Climate Feedback

One of the more irritating aspects, if you will, of global change is that air pollution has so far prevented the planet from warming more rapidly than it actually did. Clean air is of course a good thing. But reducing pollution might expose an as of yet ‘masked’ portion of global warming.

This could have a dramatic affect on the Amazon rainforest. A team led by Peter Cox of the University of Exeter, UK, reports in a paper in this week’s Nature that reductions in aerosol pollution will tremendously increase the risk of severe drought in the Amazon region. Here is an editor’s summary of the paper.

Although it accounts for nearly a quarter of the world's fresh water, drought is not unknown in Amazonia.

In the dry season, from July to October, rainfall in the region is linked to sea surface temperatures (SST) in the tropical Atlantic. In years with a pronounced temperature gradient - warming of the tropical Atlantic north of the equator relative to the south – the normal’ position of high and low atmospheric pressure systems can shift, delaying or suppressing the onset of the South American monsoon.

The effect has been observed in 2005, when large parts of the Amazon region were hit by the worst drought in decades. See a Nature news story by Mike Hopkin here (subscription required) and a New York Times story here about the devastating event.

Cox thinks that the 2005 drought was a harbinger of things to come. Their “simulations for the 21st century show a strong tendency for the SST conditions associated with the 2005 drought to become much more common, owing to continuing reductions in reflective aerosol pollution in the Northern Hemisphere.”

Droughts like in 2005 will happen every two years by 2025, and in nine out of ten years by 2060, the model suggests.

How robust is this dire prediction? The Amazonian climate, for reasons not quite understood, is notoriously difficult to simulate. But the Hadley Centre’s climate model which was used for this study has previously reproduced features of the regional climate with greater accuracy than other models.

In Mike Hopkin's words, “the ultimate fear is that the Amazon forest - often touted as an invaluable piece of armour against climate change - could become part of the problem rather than a key element of the solution. Droughts make it more likely that it will become a net source of greenhouse gases to the atmosphere, rather than mopping them up.”

Quirin Schiermeier

You can vote or comment on the importance of the new paper in the Journal Club of Nature Reports Climate Change.

Posted by Quirin Schiermeier on May 08, 2008
Categories: Biosphere feedbacks, Climate Science, Climate prediction, Extreme Events, Quirin Schiermeier, Topics | Permalink | Comments (4) | TrackBacks (0)

A paper in this week’s Nature predicts that, rather than warming, North Atlantic sea surface temperatures may actually decrease slightly in the next decade. What’s more, the paper suggests global surface temperatures may not actually increase either.

Has global warming stopped? Is this a nail in Al Gore’s coffin?

Well, no.

Despite headlines such as ‘Doubt is cast over global warming’ and ‘Global warming could stop NATURALLY for ten years, say scientists’ that is not what this paper is about.

What this new paper by Noel Keenlyside, of the Leibniz Institute of Marine Sciences in Germany, sets out to do is incorporate data on short term variations in climate into our models of climate change. By doing this they push us into the arena of creating shorter term predictions, in this case of the next decade.

In a “News and Views” commentary on the piece in the same issue of Nature Richard Wood explains:

Keenlyside and colleagues’ model uses a very simple ocean initialization method in which they add heat to or remove it from the ocean surface until sea surface temperatures across the globe are close to observed values. They use their model to produce a set of retrospective ‘forecasts’ starting from earlier states, which they test against what actually happened. Their system produces refined temperature predictions a decade ahead for large parts of Europe and North America.

Whether their prediction of a plateau for warming for a decade in North America and Europe is correct or not, their research may signal a shift that many climate researchers have been calling for for awhile now — toward service-oriented climate science ...

I am sure that this is an excellent paper by world class scientists. But when I look at the broader significance of the paper what I see is that there is in fact nothing that can be observed in the climate system that would be inconsistent with climate model predictions. If global cooling over the next few decades is consistent with model predictions, then so too is pretty much anything and everything under the sun.

Cross posted by Daniel Cressey on The Great Beyond

Posted by Olive Heffernan on May 01, 2008
Categories: Climate Science, Climate prediction, Climate variability, Daniel Cressey, In the News | Permalink | Comments (8) | TrackBacks (0)

A paper in Nature Geoscience this week (subscription required) serves up an important figure for climate modellers: the size of the greenhouse effect caused by ozone near the Earth's surface, estimated from direct observations.

