Why global warming is taking a break

Fabio Benjamin at the ETH (Switzerland): ...Global warming is currently taking a break: whereas global temperatures rose drastically into the late 1990s, the global average temperature has risen only slightly since 1998 – surprising, considering scientific climate models predicted considerable warming due to rising greenhouse gas emissions. Climate sceptics used this apparent contradiction to question climate change per se – or at least the harm potential caused by greenhouse gases – as well as the validity of the climate models. Meanwhile, the majority of climate researchers continued to emphasise that the short-term ‘warming hiatus’ could largely be explained on the basis of current scientific understanding and did not contradict longer term warming.

Researchers have been looking into the possible causes of the warming hiatus over the past few years. For the first time, Reto Knutti, Professor of Climate Physics at ETH Zurich, has systematically examined all current hypotheses together with a colleague. In a study published in the latest issue of the journal Nature Geoscience, the researchers conclude that two important factors are equally responsible for the hiatus.

One of the important reasons is natural climate fluctuations, of which the weather phenomena El Niño and La Niña in the Pacific are the most important and well known. "1998 was a strong El Niño year, which is why it was so warm that year," says Knutti. In contrast, the counter-phenomenon La Niña has made the past few years cooler than they would otherwise have been.

...According to the study, the second important reason for the warming hiatus is that solar irradiance has been weaker than predicted in the past few years....Furthermore, several volcanic eruptions, such as Eyjafjallajökull in Iceland in 2010, have increased the concentration of floating particles (aerosol) in the atmosphere, which has further weakened the solar irradiance arriving at the Earth's surface.

The scientists drew their conclusions from corrective calculations of climate models. In all climate simulations, they looked for periods in which the El Niño/La Niña patterns corresponded to the measured data from the years 1997 to 2012. With a combination of over 20 periods found, they were able to arrive at a realistic estimate of the influence of El Niño and La Niña. They also retroactively applied in the model calculations the actual measured values for solar activity and aerosol concentration in the Earth's atmosphere. Model calculations corrected in this way match the measured temperature data much more closely.

...Despite the warming hiatus, Knutti is convinced there is no reason to doubt either the existing calculations for the climate activity of greenhouse gases or the latest climate models. "Short-term climate fluctuations can easily be explained. They do not alter the fact that the climate will become considerably warmer in the long term as a result of greenhouse gas emissions," says Knutti. He believes that global warming will recommence as soon as solar activity, aerosol concentrations in the atmosphere and weather phenomena such as El Niño naturally start returning to the values of previous decades....

NASA image of a sunspot

Solar activity not a key cause of climate change

EurekAlert via the University of Edinburgh: Climate change has not been strongly influenced by variations in heat from the sun, a new scientific study shows. The findings overturn a widely held scientific view that lengthy periods of warm and cold weather in the past might have been caused by periodic fluctuations in solar activity.

Research examining the causes of climate change in the northern hemisphere over the past 1000 years has shown that until the year 1800, the key driver of periodic changes in climate was volcanic eruptions. These tend to prevent sunlight reaching the Earth, causing cool, drier weather. Since 1900, greenhouse gases have been the primary cause of climate change.

The findings show that periods of low sun activity should not be expected to have a large impact on temperatures on Earth, and are expected to improve scientists' understanding and help climate forecasting.

Scientists at the University of Edinburgh carried out the study using records of past temperatures constructed with data from tree rings and other historical sources. They compared this data record with computer-based models of past climate, featuring both significant and minor changes in the sun.

They found that their model of weak changes in the sun gave the best correlation with temperature records, indicating that solar activity has had a minimal impact on temperature in the past millennium....

A solar flare shot by NASA, Valentine's Day, 2011

Sunlight stimulates release of climate-warming gas from melting Arctic permafrost

University of Michigan News Service: Ancient carbon trapped in Arctic permafrost is extremely sensitive to sunlight and, if exposed to the surface when long-frozen soils melt and collapse, can release climate-warming carbon dioxide gas into the atmosphere much faster than previously thought.

