In August, entrepreneur Elon Musk suggested in a social-media post that Earth could be cooled by launching satellites into space to shade the planet from the Sun. These 'sentient satellites', he wrote, 'can solve global warming for ~1B years'. It's unclear whether Musk, the chief executive of aerospace firm SpaceX in Starbase, Texas, meant for this to be taken seriously. But some researchers are earnestly investigating space-based methods of reflecting sunlight away from Earth to cool the planet as temperatures rise to increasingly dangerous levels. A non-profit organization called the Planetary Sunshade Institute in Los Angeles, California, published a report this month that researchers say is the most detailed analysis yet of such geoengineering methods. The report ' which summarizes studies from a consortium of engineers and climate scientists, including some from leading space agencies such as NASA ' estimates that it could become viable to begin building a 'planetary sunshade' in as few as 20'40 years. The timeline would depend on the rate at which heavy-lift rockets are developed that can haul millions of tonnes of material into deep space to create the sunshade. (SpaceX, which is not involved in the report, did not respond to a query from Nature about whether it is conducting research on this topic.)...

Protestors demonstrate outside the US Supreme Court on 5 October, as justices hear a case whose outcome could determine whether fossil-fuel companies can be held responsible for global warming.Credit: Mehmet Eser/Anadolu via Getty Last month, a climate scientist working in the University of California system received an unsettling message from her institution. University officials asked her to submit all correspondence related to a study she had published linking emissions from fossil fuels to environmental harms caused by climate change. The university had received a public-records request from a law firm representing the Patriots Foundation in Des Moines, Iowa, which describes itself on its website as a government watchdog. The requests seem to be part of an expanding effort by groups with ties to the energy industry to discredit findings in the burgeoning field of climate attribution science, which estimates the extent to which extreme weather events, such as floods and heatwaves, are due to climate change. The demands come at a time when attribution science's role in lawsuits against major industrial emitters is growing....

If I were dictator of the world and wished to maximize economic efficiency, the answer would be fairly obvious. Impose a tax on activities that create greenhouse gases designed to reflect the marginal cost they create. That is the standard economic solution, due to Pigou, for problems of negative externalities. Since the tax brings in additional revenue, combine it with a corresponding reduction in whatever taxes currently have the largest adverse effects. To begin with, they would not be based on a realistic estimate of the marginal costs; insofar as they would be based on anything, judging by past arguments over Kyoto and similar proposals, it would be a target level of temperature. If the level of taxes needed to hold warming down to the target level turned out to be much higher than the marginal damage done at that level, as it well might be, we would be buying lower temperature at a price higher than it was worth. I offer as further evidence the arguments I have had over the years, especially back when I was posting in climate threads on Facebook, with people certain that global warming would have catastrophic consequences but unable to support that conviction with anything more than handwaving arguments. Judging by casual observation, they are the norm, not the outliers, of their movement....

President Donald Trump has responded in characteristic fashion to the recent debate around AI safety ' by declaring that these concerns are part of a long line of hoaxes 'generated by the Radical Left Dumocrats, for purposes of destroying our Country.' On Saturday, Trump began his musings on AI by writing on his social network Truth Social that 'many people think that the words 'Artificial Intelligence' are inaccurate, and very ineloquent, relative to AI, or Artificial Intelligence.' So he posted a poll where followers could vote on a new name for the technology ' Superior Intelligence, Extreme Intelligence, or Supreme Intelligence. (The poll is still ongoing as of publication time) A couple hours later, Trump followed up with a post claiming that attempts at 'the decimation, or destruction, of AI' are one of 'many' Democratic hoaxes, similar to 'RUSSIA, RUSSIA, RUSSIA, UKRAINE, UKRAINE, UKRAINE, Global Warming, Impeachment Hoax #1, Impeachment Hoax #2, Men in Women's Sports, [and] Transgender for Everyone.'...