Jean-Pascal van Ypersele

Lateral boundary conditions in regional climate models: A detailed study of the relaxation procedure

In gridpoint regional climate models (RCMs), the lateral boundary conditions are usually provided by a procedure called relaxation. The technique was originally studied in the context of numerical weather forecasting. This paper complements the preceding theoretical studies in order to assess the practical choices of model relaxation coefficients. Several profiles of coefficients used in RCMs are then evaluated. The complexity of actual model numerics makes any definite choice of the coefficients out of reach of simple theoretical considerations, but these provide practical guidelines. The latter are confirmed by pragmatic considerations such as minimizing discontinuities and keeping relaxation rates in the range of the represented physical processes. The last part of the paper presents a sensitivity study with the Modele Atmospherique Regional (MAR).

The impact of the unilateral EU commitment on the stability of international climate agreements.

The negotiation strategy of the European Union was analysed with respect to the formation of an international climate agreement for the post-2012 era. Game theory was employed to explore the incentives for key players in the climate policy arena to join future climate agreements. A −20% unilateral commitment strategy by the EU was compared with a multilateral −30% emission reduction strategy for all Annex-B countries. Using a numerical integrated assessment climate—economy simulation model, we found that leakage, in the sense of strategic policy reactions on emissions, was negligible. The EU strategy to reduce emissions by 30% (compared with 1990 levels) by 2020, if other Annex-B countries follow suit, does not induce the participation of the USA with a comparable reduction commitment. However, we argue that the original EU proposal can be reshaped so as to stabilize a larger and more ambitious climate coalition than the Kyoto Protocol in its first commitment period.

ARE NATURAL CLIMATE FORCINGS ABLE TO COUNTERACT THE PROJECTED ANTHROPOGENIC GLOBAL WARMING

A two-dimensional global climate model is used to assessthe climatic changes associated with the new IPCC SRES emissions scenarios and to determine which kind of changes in total solar irradiance and volcanic perturbations could mask the projected anthropogenic global warming associated to the SRES scenarios. Our results suggest that only extremely unlikely changes in total solar irradiance and/or volcanic eruptions would be able to overcome the simulated anthropogenic global warming over the century. Nevertheless, in the critical interval of the next two decades the externally-driven natural climate variability might possibly confuse the debate about temperature trends and impede detection of the anthropogenic climate change signal.

Europe’s renewable energy directive poised to harm global forests

This comment raises concerns regarding the way in which a new European directive, aimed at reaching higher renewable energy targets, treats wood harvested directly for bioenergy use as a carbon-free fuel. The result could consume quantities of wood equal to all Europe’s wood harvests, greatly increase carbon in the air for decades, and set a dangerous global example.