Cloud feedback is a type of climate change feedback that has been difficult to quantify in contemporary climate models. It can affect the magnitude of internally generated climate variability or they can affect the magnitude of climate change resulting from external radiative forcings. Cloud representations vary among global climate models, and small changes in cloud cover have a large impact on the climate.
Keith Peter Shine FRS is the Regius Professor of Meteorology and Climate Science at the University of Reading. He is the first holder of this post, which was awarded to the university by Queen Elizabeth II to mark her Diamond Jubilee.
Global dimming is a decline in the amount of sunlight reaching the Earth's surface, a measure also known as global direct solar irradiance. It was observed soon after the first systematic measurements of solar irradiance began in the 1950s, and continued until 1980s, with an observed reduction of 4–5% per decade, even though solar activity did not vary more than the usual at the time. Instead, global dimming had been attributed to an increase in atmospheric particulate matter, predominantly sulfate aerosols, as the result of rapidly growing air pollution due to post-war industrialization. After 1980s, reductions in particulate emissions have also caused a "partial" reversal of the dimming trend, which has sometimes been described as a global brightening. This reversal is not yet complete, and it has also been globally uneven, as some of the brightening over the developed countries in the 1980s and 1990s had been counteracted by the increased dimming from the industrialization of the developing countries and the expansion of the global shipping industry, although they have also been making rapid progress in cleaning up air pollution in the recent years.
Cloud condensation nuclei (CCNs), also known as cloud seeds, are small particles typically 0.2 µm, or one hundredth the size of a cloud droplet. CCNs are a unique subset of aerosols in the atmosphere on which water vapour condenses. This can affect the radiative properties of clouds and the overall atmosphere. Water requires a non-gaseous surface to make the transition from a vapour to a liquid; this process is called condensation.
A circumpolar vortex, or simply polar vortex, is a large region of cold, rotating air; polar vortices encircle both of Earth's polar regions. Polar vortices also exist on other rotating, low-obliquity planetary bodies. The term polar vortex can be used to describe two distinct phenomena; the stratospheric polar vortex, and the tropospheric polar vortex. The stratospheric and tropospheric polar vortices both rotate in the direction of the Earth's spin, but they are distinct phenomena that have different sizes, structures, seasonal cycles, and impacts on weather.
Ship tracks are clouds that form around the exhaust released by ships into the still ocean air. Water molecules collect around the tiny particles (aerosols) from exhaust to form a cloud seed. More and more water accumulates on the seed until a visible cloud is formed. In the case of ship tracks, the cloud seeds are stretched over a long narrow path where the wind has blown the ship's exhaust, so the resulting clouds resemble long strings over the ocean. Ship tracks are a type of homogenitus cloud.
The Saharan air layer (SAL) is an extremely hot, dry, and sometimes dust-laden layer of the atmosphere that often overlies the cooler, more humid surface air of the Atlantic Ocean. It carries upwards of 60 million tonnes of dust annually over the ocean and the Americas. This annual phenomenon sometimes cools the ocean and suppresses Atlantic tropical cyclogenesis.
Polar amplification is the phenomenon that any change in the net radiation balance tends to produce a larger change in temperature near the poles than in the planetary average. This is commonly referred to as the ratio of polar warming to tropical warming. On a planet with an atmosphere that can restrict emission of longwave radiation to space, surface temperatures will be warmer than a simple planetary equilibrium temperature calculation would predict. Where the atmosphere or an extensive ocean is able to transport heat polewards, the poles will be warmer and equatorial regions cooler than their local net radiation balances would predict. The poles will experience the most cooling when the global-mean temperature is lower relative to a reference climate; alternatively, the poles will experience the greatest warming when the global-mean temperature is higher.
Stratospheric aerosol injection is a proposed method of solar geoengineering to reduce global warming. This would introduce aerosols into the stratosphere to create a cooling effect via global dimming and increased albedo, which occurs naturally from volcanic winter. It appears that stratospheric aerosol injection, at a moderate intensity, could counter most changes to temperature and precipitation, take effect rapidly, have low direct implementation costs, and be reversible in its direct climatic effects. The Intergovernmental Panel on Climate Change concludes that it "is the most-researched [solar geoengineering] method, with high agreement that it could limit warming to below 1.5 °C (2.7 °F)." However, like other solar geoengineering approaches, stratospheric aerosol injection would do so imperfectly and other effects are possible, particularly if used in a suboptimal manner.
Cecilia M. Bitz is an American climatologist known for her research on sea ice and high-latitude climate change. She is a professor and chair in the Atmospheric Sciences Department, as well as the director of the Program on Climate Change at the University of Washington. She was featured on NPR's All Things Considered segment to speak about factors that lead to sea ice loss in 2007, and testified before the United States Senate committee of Energy and Natural Resources on arctic opportunities in 2015.
CICE is a computer model that simulates the growth, melt and movement of sea ice. It has been integrated into many coupled climate system models as well as global ocean and weather forecasting models and is often used as a tool in Arctic and Southern Ocean research. CICE development began in the mid-1990s by the United States Department of Energy (DOE), and it is currently maintained and developed by a group of institutions in North America and Europe known as the CICE Consortium. Its widespread use in Earth system science in part owes to the importance of sea ice in determining Earth's planetary albedo, the strength of the global thermohaline circulation in the world's oceans, and in providing surface boundary conditions for atmospheric circulation models, since sea ice occupies a significant proportion (4-6%) of Earth's surface. CICE is a type of cryospheric model.
Beate Gertrud Liepert is a research scientist at Columbia University, as well as in North West Research Associates, Redmond and a lecturer at Seattle University. Her research focuses on climate variability: inter-annual changes, centennial time scales, the water and energy cycles.
William Ka Ming Lau is a senior scientist at the Earth System Science Interdisciplinary Center, a research center at the University of Maryland and an Adjunct Professor of the Department of Atmospheric and Oceanic Sciences at the University of Maryland. A physicist by training, his research spans over 4 decades covering a wide range of topics in climate dynamics, tropical meteorology, ocean-atmosphere coupling, aerosol-water cycle interactions, and climate variability and change. Lau conducted pioneering research on atmospheric teleconnection, and the global monsoon climate system. He discovered the aerosol-monsoon regional feedback mechanism, i.e., the Elevated Heat Pump (EHP) effect that strongly modulate climate change in Asian monsoon regions. He was the senior author of a popular research reference book, “Intraseasonal Variability in the Atmosphere-Ocean Climate System”. As of November 2020, he has coauthored 297 refereed papers, with total citation = 33,932, h-index=101.
Lorraine Remer is research professor at University of Maryland, Baltimore County known for her work on developing algorithms to study aerosol particles using satellites with a particular focus on how aerosols impact climate processes.
Jennifer Logan is an atmospheric scientist known for her research on how human activities influence the atmosphere, particularly with respect to biomass burning and the ozone hole.
Joyce Penner is an atmospheric scientist known for her research on climate change, especially on the impact of aerosols and clouds.
Bette Otto-Bliesner is an earth scientist known for her modeling of Earth's past climate and its changes over different geological eras.
Marcia Baker is a retired professor known for her research on cloud physics which informs global climate models and defines the processes leading to the formation of lightning from clouds.
Patricia K. Quinn is a atmospheric chemist working at the National Oceanic and Atmospheric Agency's Pacific Marine Environmental Lab. She is known for her work on the impact of atmospheric aerosol particles on air quality and climate.
Rebecca Woodgate is a professor at the University of Washington known for her work on ocean circulation in polar regions.
