Archives for May 2008

In the blue corner we have Roger Pielke Jr (Prometheus) and Lucia Liljegren (The Blackboard). In the red corner we have James Annan (James’ Empty Blog) and Gavin Schmidt (RealClimate).

Interestingly, all four of the contenders accept the the IPCC consensus view on climate change, but Pielke Jr/Liljegren show that IPCC projections are currently falsified by observations, whereas Annan/Schmidt have the opposite view. Read the various blog posts and make up your own minds.

Lucia Concludes:

The IPCC projections remain falsified. Comparison to data suggest they are biased. The statistical tests accounts for the actual weather noise in data on earth.

The argument that this falsification is somehow inapplicable because the earth data falls inside the full range of possibilities for models is flawed. We know why the full range of climate models is huge: It contains a large amount of “climate model noise” due to models that are individually biased relative to the system of interest: the earth.

It will continue to admit what I have always admitted: When applying hypothesis tests to a confidence limit of 5%, one does expect to be wrong 5% of the time. It is entirely possible that the current falsification fall in the category of 5% incorrect falsifications. If this is so, the “falsified” diagnosis will reverse, and not we won’t see another one anytime soon.

However, for now, the IPCC projections remain falsified, and will do so until the temperatures pick up. Given the current statistical state ( a period when large “type 2″ error is expected) it is quite likely we will soon see “fail to falsify” even if the current falsification is a true one. But if the falsification is a “true” falsification, as is most likely, we will see “falsifications” resume. In that case, the falsification will ultimately stick.

For now, all we can do is watch the temperature trends of the real earth.

Quenching forest fires leads to more carbon in the air, says new research carried out in Californian forests. The discovery suggests that forests spared from fire may release more of the greenhouse gas into the air than they absorb.

Decades of suppressing natural fires has increased the number of surviving trees in California’s forests. But this growth has been at the expense of larger trees, which are less resilient to drought and other stresses than smaller, younger trees, resulting in a decline in the total amount of carbon stored in these forests.

Nature News.com: Forest-fire management ‘raises carbon emissions’

Governments should work together to build the supercomputers needed for future predictions that can capture the detail required to inform policy.

Few scientific creations have had greater impact on public opinion and policy than computer models of Earth’s climate. These models, which unanimously show a rising tide of red as temperatures climb worldwide, have been key over the past decade in forging the scientific and political consensus that global warming is a grave danger.

Now that that consensus is all but universal, climate modellers are looking to take the next step, and to convert their creations from harbingers of doom to tools of practical policy. That means making their simulations good enough to guide hard decisions, from targets for carbon dioxide emissions on a global scale to the adaptations required to meet changing rainfall and extreme weather events on regional and local scales.

Today’s modelling efforts, though, are not up to that job. They all agree on the general direction in which the climate will move as greenhouse gases build up, but they do not reliably capture all the nuances of today’s climate, let alone tomorrow’s. Moreover, each model differs from reality in different ways.

Editorial: The next big climate challenge

Methane outbursts from seafloor deposits are unlikely to have been the sole cause of an extreme episode of global warming around the time of the Palaeocene–Eocene Thermal Maximum some 55 million years ago.

Research Highlights: Palaeoclimate: Methane didn’t act alone

Data laboriously extracted from an Antarctic ice core provide an unprecedented view of temperature, and levels of atmospheric carbon dioxide and methane, over the past 800,000 years of Earth’s history.

The data further reinforce the tight link between greenhouse gases and climate, a link maintained by as-yet only partially understood feedbacks in the Earth system. Variations in methane levels are most probably caused by variations in the influence of temperature and rainfall on wetlands in the tropics and boreal (high-northern-latitude) regions. Carbon dioxide variability is almost universally viewed as an oceanic phenomenon, a consequence of the large pools of carbon sequestered there. Changes in ocean circulation, biological productivity, carbon dioxide solubility and other aspects of ocean chemistry have been implicated, but the exact mix of mechanisms is not clear.

