Climate change roared back into presidential campaign Thursday, as New York City Mayor Michael Bloomberg, whose city remains partially underwater and crippled by Hurricane Sandy, endorsed President Barack Obama.

In his endorsement, which appeared as an op-ed in the publication he founded, Bloomberg said Obama's position on climate change in particular had moved him to endorse the president. He also cited the president's position on abortion and marriage equality.

But Bloomberg focused mostly on global warming, and said that he believes Obama sees climate change "as an urgent problem that threatens our planet," Bloomberg said. Former Massachusetts Gov. Mitt Romney does not, he said.

"The devastation that Hurricane Sandy brought to New York City and much of the Northeast -- in lost lives, lost homes and lost business -- brought the stakes of Tuesday’s presidential election into sharp relief," Bloomberg said.

The mayor is one of the leaders of the C40 Cities Climate Leadership Group, a partnership of the world’s largest cities that have decided to take action on climate change in the absence of movement by federal governments.

Obama welcomed the Bloomberg endorsement, saying he was honored by it and that New Yorkers had his commitment that the country would "stand by New York in its time of need." The Romney campaign did not provide a response.

"I deeply respect him for his leadership in business, philanthropy and government, and appreciate the extraordinary job he's doing right now, leading New York City through these difficult days," Obama said. "While we may not agree on every issue, Mayor Bloomberg and I agree on the most important issues of our time -- that the key to a strong economy is investing in the skills and education of our people, that immigration reform is essential to an open and dynamic democracy, and that climate change is a threat to our children's future, and we owe it to them to do something about it."

Earlier this week, Bloomberg said that even if the direct cause of Sandy's severity was unknown, cities must recognize that something has changed and they'll be forced to grapple with it. "What is clear is that the storms that we've experienced in the last year or so around this country and around the world are much more severe than before," Bloomberg said Tuesday, during a press conference about storm recovery. "Whether that's global warming or what, I don't know. But we'll have to address those issues."

Bloomberg said in his op-ed that he might have been able to support what he described as "the 1994 or 2003 version" of Romney, "because like so many other independents, I have found the past four years to be, in a word, disappointing." As Massachusetts governor, Romney backed a regional cap-and-trade program, Bloomberg said, but has since "reversed course, abandoning the very cap-and-trade program he once supported."

Romney in the past "has also taken sensible positions on immigration, illegal guns, abortion rights and health care," Bloomberg wrote. "But he has reversed course on all of them, and is even running against the health-care model he signed into law in Massachusetts."

Romney has said previously that he believes climate change is occurring and that human activity is a contributing factor. During the Republican primary season, though, he said he didn't believe it was the right course to spend "trillions and trillions" to reduce carbon emissions. More recently, he said in a questionnaire submitted to Science Debate, a non-profit organization focusing on science issues in the presidential campaign, that he believes human activity contributes to global warming and that policymakers should consider the risk of negative consequences.