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 (2) | 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.

As Woods points out, colleagues of his at the Hadley Centre in the UK published a similar sort of prediction research of a similar sort, though rather different in approach and with significantly different predictions, in Science last year, as we reported at the time. Combining real world data and modelling this way has only recently become possible.

The new model predicts North Atlantic, European and North American sea surface temperatures will cool slightly; tropical Pacific temperatures will likely be almost unchanged and global temperatures will probably be offset by this variation.

This does not mean we don’t need to worry about global warming. “The natural variations change climate on this timescale and policymakers may either think mitigation is working or that there is no global warming at all,” says Keenlyside (Reuters).

As the NY Times’s Andrew Revkin notes on his blog:

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 ...

The NY Times wraps up its main piece with a useful quote from Kevin Trenberth, of the US National Center for Atmospheric Research: “Too many think global warming means monotonic relentless warming everywhere year after year. It does not happen that way.”

Not everyone is happy though. Here's the always-worth-listening-to Roger Pielke Jr on his Prometheus blog:

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.

Image: NASA Glenn Research Center (NASA-GRC)

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 (7) | TrackBacks (0)

With an uninterrupted 17-million year sediment record of Antarctic’s climatic past now available, scientists are hoping for unique new insights into the continent’s climatic past.

A few initial results of the Antarctic Geological Drilling programme (ANDRILL) were announced last week at the general assembly of the European Geosciences Union in Vienna. There is an online news story here.

Antarctica’s ice sheets, so it seems, respond more sensitively to climate fluctuations than has been assumed. During warmer periods, the West Antarctic Ice Sheet and its floating extension, the western Ross Ice Shelf, have shrunk substantially. Some 3.5 million years ago the ice seems to have disappeared completely for around 200,000 years. There were snow-capped mountains, alpine trees, gushing rivers, quiet lakes – the frozen continent was a place where you would love to go fishing or hiking, were it not for the midges.

The world was warmer then than it is today, but not substantially so. If temperatures continue to rise, glaciers in Antarctic’s warmer western part might begin to retreat again before long. A few million years ago, Antarctic melting probably raised sea levels globally by 10 metres or so. If history repeats itself, we’re headed for trouble.

Quirin Schiermeier

Posted by Quirin Schiermeier on April 24, 2008
Categories: Recent contributors, Categories, Conferences and Meetings, EGU 2008, Palaeoclimate, Quirin Schiermeier | Permalink | Comments (5) | 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)

If there was an eye in the sky keeping watch on our greenhouse gas emissions, what carbon crimes would it reveal?

The ability to measure greenhouse gases from space, soon to become a reality, could answer this question.

Currently, it’s virtually impossible to identify the exact source – and destination - of greenhouse gases, a prominent theme at this year’s European Geosciences Union conference in Vienna.

But, according to scientists speaking today at the conference, this is all set to change within the coming year when two major satellites designed to monitor greenhouse gases will be launched into space.

Due to leave Earth on December 15, the first of these is the Orbiting Carbon Observatory (OCO), a US$300 million-or-so innovation of scientists and engineers at NASA’s Jet Propulsion Laboratory in California. The Japanese version, known as the Greenhouse Gases Observing Satellite, or GOSAT, has an anticipated launch date in January or February 2009.

For a detailed low-down on the satellites and how they will work, see Amanda Haag’s news feature in Nature (subscription) last December. Since then, the scientists have mostly been testing and calibrating the instruments to make sure they work once they’re orbiting the Earth.

Within a year or two, if not sooner, they will enable scientists to identify major sources and sinks or carbon, says Charles Miller, one of the Principal Co-ordinators of the OCO mission. The greenhouse gas measurements taken by the instrument, which will orbit the planet 14.5 times per day, will be three times more precise than any trace gas measurements ever taken from space.

All-in-all, the missions represent an unprecedented effort to collect global climate data from space. While this is fascinating from a scientific perspective, it should also have some interesting political implications by enabling the easy identification of climate culprits.

“If one were to imagine a way to monitor or verify [emissions], then this would be the way to go”, says Miller. For instance, it should quash (or raise, depending on who you’re talking to) fears that nations claiming credits for avoiding deforestation under the Kyoto Protocol will be able to divert the problem elsewhere.

Miller says they often joke that the instrument could detect the greenhouse gas emissions of serious carbon heaveyweights from space. But while the new satellites won’t realistically help reporting on individual carbon crimes, it could act as a ‘big brother’ to keep countries in line with their Kyoto commitments. Personally, I’m curious to know the OCO’s own carbon footprint!

That’s all from me from this year’s European Geosciences Union conference in Vienna. Over and out….

Olive Heffernan

Posted by Olive Heffernan on April 18, 2008
Categories: Atmospheric Science, Conferences and Meetings, EGU 2008, Olive Heffernan, Technology | Permalink | Comments (0) | TrackBacks (0)