Climate Feedback

Daniel Cressey; cross-posted from The Great Beyond

The world’s carbon dioxide ‘sinks’ are not able to keep up with the amount of the greenhouse gas being produced, according to a paper published in Nature Geoscience.

Reviewing the recent literature Corinne Le Quéré, of the University of East Anglia, and colleagues report that between 1959 and 2008 43% of each year’s carbon dioxide emissions have remained in the atmosphere with the rest being absorbed by land and ocean sinks. However in the last 50 years they suggest that the fraction remaining in the atmosphere has increased from about 40% to 45%.

They also found that a 29% rise in carbon emissions between 2000 and 2008 can be attributed to a large extent to burning coal and the growth of the so-called ‘emerging economies’.

“The Earth’s carbon sinks are complex and there are some gaps in our understanding, particularly in our ability to link human-induced CO2 emissions to atmospheric CO2 concentrations on a year-to-year basis,” says Le Quéré (press release). “But, if we can reduce the uncertainty about the carbon sinks, our data could be used to verify the effectiveness of climate mitigations policies.”

Continue reading "That (carbon) sinking feeling" »

Posted by Olive Heffernan on November 18, 2009
Categories: Biosphere feedbacks, Climate Science, Daniel Cressey, Ocean science | Permalink | Comments (0) | TrackBacks (0)

Northern peatlands, typical for subarctic Scandinavia and Russia, contain one third of the world’s soil organic carbon. How much extra carbon these soils will release to the atmosphere, through accelerated respiration in a warmer climate, has been pretty much guesswork. Data from an eight-year in situ experiment carried out in Sweden now suggest that even modest warming will release enough extra carbon to effectively equalize the European Union’s emissions reductions achieved under the Kyoto Protocol.

Ellen Dorrepaal and her colleagues studied ecosystem response to climate warming at a test site near the Swedish Abisko scientific research station, some 200 kilometres inside the Arctic Circle. In a paper in Nature today (subscription required) they report that warming accelerated the respiration of carbon in peat overlaying the permafrost by almost 70 % - much more than previously thought. Here's an editor's summary.

Extrapolated to the total northern peatland area, the results suggest that climate warming of 1 degree Celsius over the next decade might lead to a global increase in respiration of 38-100 million tonnes of carbon per year. For comparison: The EU’s Kyoto target is to reduce emissions by 92 million tonnes of carbon per year.

The researchers stress that the effect is likely to last: “In contrast to long-term studies in forest, meadow and tundra ecosystems, the warming effect did not decline towards the eighth year of the study,” they write.

The net effect of warming on northern carbon reservoirs includes possible gains from increased plant growth. But in Arctic ecosystems dominated by peat and moss, there are too few productive woody shrubs growing to offset the warming effect on soils.

Quirin Schiermeier

Image: Subarctic peatland in Abisko, North Sweden where the consequences for CO2-respiration rates were investigated. Credit: Ellen Dorrepaal

Posted by Quirin Schiermeier on July 30, 2009
Categories: Categories, Biosphere feedbacks, Climate Science, GHG emissions, Quirin Schiermeier, Topics, Uncertainty | Permalink | Comments (3) | TrackBacks (0)

Why carbon dioxide concentrations over the past 24 million years or so have never dropped below 200 parts per million, despite environmental conditions that have been favourable for CO2 drawdown by rock weathering and sedimentation, has always been a bit of a mystery.

Now scientists suggest an almost provocatively simple mechanism that might have kept the planet from cooling more severely than it actually did during past glacial climates: Changes in terrestrial vegetation stopped the weathering-driven decline in atmospheric CO2 concentrations which else would have turned Earth into a lifeless freezer.

Weathering is known to be largely controlled by vegetation. So the team, led by Mark Pagani of Yale University, describes in a paper in Nature today a negative feedback whereby limited plant growth during cold conditions slows down the rate of weathering and sedimentation, thus preventing carbon dioxide levels from dropping even further. An editor's summary of the paper is here.