Whereas 20 years ago the discovery that the stratospheric ozone layer was thinning led to international prohibitions on ozone-eating chemicals, this new study reflects concerns about excess ozone produced nearer to the ground, in the troposphere, by reacting pollutants. Tropospheric ozone is a greenhouse gas - and although carbon dioxide still gets the most column inches, other greenhouse gases such as ozone (see also methane) are drawing more and more scientific attention.

Previously, the best estimates of the radiative forcing from ozone - its planet-warming power - came from simulations. The latest IPCC report used several such models to assess forcing from anthropogenic ozone alone, excluding ozone from natural sources, and came up with a range of values from 0.25 to 0.65 watts per square metre (in comparison, forcing by all anthropogenic greenhouse gases together was estimated at 1.6 watts per square metre). Now, NASA's Aura satellite has collected enough measurements of infrared radiation and ozone thickness in cloudless patches of sky to pin down the combined effects of natural and human-produced ozone. According to these data, the global average forcing in the year 2006 was 0.48 (+/- 0.14) watts per square metre. No surprises, but a palpable step forward in the hardworking and sometimes underappreciated field of Earth observation.

Anna Barnett

Image: Artist's rendering of Aura satellite, NASA

Posted by Anna Barnett on April 24, 2008
Categories: Anna Barnett, Atmospheric Science, Climate Science | Permalink | Comments (1) | TrackBacks (0)

The current issue of Nature has a feature about the state of the Greenland ice sheet (See also the related editorial dealing with the state of polar research funding).

I got started on this story at the American Geophysical Union meeting last December, in which session after session presented new data about the extent of summer melt in Greenland. Information from the GRACE satellites shows that the overall mass balance of the ice sheet is dropping steadily, and although surface melt varies quite a bit from summer to summer, two of the last three years have seen record levels of melt.

“2007 was a shocking year,” Scott Luthcke, who works with GRACE at NASA’s Goddard Space Flight Center in Maryland, told me later.

One record melt season does not spell the end of Greenland, of course, and journalists must always be wary about sounding too alarmist based on short-term records. But overall, the outlook for Greenland is simply not good: Changes in speeds of the island’s outlet glaciers show that, no matter whether they are advancing or retreating, they are far faster at changing their behavior than anyone had thought before.

As the article was going to press, we learned that another pair of key Greenland papers would appear the next day online in Science. Such is the peril of scheduling features far in advance while knowing your competitor journal has interesting papers under review.

The basic point of the two new papers -- that vast quantities of meltwater can form and then drain away atop the ice sheet each summer – made it into my feature anyway. But if you want more details, check out the original papers at the Science Express website. One paper, with lead author Sarah Das of the Woods Hole Oceanographic Institution, reports on a 4-kilometre-long melt lake that vanished into the ice sheet within the space of two hours. The other, with lead author Ian Joughin of the University of Washington’s Applied Physics Laboratory, describes seasonal speed-up in ice flow along Greenland’s western flank – though not so much in the outlet glaciers. Together, the papers confirm how meltwater likely helps lubricate the slippage of the ice sheet towards the ocean.

If you’re still looking for more things Greenland, check out the recent posting on RealClimate that again suggests the details of how Greenland melts are more complicated than we thought.

And if you just need a fix of gorgeous Greenland pictures, click on over to the Extreme Ice Survey project of photographer James Balog and others. We used only one of Balog’s iceberg images in my Nature feature, but his time-lapse work of melting glaciers is stunning.

Alexandra Witze

Image credit: NASA/GSFC VISUALISATION STUDIO; SOURCE: S. LUTHCKE

Posted by Olive Heffernan on April 22, 2008
Categories: Alex Witze, Climate Science, Cryosphere, Features, In the News | Permalink | Comments (3) | TrackBacks (0)

The North Atlantic Ocean may still be an active storehouse for atmospheric carbon dioxide, said scientists at the European Geosciences Union here in Vienna yesterday.

Following evidence published last year showing that both the Southern Ocean and North Atlantic Ocean have weakened as carbon sinks in the past two decades, the new results suggest that the trend has recently reversed in the North Atlantic.

Scientists have feared that the weakening trend could be a long-term impact of global warming and that it could be typical of the ocean as a whole, which absorbs an estimated 25 per cent of anthropogenic carbon dioxide emissions yearly. If the ocean switches from a storehouse to a source of the greenhouse gas, this would jeopardise efforts to stabilise atmospheric greenhouse gas levels.

