Rank #1: Solar Radiation, Cosmic Rays and Greenhouse Gases: What's Driving Global Warming? (23 March 2008)
During the past three decades a suite of space-based instruments has monitored the Sun’s brightness as well as the Earth’s surface and atmospheric temperatures. These datasets enable the separation of climate’s responses to solar activity from other sources of climate variability (anthropogenic greenhouse gases, El Niño Southern Oscillation, volcanic aerosols). The empirical evidence indicates that the solar irradiance 11-year cycle increase of 0.1% produces a global surface temperature increase of about 0.1 K with larger increases at higher altitudes. Historical solar brightness changes are estimated by modeling the contemporary irradiance changes in terms of their solar magnetic sources (dark sunspots and bright faculae) in conjunction with simulated long-term evolution of solar magnetism. In this way, the solar irradiance increase since the seventeenth century Maunder Minimum is estimated to be slightly larger than the increase in recent solar activity cycles, and smaller than early estimates that were based on variations in Sun-like stars and cosmogenic isotopes. Ongoing studies are beginning to decipher the empirical Sun- climate connections as a combination of responses to direct solar heating of the surface and lower atmosphere, and indirect heating via solar UV irradiance impacts on the ozone layer and middle atmosphere, with subsequent communication to the surface and climate. The associated physical pathways appear to involve the modulation of existing dynamical and circulation atmosphere-ocean couplings, including the El Nino Southern Oscillation (El Nino/La Nina cycles) and the Quasi-Biennial Oscillation.
The Sun's Role in Past, Current and Future Climate Change
Correlations of instrumental or reconstructed climate time series with indices of solar activity are often being used to suggest that the climate system is tightly coupled to the sun. Yet correlations have to be used with caution because they are not necessarily synonymous with cause-and-effect relationships. Therefore, it is critical to understand the physical mechanisms that are responsible for the signals. Independent tests can then be applied to validate or reject a hypothesized link. Spatial structures that are related to the processes that translate the solar influence into a climatic response can serve as such a test. A particularly powerful example is obtained by looking at the vertical extent of the solar signal in the atmosphere.
Dr. Judith Lean is Senior Scientist for Sun-Earth System Research in the Space Science Division of the Naval Research Laboratory in Washington, DC. She has served on a variety of NASA, NSF, NOAA and NRC advisory committees, including as Chair of the National Research Council (NRC) Working Group on Solar Influences on Global Change and, most recently, the NRC Committee on a Strategy to Mitigate the Impact of Sensor De-scopes and De-manifests on the NPOESS and GOES-R Spacecraft. A member of the AGU, IAGA, AAS/SPD and AMS, she was inducted as a Fellow of the American Geophysical Union in 2002 and a member of US National Academy of Sciences in 2003.
Dr. Caspar Ammann is a research scientist, in the Climate and Global Dynamics Division of the National Center for Atmospheric Research in Boulder, Colorado. He has a M.S. degree in Geography and Geology from the University of Bern, Switzerland and a Ph.D. in Geosciences from the University of Massachusetts. His primary research is focused on the climate of past centuries and millennia, and how the current changes compare to this natural background. He has reconstructed past climates as well as volcanic forcing from proxy (e.g., ice cores, corals etc..) records and then simulated climate variability and response to forcings in state-of-the-art coupled Atmosphere-Ocean-General Circulation Models.
Jun 06 2008
Rank #2: Climate & Health Effects of Carbon Dioxide, Black Carbon & other Air-borne Particles (16 May 2008)
Black carbon (BC) in soot is the dominant absorber of visible solar radiation in the atmosphere. Anthropogenic sources of black carbon, although distributed globally, are most concentrated in the tropics where solar irradiance is highest. Black carbon is often transported over long distances, mixing with other aerosols along the way. The aerosol mix can form transcontinental plumes of atmospheric brown clouds (ABCs), with vertical extents of 1.8 to 3.1 miles. Because of the combination of high absorption, a regional distribution roughly aligned with solar irradiance, and the capacity to form widespread atmospheric brown clouds in a mixture with other aerosols, emissions of black carbon are the second strongest contribution to current global warming, after carbon dioxide emissions. In the Himalayan region, solar heating from black carbon at high elevations may be just as important as carbon dioxide (CO2) in the melting of snowpacks and glaciers. The interception of solar radiation by atmospheric brown clouds leads to dimming at the Earth’s surface with important implications for the hydrological cycle, and the deposition of black carbon darkens snow and ice surfaces, which can contribute to melting, in particular of Arctic sea ice. Presently, populations on the order of 3 billion people are living under the influence of regional ABC hotspots.