This “bold and provocative” hypothesis provides an “elegant twist” on existing ideas about climate-vegetation interactions, Yves Goddéris and Yannick Donnadieu write in an accompanying News and Views article (subscription required).

But the proposed feedback mechanism raises contentious issues as well. For example, Goddéris and Donnadieu argue that in the tropics the role of vegetation cover in the climate system might not be as significant as proposed.

Quirin Schiermeier

Posted by Quirin Schiermeier on July 02, 2009
Categories: Categories, Biosphere feedbacks, Climate Science, GHG emissions, Palaeoclimate, Quirin Schiermeier, Topics | Permalink | Comments (0) | TrackBacks (0)

China’s forests, shrublands and soils have absorbed a third or so of China’s fossil fuel emissions from 1980 to 2000. Sequestering up to 260 million tonnes of carbon per year, the Chinese land sink is more than twice as large than that of geographic Europe, and comparable in size to that of the United States.

There has been quite some controversy over the total size of the Northern Hemisphere’s terrestrial carbon sink, so this first comprehensive estimate, published in Nature today, is filling a real gap. Given China’s 1.2 billion population and rapidly growing economy, knowledge of how much of its emissions are actually staying in the atmosphere is pretty valuable information. Globally, around 40% of annual emissions stay in the atmosphere; the rest is sequestered by plants, soils and oceans.

The Chinese data come at a time of growing speculation and guesswork over the People's Republic’s future climate and energy policies. Needless to say, the study is of no small relevance with a view to upcoming climate negotiations. The very fact that China’s land carbon sink is large is good news. But the results will also strengthen the Chinese government’s negotiation position at the United Nations climate summit in December in Copenhagen.

Continue reading "EGU: China's carbon sink - it's large" »

Posted by Anna Barnett on April 22, 2009
Categories: Biosphere feedbacks, Climate Policy, Earth science, Mitigation, Politics, Quirin Schiermeier | Permalink | Comments (0) | TrackBacks (0)

The Earth’s large forests take up substantially more atmospheric carbon dioxide through photosynthesis than they release back to the atmosphere through respiration. Thus acting as a carbon ‘sink’, they (and the oceans) are our closest natural allies in the fight against climate change.

But many forests are at threat - not only from logging and clearing, but from climate change itself.

Take drought. How will mature tropical rain forests respond to dryer conditions, which some climate models suggest might be ahead in the not-so-distant future?

The 2005 drought in the Amazon basin gave scientists an opportunity to find out. What they saw is not particularly heartening: Prolonged dryness has apparently turned some affected areas of the Amazon from a carbon sink to a carbon source, a team led by Oliver Phillips of Leeds University in Britain reports in Science today (Abstract here).

Patches subjected to a 100-milimetre decrease in rainfall released on average 5.3 tonnes of carbon per hectare – around 9 times the amount undisturbed tropical forests take up, on average, per year. Basin-wide, between 1.2-1.6 billion tonnes of carbon were released during the 2005 drought, the team estimates.

Over at Nature News, I’ve put together a little briefing on what we know and what we don’t know about the tropical carbon sink.

Quirin Schiermeier

Image: Punchstock

Posted by Quirin Schiermeier on March 06, 2009
Categories: Biodiversity and Ecology, Biosphere feedbacks, Climate Science, Deforestation, Mitigation, Quirin Schiermeier, Topics | Permalink | Comments (1) | TrackBacks (0)

Tropical forests which (still) cover around 10% of the global land area contain more carbon per hectare than any other form of vegetation. It’s obvious from that that their growth or decline has a huge impact on the global carbon budget.

Cutting down forests will add carbon to the atmosphere, no matter which kind of land cover replaces the jungle. But what’s happening in tropical forests that have long been undisturbed by logging, storms or fire? Theoretically, the carbon balance of such old-growth forest – if tree growth and death are in equilibrium, that is - should be next to zero.