University of Michigan ecologist and aquatic biogeochemist George Kling and his colleagues studied places in Arctic Alaska where permafrost is melting and is causing the overlying land surface to collapse, forming erosional holes and landslides and exposing long-buried soils to sunlight.

They found that sunlight increases bacterial conversion of exposed soil carbon into carbon dioxide gas by at least 40 percent compared to carbon that remains in the dark. The team, led by Rose Cory of the University of North Carolina, reported its findings in an article to be published online Feb. 11 in the Proceedings of the National Academy of Sciences.

"Until now, we didn't really know how reactive this ancient permafrost carbon would be — whether it would be converted into heat-trapping gases quickly or not," said Kling, a professor in the U-M Department of Ecology and Evolutionary Biology. EEB graduate student Jason Dobkowski is a co-author of the paper.

"What we can say now is that regardless of how fast the thawing of the Arctic permafrost occurs, the conversion of this soil carbon to carbon dioxide and its release into the atmosphere will be faster than we previously thought," Kling said. "That means permafrost carbon is potentially a huge factor that will help determine how fast the Earth warms."

Tremendous stores of organic carbon have been frozen in Arctic permafrost soils for thousands of years. If thawed and released as carbon dioxide gas, this vast carbon repository has the potential to double the amount of the heat-trapping greenhouse gas in the atmosphere on a timescale similar to humanity's inputs of carbon dioxide due to the burning of fossil fuels.

That creates the potential for a positive feedback: As the Earth warms due to the human-caused release of heat-trapping gases into the atmosphere, frozen Arctic soils also warm, thaw and release more carbon dioxide. The added carbon dioxide accelerates Earth's warming, which further accelerates the thawing of Arctic soils and the release of even more carbon dioxide....

University of Michigan ecologist George Kling at a landslide thermokarst on a glacial headwall near Toolik Lake, Alaska. As permafrost ice melts, the soil collapses and either creates an erosional hole in the tundra or a landslide such as this one. These features are called thermokarst failures. Photo from the University of Michigan website, courtesy of George Kling.

Feb. 23 NASA mission to tote $28 million CU-Boulder instrument and tiny student satellite

University of Colorado at Boulder News: A $28 million University of Colorado Boulder instrument developed to study changes in the sun's brightness and its impact on Earth's climate is one of two primary payloads on NASA's Glory mission set to launch from Vandenberg Air Force Base in California on Feb. 23.

Designed and built by a team from CU-Boulder's Laboratory for Atmospheric and Space Physics, the instrument called the Total Irradiance Monitor, or TIM, will point directly toward the sun to measure both short- and long-term fluctuations in the sun's energy output as it reaches the top of Earth's atmosphere. Such measurements are important because variations in the sun's radiation can influence long-term climate change on Earth, said LASP researcher Greg Kopp, principal investigator on the TIM.

The Taurus XL rocket ferrying the Glory satellite also will be carrying a tiny CU-Boulder satellite designed and built by about 100 students, primarily undergraduates, who are participating in the Colorado Space Grant Consortium. The CubeSat satellite will be ejected from the rocket at about 400 miles in altitude to orbit the Earth and study new space communications techniques.

The CU-Boulder solar instrument on Glory is the most accurate instrument ever made to study the energy output from the sun and will continue a 32-year-long data record of solar radiation by NASA and other agencies, said Kopp. NASA's Solar Radiation and Climate Experiment, a $100 million satellite designed, built and operated by CU-Boulder's LASP and launched in 2003, is equipped with a first-generation TIM instrument as well as three other solar measuring instruments.

"We'd like to know how the sun's energy changes over both the short and long term," said Kopp. "This spacecraft is carrying extremely sensitive instruments for monitoring solar variability, which makes the mission especially relevant given climate change on Earth and the importance of determining the natural influence on those changes."

Glory will join five other NASA Earth-observing satellites as part of the Afternoon Constellation, or "A-Train," a tightly grouped series of spacecraft that circle the globe several times each day to gather information on Earth's biosphere and climate, including hurricane behavior and climate change. The A-Train spacecraft follow each other in close formation, flying mere minutes apart. The A-Train orbits Earth about once every 100 minutes….

