Before Pope Francis, climate change was seen primarily as either a political or a scientific issue. His encyclical reframed it as a spiritual issue. As the spiritual leader of 1.4 billion Catholics around the world, Pope Francis presented climate activism as a moral and spiritual duty for true believers, and he made climate one of the defining issues of his papacy. Over his 12 years as head of the Catholic Church, Francis repeatedly raised concerns about human-caused global warming resulting from the burning of fossil fuels. He urged people'including world leaders'to take meaningful action. When Argentina's Jorge Mario Bergoglio was elected pope in 2013, his vision for human justice and equality was so closely linked to nature that he chose the papal name Francis, honoring the patron saint of ecology. That belief, and the passion with which he advocated for it, helped influence the direction of global climate and energy policy'most notably the 2015 Paris Agreement. Francis's 2015 papal letter, or encyclical, Laudato Si' ('Praise Be to You'), was the first devoted entirely to the issue of global warming. It wove together climate science, wealth inequality, overconsumption (which he criticized as part of a 'throwaway culture'), and the ethical use of technology in a 40,000-word message addressed to more than 1 billion Catholics around the world....

Sometime in the next several months, a team of US scientists plans to pour a solution of antacid into the waves off the coast of Massachusetts. Using boats, buoys and autonomous gliders, the scientists will track changes in water chemistry that should allow this tiny patch of the Atlantic Ocean to absorb more carbon dioxide from the sky than it normally would. The US$10-million experiment, dubbed LOC-NESS, aims to test one prominent strategy to reverse global warming by removing CO2 from the atmosphere. Doing so will be neither cheap nor easy. But with the world looking likely to blow past the temperature targets laid out in the 2015 Paris climate agreement, a growing number of scientists and policy specialists say that carbon removal will be necessary later this century if humanity is to achieve its long-term climate goals. Governments, utility companies and hundreds of start-up organizations around the globe are now investing billions of dollars in carbon-removal strategies that take three broad approaches: sucking carbon directly from the air; altering the oceans to absorb more carbon than normal; and enhancing carbon removal on land. In the United States, for example, companies are planning to build several large-scale 'direct air capture' facilities that scrub CO2 out of thin air. And in Europe, power companies are developing a strategy that captures carbon emissions from bioenergy plants that burn woodchips, straw and other plant-based materials: the captured CO2 will then be pumped into the ground beneath the North Sea. Many companies are already selling voluntary carbon-removal credits to organizations such as Microsoft and Google to help them meet their climate commitments. By some estimates, the world might need to remove more than 6 billion tonnes of CO2 from the atmosphere each year by mid-century to meet its long-term climate goals(see 'Catching carbon')1....

Years ago, after taking an Earth science class, I found myself looking at the world differently. It was the 1990s, and lakes in Wisconsin where I lived at the time were beginning to freeze later in winter and thaw earlier in spring, and flowers seemed to bloom a bit earlier. People are more likely to believe an explanation when they see direct evidence of it. In the U.S., the percentage of people who recognize that global warming is happening is higher in counties that experienced record high temperatures in the previous decade. But understanding what's happening and why also matters. That's because people's existing knowledge shapes how they interpret the evidence they see. But does higher education actually create climate concern' As an anthropologist and a researcher in computational social science, I and my colleague Ben Horne set up a study to try to answer that question. In our study, we used Census Bureau data on the percentage of the population with at least a bachelor's degree in 3,048 U.S. counties, NOAA data on recent warming by state, and Yale climate opinion survey data. We wanted to find out whether climate concern increases as a product of education and recent warming....

It's tricky to predict precisely what the impacts of climate change will be, given the many variables involved. To predict the impacts of a warmer world on plant life, some researchers look at urban 'heat islands,' where, because of the effects of urban structures, temperatures consistently run a few degrees higher than those of the surrounding rural areas. This enables side-by-side comparisons of plant responses. But a new study by researchers at MIT and Harvard University has found that, at least for forests, urban heat islands are a poor proxy for global warming, and this may have led researchers to underestimate the impacts of warming in some cases. The discrepancy, they found, has a lot to do with the limited genetic diversity of urban tree species. 'The appeal of these urban temperature gradients is, well, it's already there,' says Des Marais. 'We can't look into the future, so why don't we look across space, comparing rural and urban areas'' Because such data is easily obtainable, methods comparing the growth of plants in cities with similar plants outside them have been widely used, he says, and have been quite useful. Researchers did recognize some shortcomings to this approach, including significant differences in availability of some nutrients such as nitrogen. Still, 'a lot of ecologists recognized that they weren't perfect, but it was what we had,' he says....