Solar activity not a key cause of climate change, study shows

Dec. 22, 2013 — 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 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.

The study, published in Nature GeoScience, was supported by the Natural Environment Research Council.

Dr Andrew Schurer, of the University of Edinburgh's School of GeoSciences, said: "Until now, the influence of the sun on past climate has been poorly understood. We hope that our new discoveries will help improve our understanding of how temperatures have changed over the past few centuries, and improve predictions for how they might develop in future. Links between the sun and anomalously cold winters in the UK are still being explored."

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Protein 'motif' crucial to telomerase activity

Sep. 19, 2013 — It is difficult to underestimate the importance of telomerase, an enzyme that is the hallmark of both aging and the uncontrolled cell division associated with cancer. In an effort to understand and control telomerase activity, researchers at The Wistar Institute have discovered a protein "motif," named TFLY, which is crucial to the function of telomerase. Altering this motif disrupts telomerase function, they found, a fact that they believe will help them in their efforts to identify inhibitors of telomerase with potential cancer therapeutic properties.

Their findings are published in the October 8 issue of the journal Structure, available online now.

"Telomerase is a unique protein-RNA complex where the protein subunit uses its RNA component as a template to add identical fragments of DNA to the end of chromosomes," said Emmanuel Skordalakes, Ph.D., associate professor in the Gene Expression and Regulation program of Wistar's NCI-designated Cancer Center. "We identified a motif in the protein component of telomerase that controls how the enzyme carries out its activity in vertebrates such as ourselves."

"If you disrupt this segment of the protein, by altering its amino acid sequence, you disrupt the ability of telomerase to function," Skordalakes explained. "Obviously, this information can be used in our efforts to identify drug therapies that kill cancer cells by targeting telomerase activity."

Telomerase is an enzyme that replicates the ends of chromosomes (sections of DNA called telomeres), replacing the DNA lost when chromosomes are copied before cell division and, therefore, maintaining the stability of the genome. It performs this critical service in embryonic development, growing organisms and in a few specialized adult cell lines, including stem cells.

In most normal adult cells, however, telomerase is switched off almost entirely to prevent the dangers of runaway cell proliferation. Without telomerase, adult cells senesce (grow old) after about 50-55 rounds of cell division because the telomeres get too short to provide the buffer required to protect the ends of chromosomes and stabilize the cell's genetic code.

It is now established that nearly 90 percent of cancers develop a way of reactivating telomerase as a means of survival. Inhibiting telomerase function has been viewed as an ideal way to put the brakes on a wide range of cancers. According to Skordalakes, one way to do so would be to disrupt the protein RNA complex that comprises the core of the telomerase enzyme. The RNA binding domain (TRBD) of telomerase is a crucial component to this process and, therefore, the enzyme's ability to work.

In 2007, the Skordalakes laboratory was the first to obtain the three-dimensional structure of TRBD. Since then, his team has been creating molecular inhibitors to target the TRBD RNA-binding pockets as means to inhibit telomerase enzymatic activity.

The present study arose as the Skordalakes laboratory sought to better understand the role of TRBD in telomerase function. They engineered a truncated version of the protein subunit of a vertebrate telomerase, consisting of TRBD and a conserved portion of the N-terminal region of the protein. Within this portion they identified the TFLY, a conserved element that they showed is involved in binding the RNA component of telomerase and this interaction is important for telomerase protein-RNA assembly and activity.

"This TFLY motif comprises a significant part of the binding pocket that enables the enzyme to grapple the RNA template and guide it to the active site of the enzyme for catalysis," Skordalakes said, "but it also facilitates the stable association of the protein with its RNA component thus forming a fully functional telomerase enzyme."

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Human activity affects vertical structure of atmospheric temperature

Sep. 17, 2013 — Human influences have directly impacted the latitude/altitude pattern of atmospheric temperature. That is the conclusion of a new report by scientists from Lawrence Livermore National Laboratory and six other scientific institutions. The research compares multiple satellite records of atmospheric temperature change with results from a large, multi-model archive of simulations.

"Human activity has very different effects on the temperature of the upper and lower atmosphere, and a very different fingerprint from purely natural influences," said Benjamin Santer, the lead researcher in the paper appearing in the Sept.16 online edition of the Proceedings of the National Academy of Sciences. "Our results provide clear evidence for a discernible human influence on the thermal structure of the atmosphere."

Observational satellite data and the computer model-predicted response to human influence have a common latitude/altitude pattern of atmospheric temperature change. The key features of this pattern are global-scale tropospheric warming and stratospheric cooling over the 34-year satellite temperature record. (The troposphere is the lowest portion of Earth's atmosphere. The stratosphere lies above the troposphere.)

"Current climate models are highly unlikely to produce this distinctive signal pattern by internal variability alone, or in response to naturally forced changes in solar output and volcanic aerosol loadings," Santer said.

Natural internal fluctuations in climate are generated by complex interactions of the coupled atmosphere-ocean system, such as the well-known El Nino/Southern Oscillation. External influences include human-caused changes in well-mixed greenhouse gases, stratospheric ozone and other radiative forcing agents, as well as purely natural fluctuations in solar irradiance and volcanic aerosols. Each of these external influences has a unique "fingerprint" in the detailed latitude/altitude pattern of atmospheric temperature change.

Fingerprint information has proved particularly useful in separating human, solar and volcanic influences on climate.

"The pattern of temperature change that has been observed vertically in the atmosphere, from ground level to the stratosphere, fits with what is expected from human-caused increases in greenhouse gases. The observed pattern conflicts with what would be expected from an alternative explanation, such as fluctuations in the sun's output," Santer said.

Another LLNL co-author of the paper, Celine Bonfils, noted that major volcanic eruptions also can profoundly disturb the vertical structure of atmospheric temperature. "During the recovery from such eruptions, tropospheric warming and stratospheric cooling also occur" Bonfils said. "But in contrast to volcanic influences, human-caused atmospheric temperature changes affect all latitudes and last longer. This suggests that the recent changes in temperature are not simply a recovery from past volcanic events."

Other Livermore scientists include Jeff Painter, Peter Gleckler, Charles Doutriaux and Karl Taylor. The research team included scientists from Remote Sensing Systems (Carl Mears and Frank Wentz), the Massachusetts Institute of Technology (Susan Solomon), the University of Adelaide, Australia (Tom Wigley), the NASA/Goddard Institute of Space Studies (Gavin Schmidt), the Canadian Centre for Climate Modelling and Analysis (Nathan Gillett) and the Nansen Environmental and Remote Sensing Center, Norway (Peter Thorne).

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