Legal & Scientific Integrity in Advancing a Land Degradation Neutral World

It is no secret that the fight against desertification isn\u27t going well. In the two decades since the United Nations Convention to Combat Desertification ( UNCCD ) came into force, desertification – defined as degradation in the quality of arid, semi-arid, and dry subhumid land areas – has worsened considerably. Recent United Nations estimates suggest that fifty-two percent of drylands currently under agricultural cultivation are moderately or severely degraded, and 12 million hectares of productive land become barren each year due to desertification and drought. And while drylands are the focus of the UNCCD, the challenge isn\u27t limited to them: somewhere around twenty percent of land worldwide is moderately or severely degraded and most experts predict this percentage will increase in coming decades

Projected Changes in the Seasonal Cycle of Surface Temperature

When forced with increasing greenhouse gases, global climate models project a delay in the phase and a reduction in the amplitude of the seasonal cycle of surface temperature, expressed as later minimum and maximum annual temperatures and greater warming in winter than in summer. Most of the global mean changes come from the high latitudes, especially over the ocean. All 24 Coupled Model Intercomparison Project phase 3 models agree on these changes and, over the twenty-first century, average a phase delay of 5 days and an amplitude decrease of 5% for the global mean ocean surface temperature. Evidence is provided that the changes are mainly driven by sea ice loss: as sea ice melts during the twenty-first century, the previously unexposed open ocean increases the effective heat capacity of the surface layer, slowing and damping the temperature response. From the tropics to the midlatitudes, changes in phase and amplitude are smaller and less spatially uniform than near the poles but are still prevalent in the models. These regions experience a small phase delay but an amplitude increase of the surface temperature cycle, a combination that is inconsistent with changes to the effective heat capacity of the system. The authors propose that changes in this region are controlled by changes in surface heat fluxes

Projected changes in US rainfall erosivity

Downscaled rainfall projections from 21 climate models from the CMIP5 (Coupled Model Intercomparison Project Phase 5) archive are used to estimate future changes in rainfall erosivity in the continental Unites States. To estimate erosivity from rainfall in the absence of sub-hourly data, we have used both daily rainfall values and the modified Fournier index – which is based on monthly rainfall accumulation – and derived the scaling relationship between rainfall and erosivity from observational estimates of both. The expectation of overall increase in erosivity is confirmed by these calculations, but a quantitative assessment is marred by large uncertainties. Specifically, the uncertainty in the method of estimation of erosivity is more consequential than that deriving from the spread in climate simulations and leads to changes of uncertain sign in parts of the southwest and Texas. We suggest that progress can be made by establishing a more reliable functional relationship between daily rainfall and erosivity

Projected changes in the physical climate of the Gulf Coast and Caribbean

As the global climate warms due to increasing greenhouse gases, the regional climate of the Gulf of Mexico and Caribbean region will also change. This study presents the latest estimates of the expected changes in temperature, precipitation, tropical cyclone activity, and sea level. Changes in temperature and precipitation are derived from climate model simulations produced for the Fourth Assessment Report of the Intergovernmental Panel on Climate Change (IPCC AR4), by comparing projections for the mid- and late-21st century to the late 20th century and assuming a “middle-of-the-road” scenario for future greenhouse gas emissions. Regional simulations from the North America Regional Climate Change Program (NARCCAP) are used to corroborate the IPCC AR4 rainfall projections over the US portion of the domain. Changes in tropical cyclones and sea level are more uncertain, and our understanding of these variables has changed more since IPCC AR4 than in the case of temperature and precipitation. For these quantities, the current state of knowledge is described based on the recent peer-reviewed literature

A global perspective on African climate

We describe the global climate system context in which to interpret African environmental change to support planning and implementation of policymaking action at national, regional and continental scales, and to inform the debate between proponents of mitigation v. adaptation strategies in the face of climate change. We review recent advances and current challenges in African climate research and exploit our physical understanding of variability and trends to shape our outlook on future climate change. We classify the various mechanisms that have been proposed as relevant for understanding variations in African rainfall, emphasizing a “tropospheric stabilization” mechanism that is of importance on interannual time scales as well as for the future response to warming oceans. Two patterns stand out in our analysis of twentieth century rainfall variability: a drying of the monsoon regions, related to warming of the tropical oceans, and variability related to the El Niño–Southern Oscillation. The latest generation of climate models partly captures this recent continent-wide drying trend, attributing it to the combination of anthropogenic emissions of aerosols and greenhouse gases, the relative contribution of which is difficult to quantify with the existing model archive. The same climate models fail to reach a robust agreement regarding the twenty-first century outlook for African rainfall, in a future with increasing greenhouse gases and decreasing aerosol loadings. Such uncertainty underscores current limitations in our understanding of the global climate system that it is necessary to overcome if science is to support Africa in meeting its development goals