But apparently it’s not. In a paper in Nature today (subscription), a team led by Simon Lewis of Leeds University in Britain reports that tree biomass in intact African forests increased between 1968 and 2007. Across 79 plots monitored in ten countries large living trees added an average 0.63 tonnes of carbon per hectare each year. Scaled up to the continent, and including roots, smaller trees and dead wood, African forests seem to have stored 340 million tonnes of carbon per year during recent decades. Previous studies suggested that Amazonian forests are accumulating biomass and carbon at a similar rate. Globally, intact tropical forests seem to take up 1.3 billion tonnes of carbon per year – equivalent to almost 20% of annual carbon dioxide emissions worldwide.

Continue reading "Jungle Fit!" »

Posted by Quirin Schiermeier on February 18, 2009
Categories: Categories, Biosphere feedbacks, Deforestation, GHG emissions, Mitigation, Quirin Schiermeier, Topics | Permalink | Comments (2) | TrackBacks (0)

Researchers have discovered new hot spots for emissions of the greenhouse gas nitrous oxide: barren patches of peat dotted across northern tundra. And warming in the Arctic - just as it threatens to multiply emissions of carbon dioxide and methane from thawing permafrost and drying bogs - could accelerate the output of this lesser-known climate change culprit, according to a study in Nature Geoscience this week (subscription).

Nitrous oxide is the other other greenhouse gas. In the new paper, Pertii Martikainen of the University of Kuopio in Finland and colleagues call it third most important behind carbon dioxide and methane, noting that it contributes a reported 6% to global warming. It’s not been considered a player at all in the Arctic, where the few scientists who’ve looked for the gas have found negligible emissions. But that’s because they’ve been looking in the wrong places, say Martikainen’s team.

Continue reading "New Arctic feedback: vicious peat circles" »

Posted by Anna Barnett on February 17, 2009
Categories: Anna Barnett, Biosphere feedbacks, Cryosphere, GHG emissions | Permalink | Comments (0) | TrackBacks (0)

Cross posted from Heliophage

I wrote a little piece for Nature today today about a paper by Andy Ridgwell at Bristol and some of his colleagues on changing the albedo of crops. The gist as published:

Manipulating the waxiness of crops through traditional breeding techniques or genetic modification should raise their albedo by about 20%, from 0.2 to 0.24. On the basis of climate modelling they calculate that the planet would cool by a modest 0.11 ºC. "It's very small on the global average," says Ridgwell. But "what is more important is the summertime effect in specific regions". The mid-latitudes of North America and Eurasia could cool by as much as 1 °C in June, July and August, according to the models. Ridgwell and his colleagues report their results in Current Biology.

The models also show pronounced cooling in the North Atlantic Ocean and the Barents Sea in the wintertime — which might have a positive effect on sea ice — but a drying out of the soil in some parts of the subtropics. Ridgwell points out that climate models do not predict future precipitation well on a regional basis and treats the latter results more as evidence that there might be effects far from the fields being changed than as a clear indication that there would be damaging consequences.

Making the plants more reflective, if it proved a good idea at all, might well necessitate genetic engineering, which in some places is distrusted. That engineering might be more acceptable in energy crops than it is in food crops. It might make sense, if people are going to engineer energy crops for other purposes, to make them a little lighter too, all other things being equal.

Continue reading "Leaf albedo engineering" »

Posted by Oliver Morton on January 15, 2009
Categories: Biosphere feedbacks, Oliver Morton | Permalink | Comments (0) | TrackBacks (0)

Stimulating algal growth by adding iron to nutrient-poor ocean regions is one of several geo-engineering methods that could possibly mitigate greenhouse warming. But given widespread worries about possibly harmful side-effects on marine life, large-scale ocean ‘fertilization’ is currently not considered advisable.

Predictably, environmental groups have therefore jumped on an iron fertilization experiment which an international team of oceanographers is set to conduct over the next two months in the Southern Ocean near the island of South Georgia. Critics claim that LOHAFEX violates the moratorium on ocean fertilization activities which the United Nations had agreed upon last year. The Nature news story here has more details.

