Anomalous Emissions of SO2 During the Recent Eruption of Santa Ana Volcano, El Salvador, Central America

Santa Ana volcano in western El Salvador, Central America, had a phreatic eruption at 8:05 am (local time) on October 1, 2005, 101 years after its last eruption. However, during the last one hundred years this volcano has presented periods of quiet degassing with fumarolic activity and an acidic lake within its crater. This paper presents results of frequent measurements of SO₂ degassing using the MiniDOAS (Differential Optical Absorption Spectroscopy) system and a comparison with the volcanic seismicity prior to the eruption, during, and after the eruption. Vehicle measurements of SO₂ flux were taken every hour during the first nine days of the eruption and daily after that. The period of time reported here is from August to December, 2005. Three periods of degassing are distinguished: pre-eruptive, eruptive, and post-eruptive periods. The intense activity at Santa Ana volcano started in July 2005. During the pre-eruptive period up to 4306 and 5154 ton/day of SO₂ flux were recorded on October 24 and September 9, 2005, respectively. These values were of the same order of magnitude as the recorded values just after the October 1^st eruption (2925 ton/day at 10:01 am). Hourly measurements of SO₂ flux taken during the first nine days after the main eruptive event indicate that explosions are preceded by an increase in SO₂ flux and that this parameter reaches a peak after the explosion took place. This behavior suggests that increasing accumulation of exsolved magmatic gases occurs within the magmatic chamber before the explosions, increasing the pressure until the point of explosion. A correlation between SO₂ fluxes and RSAM (Real Time Seismic Amplitude Measurements) is observed during the complete sampling period. Periodic fluctuations in the SO₂ and RSAM values during the entire study period are observed. One possible mechanism explaining these fluctuations it that convective circulation within the magmatic chamber can bring fresh magma periodically to shallow levels, allowing increasing degasification and then decreasing degasification as the batch of magma lowers its gas content, becomes denser, and sinks to give space to a new magma pulse. These results illustrate that the measurements of SO₂ flux can provide important warning signals for incoming explosive activity in active volcanoes.     

The Energy Balance Experiment EBEX-2000. Part I: overview and energy balance

An overview of the Energy Balance Experiment (EBEX-2000) is given. This experiment studied the ability of state-of-the-art measurements to close the surface energy balance over a surface (a vegetative canopy with large evapotranspiration) where closure has been difficult to obtain. A flood-irrigated cotton field over uniform terrain was used, though aerial imagery and direct flux measurements showed that the surface still was inhomogeneous. All major terms of the surface energy balance were measured at nine sites to characterize the spatial variability across the field. Included in these observations was an estimate of heat storage in the plant canopy. The resultant imbalance still was 10%, which exceeds the estimated measurement error. We speculate that horizontal advection in the layer between the canopy top and our flux measurement height may cause this imbalance, though our estimates of this term using our measurements resulted in values less than what would be required to balance the budget. The National Center for Atmospheric Research is supported by the National Science Foundation     

Did Humankind Prevent a Holocene Glaciation?

Recently, W.F. Ruddiman (2003, Climatic Change, Vol. 61, pp. 261–293) suggested that the anthropocene, the geological epoch of significant anthropospheric interference with the natural Earth system, has started much earlier than previously thought (P. I. Crutzen and E. F. Stoermer, 2000, IGBP Newsletter, Vol. 429, pp. 623–628). Ruddiman proposed that due to human land use, atmospheric concentrations of CO₂ and CH₄ began to deviate from their natural declining trends some 8000 and 5000 years ago, respectively. Furthermore, Ruddiman concluded that greenhouse gas concentrations grew anomalously thereby preventing natural large-scale glaciation of northern North America that should have occurred some 4000–5000 years ago without human interference. Here we would like to comment on (a) natural changes in atmospheric CO₂ concentration during the Holocene and (b) on the possibility of a Holocene glacial inception. We substantiate our comments by modelling results which suggest that the last three interglacials are not a proper analogue for Holocene climate variations. In particular, we show that our model does not yield a glacial inception during the last several thousand years even if a declining trend in atmospheric CO₂ was assumed.     

