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The article highlights the paper by Srinivasan and colleagues that was published in a previous issue of the journal in 2008. The paper focuses on tracking the worldwide depletion of ecosystem resources. According to the author, the paper have used a simplified accounting framework to link populations who experience ecological damage to those who cause it. It reveals that the largest and most blatant imbalance is the debt we owe to low-income countries because of climate change. It states that on a per capita basis, people in high-income countries are responsible for almost six times more greenhouse gas emissions than their low-income counterparts.

The article presents information related to global temperature changes, with reference to articles published in the March 24, 2006 issue. The relationship between greenhouse gas levels and temperature, as evident in data from ice cores, illuminates climates in the geological past and may be a more useful guide to the future. At this time in the Miocene, there were no major ice sheets in Greenland, sea level was several meters higher than today's envision a very skinny Florida, and temperatures were several degrees higher. A more recent point of reference, and the subject of two papers in this issue, is the Eemian: the previous interglacial, about 130,000 to 120,000 years ago. Evidence presented in two papers, a News story, and two perspectives in this issue demonstrates an accelerating decay of ice sheets in Greenland and Antarctica.

When drought hit the marginally habitable land along the southern edge of the Sahara in the 1970s and '80s, the people of the Sahel suffered greatly. Soon some researchers were hypothesizing that intensive use of the land might have altered the surface of the Sahel enough to dry it out. In a paper published online, climate dynamicist Alessandra Giannini of the International Research Institute for Climate Prediction in Palisades, New York and her colleagues report results from the first climate model to simulate accurately the history of Sahel rainfall. In their model, the Indian Ocean's warming over the decades was the dominant driver of the drying of the Sahel. The model's greenhouse gas amounts were not changed over the 70 years, nor was the vegetation or any other surface property in or around the Sahel. Tropical Pacific temperatures accounted for much of the year-to-year variability of Sahel rain but not much of the long-term trend. The warming of the tropical Atlantic did play some role in long-term drying, but it was the Indian Ocean that drove most of the drying in the model. The link between the Indian Ocean and Sahel rainfall is only the latest ocean-drought connection.

The article reports that the climate change hot spots mapped across the United States. According to climate modeler Gerald Meehl of the National Center for Atmospheric Research (NCAR) in Boulder, Colorado, the latest regional climate highlights regios where climate changes will be bigger than others. Climate modeler Noah Diffenbaugh of Purdue University in West Lafayette, Indiana lay out in the paper, regional climate modeling, which is in press in "Geophysical Research Letters" (GRL). According to the model, the strongest U.S hot spot by far stretches across the Southwest from southern California to west Texas, and intensifies over northern Mexico.

This article reports that one of the most important aspects of global climate is precipitation, and variations in its timing or amount can have an enormous impact on human resources and activities. A pair of papers illustrate two different aspects of this type of variability. El Niño and La Niña events have dramatic effects on patterns of precipitation all across the globe and are often cited as the cause of large economic losses, because these events are associated with extremes of weather. However, it was found that climate anomalies during these events are not greater than those that occur in the intervening periods.