The somewhat ambivalent wording of the legally binding UN Convention on Biological Diversity adds to the controversy. ‘Small-scale’ scientific experiments in ‘coastal waters’ are exempted from the moratorium, it reads. But ‘small-scale’ is a relative term, and where exactly coastal waters give way to the open ocean remains also undefined.

Picture: The Polarstern (Alfred Wegener Institute)

The team on board the German ‘Polarstern’, who plan to spread 20 tonnes of iron sulphate over less than 20 by 20 kilometres-large patch of ocean surface in the Scotia Sea, hope that the study will provide new insight into how ocean ecosystems respond to fertilization – the very data, hence, that are needed to assess whether or not larger-scale future activities might be justified. But opponents counter that such doing already qualifies as an activity banned by UN law. Pressure groups have launched a signature campaign aimed at stopping the Polarstern crew, which will reach its destination by the end of the week, from dumping its load.

A number of companies, such as the now defunct Planktos Inc., had in the past hoped to commercialize ocean fertilization for the carbon credit market. Scientists and institutes participating in LOHAFEX stress that the experiment has no commercial background whatsoever.

UPDATE:
The Indo-German ocean fertilization experiment, LOHAFEX, has been suspended. The German science ministry, in response to environmental concerns, has asked the Alfred Wegener Institute (AWI) in Bremerhaven that an additional independent assessment be conducted before the planned activities can commence.

Meanwhile, the Polarstern, scheduled to reach the planned study region in the Scotia Sea by the end of the week, will continue its journey as planned. On arrival, the 48 scientists on board will start doing preparatory work, but the team will have to await permission from the ministry before they can dump any nutrients into the ocean. AWI has today commissioned two undisclosed institutions to carry out the required extra assessment. It hopes the reports will be delivered within ten days.

Quirin Schiermeier

Posted by Quirin Schiermeier on January 14, 2009
Categories: Biosphere feedbacks, Business, Carbon markets, In the News, Mitigation, Ocean science, Politics, Quirin Schiermeier, Research, Technology | Permalink | Comments (3) | TrackBacks (0)

It's a buried time bomb of greenhouse emissions - and it's even less photogenic than melting permafrost. A team of researchers led by Takeshi Ise of the Japan Agency for Marine-Earth Science and Technology has been watching peat dry.

Peat - "an accumulation of partially decayed vegetation matter", in Wikipedia's appetizing phrase - forms in bogs and swamps where the acidic, waterlogged, oxygen-poor soil smothers the decomposition process, just as permafrost freezes it out. That makes it a big sink for carbon that would otherwise have joined the atmosphere as the plants composted. But peat's not just a sink, it's a sump - and a snowballing one. The large amount of water peat can hold lowers the oxygen available, which makes more peat accumulate, which sucks up more groundwater and blocks it from draining.

It's this feedback process, as it occurs in the northern bogs of Manitoba, Canada, that Ise et al. succeeded in accurately modeling for the first time in a paper published this week in Nature Geoscience (subscription required). Their bad news is that warming air temperatures reverse the loop: the peat dries and decays, then can't hold as much water and dries and decays some more.

As Joseph Romm points out on Grist and Climate Progress, that potentially makes the peat loop a link in a bigger, and climatically more important, vicious circle - the one where temperatures raised by human emissions start an uncontrollable release of methane and carbon dioxide from natural stores like peat and permafrost.

Continue reading "Watching peat dry" »

Posted by Anna Barnett on October 16, 2008
Categories: Anna Barnett, Biosphere feedbacks, Climate Science, Earth science | Permalink | Comments (0) | TrackBacks (0)

If carbon dioxide is trump, then methane is the joker in the greenhouse game. The flammable gas (CH4) is produced in wetlands, landfills and in the guts of cattle and sheep, and it is stored in vast amounts in so-called clathrates, or gas hydrates, in the ocean floor.