Speaking at a press conference at the EGU assembly yesterday, Ute Schuster from the University of East Anglia in Norwich, UK and Christoph Heinze at the University of Bergen, Norway, presented the results of a yearly analysis of carbon dioxide fluxes across the North Atlantic Ocean.

Previously, Schuster and colleagues showed that carbon uptake by the North Atlantic had halved between the mid-1990s and the early 21st century. But further analysis of the data on a year-by-year basis has shown that the uptake of carbon dioxide in the region has been increasing since 2002 and showed an even greater increase, relative to the early 2000s, in 2005.

The researchers caution that the results are preliminary and are not yet published. The coverage was poor in 2006 and they have not yet finished the analyses for 2007, but they say that the results so far indicate that the trend in weakening of the North Atlantic carbon sink is not linear.

The reasons for this variation are unclear. “I personally think we can’t say with confidence that the trend [in weakening sinks] is attributable to [anthropogenic] climate change”, says Schuster. Surface circulation in the North Atlantic has changed in recent years, she says, but these changes could be due to natural climate variability. Specifically, the North Atlantic Oscillation, a large-scale atmospheric pattern that has important impacts on European climate, could be influencing the rate of carbon dioxide uptake.

Continue reading "EGU: North Atlantic Ocean may regain status as carbon sink" »

Posted by Olive Heffernan on April 17, 2008
Categories: Biosphere feedbacks, Climate Science, Conferences and Meetings, EGU 2008, Ocean science, Olive Heffernan | Permalink | Comments (0) | TrackBacks (0)

The dizzying economic growth in Asia threatens to disappoint expectations that new technologies will provide an easy fix for our climate problem, warn the authors of a commentary article in Nature this week.
Roger Pielke, Tom Wigley and Christopher Green believe that the Intergovernmental Panel on Change Change, which was awarded the Nobel Peace Prize last year for its work, plays “a risky game” when assuming that “spontaneous advances in technological innovation will carry out most of the burden of achieving future emissions reductions.”

Most of the emissions scenarios that the IPCC considered for its last report include significant ‘built-in’ technological change. In other words, the IPCC assumes that a good deal of climate-friendly innovation will happen spontaneously, in the absence of climate policy measures.

Now, necessity, economic growth and pursuit of profit do generate all kinds of more or less useful new technologies, from atomic bombs to iPods. But assuming that pure market forces will readily come to our aid in matters of climate change might be too optimistic, the commentary authors warn. Worse, they say, the assumption of a lot of spontaneous technological change could be misinterpreted as a license for policymakers not to take aggressive action.

Pielke, Wigley and Green have stirred up a hornets’ nest with their analysis. Some initial reactions to their call to arms are collected in an accompanying news piece. Expert opinions range from “overdue” to “totally misleading”.

So who’s right and who’s wrong, then? Are we dramatically underestimating the challenge of climate change? Or is this just one more twist exercised to unnecessarily dramatize an admittedly serious problem? Or is it all just shadow-boxing in the arcane world of scenario-making?

Economics of climate change are a politicized field. Depending on one’s standpoint (on what market forces can or cannot do, for example), one may find different answers to these questions. Less disputable is the fact that some two billion people in China and India are on the point of adapting to western living standards. Their consumptive power and increasing mobility will add to the global climate and energy problem. Let’s hope that their creativity and engineering skills will also add to its solution.

Quirin Schiermeier

Illustration: B. Mellor

Posted by Anna Barnett on March 31, 2008
Categories: Climate Science, Quirin Schiermeier, Technology | Permalink | Comments (8) | TrackBacks (0)

In a Science paper last year (subscription required), Rahmstorf et al. pointed to 2001-2006 measurements of global temperature at the top end of the IPCC's 2001 projections - and global sea level rise well beyond the range predicted in 2001 - as evidence that "the climate system, in particular sea level, may be responding more quickly to climate change than our current generation of models indicates." Today in a letter to Nature Geoscience (subscription required), Roger Pielke, Jr, questions whether models from that 2001 generation improve on the predictive power of their forbears.

Pielke checks predictions from all four IPCC reports, dating back to 1990, against reality. Each report made a series of 'if-then' statements about the likely results of various emissions scenarios; in hindsight, Pielke can pick out which of these possible greenhouse experiments has actually been running on Earth since 1990 and compare the results to the IPCC's shifting hypotheses.

