Massachusetts and the Virgin Islands have backed the New York State attorney general’s investigation into whether Exxon Mobil lied to its investors and the public about the threat of climate change, reports the New York Times. A news conference, attended by 15 states and former vice president Al Gore, also backed president Obama’s Clean Power Plan. In total, 17 attorneys general are cooperating on probes into whether fossil fuel firms misled investors, reports Reuters. The states’ attorney generals have joined an alliance that will press for urgent climate action on multiple legal fronts, reports Inside Climate News. The group includes 20 attorneys general, according to the Hill. The group “just declared war on big polluters”, says Climate Progress. A filing from 18 states yesterday backed the “reasonable and legitimate” Clean Power Plan, reports the Hill. Legislation introduced in California would extend the statute of limitations for misleading investors from four to 30 years, reports Inside Climate News. The Times also covers the joint attorneys general climate initiative.

Poorer nations should delay signing the Paris climate agreement in order to extract political leverage from consenting to the deal, according to a briefing from a Malaysian thinktank sent to the Arab Group of nations last week and seen by Climate Home. Countries should refuse to sign up until they receive stronger assurances on finance, technology and loss and damage, the briefing says.

Plans to invest $1tn in 1,500 new coal plants around the world could be wasted if climate and pollution curbs prevent them from being used, according to a report from the Sierra Club, Greenpeace and Coal Swarm covered by the Guardian. The plans to expand coal capacity come even as electricity generation from coal has fallen, the report says. Some 84 gigawatts of new coal capacity came online last year, says Desmog UK. The report estimates that 338 gigawatts of new coal is under construction, mostly in Asia, says Greenpeace Energy Desk. The Financial Times covers a separate study that finds energy companies can only build new coal and gas plants for another year, if the world is to avoid dangerous climate change.

India conglomerate Tata Steel plans to sell its UK plants, reports the BBC. The company cites a global oversupply of steel, high costs and the weak pound. The BBC cites other factors including “relatively high energy prices and the extra cost of climate change policies”. Carbon Brief looked at these factors in detail, finding policy costs amount to perhaps 1-2% of steel production costs, with additional compensation set to bring this down to a fraction of 1%.

A climate policy public relations offensive, modelled on the successful same-sex marriage campaign, has started two months out from a federal court hearing on president Obama’s Clean Power Plan, reports the New York Times. The appeals court hearing is due to be argued on 2 June.

Senior engineers at French utility EDF have called for two-year delay to the Hinkley Point new nuclear scheme and a reactor redesign, reports the Financial Times. It cites an “internal white paper written by dissenting EDF engineers”, who want a 2027 target completion date. EDF tells the FT the (already much-delayed) 2025 target has not changed. Reuters also covers the story.

Wind and solar power has benefitted from decades of slow and steady engineering and financing improvements that have driven down costs, says Kalina Oroschakoff in a special report for Politico. Onshore wind and solar in sunnier European locations are now the cheapest form of new electricity generation, the article shows. A second article by Anca Gurzu says wind and solar will find it tough to compete against nuclear and gas “without a huge leap in battery technology”. A third feature says “trees are green, but burning them isn’t” and looks at European Commission plans to amend sustainability rules for bioenergy.

The Boundary Dam carbon capture and storage demonstration plant in Canada has been “plagued by multiple shutdowns…and faces an unresolved problem with its core technology”, reports the New York Times, in an extended feature. Issues include the system only working at 45% capacity and coal ash contaminating the carbon capture agent. SaskPower, the company behind the scheme, and carbon capture advocates, “argue that the setbacks are typical teething problems”, the paper says.

The Financial Times’s Kiran Stacy and Jim Pickard look ahead to 2025, “set to be a pivotal moment” for UK energy. It is the date coal power is to have been phased out and the new nuclear plant at Hinkley C is to have opened. With accelerating coal closures and progress for Hinkley anything but smooth, however, a potential gap in supplies is opening up. Though this could be filled, it might be at the expense of higher carbon emissions, they suggest.

A new study examines the implications for greenhouse gases on turning existing cropland, grassland or woodland into bioenergy crops in the UK. Overall, short rotation poplar offers a greater beneficial impact on soil GHG balance than oil seed rape, wheat, sugar beet, Miscanthus or coppice willow. The authors acknowledge, however, that the study does not consider GHG emission increases/decreases resulting from displaced food production, the energy-density of the crop and socio-economic factors, such as expenditure on harvesting equipment.