Black carbon (BC) is an important part of the combustion product commonly referred to as soot. BC in indoor environments is largely due to cooking with biofuels such as wood, dung and crop residue. Outdoors, it is due to fossil fuel combustion (diesel and coal), open biomass burning (associated with deforestation and crop residue burning), and cooking with biofuels.
Soot aerosols absorb and scatter solar radiation. BC refers to the absorbing components of soot. Dust, which also absorbs solar radiation, is not included in the definition of BC. Globally, the annual emissions of BC are (for the year 1996) roughly 8.8 tons per year, with about 20% from biofuels, 40% from fossil fuels and 40% from open biomass burning. The uncertainty in the published estimates for BC emissions is a factor of two to five on regional scales and at least ±50% on global scales. High BC emissions occur in both the northern and the Southern Hemisphere, resulting largely from fossil fuel combustion and open burning, respectively.
Atmospheric brown clouds are composed of numerous submicrometer aerosols, including BC, but also sulphates, nitrates, fly ash and others. BC is also internally mixed with other aerosol species such as sulphates, nitrates, organics, dust and sea salt. BC is removed from the atmosphere by rain and snowfall. Removal by precipitation, as well as direct deposition to the surface, limits the atmospheric lifetime of BC to about one (±1) week.
Causal Link between Carbon Dioxide and Air Pollution Mortality
Recent research suggests that carbon dioxide, through its increase in temperatures and water vapor, increases U.S. air pollution deaths. This effect is greatest in locations where air pollution is already high. The causes of the increased death rate are increased respiratory illness, cardiovascular diseases, and complications from asthma due to increases in ozone and particulate matter. Ozone increases with more carbon dioxide because, in urban areas, higher temperatures and water vapor independently increase ozone through enhanced chemical reactions. These effects are not so important in rural areas. However, in rural areas, higher temperatures increase organic gas emissions from vegetation, increasing ozone slightly. Particles increase with more carbon dioxide because carbon dioxide increases air temperatures more than ground temperatures, reducing vertical and horizontal dispersion of pollutants.
May 30 2008
AMS Climate Change Audio - Environmental Science Seminar Series (ESSS)
Coping with Climate Change: Life After Copenhagen
Climate Change (Video)
Climate History Podcast
Adaptation to Climate Change
Environmental Change Institute
Citizens' Climate Lobby
America Adapts the Climate Change Podcast
Climate Conversations: A Climate Change Podcast
Climate Change (Audio)
Environment and Climate News Podcast
Rank #3: Biofuels, Land Conversion and Climate Change
It is possible to make biofuels that reduce carbon emissions, but only if we ensure that they do not lead to additional land clearing.
When land is cleared for agriculture, carbon that is locked up in the plants and soil is released through burning and decomposition. The carbon is released as carbon dioxide, which is an important greenhouse gas, and causes further global warming.
Converting rainforests, peatlands, savannas, or grasslands to produce food crop–based biofuels in Brazil, Southeast Asia, and the United States creates a “biofuel carbon debt” by releasing 17 to 420 times more carbon dioxide than the annual greenhouse gas reductions that these biofuels would provide by displacing fossil fuels.
Present Generation of Biofuels: Reducing or Enhancing Greenhouse Gas Emissions?
Previous studies have found that substituting biofuels for gasoline will reduce greenhouse gasses because growing the crops for biofuels sequesters takes carbon out of the air that burning only puts back, while gasoline takes carbon out of the ground and puts it into the air. These analyses have typically not taken into consideration carbon emissions that result from farmers worldwide converting forest or grassland to produce biofuels, or that result from farmers worldwide responding to higher prices and converting forest and grassland into new cropland to replace the grain (or cropland) diverted to biofuels. Our revised analysis suggests that greenhouse gas emissions from the land use changes described above, for most biofuels that use productive land, are likely to substantially increase over the next 30 years. Even advanced biofuels from biomass, if produced on good cropland, could have adverse greenhouse gas effects.
