fourth warmest year recorded

FOR IMMEDIATE RELEASE
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

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