Whereas the 2001 projections undershot the observed temperatures and sea levels, the 1990 projections overshot them, he concludes. Projections of temperature and sea level fell substantially between the 1990 and 1995 IPCC reports, when aerosols were added to models and carbon-cycle simulations were tweaked. But because they dropped too far, the adjusted post-1995 projections "are not obviously superior in capturing climate evolution", says Pielke.

That's not to say that 2001 models were no better than those a decade older. Including more information has made recent simulations more sophisticated - but so far it hasn't much improved their ability to sketch out future climates, probably because important factors are still missing. Predictions from the two most recent reports do, however, seem to have crept toward the actual climate evolution, and additional rounds of of refinements may help the models to home in further.

Anna Barnett

Posted by Anna Barnett on March 31, 2008
Categories: Anna Barnett, Climate Science, Climate prediction | Permalink | Comments (5) | TrackBacks (0)

The Guardian was far from alone in reporting this week that "A vast hunk of floating ice has broken away from the Antarctic peninsula, threatening the collapse of a much larger ice shelf behind it, in a development that has shocked climate scientists." On The Great Beyond, Quirin Schiermeier points out that the the most noteworthy thing about this delicately poised hunk of the Wilkins ice shelf may be its media visibility: the loss of a 400-square-kilometre piece of the same shelf earlier this year received no such fanfare.

Still, that visibility is pretty spectacular. Check out this mashup of the Twin Otter plane's flyover footage with the satellite images that tipped off British Antarctic Survey scientists:

"The ice shelf is hanging by a thread," said David Vaughan of the British Antarctic Survey. "We'll know in the next few days or weeks what its fate will be."

Anna Barnett

Posted by Anna Barnett on March 28, 2008
Categories: Anna Barnett, Climate Science, Cryosphere, In the News | Permalink | Comments (3) | TrackBacks (0)

On Nature Reports Climate Change , Gywn Prins of the LSE has reviewed The Hot Topic by science writer (and once climate change editor at Nature) Gabrielle Walker and former UK chief science advisor Sir David King.

The book has with the odd exception, received mostly favourable - and a few oustanding reviews - namely Chris Mooney's for New Scientist and Dave Reay's in the March 6 issue of Nature.

Indeed, Reay compares it Rachel Carson’s celebrated Silent Spring in its ability to engage millions and commends its even-handed coverage of the ‘climate debate’. Reay writes:

The Hot Topic has an authoritative clarity that scythes through the junk science and brushes aside the brigades of doom-mongers and overly earnest environmentalists.

Over on The Intersection Chris Mooney refers to it as "the best global warming book I've ever read", and has a similar stance to Reay. Of Walker and King, he writes:

Their overview of the science and policy of climate change is a model of clarity, comprehensiveness and, above all, sanity. It truly does find a middle ground in the climate debate.

On the contrary, Prins (who authored a Commentary in Nature last year with Steve Rayner calling for a radical alternative to the Kyoto Protocol) argues that the book is both “troubling” and “relentlessly normative” in that it represents “an unquestioning acceptance of the received wisdom”.

Prins is especially disgruntled with how Walker and King, in his view, polarize perspectives on the way forward on climate policy:

[They] have no scintilla of doubt that the Kyoto Protocol is the road to follow and that anyone who deserts it is wrong and possibly corrupt. So we have as heroes the EU, which doesn't "duck" the problem, and as villains the US, languishing under the rule of "President Bush and his fiercely partisan advisers". They lump all "sceptics" — anyone who disagrees with them — together like the damned in a Hieronymus Bosch painting of heaven and hell.

He then compares The Hot Topic to Bjorn Lomborg’s The Skeptical Environmentalist (albeit at the other end of the polemical spectrum) in it’s treatment of uncongenial information, essentially making the point that the authors choose their supporting arguments carefully and disregard the rest.

Continue reading "Review of The Hot Topic: The road well travelled " »

Posted by Olive Heffernan on March 17, 2008
Categories: Climate Policy, Climate Science, Features, Olive Heffernan, Reviews | Permalink | Comments (1) | TrackBacks (0)

Historian Will Durant ... is said to have cautioned: "Civilization exists by geological consent, subject to change without notice."