Image of the Glory satellite from NASA

First large-scale, physics-based space weather model transitions into operation

National Science Foundation (US): The first large-scale, physics-based space weather prediction model is transitioning from research into operation. Scientists affiliated with the National Science Foundation (NSF) Center for Integrated Space Weather Modeling (CISM) and the National Weather Service reported the news today at the annual American Meteorological Society (AMS) meeting in Seattle, Wash.

The model will provide forecasters with a one-to-four day advance warning of high speed streams of solar plasma and Earth-directed coronal mass ejections (CMEs). These streams from the Sun may severely disrupt or damage space- and ground-based communications systems, and pose hazards to satellite operations.

CISM is an NSF Science and Technology Center (STC) made up of 11 member institutions. Established in 2002, CISM researchers address the emerging system-science of Sun-to-Earth space weather. The research-to-operations transition has been enabled by an unprecedented partnership between the Boston University-led CISM and the National Oceanic and Atmospheric Administration (NOAA)'s Space Weather Prediction Center.

"It's very exciting to pioneer a path from research to operations in space weather," says scientist Jeffrey Hughes of Boston University, CISM's director. "The science is having a real impact on the practical problem of predicting when 'solar storms' will affect us here on Earth."

The development comes in response to the growing critical need to protect the global communications infrastructure and other sensitive technologies from severe space weather disruptions. This transition culminates several years of close cooperation between CISM and its partner organizations to integrate, improve and validate a model for operational forecast use.

"This milestone represents important scientific progress, and underscores the effectiveness of NSF's Science and Technology Centers in applying research results to real-world problems," says Robert Robinson of NSF's Division of Atmospheric and Geospace Sciences, which funds CISM…

A coronal mass ejection (CME) in a model; the CME is the gray cloud toward the lower right. Credit: Dusan Odstrcil, George Mason University

New earth-observing satellite to address climate uncertainties

Environment News Service: NASA is about to launch an Earth-observing satellite with new technology onboard designed to broaden our understanding of how the Sun and tiny atmospheric particles called aerosols affect Earth's climate. Aerosols represent one of the greatest areas of uncertainty in understanding Earth's climate system.

Called Glory, the mission is scheduled to launch from Vandenberg Air Force Base in California early in the morning of February 23. "Glory is going to help scientists tackle one of the major uncertainties in climate change predictions identified by the United Nations' Intergovernmental Panel on Climate Change: the influence of aerosols on the energy balance of our planet," said Michael Freilich, director of NASA's Earth Science Division in the Science Mission Directorate at the agency's headquarters in Washington.

Glory also will extend a legacy of long-term solar measurements needed to address other key uncertainties about climate change. "This mission also marks the first satellite launch under President Obama's climate initiative that will advance the United States' contribution to cutting-edge and policy-relevant climate change science," Freilich said.

Glory will join a fleet of other Earth-observing satellites that fly in tight formation. NASA scientists call them the "Afternoon Constellation" or "A-train" of satellites.

…The mission carries two primary instruments, the Aerosol Polarimetry Sensor and the Total Irradiance Monitor. APS will improve measurement of aerosols, the airborne particles that can influence climate by reflecting and absorbing solar radiation and modifying clouds and precipitation. APS will collect data at nine different wavelengths, from the visible to short-wave infrared, giving scientists a much-improved understanding of aerosols.

NASA's first Earth-orbiting polarimeter, APS will help scientists distinguish between natural and human-produced aerosols. The information will be used to refine global climate models and help scientists determine how our planet is responding to human activities….

Improved measurements of sun to advance understanding of climate change

University of Colorado at Boulder: Scientists have taken a major step toward accurately determining the amount of energy that the sun provides to Earth, and how variations in that energy may contribute to climate change. In a new study of laboratory and satellite data, researchers report a lower value of that energy, known as total solar irradiance, than previously measured and demonstrate that the satellite instrument that made the measurement—which has a new optical design and was calibrated in a new way—has significantly improved the accuracy and consistency of such measurements.

