Some 30 years ago, as the United States began to tighten its environmental regulations on residential and industrial wastewater, operators of sewage-treatment plants embraced what seemed an eminently sensible idea. They decided to take the rich organic sludge left over after clean water is extracted and sell it to farmers as fertilizer. The programme might well be as sensible as it seems. It is possible that the millions of tonnes of sludge being spread across the rural landscape contain no significant levels of toxic chemicals, heavy metals or disease-causing organisms.

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. (Editorial)

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 the authors 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.

Despite two centuries of effort in characterizing environmental gradients of species richness in search of universal patterns, surprisingly few of these patterns have been widely acknowledged. Here we show that when resampling a data set comprising 400,000 records for 3,046 Pyrenean floristic species at different scales of analysis (achieved by varying grain size and the extent of the gradients sampled), the derived species richness pattern changed progressively from hump-shaped to a monotonic pattern as the scale of extent diminished.

The Amazon rainforest plays a crucial role in the climate system, helping to drive atmospheric circulations in the tropics by absorbing energy and recycling about half of the rainfall that falls on it. This region (Amazonia) is also estimated to contain about onetenth of the total carbon stored in land ecosystems, and to account for one-tenth of global, net primary productivity.

In the Commentary 'Dangerous assumptions' (Nature 452, 531

In their Commentary 'Dangerous assumptions' (Nature 452, 531

In their Commentary 'Dangerous assumptions' (Nature 452, 531

Pielke et al. correctly point out in their Commentary 'Dangerous assumptions' (Nature 452, 531

I largely agree with the overall conclusion of Pielke et al. in their Commentary 'Dangerous assumptions' (Nature 452, 531