A variable lacustrine environment in Lake Winnipeg, Manitoba: Evidence from modern thecamoebian distribution

Thecamoebians (testate protozoan) were examined in 18 surface sediment samples from the North and South basins and the Narrows of Lake Winnipeg, Manitoba. Significantly higher numbers of thecamoebians and tintinnids in the North Basin compared to the Narrows and South Basin are attributed to the effects of urban development around the South Basin of Lake Winnipeg. Human population growth in this area has led to increased nutrient concentration in runoff, causing eutrophication of the southern lake, which in turn allows for increased algal productivity. Cucurbitella tricuspis is found in large abundances in the South Basin, particularly close to the inlet of the Red and Assiniboine rivers. High abundances of this species have been attributed to eutrophic conditions, which this species appears to withstand more successfully than other species. Increases in domestic waste output, that have led to elevated heavy metal concentrations in lake bottom sediments of the South Basin, may have resulted in lower abundances of thecamoebians, further reducing competition.Strong currents in the Narrows cause a slightly coarser substrate and sweep away food sources such as phytoplankton. This results in a lower faunal abundance and slightly lower species richness of thecamoebians. Robust species such as the coarse-grained Difflugia viscidula and species which feed on bacteria such as Centropyxis aculeata show increased abundances.Modern thecamoebian assemblages are comparable to Late Holocene faunal associations in terms of species composition. Individual species abundances, however, have changed. For example, in the North Basin the Late Holocene dominance of Difflugia manicata is replaced by various strains of Difflugia oblonga during recent times. A common species of the South Basin from Late Holocene to recent times is Difflugia globulus. It would appear that faunal differences between basins are the result of differences in algal food sources.     

An evaluation of the CMIP3 and CMIP5 simulations in their skill of simulating the spatial structure of SST variability

The natural sea surface temperature (SST) variability in the global oceans is evaluated in simulations of the Climate Model Intercomparison Project Phase 3 (CMIP3) and CMIP5 models. In this evaluation, we examine how well the spatial structure of the SST variability matches between the observations and simulations on the basis of their leading empirical orthogonal functions-modes. Here we focus on the high-pass filter monthly mean time scales and the longer 5 years running mean time scales. We will compare the models and observations against simple null hypotheses, such as isotropic diffusion (red noise) or a slab ocean model, to illustrate the models skill in simulating realistic patterns of variability. Some models show good skill in simulating the observed spatial structure of the SST variability in the tropical domains and less so in the extra-tropical domains. However, most models show substantial deviations from the observations and from each other in most domains and particularly in the North Atlantic and Southern Ocean on the longer (5 years running mean) time scale. In many cases the simple spatial red noise null hypothesis is closer to the observed structure than most models, despite the fact that the observed SST variability shows significant deviations from this simple spatial red noise null hypothesis. The CMIP models tend to largely overestimate the effective spatial number degrees of freedom and simulate too strongly localized patterns of SST variability at the wrong locations with structures that are different from the observed. However, the CMIP5 ensemble shows some improvement over the CMIP3 ensemble, mostly in the tropical domains. Further, the spatial structure of the SST modes of the CMIP3 and CMIP5 super ensemble is more realistic than any single model, if the relative explained variances of these modes are scaled by the observed eigenvalues.     

Analysis of the Slab Ocean El Nino atmospheric feedbacks in observed and simulated ENSO dynamics

