The political leaders coming from around the world for Gov. Jerry Brown’s climate action summit this week will grapple with a lot of urgent deadlines to drive down emissions, but one date is especially exasperating. It is 2035 — the year advocates aim to kill off production of gasoline and diesel powered vehicles. Transportation is the most vexing problem the summit will confront. The sector sends more greenhouse gases into the air than any other, recently outpacing power plants, which are getting cleaner every year. “Even during the Obama administration, when the country was pushing as hard and fast as it could on climate policy, it still wasn’t enough” to meet the goals on auto emissions, said Kate Larsen, a director at Rhodium Group and member of the Lab.