Energy giants including Exxon Mobil and Royal Dutch Shell risk wasting more than a third of their budgets on projects that will not be needed if climate targets are to be met, a think tank report shows. More than $2 trillion of planned investment in oil and gas projects by 2025 could be redundant if governments stick to targets to lower carbon emissions to limit global warming to two degrees Celsius, according to a report by the Carbon Tracker think tank and institutional investors.