News and Views: Palaeoclimate: Windows on the greenhouse

The climate is changing, and so are aspects of the world’s physical and biological systems. It is no easy matter to link cause and effect — the latest attack on the problem brings the power of meta-analysis to bear. It uses a larger database than the recent IPCC report, and it takes account of land-use change and other complications. The authors conclude that anthropogenic climate change is affecting physical and biological systems globally. But as Francis Zwiers and Gabriele Hegerl point out in News & Views, this proof based on the principle of joint attribution stops short of the statistical certainty that would be provided by ‘end-to-end’ models linking human activity directly to the observed changes, rather than via effects on the climate system.

News and Views: Climate change: Attributing cause and effect

Significant changes in physical and biological systems are occurring on all continents and in most oceans, with a concentration of available data in Europe and North America. Most of these changes are in the direction expected with warming temperature. Here we show that these changes in natural systems since at least 1970 are occurring in regions of observed temperature increases, and that these temperature increases at continental scales cannot be explained by natural climate variations alone. Given the conclusions from the Intergovernmental Panel on Climate Change (IPCC) Fourth Assessment Report that most of the observed increase in global average temperatures since the mid-twentieth century is very likely to be due to the observed increase in anthropogenic greenhouse gas concentrations, and furthermore that it is likely that there has been significant anthropogenic warming over the past 50 years averaged over each continent except Antarctica, we conclude that anthropogenic climate change is having a significant impact on physical and biological systems globally and in some continents.

Article: Attributing physical and biological impacts to anthropogenic climate change

Changes in past atmospheric carbon dioxide concentrations can be determined by measuring the composition of air trapped in ice cores from Antarctica. So far, the Antarctic Vostok and EPICA Dome C ice cores have provided a composite record of atmospheric carbon dioxide levels over the past 650,000 years1, 2, 3, 4. Here we present results of the lowest 200 m of the Dome C ice core, extending the record of atmospheric carbon dioxide concentration by two complete glacial cycles to 800,000 yr before present. From previously published data1, 2, 3, 4, 5, 6, 7, 8 and the present work, we find that atmospheric carbon dioxide is strongly correlated with Antarctic temperature throughout eight glacial cycles but with significantly lower concentrations between 650,000 and 750,000 yr before present. Carbon dioxide levels are below 180 parts per million by volume (p.p.m.v.) for a period of 3,000 yr during Marine Isotope Stage 16, possibly reflecting more pronounced oceanic carbon storage. We report the lowest carbon dioxide concentration measured in an ice core, which extends the pre-industrial range of carbon dioxide concentrations during the late Quaternary by about 10 p.p.m.v. to 172–300 p.p.m.v.

Letter: High-resolution carbon dioxide concentration record 650,000–800,000 years before present

Atmospheric methane is an important greenhouse gas and a sensitive indicator of climate change and millennial-scale temperature variability1. Its concentrations over the past 650,000 years have varied between 350 and 800 parts per 109 by volume (p.p.b.v.) during glacial and interglacial periods, respectively2. In comparison, present-day methane levels of 1,770 p.p.b.v. have been reported3. Insights into the external forcing factors and internal feedbacks controlling atmospheric methane are essential for predicting the methane budget in a warmer world3. Here we present a detailed atmospheric methane record from the EPICA Dome C ice core that extends the history of this greenhouse gas to 800,000 yr before present. The average time resolution of the new data is 380 yr and permits the identification of orbital and millennial-scale features. Spectral analyses indicate that the long-term variability in atmospheric methane levels is dominated by 100,000 yr glacial–interglacial cycles up to 400,000 yr ago with an increasing contribution of the precessional component during the four more recent climatic cycles. We suggest that changes in the strength of tropical methane sources and sinks (wetlands, atmospheric oxidation), possibly influenced by changes in monsoon systems and the position of the intertropical convergence zone, controlled the atmospheric methane budget, with an additional source input during major terminations as the retreat of the northern ice sheet allowed higher methane emissions from extending periglacial wetlands. Millennial-scale changes in methane levels identified in our record as being associated with Antarctic isotope maxima events1, 4 are indicative of ubiquitous millennial-scale temperature variability during the past eight glacial cycles.

Letter: Orbital and millennial-scale features of atmospheric CH4 over the past 800,000 years