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Climate costs ‘may prove much higher’

April 16, 2014 in Atlantic Multidecadal Oscillation, Economy, Greenhouse Gases, Methane, Permafrost, Warming slowdown


A meat store built in the melting  permafrost of Herschel Island in the Arctic Ocean Image: Ansgar Walk via Wikimedia Commons

A meat store built in the melting permafrost of Herschel Island in the Arctic Ocean
Image: Ansgar Walk via Wikimedia Commons

By Tim Radford

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

Hotter extremes belie warming ‘pause’

March 1, 2014 in El Niño, Ocean Warming, Trade Winds, Warming slowdown


California's Death Valley is among the world's hottest places - but many are steadily getting hotter still Image: Pandat at de.wikipedia via Wikimedia Commons

California’s Death Valley is among the world’s hottest places – but many are steadily getting hotter still
Image: Pandat at de.wikipedia via Wikimedia Commons

By Tim Radford

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

Trade winds draw ‘missing’ warmth to deep ocean

February 10, 2014 in Deep Ocean, Ocean Warming, Pacific Ocean, Trade Winds, Warming slowdown


The trade winds make their mark on Hawaii - and they may explain where the "missing" warmth has gone Image: Richard B. Mieremet, Senior Advisor, NOAA OSDIA

The trade winds make their mark on Hawaii – and they may explain where the “missing” warmth has gone
Image: Richard B. Mieremet, Senior Advisor, NOAA OSDIA

By Tim Radford

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

There’s no warming standstill says WMO

February 5, 2014 in Climate risk, El Niño, Temperature Increase, Warming slowdown


Aerial fire-fighting in Australia, which in 2013 had its hottest year on record Image: Bidgee via Wikimedia Commons

Aerial fire-fighting in Australia, which in 2013 had its hottest year on record
Image: Bidgee via Wikimedia Commons

By Alex Kirby

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

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

World went on warming in 2013

January 3, 2014 in Climate, Climate deniers, Temperature Increase, United Kingdom, Warming, Warming slowdown


It still means it: Five years after the 2007/8 drought, Australia ran dry again Image: Peripitus via Wikimedia Commons

It still means it: Five years after the 2007/8 drought, Australia ran dry again
Image: Peripitus via Wikimedia Commons

By Alex Kirby

British climate scientists think 2013 will prove to have been one of the warmest recorded, and they expect 2014 to continue the trend.

LONDON, 3 January – The global average temperature in 2014 is expected to make it one of the warmest years on record, according to the UK Met Office.

It says in its annual global temperature forecast that 2014 will probably be between 0.43°C and 0.71°C warmer than the long-term (1961-1990) average of 14.0°C, with a central estimate of 0.57°C.

Allowing for uncertainty in the forecast, it expects 2014 will be one of the warmest ten years in the record, which goes back to 1880. The forecast range and central estimate for 2014 are the same as were forecast by the Met Office for 2013.

Using observations up to the end of last October, the Met Office estimated the 2013 global average temperature anomaly at between 0.39°C and 0.59°C, with a central estimate of 0.49°C. Using this central estimate, 2013 currently ranks as the ninth warmest year on record, but final figures for the whole year will not be available until March 2014.

The current central estimate of the global temperature for 2013 is within the range forecast by the Met Office last year. 2013 is also in the top ten warmest years and is more likely than not to be warmer than 2012, both of which were predicted in last year’s global average temperature forecast.

Observationally-based estimates of global average temperature are an average of the three main global temperature datasets, which are compiled by the Met Office and University of East Anglia (HadCRUT4), NOAA National Climatic Data Center (NOAA NCDC) and NASA Goddard Institute of Space Studies (NASA GISS).

This table shows the 10 warmest years globally ranked according to their central estimates. 2013 includes data only from January to October, so it may change. All temperatures from observations have an uncertainty range of ± 0.1°C. The anomaly is in °C above the long-term (1961-1990) average of 14.0°C.


Rank        Year            WMO Global Temperature Anomaly

1        2010                    0.56

2        2005                    0.55

3        1998                    0.52

4        2003                    0.51

5        2002                    0.50

6        2007                    0.50

7        2006                    0.49

8        2009                    0.49

9        2013 (Jan-Oct)    0.49

10      2012                    0.47

Source: Met Office


By contrast, the world’s longest instrumental temperature record, which charts English temperatures over the last 350 years, is expected to show that part of southern Britain was colder than recent years in 2013.