This warning, re-broadcast in an essay by eminent public scientist Frank Press, wraps up an excellent special supplement on Earth science in this week's Nature. In honor of the International Year of Planet Earth, the supplement features more than a dozen in-depth commentaries on current topics in geoscience, almost all looking warily toward past, present and future climate change (with or without notice).

As an overview of several leading-edge climate science issues, it's well worth a look - and the thoughtful opening article on historical drivers of geoscientific progress is also not to be missed. Act now, because the entire supplement is currently free to access.

Anna Barnett

Photo: NASA

Posted by Anna Barnett on January 21, 2008
Categories: Anna Barnett, Climate Science | Permalink | Comments (0) | TrackBacks (0)

If you like coral reefs you should enjoy them while you can, they won’t be around for long. Global warming and the ocean acidification that comes with it will decimate reefs by the end of this century, according to a new review article in Science.

“The impact of climate change on coral reefs is much closer than we appreciated. It's just around the corner,” says study author Ove Hoegh-Guldberg, of the University of Queensland. “... The warmer and more acidic oceans caused by the rise of carbon dioxide from the burning of fossil fuels threaten to destroy coral reef ecosystems, exposing people to flooding, coastal erosion and the loss of food and income from reef-based fisheries and tourism. And this is happening just when many nations are hoping that these industries would allow them to alleviate their impoverished state.” (Reuters ... Telegraph)

Although there is no new original research here, when all the numbers are brought together they are pretty frightening. Atmospheric carbon dioxide will exceed 500 parts per million sometime between 2050 and 2100. This will drive global temperatures up at least 2°C, “values that significantly exceed those of at least the past 420,000 years during which most extant marine organisms evolved” says the paper.

It adds ominously, “Under these conditions, reefs will become rapidly eroding rubble banks such as those seen in some inshore regions of the Great Barrier Reef, where dense populations of corals have vanished over the past 50 to 100 years.”

This year marks not only the release of a clarion IPCC report and the convening of an enormous UN climate conference, but also the 50th anniversary of the Keeling curve -- the longest continuous recording of atmospheric carbon dioxide levels, revealing a gradually rising carbon dioxide profile that helped trigger early concern about global warming. As part of this week's Earth Observation special (subscription required), Nature has a commentary by Euan Nisbet, atmospheric scientist at Royal Holloway, on the Keeling curve -- which "ranks very high indeed among the achievements of twentieth-century science", he says -- and similar studies in the field of Earth monitoring. Nisbet writes:

Monitoring is science's Cinderella, unloved and poorly paid. Sustaining a long-term, ground-based programme that demands high analytical standards remains challenging. Funding agencies are seduced either by 'pure' notions of basic science as hypothesis-testing, or by the satanic mills of commercial reward. Neither motive fosters 'dull' monitoring because meeting severe analytical demands is not seen as a worthwhile investment. At one stage, Keeling was ordered to guarantee two discoveries per year and today, modern research has become a planned journey through set 'milestones' to deliverable destinations.

What do you think -- how important is this 'Cinderella science' to ongoing climate research and policy, and how could we secure reliable long-term support?

Image credit: Global Warming Art

Anna Barnett

Posted by Anna Barnett on December 05, 2007
Categories: Anna Barnett, Climate Science, GHG emissions, Opinion | Permalink | Comments (3) | TrackBacks (0)

Signs of a very different 21st-century climate are already showing up, and not just in the melting arctic. A new review in Nature Geoscience highlights reports that the boundaries of the tropics, defined by temperature, rainfall, wind, and ozone patterns, have shifted poleward by at least 2 degrees latitude in the last 25 years. According to climate models, that's as far as the tropical belt was supposed to creep by the end of this century. Five different methods used to measure the tropics all show more or less breakneck rates of expansion -- one gives as much as 4.8 degrees in 25 years.

Continue reading "Tropics expanding fast " »

Posted by Anna Barnett on December 04, 2007
Categories: Anna Barnett, Climate Science, Extreme Events | Permalink | Comments (1) | TrackBacks (0)

Those bored of playing with Google Earth may be interested in NASA’s new toy – a stunningly detailed map of Antarctica. Claiming to be ten times more detailed than previously available equivalents, the map was painstakingly constructed by the stitching together of 1,100 hand-selected photos from Landsat satellites (NASA press release).

