Atmospheric heat transport is governed by meridional gradients in surface evaporation in modern-day earth-like climates.

Evaporation adds moisture to the atmosphere, while condensation removes it. Condensation also adds thermal energy to the atmosphere, which must be removed from the atmosphere by radiative cooling. As a result of these two processes, there is a net flow of energy driven by surface evaporation adding energy and radiative cooling removing energy from the atmosphere. Here, we calculate the implied heat transport of this process to find the atmospheric heat transport in balance with the surface evaporation. In modern-day Earth-like climates, evaporation varies strongly between the equator and the poles, while the net radiative cooling in the atmosphere is nearly meridionally uniform, and as a consequence, the heat transport governed by evaporation is similar to the total poleward heat transport of the atmosphere. This analysis is free from cancellations between moist and dry static energy transports, which greatly simplifies the interpretation of atmospheric heat transport and its relationship to the diabatic heating and cooling that governs the atmospheric heat transport. We further demonstrate, using a hierarchy of models, that much of the response of atmospheric heat transport to perturbations, including increasing CO2 concentrations, can be understood from the distribution of evaporation changes. These findings suggest that meridional gradients in surface evaporation govern atmospheric heat transport and its changes.

Cold Temperature Limits to Biodiesel Use under Present and Future Climates in North America.

Cold weather operability is sometimes a limiting factor in the use of biodiesel blends for transportation. Regional temperature variability can therefore influence biodiesel adoption, with potential economic and environmental implications. This study assesses present and future biodiesel cold weather operability limits in North America according to temperature data from weather stations, atmospheric reanalysis, and global climate models with highest resolution over Ontario, Canada. Future temperature projections using the RCP8.5 climate change scenario show increases in the potential duration for certain seasonal fuel blends. For example, biodiesel blends whose cloud point temperature is -9 °C may expand their duration by 3-7% in North America for nonwinter seasons according to projections for 2040. Cloud point specifications among supply orbits in Ontario increase up to +6 °C during nonwinter seasons, with most increases observed in Fall and Spring. In winter, however, the modeling suggests no change in Ontario cloud point specifications because the coldest temperatures by mid-century are not significantly warmer than the past climate normal according to our climate simulations. This study provides a quantitative analysis on biodiesel usage scenarios under a changing climate, including Ontario region geographic temperature clusters that could prove useful for biodiesel blend-related decision-making.

Quantifying climate feedbacks in polar regions.

The concept of feedback is key in assessing whether a perturbation to a system is amplified or damped by mechanisms internal to the system. In polar regions, climate dynamics are controlled by both radiative and non-radiative interactions between the atmosphere, ocean, sea ice, ice sheets and land surfaces. Precisely quantifying polar feedbacks is required for a process-oriented evaluation of climate models, a clear understanding of the processes responsible for polar climate changes, and a reduction in uncertainty associated with model projections. This quantification can be performed using a simple and consistent approach that is valid for a wide range of feedbacks, offering the opportunity for more systematic feedback analyses and a better understanding of polar climate changes.