The Central England Temperature (CET) dataset has been recording monthly temperatures across the English Midlands since 1659, and daily temperatures since 1772.

The website Not a lot of people know that says the data show that 2013 “was the second coldest since 1996, second only to 2010, one of the coldest years of the last century”. The site describes its role as being based on the realisation that “we cannot always rely on what the climate establishment tell us”. – Climate News Network

Deep oceans may be storing heat

November 24, 2013 in Climate, Ocean Warming, Warming, Warming slowdown


View of Pacific Ocean from space. Image:NASA

View of Pacific Ocean from space.

By Tim Radford

More evidence has emerged that the apparent slowdown in the rate of atmospheric warming may be explained by heat absorption in the deep ocean.

LONDON, 24 November –  Far below the surface, the waters of south-east Asia are heating up. A region of the Pacific is now warming at least 15 times faster than at any time in the last 10,000 years. If this finding – so far limited to the depths where the Pacific and Indian Oceans wash into each other – is true for the blue planet as a whole, then the questions of climate change take on a new urgency.

Yair Rosenthal of Rutgers University in New Brunswick and colleagues from the Lamont-Doherty Earth Observatory at Columbia University in New York, and at the Woods Hole Oceanographic Institution in Massachusetts, report in the journal Science that deep ocean warming could right now be taking much of the heat that meteorologists had expected to find in the atmosphere.

In the last few years, even though greenhouse gas levels in the atmosphere have gone up, the rate of increase in global average temperatures has slowed and there is evidence that much of the expected heat is being absorbed by the oceans and carried beneath the surface.

Record in shells

But records of ocean temperatures are patchy, and in any case date back only half a century. Rosenthal and his colleagues decided that they could reliably calculate a pattern of temperature changes by looking at a record of deposition through time.

One little single-celled organism called Hyalinea balthica has evolved to live only at depths of 500 to 1,000 metres. H.balthica makes a microscopic shell, and when it dies, this shell falls to the ocean bottom. It takes the ingredients for the shell from the elements dissolved in the water around it, and the chemical mix available varies with temperature: the warmer the water, the greater the ratio of magnesium to calcium – and this difference is then recorded in the surviving shell.

So the marine sediments around Indonesia preserve a thermal record of changes with time. The scientists studied ocean cores to “read” a pattern of climate change over the last 10,000 years, since the end of the Ice Age. The readings from the sediments mirror a series of already-known climate shifts – a very warm spell at the end of the Ice Age, a “medieval warm period” when vineyards flourished in Britain, and a “Little Ice Age” when rivers like the Thames of London routinely froze.

So equipped with a reliable guide to change the scientists were able to make sense of the changes in the last 60 years. And they found that ocean temperatures, at such depths, had warmed 15 times faster in the last 60 years that they did during the natural warming cycles of the last 10,000.

The research is incomplete, and its chief value may be in helping to improve the models used by climate scientists. But the implication is that the heat that should be registered in the atmosphere is now being absorbed by the deep oceans.

No cause for complacency

This does not mean that climate scientists can stop worrying about global warming. “We may have underestimated the efficiency of the oceans as a storehouse for heat and energy,” Rosenthal said. “It may buy us some time – how much time I don’t really know – to come to terms with climate change. But it’s not going to stop climate change.”

His colleague Braddock Linsley of Lamont-Doherty said: “Our work showed that the intermediate waters in the Pacific had been cooling steadily from about 10,000 years ago. This places the recent warming of the Pacific intermediate waters in temporal context. The trend has now reversed in a big way and the deep ocean is warming.” – Climate News Network

Warming is twice as fast – or half

November 21, 2013 in Arctic, CFCs, Climate Sensitivity, El Niño, Ozone, Warming slowdown


Alaska's North Slope: Scientists think some Arctic warming may be going undetected Image: US NOAA vis Wikimedia Commons

Alaska’s North Slope: Scientists think some Arctic warming may be going undetected
Image: US NOAA vis Wikimedia Commons

By Tim Radford

The world may be warming more than twice as fast as thought because some key data has been overlooked, two scientists argue. But others think seasonal changes in the Pacific have led to an over-estimate of the warming.

