Time to act now? Assessing the costs of delaying climate measures and benefits of early action

This paper compares the results of the three state of the art climate-energy-economy models IMACLIM-R, ReMIND-R, and WITCH to assess the costs of climate change mitigation in scenarios in which the implementation of a global climate agreement is delayed or major emitters decide to participate in the agreement at a later stage only. We find that for stabilizing atmospheric GHG concentrations at 450?ppm CO₂-only, postponing a global agreement to 2020 raises global mitigation costs by at least about half and a delay to 2030 renders ambitious climate targets infeasible to achieve. In the standard policy scenario??in which allocation of emission permits is aimed at equal per-capita levels in the year 2050??regions with above average emissions (such as the EU and the US alongside the rest of Annex-I countries) incur lower mitigation costs by taking early action, even if mitigation efforts in the rest of the world experience a delay. However, regions with low per-capita emissions which are net exporters of emission permits (such as India) can possibly benefit from higher future carbon prices resulting from a delay. We illustrate the economic mechanism behind these observations and analyze how (1) lock-in of carbon intensive infrastructure, (2) differences in global carbon prices, and (3) changes in reduction commitments resulting from delayed action influence mitigation costs.     

An assessment of land use and other factors affecting sediment loads in the Rio Puerco watershed, New Mexico

Rapid channel erosion in the Rio Puerco watershed of northwest New Mexico has been attributed to land use, climate changes, and internal channel adjustments. The objectives of this study were to assess (1) the impacts of land uses on sediment load, (2) the quantitative relationships between land use and sediment load, and (3) the effectiveness of different erosion control methods. The impacts of land uses on sediment load were assessed via hypotheses that, holding other erosion-related variables constant, sediment load correlates positively with grazing intensity and with density of unpaved roads, and correlates negatively with the number of erosion control treatments. We calculated the average annual sediment load for 17 subbasins of 0.67–17.97 km² by comparing sediment accumulation at two points in time (mid-1960s and 1999) behind intact sediment retention structures. We assessed land use via grazing records and measurements of unpaved roads generated from aerial photographs. Soil characteristics, vegetation, and physical factors were quantified for each subbasin. Using 18 variables for each subbasin, we employed Mallow's C_p as a selection criterion. We used six statistical models, including multiple regression and principal components analysis, to determine inherent mathematical relationships between significant independent variables and sediment load. The results indicate that sediment load does not correlate with grazing intensity except in small, relatively low-relief basins with fewer bedrock exposures. However, this interpretation may be compromised by the low quality of data available to quantify grazing. Sediment load is highly sensitive to the presence of unpaved roads, which serve as high gradient, channelized conduits of water and sediment during storms. Sediment load does not correlate with erosion control except in the subset of small, relatively low-relief subbasins that also proved sensitive to grazing intensity. Overall, the statistical analyses suggest that the impact of land uses on sediment load can be assessed using the data available although physical factors appear more significant than land use in producing high sediment loads in the Rio Puerco subbasins. Historical erosion control techniques, as implemented in the Rio Puerco watershed, prove largely ineffective against accelerated sediment loads because they have not been appropriately implemented or maintained.