The map was produced in collaboration with the National Science Foundation and the British Antarctic Survey. It’s already attracting media attention (BBC, Bloomberg, ABC, Herald Sun, Wired).

“This innovation, compared to what we had available most recently, is like watching the most spectacular high-definition TV in living colour versus watching the picture on a small black-and-white television,” says Robert Bindschadler, chief scientist of the Hydrospheric and Biospheric Sciences Laboratory at Goddard (NSF press release).

Those who sifted through all the photos and put them together are hoping that the Landsat Image Mosaic of Antarctica will be rather more than a fun distraction for desk workers avoiding work.

“...LIMA is also a fundamental tool for scientists,” says Scott Borg, director of NSF's division of Antarctic sciences. “It will be used in every discipline from biology to geology to glaciology, both to answer scientific questions and plan fieldwork in the vast unexplored tracts of Antarctica. For educators, students, and the general public, LIMA will bring to life the Antarctic continent like nothing before it.”

The images will apparently eventually make their way to Google Earth, but why wait for that – the map is online now.

Images: top – mosaic of Antarctic shots, bottom – diagram of photos used in LIMA / all courtesy of NASA

Cross-posted from Daniel Cressey on The Great Beyond.

Posted by Anna Barnett on November 28, 2007
Categories: Climate Science, Daniel Cressey | Permalink | Comments (0) | TrackBacks (0)

World experts have gathered in Valencia to produce a synthesis of all the Intergovernmental Panel on Climate Change reports released to date (Nature – subscription required). Thus, there is a rash of climate change news.

The Valencia meeting’s report will, according to AFP, “serve as a guide for policymakers for years to come”. Now traditional arguments between Europe, the US and other participants over the exact wordings are already underway (AP).

Even OPEC is getting in on the action. The group of oil producing nations said this week it would assist in cutting or capturing carbon emissions (Reuters). Some reports even say it is mulling over the creation of a $3 billion fund invest in emission capture technology (Times).

In Australia the former head of the country’s Commonwealth Scientific and Research Organization’s atmospheric research unit warned before the meeting that current policy is based on science that is already out of date (ABC). “If you think climate change is on the agenda, just wait another couple of years,” he told the Sydney Morning Herald.

Cross posted from Daniel Cressey on The Great Beyond

Posted by Olive Heffernan on November 16, 2007
Categories: Climate Policy, Climate Science, Daniel Cressey, Features, In the News | Permalink | Comments (1) | TrackBacks (0)

Kevin Trenberth

The recent Asian Pacific Economic Cooperation (APEC) summit has brought further attention to climate change and what, if anything, to do about it. In spite of the IPCC findings that global warming is “unequivocal”, doubt remains in some quarters about the reality of climate change and the human cause. Issues are continually raised that have no basis, as highlighted by the recent Commentary from Syun-Ichi Akasofu in the Wall Street Journal.

Akasofu immediately starts out on the wrong foot by claiming there are two sides, those of believers and non-believers, but it is not a matter of belief, it is a matter of scientific facts! He further fails to understand the nature of the IPCC process and the extensive reviews in which all comments are addressed rigorously as the report is developed over three years. Contrary to the claim, there is no assumption by IPCC that recent warming was due to the increased greenhouse effect from increasing human produced carbon dioxide. Rather, climate models that run with and without the human-induced changes in atmospheric composition demonstrate that human warming has emerged from natural climate variability since about 1970.

Over the past 500,000 years or so, temperatures, carbon dioxide and methane have gone up and down more or less in tandem through the major ice ages and interglacial periods, as shown in ice cores. As detailed in a Real Climate blog post on this topic, in the absence of human intervention, these changes happen over time, but not at the rate at which CO2 is currently increasing in the atmosphere. Scientists know that carbon dioxide and methane changes follow rather than cause these changes in temperature between glacial periods, but they also know that these changes in greenhouse gases amplify a relatively weak forcing to help drive temperature change. To suggest otherwise, as Akasofu does, is misleading at best.

Akasofu then trots out the mistaken view that the “hockey stick” curve of temperatures over the past 1000 years showing an upward bend at the end has been discredited. In fact, it has been reinforced in the latest IPCC report, although it is given less emphasis as it is now backed up and confirmed by evidence from multiple independent studies.