The latter stuff has always kindled imagination. In the 1930s, dumbfounded Russian sailors who had lit dynamite for navigational purposes in the Siberian Arctic reported that the air around them started to burn. Had they set on fire methane released from clathrate reservoirs? Perhaps.

Less likely is that methane bubbling up from the ocean floor can makes the water so foamy that ships floating above sink like a rock. File this under Bermuda triangle myths.

But catastrophic methane bursts do seem to be linked with anomalous warming episodes in the Earth’s past, such as the one that occurred at the Palaeocene-Eocene Thermal Maximum around 55 million years ago. Dissociating clathrates may well have been the culprit then.

What had uncorked the bottle is unclear. But in any case, reports this week of methane emissions from sub-sea permafrost beneath the Siberian shelf, and from the seabed off Svalbard, sound alarming.

Geologists assume there are large methane hydrate reservoirs in both regions. Are they beginning to destabilize? Have we lit a time bomb? Is global warning getting out of control?

Media reports this week imply all this, some more and some less cautiously. It’s a wonderful story of course: Weird things happening in the Arctic, strange tales from the bottom of the ocean, Apocalypse Soon! It’s new, it’s exciting, it’s scary - no wonder journalists love it.

But wait a minute. The methane system discovered off Svalbard has probably been active for thousands of years, it’s only that no-one has ever looked for it.

The methane emissions detected in the Laptev Sea are also not a new phenomenon. Russian scientists have observed methane plumes there since the mid-1990s when they began to regularly visit the remote and inaccessible region. It does seem that there are many more, and possibly more vigorous, emission hotspots than was previously thought. But observations are still few; it’s not too much of a surprise that the harder they look the more they will find. I have tried to put the recent discoveries in context in my news story here.

That’s not to say that rising methane emissions, and thawing permafrost, are no concerns. They are, and their sources and causes need to be studied carefully. Long-overlooked methane emissions from living plants, as were just recently confirmed, are proof enough for how poorly methane cycles are actually understood.

But not only in matters climate change there’s a danger of confusing people by media coverage that alternates between alarmism and appeasement. Andrew Revkin of the New York Times has appositely termed the effect a journalistic whiplash for the public.

Science, although intrinsically a never-ending process, will every so often generate journalistic scoops - and sometimes journalistic kitsch. The methane story is exciting, but inflationary use of ‘dramatic’, 'alarming' etc in science stories produces only cheap thrills.

Quirin Schiermeier

Posted by Quirin Schiermeier on September 28, 2008
Categories: Recent contributors, Biosphere feedbacks, GHG emissions, In the News, Ocean science, Palaeoclimate, Quirin Schiermeier | Permalink | Comments (2) | TrackBacks (0)

Hard to believe: The long-standing notion that old forests are carbon neutral – that is, that from a certain age forests cease to absorb and accumulate carbon – has its origin from a mere decade worth of data from one single site.

Although timidly questioned every so often, this apparently wrong postulate has prevailed for more than 30 years, leaving its mark in the Kyoto Protocol which excludes old-growth forests from national carbon budgets.

The finding, reported in this week’s Nature, that old forests do accumulate carbon, and apparently in vast amounts, is therefore anything but marginal. Tropical forests were excluded from the study, because there are too few monitoring sites. But primary forests in the boreal and temporary regions of the Northern Hemisphere alone capture some 1.3 gigatonnes of carbon a year, the meta-analysis of data from 519 plots of forests between 15 and 800 years of age has revealed. An editor's summary of the paper is here.

“Hence, 15 % of the global forest surface, which is currently not being considered for offsetting increasing atmospheric CO2 concentrations, is responsible for at least 10% of the global net ecosystem production,” the authors write.

Obviously, the carbon sequestered in old forest was previously accounted for elsewhere. Disturbingly, given that some offset profiteers praise tree planting as a panacea of sorts for climate change, young forests may actually be sources, rather than sinks, of CO2, if decomposition of soils and older vegetation preceded their creation.

Leaving intact and protecting old forests seems a far better option. This insight comes rather late, but better late than never. Oh, and it will really give climate negotiators something to think about.