LONDON, 21 November – Two scientists have yet another explanation for the apparent slowdown in global warming: the meteorologists just haven’t been looking in the right places. And two climate researchers in Alabama have a counter proposal: the influence of a natural cycle of warming and cooling in the Pacific is more powerful than anybody first thought and right now, the ocean is in a cooling phase.

First, a restatement of the puzzle: carbon dioxide emissions in the atmosphere are increasing. Carbon dioxide traps infrared radiation, which means that the planet warms. From 1970 to 1998, average global temperatures rose at a rate of 0.17°C per decade. Since 1999, the rate of warming has slowed to 0.04°C per decade.

But the world is still burning fossil fuels. The planet ought to be hotter by now than the measurements suggest. Where is the missing heat?

Global warming sceptics scoffed and claimed that climate scientists had been wrong all along. Climate scientists patiently explained that the heat must be going somewhere, perhaps into the deep oceans far below the surface.

One team recently proposed that the apparent slowdown could be a consequence of the phasing out of ozone-destroying chlorofluorocarbon (CFC) refrigerant gases: these were released in small quantities but were very potent greenhouse gases.

Yet another group suggested that there was a long-term cycle of fluctuation – they called it the stadium wave theory – that meteorologists had simply not yet noticed, because climate records were all relatively recent.

No warming pause detected

And now Kevin Cowtan, a computational scientist at the University of York in the United Kingdom, and Robert Way of the University of Ottawa in Canada have put forward yet another suggestion. They propose, in the Quarterly Journal of the Royal Meteorological Society, that the warming is there but is not being measured.

The dataset used by the UK Met Office, for instance, covers five sixths of the globe – but some of the missing one-sixth is around the Arctic Circle, and that might be crucial. The Arctic is warming at about eight times the rate of the rest of the planet and the polar ice is in dramatic retreat.

Data tends to be collected most intensely where the scientists are based, which is why parts of Africa and the very high latitudes are not well-represented in the measurements. So Cowtan and Way reconstructed the “missing” global temperatures with observations from satellites and surface data from weather stations and ships around the unsampled regions.

And they conclude that with this extra, hitherto absent information, the world could be warming at two and a half times the rate that the Met Office findings suggest.

Cowtan is not a climate scientist, although his calculations are good enough for a respected meteorological journal, and in any case the conclusions are tentative. He says: “There’s a perception that global warming has stopped, but in fact our data suggests otherwise.

“The reality is that 16 years is too short a period to draw a reliable conclusion. We find only weak evidence of any change in the rate of global warming.”

Climate sensitivity halved?

But across the Atlantic at the University of Alabama in Huntsville, Roy Spencer and Danny Braswell propose another explanation. More frequent natural cooling in the oceans – these are the so-called La Niña events – could be offsetting any expected global warming.

Conversely, some of the already observed global warming since 1950 could be a consequence of a series of sweltering El Niño events in the Pacific up to 1998. El Niño means The Child, and Spanish-speaking fishermen gave the phenomenon that name because it tends to occur around Christmastide.

These natural cycles of warming and cooling in the oceans complicate the picture and cause head-scratching among climate researchers, but they also present much more alarming portents for farmers and townspeople on both sides of the Pacific, and far beyond, as weather patterns reverse, fish catches fail, tropical rainforests catch fire, harvests shrivel, normally dry and sunny coasts become flooded and so on.

Spencer and Braswell’s research, published in the Asia-Pacific Journal of Atmospheric Sciences, is also based on computational calculation, but it reveals a pattern of change in cloud cover that if confirmed might make a serious difference to long-term climate projections.

During La Niña events, global cloud cover increases, and more solar energy is reflected back into space, with a consequent lowering of global average temperatures. During an El Niño event, the skies are clearer, and the world palpably hotter.

“As a result, because as much as 50% of the warming could be attributed to stronger El Niño activity, it suggests that the climate system is only about half as sensitive to increasing CO2 as previously believed,” said Spencer. – Climate News Network

Saving ozone may slow warming rate

November 10, 2013 in Atlantic Multidecadal Oscillation, CFCs, Ozone, Warming slowdown

EMBARGOED until 1800 GMT on Sunday 10 November

Stadium wave: One possible clue to this century's apparent warming slow-down Image: Florian K via Wikimedia Commons

Stadium wave: One possible clue to this century’s apparent warming slow-down
Image: Florian K via Wikimedia Commons

By Tim Radford

What appears to be a slowdown in the rate of atmospheric warming this century may have a simple explanation, Mexican scientists say. It could be the consequence of protecting the ozone layer.