He further claims that natural climate variations have been forgotten and attributes recent warming to the “rebounding effect from the little ice age”, but fails to realize that natural climate variability also has a cause. While it is true that we do not have the measurements to show what was happening in the ocean during this time, for instance, we have good reason to believe that natural internal variability played a role. To the extent that the "Little Ice Age" and "Medieval Warm Period" can be meaningfully defined, there has been much work showing that the main variations can be explained in terms of the response of the climate system to natural variability in solar and volcanic events that would have influenced surface temperature. And warm periods in the past, such as the warming in the Greenland region in the mid-twentieth century, were not global in contrast to recent warming, which is.

Climate models are not perfect, but they are useful tools for quantifying the effects of various climate processes and drivers of climate change. Akasofu decries the confused state of climatology, but it is he who is really confused, and his article only serves to confuse the general public. It is sad that a once distinguished newspaper published such misleading half-truths without verifying them.

Kevin Trenberth

Posted by Olive Heffernan on September 19, 2007
Categories: Climate Science, Communicating Climate Change, In the News, Kevin Trenberth | Permalink | Comments (39) | TrackBacks (0)

Kevin Trenberth

The situation on how hurricanes have changed and will likely change in the future are outlined in my recent Scientific American article, but may seem as murky as ever to the public although clarity is actually emerging.

A recent news report in the Press Register outlines some sources of confusion related to just how well the past record is known. It cites work by Landsea that relied on numbers of land-falling storms as a way to calibrate the Atlantic hurricane record, and which concluded that there may be an undercount of 3.2 storms per year prior to 1966. The most recent Eos Transactions has two articles that follow up and point out why use of land-falling storms is misleading [Holland 2007; Eos 88 (36) 348-349] and that the conclusions of increased activity do not change anyway [Mann et al., 2007; Eos 88 (36) 349-350].

The Holland article points out that there are good reasons why the fraction of storms making landfall should change, both because of natural variations and especially if the climate changes. The Mann et al. article adopts the Landsea-suggested changes for the past as a “what if” test and goes on to show that even a substantial underestimate of early 20th century storms does not change the significance of the increase in activity since 1994. Nor does it change the strong relationship with observed sea surface temperatures (SSTs) in the region; the SSTs have a much more reliable observational record and have clearly increased.

Surprisingly, none of these studies refers to what seems to me to be the most definitive analysis of the likely missed storms in the historical counts by Chang and Guo (2007) in which they analyze in detail the actual ship tracks in the past compared with modern tropical storm tracks. To quote their main conclusions: “It is estimated that the number of tropical cyclones not making landfall over any continent or the Caribbean may have been underestimated by up to 2.1 per year during 1904–1913, with this number decreasing to 1.0 per year or less during the 1920s and later decades. Our results suggest that the characteristics of North Atlantic tropical cyclone track statistics might have changed during the 20th century.”

In 2007 the tropical storm season has been fairly normal in many respects up to now. Only 3 hurricanes have been recorded (versus average 3 to 4) but two were category 5 storms, and that is highly unusual. Forecasts of hurricane activity by NOAA and Bill Gray continue to forecast substantially above normal activity in the Atlantic. To me, observing the events thus far, the incredibly intense convective activity in the Indian Ocean from May to July was an important and totally overlooked factor. The subsequent heavy rains and flooding in India and China were no doubt related. The fact that Atlantic hurricane activity is influenced by events in the Indian Ocean seems to be overlooked by the hurricane forecasters.

Kevin Trenberth

Posted by Olive Heffernan on September 17, 2007
Categories: Climate Science, Hurricanes, Kevin Trenberth | Permalink | Comments (3) | TrackBacks (0)

Just when everyone was getting sick of explaining that climate models are producing projections not predictions per se, it seems that some of them are indeed producing predictions. There's a paper (pdf) in Science from a team at the Hadley Center that shows how using real initial conditions improves the accuracy of ten year climate forecasts. They do a bit for hindcasting first, looking at historical data and comparing model runs with real initial conditions with run-of-the-mill runs. Then they do some prediction. This prediction is being treated as saying that we're at the end of a little plateau, and that at the end of this decade things will warm up further, giving a run of years in the early 2010s where the chances for new global records are good. Quirin Schiermeier wrote a story on this for news@nature, reporting that the modelling community seems pretty impressed. Here's a bunch more coverage (88 pieces at the time of googling), and for those with a subscription to Science here's the estimable Dick Kerr, who had longer to write the story than the rest of us...