My colleague Emma Marris has more in her news story here.

Quirin Schiermeier

Posted by Quirin Schiermeier on September 11, 2008
Categories: Biosphere feedbacks, Deforestation, Mitigation, Personal action, Quirin Schiermeier | Permalink | Comments (2) | TrackBacks (0)

For all tree huggers out there, this week’s Science is dedicated to ‘forests in flux’, paying tribute to the trees and their contribution to the greater good. A special collection of articles in print, with complementary and online material, examines the fate of the world’s forests, in the face of climate change and an escalating human population.

If it’s been a while since you’ve had the chance to appreciate the languid leafiness of forest foliage, check out the online video. Or for those of you hoping for a more ‘hands on’ experience, there’s a whole section of Science Careers dedicated to opportunities in forest ecology.

There’s lots of serious science, with six Perspectives and one Review by researchers from all over the globe who give their tuppence worth on what’s needed to better understand forests and manage them properly.

Of particular relevance to discussions on how forests can mitigate global warming, Lera Miles and Valerie Kapos have a Perspective highlighting the risks involved in proposed schemes such as REDD (reduced emissions from deforestation and forest degradation) and how to minimize them. Also on this topic, Josep Canadell and Michael Raupach write on what science currently tells us is the best way to manage forests for sequestering carbon.

Drew Purves and Stephen Pacala discuss how forest dynamics remain one of the largest uncertainties in predicting future climate change and detail some of the efforts underway to improve their representation in models. Or for a really solid review of how forests affect climate change, check out Gordan Bonan’s piece here.

Or if that seems like a lot of tree pulp to get through, here are some interesting stats from the issue:

Forests cover ~42 million km2 in tropical, temperate, and boreal lands, and cover ~30% of the land surface

They store ~45% of terrestrial carbon and account for ~50% of terrestrial net primary production.

Forests hold more than double the amount of carbon in the atmosphere.

Carbon uptake by forests in the 1990s contributed to ~33% of anthropogenic carbon emission from fossil fuel and landuse change.

Olive Heffernan

Image: Plantations of Pinus radiata and Eucalyptus nitens in Gippsland (Victoria, Australia); courtesy of Michael Ryan.

Posted by Olive Heffernan on June 13, 2008
Categories: Biodiversity and Ecology, Biosphere feedbacks, Carbon markets, Climate Policy, Climate Science, Climate prediction, Deforestation, GHG emissions, Mitigation, Olive Heffernan, Uncertainty | Permalink | Comments (1) | TrackBacks (0)

Cross-posted from The Great Beyond

Over at Canada's Financial Post, Lawrence Solomon is excited about the increase in biomass over the past two decades.

Planet Earth is on a roll! GPP is way up. NPP is way up. To the surprise of those who have been bearish on the planet, the data shows global production has been steadily climbing to record levels, ones not seen since these measurements began.

GPP is Gross Primary Production, a measure of the daily output of the global biosphere --the amount of new plant matter on land. NPP is Net Primary Production, an annual tally of the globe's production. Biomass is booming. The planet is the greenest it's been in decades, perhaps in centuries.

Judging by his record Mr Solomon likes to find new, surprising stories that over turn the evil IPCC-led consensus on climate science. Not clear, though, that he's very successful: this is neither new nor surprising. The work cited seems to be a 2004 paper by Steve Running and colleagues on monitoring NPP using the MODIS satellite data set (BioScience 54, 547-560 (2004) -- pdf), so it's hardly news. What's more, everyone studying carbon dioxide levels agrees that there are "biological sinks" -- places where more carbon-dioxide means more biomass, either because of the direct carbon-dioxide-fertilisation effect (it is, after all, plant food) or because the climatic effects are to the benefit of plants. Growth in sinks = growth in biomass. And a billion tonnes of carbon or so flowing into sinks every year will add up, over time. No denying that.