LONDON, 10 November – Scientists who looked at the whole history of climate in the 20th century have come up with a new possible explanation for the apparent slowdown in global warming. It is because, they say, of the Montreal Protocol that banned chlorofluorocarbons, also known as CFCs, and saved the ozone layer.

The ozone layer was the second great atmospheric crisis of the late 20th century (the first involved the urban smog and acid rain that triggered clean air legislation in Europe and the US). CFCs were the safe, enduring gases used as refrigerants: their only problem was that – once they reached the stratosphere – they unexpectedly began to destroy the ozone layer that screens out harmful ultraviolet light.

Within four years of the dramatic discovery of a huge “hole” in the ozone layer over the Antarctic, these gases were phased out, in a rare act of international agreement, by the 1989 Montreal Protocol.

But CFCs had a second unexpected property. They were greenhouse gases of unusual potency: molecule for molecule, one of them was rated at more than 17,000 times more effective at trapping infra-red radiation than carbon dioxide. CFCs were released only in comparatively tiny quantities, but they were calculated to account for up to 24% of global warming.

Francisco Estrada of the National Autonomous University of Mexico and colleagues report in Nature Geoscience that they spotted the signal of the missing CFCs when they used statistical analysis to examine average temperature records in the two hemispheres from 1880 to 2010.

Tentative results, clear pattern

Exercises such as these are not simple: the scientists had to find a way of eliminating natural cycles that keep the weather in a permanent pattern of change, and identify long-term trends that could be identified as evidence of human activity.

In the first place, for a mix of reasons, rates of change in the two hemispheres are out of step; in the second place there are natural cycles linked to ocean and atmospheric circulation such as the Atlantic Multidecadal Oscillation that are associated with extended periods of warming and cooling; in the third place things like greenhouse gas emissions are tied into cycles of economic growth, and affected again in many cases by legislation, perhaps to reduce the aerosols that make citizens cough and splutter, but that also block sunlight and have a mild cooling effect.

And to get the results that they did, the researchers had to use advanced statistical methods (for example, they say, the “Perron-Yabu testing procedure, valid with integrated or stationary noise”) that would baffle most of the human race.

So like all research results, the findings are tentative and published to provoke more research. But even so, the graphs in Nature Geoscience show a pattern of human influence in global average temperatures.

In the last century, the planet warmed overall by 0.8°C. In the trend discernible in the sometimes dramatic oscillations of temperature, there is evidence of a slowdown in this warming during two world wars, and the Great Depression of the 1930s, when world trade came to a standstill, factories closed everywhere, and chimneys stopped smoking.

The authors see a pronounced rise in both greenhouse gas emissions and in global temperatures in the 1960s – the start of sustained global warming. But they also see a distinct slowdown that begins in the 1990s in response to the Montreal Protocol, which began the phase-out of the CFCs and the slow restoration of the ozone screen.

Slowdown caused by humans

The Montreal Protocol is not the only possible explanation for the apparent slowdown. There is also evidence that at least one sector of deep ocean is warming 15 times faster than at any time in the last 10,000 years, which suggests that ocean circulation may be carrying away the heat that meteorologists expected to record in the atmosphere.

Two scientists in October proposed that the slowdown in the rate of global warming could possibly be explained by a much longer-term natural cycle that nobody had yet identified: a climate signal could propagate across the northern hemisphere in a self-organising way, just as the so-called “stadium wave” propagates around a sports arena as excited spectators stand and sit down again.

They say in Climate Dynamics that such a phenomenon could be linked to a brake-and-accelerator pattern of influence of northern sea ice on atmosphere and ocean circulation.

If this pattern exists, it would explain why climate modellers had not predicted the present lull or slowdown in global warming. But the wave itself would have nothing to do with global warming, the two authors say. It would just offer a new perspective for climate science.

