Current economic models tend to underestimate seriously both the potential impacts of dangerous climate change and the wider benefits of a transition to low-carbon growth. There is an urgent need for a new generation of models that give a more accurate picture.

Dark impacts

...The Fifth Assessment Report of the Intergovernmental Panel on Climate Change (IPCC), published in 2013 and 2014, provided a comprehensive overview of the literature on the costs of action and inaction. But the assessment understated the limitations of the research done so far. Essentially, it reported on a body of literature that had systematically and grossly underestimated the risks of unmanaged climate change. Furthermore, that literature had failed to capture the learning processes and economies of scale involved in radical structural and technical change, and the benefits of reducing fossil-fuel pollution, protecting biodiversity and forests, and so on...

This figure is compelling because it shows a clear linear relationship between cumulative CO2 emissions and a measure of the global climate response. The obvious consequences are (1) that every tonne of CO2 contributes about the same amount of global warming no matter when it is emitted, (2) that any target for the stabilization of ?Tglob implies a finite CO2 budget or quota that can be emitted, and (3) that global net emissions at some point need to be zero2, 3, 4, 5, 6.

There is considerable concern over declines in insect pollinator communities and potential impacts on the pollination of crops and wildflowers1, 2, 3, 4. Among the multiple pressures facing pollinators2, 3, 4, decreasing floral resources due to habitat loss and degradation has been suggested as a key contributing factor2, 3, 4, 5, 6, 7, 8. However, a lack of quantitative data has hampered testing for historical changes in floral resources. Here we show that overall floral rewards can be estimated at a national scale by combining vegetation surveys and direct nectar measurements. We find evidence for substantial losses in nectar resources in England and Wales between the 1930s and 1970s; however, total nectar provision in Great Britain as a whole had stabilized by 1978, and increased from 1998 to 2007. These findings concur with trends in pollinator diversity, which declined in the mid-twentieth century9 but stabilized more recently10. The diversity of nectar sources declined from 1978 to 1990 and thereafter in some habitats, with four plant species accounting for over 50% of national nectar provision in 2007. Calcareous grassland, broadleaved woodland and neutral grassland are the habitats that produce the greatest amount of nectar per unit area from the most diverse sources, whereas arable land is the poorest with respect to amount of nectar per unit area and diversity of nectar sources...

Our findings provide new evidence based on floral resources to support habitat conservation and restoration. First, we provide evidence of the high nectar value of calcareous grassland for pollinating insects. Calcareous grassland area has declined drastically in Great Britain, and only a small fraction of the historical national cover remained by 2007 (refs 13, 14). Second, the low availability and diversity of nectar sources in arable habitats highlights the need to provide supplementary resources to support pollination services in farmlands, especially as the use of insect-pollinated crops has increased nationally24 and globally25. The conservation and restoration of broadleaf woodland and neutral grassland as components of the farmland matrix could help to support diverse flower-visiting insect communities in arable land. The contrast in nectar productivity between linear features and the surrounding vegetation is particularly high in arable land, suggesting that linear features, especially hedgerows, provide an efficient means to enhance floral resources in farmlands if they are managed appropriately to allow flowering26. While agri-environment options such as nectar flower mixtures can also enhance the supply of floral resources locally, their contribution to nectar provision nationally remains low. The higher profile given to floral resource provision in the revised Countryside Stewardship guidelines for England16 may substantially enhance resources in future. Finally, our results indicate that improved grassland has the potential to contribute massively to the nectar available nationally. Small adjustments to the management cycle in improved grasslands, allowing white clover, the dominant resource species, to flower, would help realize this potential, although its utility might be restricted to a limited number of pollinator species (Extended Data Table 2). Together, our results on the nectar values of the commonest British plants and the historical changes in plant communities provide the evidence base needed to understand recent national changes in nectar provision and identify the management options needed to restore national nectar supplies.