Biofuels and a Low-Carbon Economy
The low-carbon fuel standard is a concept and legal requirement in California and an expanding number of states that targets the amount of greenhouse gases produced per unit of energy delivered to the vehicle, or carbon intensity. In January 2007, California Gov. Arnold Schwarzenegger signed Executive Order S-1-07 (http://gov.ca.gov/executive-order/5172/), which called for a 10-percent reduction in the carbon intensity of his state’s transportation fuels by 2020. A research team in which Dr. Kammen participated developed a technical analysis (http://www.energy.ca.gov/low_carbon_fuel_standard/UC-1000-2007-002-PT1.PDF) of low-carbon fuels that could be used to meet that mandate. That analysis employs a life-cycle, ‘cradle to grave’ analysis of different fuel types, taking into consideration the ecological footprint of all activities included in the production, transport, storage, and use of the fuel.
Under a low-carbon fuel standard, fuel providers would track the “global warming intensity” (GWI) of their products and express it as a standardized unit of measure--the amount of carbon dioxide equivalent per amount of fuel delivered to the vehicle (gCO2e/MJ). This value measures vehicle emissions as well as other trade-offs, such as land-use changes that may result from biofuel production. For example, an analysis of ethanol shows that not all biofuels are created equal. While ethanol derived from corn but distilled in a coal-powered refinery is in fact worse on average than gasoline, some cellulosic-based biofuels -- largely those with little or no impact on agricultural or pristine lands have the potential for a dramatically lower GWI.
Biofuels and Greenhouse Gas Emissions: A Better Path Forward
The recent controversy over biofuels notwithstanding, the US has the potential to meet the legislated 21 billion gallon biofuel goal with biofuels that, on average, exceed the targeted reduction in greenhouse gas release, but only if feedstocks are produced properly and biofuel facilities meet their energy demands with biomass.
May 09 2008
Rank #4: Assessing Greenhouse Gas Emissions Reduction Policies: New Science Tools in the Service of Policy and Negotiations
As negotiations towards a post-Kyoto agreement on Greenhouse Gas (GHG) emissions intensify, there is a pressing need for flexible, user-friendly analytical tools to quickly yet reliably assess the impacts of the rapidly evolving policy proposals for emissions of greenhouse gases and their impact on the global climate. Such tools would enable negotiators, policymakers and other stakeholders, including the general public, to understand the relationships among proposals for emissions reductions, concentrations of GHGs in the atmosphere, and the resulting changes in climate.
The new Climate-Rapid Overview And Decision Support Simulator (C-ROADS) developed by MIT, the Sustainability Institute, and Ventana Systems, in partnership with the Heinz Center, is just such a tool. C-ROADS is a user-friendly, interactive computer model of the climate system consistent with the best available science, data and observations.
An international scientific review panel, headed by Dr. Robert Watson, former chair of the IPCC, finds that the C-ROADS model “reproduces the response properties of state-of- the-art three dimensional climate models very well” and concludes “Given the model’s capabilities and its close alignment with a range of scenarios published in the Fourth Assessment Report of the IPCC we support its widespread use among policy makers and the general public.”
Dr. John D. Sterman is the Jay W. Forrester Professor of Management at the MIT Sloan School of Management, Professor of Engineering Systems and Director of MIT's System Dynamics Group. He is an expert on nonlinear dynamics particularly as applied in economic and socio-technical systems including energy, the environment and climate policy.
Prof. Sterman's research centers on improving managerial decision making in complex systems. He has pioneered the development of "management flight simulators" of economic, environmental, and organizational systems. These flight simulators are now used by corporations and universities around the world. His recent research includes studies assessing public understanding of global climate change, the development of management flight simulators to assist climate policy design, and the development of markets for alternative fuel vehicles that are sustainable not only ecologically but economically.