Continue reading "Biomass boosting" »

Posted by Oliver Morton on June 09, 2008
Categories: Biosphere feedbacks, Oliver Morton | Permalink | Comments (1) | TrackBacks (0)

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 (5) | 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)

An interesting contribution from the comments thread on Lovelock and Rapley propose cure for global warming by Peter Williams which I thought I'd hoist up here for wider circulation. -- Oliver

Lovelock and Rapley (Nature, 449,403, 2007) put forward the idea that by pumping up nutrient rich deep oceanic water, the subsequent stimulation of planktonic photosynthetic production would give rise to a very significant drawdown atmospheric CO2. The concept is flawed scientifically on two accounts. Planktonic photosynthesis results in the assimilation of inorganic nitrogen and CO2 in a ratio which has a modal value in the region of 6.6 – the so-called Redfield ratio. A fraction of the organic particles that arise as a consequence of photosynthetic production, sink into the deeper parts of the ocean. The C/N ratio of these particles is somewhat higher than the Redfield ratio, as there is some fast decomposition of the nitrogen (and phosphorus) rich organic components before the particles reach deep water. The particles are eventually decomposed in the deeps, with the production in inorganic nutrients, along with CO2. If this water, now enriched in inorganic nitrogen (and phosphorus), were brought to the surface, it would indeed stimulate planktonic photosynthesis and result in the assimilation of CO2. However, the upwelled water is not only enriched in inorganic nitrogen but also CO2 produced at the same time, the latter being slightly in excess of the Redfield requirement due to the elevated C/N ratio of the settling particles. Thus, rather than drawing down atmospheric CO2 from the atmosphere, there would be export of CO2. The situation in fact would be worse, as the upwelled water would need to warm up (otherwise it would simply sink back again) this would reduce the solubility of CO2, resulting in further export of oceanic CO2 into the atmosphere.

Further, from the engineering point of view the concept is infeasible – to lift up a 10m diameter column of dense (cold) to the surface would require a net lift of a number of tonnes and would almost certainly collapse a flexible tube or would cause a ribbed tube to concertina.

Even if the engineering problems could be solved, and the system made cost effective, both of which seem very doubtful, the proposal would have the reverse effect of that claimed.

Posted by Oliver Morton on October 08, 2007
Categories: Biosphere feedbacks, Ocean science | Permalink | Comments (4) | 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)

Further to the post and subsequent discussion on Sunshades, which grew out of this article on geoengineering, I thought I'd point to the new paper by Damon Matthews and Ken Caldeira in PNAS (Proc. Natl. Acad. Sci. USA, 10.1073/pnas.0700419104). It's an interesting paper that has some fascinating insights into the links between climate and the carbon cycle, and I think contains some pretty bad news for would-be geoengineers.

The paper uses a University of Victoria inermediate complexity GCM along with a land cover and carbon cycle model (the Hadley Centre MOSES2 and TRIFFID -- which is pretty much the best acronym in the business) to track climate from 1900 to 2100, using historical data up to the end of the twentieth century and the IPCC A2 carbon-dioxide emissions scenario from then on. Left to itself this gives a temperature increase of 3.5 centigrade over the 200 years. They then compared this baseline to alternative scenarios in which geoengineering strategies were turned on and off at various times. The geoengineering effect -- think of it as a layer of sulphates in the stratosphere, though the model wasn't that specific -- was calibrated to reduce the incoming sunlight in such a way as to counteract the radiative forcing of the carbon dioxide at any given time.

They found that the geoengineering could reduce the change in temperature in the model to something pretty negligible, though with some latitude-dependent effects; in the geoengineered world the poles warm a little compared to 1900 while the tropics cool a little. It also appeared that you could get back to 1900 temperatures even if you started the geoengineering well into the twentyfirst century, as long as you did enough of it.

