Severe Turbulence on Flights May Increase Dramatically due to Climate Change
Turbulence accounts for the majority of weather-related accidents on flights. Clear-air turbulence (CAT) occurs in relatively clear air devoid of thunderstorms or major clouds. It is caused by strong vertical changes in wind strength and direction due to instabilities in the atmosphere. Airplanes do not contain sensors to detect CAT, so pilots rely on coarse regional turbulence forecasts. CAT occurs over distances of less than one kilometer, which is a smaller scale than currently feasible for computers to model or forecast with the speed or accuracy needed for aircraft.
Researchers at the University of Reading and the University of East Anglia, UK, have built on other recent climate modeling to show that CAT will increase dramatically due to climate change. Using current climate models at a higher resolution than previous studies, the researchers modelled twenty different indicators that are linked to CAT over all regions of the world, all seasons, and two typical aircraft cruising altitudes. They compare the percent change in these indicators from an atmosphere with pre-industrial carbon dioxide (CO2) levels to a representative scenario that approximately triples the current CO2 concentrations in the atmosphere by 2100. By 2050-2080, all regions of the world show increases in turbulence under all 40 indicators, with the most popular flight paths in the mid-latitudes and northern Atlantic experiencing 100 to 500 percent increases in CAT. Severe turbulence increases more than light or moderate turbulence.
The study recommends that a more turbulent atmosphere be considered when designing new and future aircraft equipment. Technologies that can visualize CAT should be installed on planes, if feasible. In addition, as computational power improves, turbulence prediction models could be downscaled and improved. The magnitude of the CAT increase may change depending on the trajectory of global CO2 emissions.
See, Storer, L.N., Williams, P.D., & Joshi, M.M. Global Response of Clear-Air Turbulence to Climate Change. Geophysical Research Letters, 2017. DOI: 10.1002/2017GL074618
Warmer Soil Can Lead to Increased Release in Carbon
In natural ecosystems, plants convert atmospheric carbon dioxide into carbon stock within the plant itself as part of photosynthesis. As leaves and branches fall to the ground, the carbon that they store become part of the soil. Microbes and fungi in the soil break down this organic matter, releasing carbon dioxide back into the atmosphere. In warmer temperatures, they break down organic material faster, releasing more carbon dioxide into the atmosphere. What is not known is how warming temperatures resulting from climate change will accelerate this soil carbon cycle.
Jerry Melillo of the Marine Biological Laboratory led a team of researchers on a 26-year soil warming study to understand the impact of global warming on the soil carbon cycle. He acquired underground road cables used to heat up roads in the winter and buried them in six test sites, with another six test sites serving as controls. In the Harvard Forest experiment, as it was called, the soil was heated to 5 degrees Celsius above ambient temperature. His research group then measured how much carbon dioxide was released over the next 26 years.
Their findings showed four phases of carbon loss. In the first several years there was substantial carbon loss, followed by several years of stability, then another period of loss, and then finally another period of stability. By using genetic tools, they have been able to identify what kinds of microbes are at work during these different periods in time. Melillo suggests that the microbes are “reorganizing” their genetic material to adapt to the changing soil temperatures.
Their results support projections of positive carbon feedback from forest areas as the world warms. The impacts of this positive feedback can be significant. In the 26 years of the Harvard Forest experiment, the heated plots lost 17 percent of its carbon. If other forest ecosystems around the world lost 17 percent of its carbon, there would be a release of 200 billion metric tons.
See, J. M. Melillo, S. D. Frey, K. M. DeAngelis, W. J. Werner, M. J. Bernard, F. P. Bowles, G. Pold, M. A. Knorr, A. S. Grandy. Long-term pattern and magnitude of soil carbon feedback to the climate system in a warming world. Science, 2017. DOI: 10.1126/science.aan2874
Tropical Forests No Longer Carbon Sinks Due to Widespread Loss
A new study from the Woods Hole Research Center (WHRC) and Boston University quantifies changes to tropical forest cover with a granularity not previously captured. The study finds that forests in tropical Africa, Asia, and the Americas are a net source of carbon to the atmosphere, contrary to popular belief.
Earlier monitoring efforts surveyed areas where deforestation, or total loss of forest, was occurring. The research team was able to look at areas of deforestation, forest growth, and subtler changes like degradation and disturbance. The WHRC team combined field measurements, satellite images, and remotely sensed laser data to compile 12 years of forest changes, spanning 2003-2014. This method showed that losses of carbon to the atmosphere totaled approximately 862 teragrams (one teragram = one trillion grams) and gains were approximately 437 teragrams, balancing to net emissions of 425 teragrams each year.
The team also found that changes to forest cover are distributed unevenly across the studied regions. The Americas are responsible for the biggest share of both total loss and total gain values (60 percent and 43 percent, respectively), followed by Africa (24 percent and 30 percent), and Asia (16 percent and 26 percent). Furthermore, degradation and disturbance accounts for a significant portion of losses, comprising 70 percent, 81 percent, and 46 percent of forest loss across tropical America, Africa, and Asia, respectively.
Ending deforestation and degradation would result in emissions savings roughly equal to 8 percent of global annual greenhouse gas emissions. The results of this research effort are valuable to countries conducting annual monitoring of tropical forest carbon, particularly for the purpose of meeting emissions reductions targets under the United Nations Paris Climate Agreement through the Reducing Emissions from Deforestation and Forest Degradation (REDD+) program.
See, A. Baccini, W. Walker, L. Carvalho, M. Farina, D. Sulla-Menashe, R. A. Houghton. Tropical forests are a net carbon source based on aboveground measurements of gain and loss. Science, 2017 DOI: 10.1126/science.aam5962
Solar-To-Chemical Fuel Cell Offers Efficiencies Much Greater than Plant Photosynthesis
Scientists at Lawrence Berkeley National Laboratory’s Joint Center for Artificial Photosynthesis (Berkeley Lab’s JCAP) and the University of California, Berkeley have created a solar-powered fuel cell that converts carbon dioxide (CO2) to useful chemical energy. Their photovoltaic electrochemical cell runs in a process analogous to plant photosynthesis, but at far higher efficiencies than is found in nature.
In the long-term view of Berkeley Lab’s artificial photosynthesis efforts, which date back to 2010, this research clears the second of two major hurdles. The first, completed in JCAP’s first five years, was achieving the efficient splitting of water molecules. The second, which motivated this publication, was achieving the efficient reduction of CO2. While other studies have demonstrated efficient reduction of CO2 to various products including carbon monoxide or formates, further processing is required to make those compounds usable as fuels.
The Berkeley research team engineered a highly efficient catalyst that reduces carbon, converting carbon dioxide to various hydrocarbons (like ethylene) and oxygenates (like ethanol), which are end-use fuels. The electrochemical conversion is achieved using a copper and silver bimetallic catalyst in an electrolysis cell, which is powered by photovoltaic cells. The fuel cell achieved a conversion efficiency (in other words, the conversion of CO2 to products) of over 5 percent, far greater than the range of plant photosynthesis. The research team’s efforts mark an important step along the path towards sustainable sources of fuel.
See, G. Gurudayal, J.Bullock, D. F. Srankó, C. M. Towle, Y. Lum, M. Hettick, M. C. Scott, A. Javey, J. Ager. Efficient solar-driven electrochemical CO2 reduction to hydrocarbons and oxygenates. Energy Environ. Sci., 2017; DOI: 10.1039/c7ee01764b
(David Kim, Malini Nambiar, Shaena Berlin Ulissi)