Dr. Robert W. Corell, Vice President of Programs for The H. John Heinz III Center for Science, Economics, and the Environment’s Global Change Director is also a Council Member for the Global Energy Assessment and a Senior Policy Fellow at the Policy Program of the American Meteorological Society. Dr. Corell also shared in the Nobel Peace Prize Award in 2007 for his extensive work with the IPCC assessments. In 2005, he completed an appointment as a Senior Research Fellow at the Belfer Center for Science and International Affairs of the Kennedy School for Government at Harvard University.
Dr. Corell is actively engaged in research concerned with both the science of global change and with the interface between science and public policy, particularly research activities that are focused on global and regional climate change and related environmental issues. He currently chairs an international initiative, the overall goal of which is to strengthening the negotiating framework intended to prevent dangerous anthropogenic interference with the climate system, central to which is the development and use of analytical tools that employ real-time climate simulations. Dr. Corell also chairs the Arctic Climate Impact Assessment as well as an 18-country international planning effort to outline the major Arctic-region research challenges for the decade or so ahead. He recently led an international strategic planning group that developed strategies and programs designed to merge science, technology and innovation in the service of sustainable development.
Apr 16 2009
Most Popular Podcasts
Rank #5: Two Engineering Measures to Reduce Global Warming: Injecting Particles into the Atmosphere and "Clean" Coal
Largely out of concern that society may fall short of taking large and rapid enough measures to effectively contain the problem of global warming, two prominent atmospheric scientists - Paul Crutzen, who won a Nobel Prize in chemistry in 1995, and Tom Wigley, a senior scientist at the National Center for Atmospheric Research - published papers in 2006, suggesting that society might consider using geoengineering schemes to identify a temporarily "fix" to the problem. The schemes were suggested as an interim measure intended to buy time to prevent the worst damage from global warming while society used that time to identify and deploy measures to address the root cause of the problem. Such suggestions however, are not new.
The concept of geoengineering - deliberately using technology to modify Earth's environment - has been discussed in the context of climate change since at least 1960. Over the years, proposals have included everything from carbon sequestration through ocean fertilization to damming the oceans. Crutzen and Wigley argued that geoengineering schemes, if done continuously, could reduce global warming enough to buy society time to address mitigation. However, geoengineering schemes may not be the answer. And in fact, such measures have the potential to create more problems than they solve.
In particular, Crutzen and Wigley focused on blocking incoming solar radiation, an idea that has generated much interest in the press and the scientific community. Nature offers an example of how to do this. Volcanic eruptions cool the climate for up to a couple of years by injecting precursors to sulfate aerosol particles into the stratosphere, which has the effect of temporarily blocking incoming sunlight.
Clean Coal Technology and Future Prospects
Clean coal technologies are real, commonly used in commercial industrial gasification and likely essential to reduce CO2 due to the fast growing use of coal worldwide, especially in China. Commercial example of clean coal technology in the USA is the 25 year-old coal to synthetic natural gas (SNG) plant in North Dakota where all of the CO2 is captured and most is geologically storage for use in enhanced oil recovery (EOR) in Canada.
The key issue is expanding clean coal technologies into coal-based electric power generation. This expansion presents additional challenges - more technology options and higher cost of CO2 capture than for industrial gasification. This also requires large-scale demonstration of all three CO2 capture technology options: pre, post and oxygen combustion. In time, the CO2 capture and storage costs will be reduced by both “learning by doing” and developing advanced technologies already moving in to small-scale demonstrations.
Dr. Alan Robock is a Distinguished Professor of atmospheric science in the Department of Environmental Sciences at Rutgers University and the associate director of its Center for Environmental Prediction. He also directs the Rutgers Undergraduate Meteorology Program. He graduated from the University of Wisconsin, Madison, in 1970 with a B.A. in Meteorology, and from the Massachusetts Institute of Technology with an S.M. in 1974 and Ph.D. in 1977 in Meteorology. Before graduate school, he served as a Peace Corps Volunteer in the Philippines. He was a professor at the University of Maryland, 1977-1997, and the State Climatologist of Maryland, 1991-1997, before coming to Rutgers.
Dale Simbeck joined SFA Pacific in 1980 as a founding partner. His principal activities involve technical, economic and market assessments of energy and environmental technologies for the major international energy companies. This work includes electric power generation, heavy oil upgrading, emission controls and synthesis gas production plus utilization.
Jan 05 2009