The new findings give confidence, the researchers say, that other, newer satellites expected to launch starting early this year will measure total solar irradiance with adequate repeatability – and with little enough uncertainty – to help resolve the long-standing question of how significant a contributor solar fluctuations are to the rising average global temperature of the planet.

…The new work will help advance scientists' ability to understand the contribution of natural versus anthropogenic causes of climate change, the scientists said. That's because the research improves the accuracy of the continuous, 32-year record of total solar irradiance, or TSI. Energy from the sun is the primary energy input driving Earth's climate, which scientific consensus indicates has been warming since the Industrial Revolution.

Lean specializes in the effects of the sun on climate and space weather. She said, "Scientists estimating Earth's climate sensitivities need accurate and stable solar irradiance records to know exactly how much warming to attribute to changes in the sun's output, versus anthropogenic or other natural forcings."…

NASA image of a solar flare

The role of solar radiation in climate change

Science Daily: A special volume of the Journal of Geophysical Research reviews the growing research field of “global dimming” and “global brightening” in over 20 articles. These phenomena, supposedly human-induced, control solar radiation incident at the Earth’s surface and thus influence climate.

…Investigating which factors reduce or intensify solar radiation and thus cause “global dimming” or “global brightening” is still very much a nascent field of research. The American Geophysical Union (AGU) has now published a special volume on the subject which presents the current state of knowledge in detail and makes a considerable contribution to climate science.

…In analyzing more recently compiled data, however, Wild and his team discovered that solar radiation has gradually been increasing again since 1985. In a paper published in “Science” in 2005, they coined the phrase “global brightening” to describe this new trend and to oppose to the term “global dimming” used since 2001 for the previously established decrease in solar radiation. Only recently, an article in the journal Nature, which Wild was also involved in, brought additional attention to the topic of global dimming/brightening.

… A further challenge for the researchers is to incorporate the effects of global dimming/brightening more effectively in climate models, to understand their impact on climate change better. After all, studies indicate that global dimming masked the actual temperature rise – and therefore climate change – until well into the 1980s. Moreover, the studies published also show that the models used in the Intergovernmental Panel on Climate Change’s (IPCC) fourth Assessment Report do not reproduce global dimming/brightening adequately: neither the dimming nor the subsequent brightening is simulated realistically by the models. According to the scientists, this is probably due to the fact that the processes causing global dimming/brightening were not taken into account adequately and that the historical anthropogenic emissions used as model input are afflicted with considerable uncertainties….

The sun's corona, shot by Rogilbert, who has released the image into the public domain

Sunspot data vital clues to climate change

University of New England News (Australia): New discoveries linking periodic changes in the Sun’s magnetic field with global weather patterns could enable scientists to gain a clearer understanding of how additional factors – such as greenhouse gases – contribute to those weather patterns. A newly-published paper by the University of New England’s Dr Robert Baker establishes the connection between solar cycles and the weather by correlating sunspot activity and rainfall figures for south-eastern Australia over the past 130 years.

Cycles of sunspot activity are a visible indication of the periodic changes in magnetic forces within the Sun. The most well-known sunspot cycle is the 11-year “Schwab” cycle, which comprises alternating five-and-a-half-year periods of relatively high and low sunspot activity.

Dr Baker’s paper, “Exploratory analysis of similarities in solar cycle magnetic phases with Southern Oscillation Index fluctuations in Eastern Australia” (Geographical Research, December 2008), shows that periods of increased sunspot activity are consistently associated with those periods of high rainfall in south-eastern Australia predicted by the Southern Oscillation Index (SOI). Periods of drought, such as that which has afflicted Australia for the past six years, are associated with minimal sunspot activity.

...“We have to benchmark the natural system (i.e., the Sun) before looking at additions to it (e.g. carbon dioxide),” he explained. “Comparing current data with those of a century ago can give us an idea of the added effect of greenhouse gases. But sticking your head in the sand and saying the Sun has no effect on climate change is a virtual denial of historical reality.”

It was a quiet day on the Sun in September of 2000. The above image from NASA's sun-observing TRACE spacecraft shows, however, that even during "off days" the Sun's surface is a busy place. Shown in ultraviolet light, the relatively cool dark regions have temperatures of thousands of degrees.