Posted by Oliver Morton on August 10, 2007
Categories: Climate Science, Climate variability, Oliver Morton | Permalink | Comments (8) | TrackBacks (0)

Over at News@nature, Mike Hopkin reports from the Ecological Society of America's meeting in San Jose on research into tropical forest growth rates. Looking at plots in Panama and Malaysia, the researchers found that increases in mean daily minimum temperature over a couple of decades correlated with decreases in growth rates. They associate this with lower net photosynthetic activity.

The team, led by Harvard's Ken Feeley, suggests that if this sort of effect were repeated in bigger rainforests (most of which have only experienced marginal warming to date, as I understand it) then what are now stable stores of carbon would become net sources as theworld heats up. This is obviously a considerably less optimistic scenario than the possibility that carbon-dioxide fertilisation would make them sinks. It would presumably make the net effect of the increase in soil respiration that Peter Cox and others always stress (Nature paper from 2000) an even worse problem.

It's not a dead cert that the change is due to temperature -- the paper (published in Ecology Letters) seems to suggest that increased cloudiness could be playing a role. And there could be internal botanical changes too -- maybe the lianas are doing more damage? But all in all it doesn't sound good.

Mike is blogging the conference on the newsblog.

Posted by Oliver Morton on August 10, 2007
Categories: Biosphere feedbacks, Climate Science, Oliver Morton | Permalink | Comments (0) | TrackBacks (0)

Olive Heffernan

Much like the rest of Britain, I’m beginning to wonder if it’s ever going to stop raining. And despite feeling slightly miffed at an appalling excuse for a summer, I realise I'm lucky to be based in slightly soggy London, given that large areas of the country are currently besieged by some of the worst flooding in recent British history.

Calling it a ‘21st century catastrophe’, Michael McCarthy at the Independent writes that “Britain is suffering from a wholly new type of civil emergency: a disaster caused by 21st-century weather,” which has left more than a third of a million people without drinking water, nearly 50,000 people without power, thousands more people homeless and caused more than £2bn worth of damage so far.

Britain is not alone in experiencing extremely heavy rainfall. As reported on MSNBC, “parts of China had the heaviest rainfall since records began, killing more than 700 so far this year. Hundreds of thousands have been displaced by flash floods in southern Pakistan.”

While these single events cannot be attributed to climate change, many are questioning if the flash flooding is a sign of what is in store for the future. And scientists have some of the answers.

In a paper coming out in Nature this Thursday, Francis Zwiers of the Canadian Centre for Climate Modelling and Analysis in Toronto and colleagues present the first evidence that human-generated greenhouse gas emissions have altered rainfall patterns in the 20th Century. In the region between 40 and 70 degrees North, covering northern Europe, Russia and parts of North America, rainfall increased by 62 millimetres per century between 1925 and 1999. Zwiers and colleagues say that 50-85% of this increase can be attributed to human activity. For further discussion and comments on the paper, there’s a news story by my colleague Daniel Cressy on News@Nature. And it’s also been picked up by the BBC.

And a recent paper published in Science in June suggests that global warming may result in even more rainfall worldwide than is currently evident in climate model simulations. Frank J. Wentz of Remote Sensing Systems in Santa Rosa, California and co-workers compared global satellite data from 1987 to 2006 and found that rainfall increased at the same rate as atmospheric water vapour per degree Celsius of surface warming. Climate models had projected a dampened response of rainfall to global warming owing to a decrease in surface winds, but Wentz and colleagues found that surface winds have in fact become stronger, leading to heavier rainfall (more on this in Nature Reports Climate Change soon).

Coming back to Britain… the situation is likely to worsen over the next 24 hours. Eight severe warnings have been issued covering the rivers Thames, Severn and Ouse, in particular for towns such as Gloucester, Tewkesbury, Oxford, Abingdon, Reading and Bedford. Fifty other flood warnings are in place across England and Wales.

To see the areas generally most at risk of flooding in England and Wales, visit the Environment Agency’s flood map online, where you view flood risk by postcode. For an up to date interactive on the current situation, the Guardian has quite a snazzy interactive highlighting areas most at risk.

Olive Heffernan
News Editor
Nature Reports Climate Change

Posted by Olive Heffernan on July 24, 2007
Categories: Climate Science, Extreme Events, In the News, Olive Heffernan | Permalink | Comments (3) | TrackBacks (0)