The Nature Geoscience paper, however, does once again confirm the link between average temperatures and greenhouse gas emissions. “Paradoxically the recent decrease in warming, presented by global warming sceptics as proof that humankind cannot affect the climate system, is shown to have a direct human origin,” the authors conclude.- Climate News Network

Cooler Pacific ‘is slowing warming’

August 31, 2013 in Pacific decadal oscillation, Science, Warming slowdown


Scientists say the 2011 Texas drought began when the PDO's cooling phase started Image: Erik A. Ellison via Wikimedia Commons

Scientists say the 2011 Texas drought began when the PDO’s cooling phase started
Image: Erik A. Ellison via Wikimedia Commons

By Alex Kirby

Climatologists are puzzled that greenhouse gas emissions continue unabated, while the atmosphere is warming more slowly than they expected. Now two scientists in the US think they know why.

LONDON, 31 August – Scientists believe they have made significant progress towards explaining why global average surface temperatures have risen more slowly this century than previously.

They say cooling waters in the tropical Pacific Ocean have played a large part in slowing recent warming, a finding which challenges those who argue that the slowdown means climate change is not as serious a problem as most climate scientists are convinced it is.

Before 2000 global temperatures had risen at a rate of 0.13ºC per decade since 1950. The hiatus has occurred while levels of carbon dioxide, the main greenhouse gas from human activities, continued a steady rise, reaching 400 parts per million for the first time in human history in May this year.

The eastern tropical Pacific has been distinctly cooler in the last few years, thanks to the influence of one of the world’s biggest ocean circulation systems, the Pacific decadal oscillation (PDO).

The better-known El Niño and La Niña weather systems, which also originate in the Pacific and can affect the weather thousands of miles away, occur just a few years apart. Both are parts of the much bigger PDO, which comes and goes over decade-long timescales.

It is now in a cooling phase which could last for years – the last one stretched from the 1940s to the 1970s when warmer, drier weather dominated in the midwestern US. During this period global average temperatures cooled by about 0.2°C before resuming their rapid climb.

‘Compelling’ research

In such a phase the temperature of the eastern Pacific’s waters falls while those in the west warm. In the oscillation’s warming phases this is reversed. In winter the PDO’s cooler phase lowers northern hemisphere temperatures slightly, but in the summer this cooling has less impact.

The scientists are from the Scripps Institution of Oceanography in California. Their study is published in the journal Nature. Dan Barrie, programme manager at the US National Oceanic and Atmospheric Administration (NOAA), which supported their research, called it “compelling” and said: “[It] provides a powerful illustration of how the remote eastern tropical Pacific guides the behaviour of the global ocean-atmosphere system, in this case exhibiting a discernible influence on the recent hiatus in global warming.”

The Scripps team, using computer models, compared their results with observations and concluded that global average annual temperatures have been lower than they would otherwise have been because of the oscillation.

But they say the observed recent higher summer temperatures show more of the true effects of global warming. Global average temperatures are calculated over the whole year, blurring the effect of this seasonal variation.

Shang-Ping Xie, professor of environmental science at Scripps and co-author of the study, said: “In summer, the equatorial Pacific’s grip on the northern hemisphere loosens, and the increased greenhouse gases continue to warm temperatures, causing record heat waves and unprecedented Arctic sea ice retreat.”

Oceans’ key role

Dr Alex Sen Gupta, of the Climate Change Research Centre at the University of New South Wales, who was not part of the study team, told the London Guardian: “The authors have set up some elegant experiments using a climate model to test whether a natural oscillation that has gone through a large swing in the tropical Pacific Ocean over the last decade can explain the recent halt in surface global warming…

“…[T]he new simulation accurately reproduces the timing and pattern of changes that have occurred over the last four decades with remarkable skill. This clearly shows that the recent slowdown is a consequence of a natural oscillation.”

Research shows that much of the heat caused by global warming has been absorbed by the oceans, and about a third of the extra carbon dioxide emitted since the Industrial Revolution.

Scientists also think the heat is not staying near the ocean surface but is now penetrating to deeper water, and that this may be another factor which can create the impression of a slowdown in global warming. In any case, they say, the slower pace of recent warming is easily explained by natural climate variability – such as the PDO.

The Scripps scientists say that when the PDO’s cooling phase ends the growth of global average temperatures is likely to resume, perhaps faster than before as greenhouse gas emission rates will be higher. – Climate News Network