In a recent study it was illustrated that the El Nino Southern Oscillation (ENSO) mode can exist in the absence of any ocean dynamics. This oscillating mode exists just due to the interaction between atmospheric heat fluxes and ocean heat capacity. The primary purpose of this study is to further explore these atmospheric Slab Ocean ENSO dynamics and therefore the role of positive atmospheric feedbacks in model simulations and observations. The positive solar radiation feedback to sea surface temperature (SST), due to reduced cloud cover for anomalous warm SSTs, is the main positive feedback in the Slab Ocean El Nino dynamics. The strength of this positive cloud feedback is strongly related to the strength of the equatorial cold tongue. The combination of positive latent and sensible heat fluxes to the west and negative ones to the east of positive anomalies leads to the westward propagation of the SST anomalies, which allows for oscillating behavior with a preferred period of 6–7 years. Several indications are found that parts of these dynamics are indeed observed and simulated in other atmospheric or coupled general circulation models (AGCMs or CGCMs). The CMIP3 AGCM-slab ensemble of 13 different AGCM simulations shows unstable ocean–atmosphere interactions along the equatorial Pacific related to stronger cold tongues. In observations and in the CMIP3 and CMIP5 CGCM model ensemble the strength and sign of the cloud feedback is a function of the strength of the cold tongue. In summary, this indicates that the Slab Ocean El Nino dynamics are indeed a characteristic of the equatorial Pacific climate that is only dominant or significantly contributing to the ENSO dynamics if the SST cold tongue is sufficiently strong. In the observations this is only the case during strong La Nina conditions. The presence of the Slab Ocean ENSO atmospheric feedbacks in observations and CGCM model simulations implies that the family of physical ENSO modes does have another member, which is entirely driven by atmospheric processes and does not need to have the same spatial pattern nor the same time scales as the main ENSO dynamics.     

Contributions of individual countries?? emissions to climate change and their uncertainty

We have compiled historical greenhouse gas emissions and their uncertainties on country and sector level and assessed their contribution to cumulative emissions and to global average temperature increase in the past and for a the future emission scenario. We find that uncertainty in historical contribution estimates differs between countries due to different shares of greenhouse gases and time development of emissions. Although historical emissions in the distant past are very uncertain, their influence on countries?? or sectors?? contributions to temperature increase is relatively small in most cases, because these results are dominated by recent (high) emissions. For relative contributions to cumulative emissions and temperature rise, the uncertainty introduced by unknown historical emissions is larger than the uncertainty introduced by the use of different climate models. The choice of different parameters in the calculation of relative contributions is most relevant for countries that are different from the world average in greenhouse gas mix and timing of emissions. The choice of the indicator (cumulative GWP weighted emissions or temperature increase) is very important for a few countries (altering contributions up to a factor of 2) and could be considered small for most countries (in the order of 10%). The choice of the year, from which to start accounting for emissions (e.g. 1750 or 1990), is important for many countries, up to a factor of 2.2 and on average of around 1.3. Including or excluding land-use change and forestry or non-CO₂ gases changes relative contributions dramatically for a third of the countries (by a factor of 5 to a factor of 90). Industrialised countries started to increase CO₂ emissions from energy use much earlier. Developing countries?? emissions from land-use change and forestry as well as of CH₄ and N₂O were substantial before their emissions from energy use.     

Who participates in the Intergovernmental Panel on Climate Change and why: A quantitative assessment of the national representation of authors in the Intergovernmental Panel on Climate Change

This paper presents a quantitative analysis of international representation in the activities of the Intergovernmental Panel on Climate Change using expert authorship counts by country in each of the four IPCC assessment reports (1990, 1995, 2001 and 2007). Overall, we find that 45% of countries, all Non-Annex 1, have never had authors participate in the IPCC process; on the other hand, European and North American experts are make up more than 75% of all authors (N = 4394). Generalized linear models using negative binomial regression were used to quantitatively estimate the effect of a number of socio-economic, environmental and procedural factors influencing country-level participation in the IPCC. Per capita gross domestic product, population, English-speaking status, and levels of tertiary education were all found to be statistically significant drivers of authorship counts. In particular, participation by authors from English-speaking Non-Annex 1 countries is 2.5 times greater than those that are non-English speaking. Regionally small island nations of Oceania were the most severely under-represented group. South American and Asian countries had fewer authors, and African countries had more authors than what might be expected on the basis of demographic and socio-economic data. These differences across nations partly reflect existing scientific capacity that will be slow to change. However, the on-going under-representation of developing country scientists in the IPCC, particularly in the assessment of climate science (WGI) and climate mitigation (WGIII) warrants greater efforts to close the capacity gap.