Hillary Clinton's choice of Sen. Tim Kaine as her running mate was largely considered a safe political choice, adding a moderate Democrat from the swing state of Virginia to her ticket. Kaine has mostly shared Clinton's views on climate and clean energy, but his selection unsettled those who wanted a vice president with more appeal to ardent environmentalists who flocked to Bernie Sanders' campaign.

Groups like the Sierra Club and the League of Conservation came out strongly in his support, but others such as 350.org and Climate Hawks Vote were more skeptical. The latter summed up its view in one terse, laconic word: "Meh."

According to the green group 350.org, "Tim Kaine won't energize the climate base, so it's up to Hillary to start staking out some clearer positions."

The League of Conservation Voters, however, celebrated the decision, calling Kaine "an environmental leader." The Sierra Club called it "the strongest environmental ticket we've ever seen."

Activists including Climate Hawk co-founder RL Miller and 350 Action Director May Boeve don't like his record favoring offshore drilling and exporting liquefied natural gas (LNG). Anticipating his selection, which was not unexpected, some have criticized the senator's support for the Trans Pacific Partnership Agreement, a trade pact they believe would weaken environmental and climate protections. His recent stance on loosening banking regulations has also earned him scorn from the left.

But Kaine also opposed the Keystone XL oil sands pipeline, worked to prepare Virginia's coastal communities for sea level rise and advocated for a transition to a clean energy economy--efforts cheered by activists.

He's also recently won over fans with a vigorous defense of the scientific consensus on the urgency of the climate crisis and an outspoken condemnation of those who deny global warming.

On the Senate floor last week, Kaine joined other Democrats in a prolonged colloquy against the fossil fuel interests and their allies in Congress—part of a concerted campaign called Web of Denial initiated by Sen. Sheldon Whitehouse, a Democrat from Rhode Island and a strong advocate of climate action.

"Climate change is not an abstraction. Climate change is not a next year, next decade issue. Climate change in Virginia is a today issue," Kaine said, noting that the coastal town of Norfolk is the second most vulnerable city in the country to rising sea levels, behind New Orleans. Kaine condemned "shadowy organizations" that have received funding from conservative donors with links to the energy industry, and accused them of supporting the spread of misinformation about climate change.

"To hear Kaine take such a strong stance against them, I was agog. I was pleased," said Scott Peterson, executive director of the watchdog group Checks & Balances based in Virginia. Peterson told InsideClimate News that Kaine wasn't on his radar as an environmental leader before that speech. Instead, he thought of Kaine as one of the state Democrats who had received some donations from the utility Dominion Virginia Power, which activists accuse of pushing for dirty power plants and resisting climate solutions.

Clinton announced her running mate in a text message to her supporters on Friday night. She expanded on the decision on Twitter, writing from her account: "@TimKaine is a relentless optimist who believes no problem is unsolvable if you put in the work to solve it." Both President Obama and former President Bill Clinton endorsed Kaine this week.

Kaine, 58, was elected to the Senate in 2012. He previously served as chair of the Democratic National Committee (2009-11), spent a term as Virginia's governor (2006-10) and held other positions in state government. He worked as a lawyer and teacher before entering politics. He also spent a year as a missionary in Latin America and speaks Spanish fluently.

The conventional wisdom is that he could help win Virginia. President Obama won in Virginia in both 2008 and 2012, after George W. Bush won the state in 2004 and 2000.

One of Kaine's biggest donors during his Senate campaign was the League of Conservation Voters (LCV). In 2012, LCV spent about $2 million on a television advertising and mailer campaign against Kaine's opponent George Allen, a Republican that's denied climate change. Environmentalists raised additional money for Kaine in 2012 through GiveGreen, an environmental bundling platform partly supported by the LCV Action Fund.

LCV, which rates the environmental voting record of every member of Congress, gave Kaine a lifetime rating of 91 percent. (Trump's running mate Indiana Gov. Mike Pence, in contrast, earned a 4 percent lifetime rating from LCV for his consistent voting against green issues during more than a decade in the House.)

"We're thrilled," Tiernan Sittenfeld, senior vice president for government affairs at LCV, said of Clinton choosing Kaine. "Senator Kaine is an environmental champion and we are so excited to do everything we can to help elect Secretary Clinton and Senator Kaine to White House." The group endorsed Clinton early in the primary season.

Kaine is a supporter of the Clean Power Plan, rules designed to reduce greenhouse gas emissions from power plants. After the final rules were published last year, he said the regulations were "the biggest step the United States has ever taken to address the pollution responsible for climate change." The rules were challenged by several states and the Supreme Court has stayed them; Kaine is among the group of lawmakers to file an amicus brief defending the rules.

Additionally, Kaine has voted to expand clean energy tax cuts and set goals for how much electricity in the nation should come from renewable sources; he's also backed reform of the nation's flood insurance program and blocked Republican-led efforts to repeal the Clean Power Plan. He has also consistently opposed the Keystone XL pipeline.

In an anti-Keystone op-ed, he wrote: "I'm a pro-pipeline senator. As a former mayor of Richmond, a city with a gas utility, I think it makes no sense to be anti-pipeline. But I oppose the Keystone XL project. ... Although the president's decision is technically over whether to allow a pipeline to deliver oil from Alberta to the coast of the Gulf of Mexico, the real issue isn't the pipeline. It's the wisdom of using tar sands oil. By most accounts, oil from tar sands is 15 to 20 percent dirtier than conventional petroleum, and the process of extracting and refining it is more difficult and resource-intensive. With so many cleaner alternatives, there is no reason to embrace the use of a dirtier fuel source."

Clinton only lately spoke out against the Keystone line, after facing intense pressure on the campaign trail from activists. That was just a few months before President Obama rejected the project on climate grounds.

Kaine's support of offshore oil drilling in the Atlantic Ocean, is shared by several other prominent Virginia Democrats. He has also supported funding and research for carbon capture and storage technologies for coal-fired power plants, and introduced a bill last year to streamline the approval process for exports of liquefied natural gas. (However, Kaine voted in 2015 against legislation to limit the Department of Energy's role in considering applications to export LNG.)

Virginia is the 15th largest coal-producing state in the nation, according to the Energy of Information Agency. Coal production has declined in the state, and nationwide, in recent years due to increased competition from natural gas and other energy sources, along with new air pollution regulations for power plants.

The Clinton-Kaine ticket comes at a time when the Democratic Party platform is expected to be the strongest yet on climate issues, in stark contrast to the Republican platform's adamant stance in favor of fossil fuels and against pollution regulations.

"Kaine has not yet earned the support of climate voters," said RL Miller, cofounder of Climate Hawks Vote, in a statement. "Kaine might be a fledgling climate hawk - this month he participated in the Web of Denial speech-a-thon, calling out the fossil-fuel industry's decades of climate deception. But Kaine needs to stop advocating for clean coal, fracked gas, and offshore oil, and start advocating for clean solar and offshore wind, if he wants the United States to be the clean energy superpower of the world."

If Kaine is elected vice president, his Senate seat would be temporarily filled by the governor and then open to a special election in 2017. Democrats are concerned his Senate seat could fall to the Republicans, whose majority there is under pressure this year.