There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality.

Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

I and i

The planetary boundaries framework defines a safe operating space for humanity based on the intrinsic biophysical processes that regulate the stability of the Earth system. Here, we revise and update the planetary boundary framework, with a focus on the underpinning biophysical science, based on targeted input from expert research communities and on more general scientific advances over the past 5 years. Several of the boundaries now have a two-tier approach, reflecting the importance of cross-scale interactions and the regional-level heterogeneity of the processes that underpin the boundaries. Two core boundaries—climate change and biosphere integrity—have been identified, each of which has the potential on its own to drive the Earth system into a new state should they be substantially and persistently transgressed.

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Planetary boundaries: Guiding human development on a changing planet

THE major active ingredient of marijuana, Δ9-tetrahydrocannabi-nol (Δ9-THC), has been used as a psychoactive agent for thousands of years. Marijuana, and Δ9-THC, also exert a wide range of other effects including analgesia, anti-inflammation, immunosuppression, anticonvulsion, alleviation of intraocular pressure in glaucoma, and attenuation of vomiting1. The clinical application of cannabinoids has, however, been limited by their psychoactive effects, and this has led to interest in the biochemical bases of their action. Progress stemmed initially from the synthesis of potent derivatives of δ9-THC4,5, and more recently from the cloning of a gene encoding a G-protein-coupled receptor for cannabinoids6. This receptor is expressed in the brain but not in the periphery, except for a low level in testes. It has been proposed that the non-psychoactive effects of cannabinoids are either mediated centrally or through direct interaction with other, non-receptor proteins1,7,8. Here we report the cloning of a receptor for cannabinoids that is not expressed in the brain but rather in macrophages in the marginal zone of spleen.

Molecular characterization of a peripheral receptor for cannabinoids

This paper contrasts the natural and anthropogenic controls on the conversion of unreactive N2 to more reactive forms of nitrogen (Nr). A variety of data sets are used to construct global N budgets for 1860 and the early 1990s and to make projections for the global N budget in 2050. Regional N budgets for Asia, North America, and other major regions for the early 1990s, as well as the marine N budget, are presented to highlight the dominant fluxes of nitrogen in each region. Important findings are that human activities increasingly dominate the N budget at the global and at most regional scales, the terrestrial and open ocean N budgets are essentially dis- connected, and the fixed forms of N are accumulating in most environmental reservoirs. The largest uncertainties in our understanding of the N budget at most scales are the rates of natural biological nitrogen fixation, the amount of Nr storage in most environmental reservoirs, and the production rates of N2 by denitrification.

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Nitrogen cycles: past, present, and future

Relationships between wind speed and gas transfer, combined with knowledge of the partial pressure difference of CO2 across the air-sea interface are frequently used to determine the CO2 flux between the ocean and the atmosphere. Little attention has been paid to the influence of variability in wind speed on the calculated gas transfer velocities and the possibility of chemical enhancement of CO2 exchange at low wind speeds over the ocean. The effect of these parameters is illustrated using a quadratic dependence of gas exchange on wind speed which is fit through gas transfer velocities over the ocean determined by the natural-14C disequilibrium and the bomb-14C inventory methods. Some of the variability between different data sets can be accounted for by the suggested mechanisms, but much of the variation appears due to other causes. Possible causes for the large difference between two frequently used relationships between gas transfer and wind speed are discussed. To determine fluxes of gases other than CO2 across the air-water interface, the relevant expressions for gas transfer, and the temperature and salinity dependence of the Schmidt number and solubility of several gases of environmental interest are included in an appendix.

Relationship between wind speed and gas exchange over the ocean

There have been several recent advances in our understanding of the geochemistry of iron and its effect on the marine biota. In this contribution, we highlight two such advances, namely results of the Ironex experiments in the equatorial Pacific and the recent publication of the first global data set for iron concentrations in the oceans. These have profound consequences for our understanding of the factors that set the pre-anthropogenic concentration of carbon dioxide in the atmosphere, and how these may have changed between glacial and interglacial time. Some of these consequences we are able to quantify and explore, but others open new questions for which we have as yet no answers.

The sensitivity of atmospheric CO2 concentrations to input of iron to the oceans

The Dependence of Flame Spread and Probability of Ignition on Atmospheric Oxygen

A detailed evaluation of the radiative transfer code used in the Met Office Unified Climate/Forecast Model is performed, comparing it with a line-by-line model and testing the climatic effects of errors in a radiative--convective model. The radiative forcing at the tropopause due to CO2 changes within SRES scenarios and across Quaternary glacial cycles is represented with reasonable accuracy, suggesting that surface temperature will be correctly predicted. However, this is achieved by partial cancellation of opposing errors in upward and downward fluxes. The changes in the vertical profiles of radiative fluxes and the changes to surface and top-of-atmosphere fluxes all show significant errors, even at twice pre-industrial CO2. This causes a sign error in the change in the convective flux in the radiative--convective model. Performance of the code deteriorates rapidly above four times pre-industrial CO2. For less-abundant greenhouse gases, CH4 and N2O, the errors are larger as a proportion of their radiative forcings. Errors for surface and top-of-atmosphere fluxes for CO2 are similar to those from the mean of the general circulation model (GCM) codes submitted to the intercomparison of radiation codes for IPCC AR4, implying that errors as found here may not be uncommon in climate models. A renewed emphasis on accuracy in radiative transfer calculations and openness in intercomparison studies is necessary to improve the modelling of climate change. Copyright © 2009 Royal Meteorological Society

An evaluation of the long‐wave radiative transfer code used in the Met Office Unified Model

Despite great advances in understanding of the earth’s climate, our estimate of the global temperature rise due to a doubling of atmospheric CO2 has not greatly changed in a hundred years, and the estimate of the uncertainty on that number has actually increased. This is because while the basic mechanism of greenhouse-gas forcing of climate is well understood, the multiple, mostly positive, feedback loops that amplify this effect are not. The combined effect of many of these feedbacks can be seen in the record of past climate, and analysis of these suggests that our present models tend to under-predict the eventual, equilibrium climate change due to a given increase in atmospheric CO2. In the foreseeable future (next 20 years) climate modelling research will probably not materially decrease the uncertainty on predictions for the climate of 2100. The uncertainty will only start to decrease as we actually observe what happens to the climate. The best use of climate models at present is via ensembles of predictions that give a probabilistic description of the range of uncertainty involved in future climate. Recent studies suggest a skewed probability distribution, with a tail stretching out to high climate sensitivities. Combined with estimates of the likely economic impact of climate change, this strongly suggests that research should be concentrated on trying to reduce the uncertainty represented by this tail of low probability, but high impact, scenarios.

Certainty and Uncertainty in Climate Change Predictions: What Use are Climate Models?

Hyaluronic acid fluid agents for the prevention of adhesions after fertility-preserving gynecological surgery: a meta-analysis of randomized controlled trials

Andrew J. Watson

Papers

The sensitivity of atmospheric CO2 concentrations to input of iron to the oceans

The Dependence of Flame Spread and Probability of Ignition on Atmospheric Oxygen

An evaluation of the long‐wave radiative transfer code used in the Met Office Unified Model

Certainty and Uncertainty in Climate Change Predictions: What Use are Climate Models?

Hyaluronic acid fluid agents for the prevention of adhesions after fertility-preserving gynecological surgery: a meta-analysis of randomized controlled trials