Various reports of this work have highlighted a fairly obvious subsequent finding: if you stop the geoengineering while having done nothing about carbon emissions you can get some truly horrendously quick warming; your protection vanishes almost instantaneously and the potential warming you have stored up by allowing carbon-dioxide levels to rise suddenly all appears at once. Though it's nice to have some figures on this, it hardly comes as a surprise. Stephen Schneider has been going on about the fact that once you start you can't stop for decades, and in Tom Wigley's Science article (Science 314 pp. 452 - 454 (2006) DOI: 10.1126/science.1131728) last year, which explored the possibility of using a brief period of geoengineering to buy time in which to develop and field the technology needed for radical emissions reduction, there was a nasty looking blip in the warming rate at the point where the geoengineering was turned off. But it's still a sobering thought. While geoengineering through something like sulphate in the stratosphere is "reversible", in that if it starts having nasty effects you can just turn it off and the sulphate will fall out in a few years, that doesn't just leave you with the status quo ante -- it leaves you facing a far faster rate of warming that ypu have ever seen, and the adaptation challenges that go along with that.

There's an extra wrinkle in this paper, too; in the geoengineered world, you get increased carbon-dioxide uptake by the biosphere through the carbon-dioxide fertilisation effect on plants, but no offsetting increase in the carbon dioxide given off by soil respiration, which is taken to be temperature dependent. Turn the geoengineering off and the resultant warming drives up soil respiration in a positive feedback, releasing yet more carbon dioxide and pushing temperatures yet higher. It's a good example of the links between climate and the carbon cycle and the ways they can mess you up. Not as good an example, though, as that offered by the precipitation outlook, which seems to me the most startling result here.

Continue reading "More on geoengineering" »

Posted by Oliver Morton on June 10, 2007
Categories: Biosphere feedbacks, Climate Science, Oliver Morton | Permalink | Comments (1) | TrackBacks (0)

This week in Nature we have a news story on an attempt to follow up Frank Keppler's work on methane produced aerobically by green plants which we published early last year (news story | paper). The Keppler piece, which suggested that methane emissions from green plants were a significant but previously unappreciated factor in global methane emissions, caused quit a lot of fuss, understandably, in the media -- since methane is a greenhouse gas which, over short time horizons, is about 75 times more powerful than carbon dioxide -- and quite a lot of befuddlement among plant scientists. If it were true, it would have significant implications for the way that people model methane production, and the levels of production that one might predict in a warming world. The debate rumbled on last year (another news report, this time by my colleague Quirin).

The new work that Tom Dueck and colleagues have published in New Phytologist (paper), though , finds no methane emissions from plants at all.

Obviously, not necessarily the last word. As Mike Hopkin reports:

Both groups have criticized the other's choice of experimental method. Dueck says that Keppler's group kept plants in sealed plastic containers instead of flow chambers, and exposed them to sources of stress such as bright sunlight and high temperature, which could have produced methane as an artefact. Keppler retorts that the use of ¹³C is an artificial piece of chemical trickery with unknown effects on plant metabolism, and also argues that methane production can vary by up to three orders of magnitude between species.

What Mike doesn't mention, because an evil news editor (me) wouldn't give him the space, is that various people in the community have pointed to an interesting contrast between the way plant scientists responded to the discovery of isoprene emissions and the Keppler work. With isoprene people said oh that's interesting, replicated, and got on with it. This work has had a far frostier welcome.

On isoprene, this is as good a place as any to mention an interesting perspective by Manuel Lerdau in Science a few weeks ago on a possible isoprene-ozone positive feedback (paper). Isoprene within leaves protects the plants that produce it against ozone. But when isoprene gets out into the air, as it will, it can react with nitrogen oxides to make ozone. Only some species produce isoprene, and so these isoprene-producing plants both protect themselves against ozone and, in Nox-rich environments, increase the ozone stress on their non-isoprene-producing neighbours.

If this effect is real, it might have significant effects on forest composition over the next century.

One last thing to note on the Keppler story: it led to Carl Zimmer saying something nice about us, and that is always a good thing. As of course is Carl.

Posted by Oliver Morton on May 04, 2007
Categories: Biosphere feedbacks, Oliver Morton | Permalink | Comments (8) | TrackBacks (0)