On June 3, 2008, Barack Obama clinched the Democratic nomination for the presidency. That night, he spoke from St. Paul, Minn.

As the half hour speech culminates, Obama outlines what he hopes will be his legacy. "Generations from now," he says:

… we will be able to look back and tell our children that this was the moment when we began to provide care for the sick and good jobs to the jobless. This was the moment when the rise of the oceans began to slow and our planet began to heal. This was the moment when we ended a war, and secured our nation, and restored our image as the last, best hope on Earth.

Four points: Health care. Jobs. Ending the wars in Iraq and Afghanistan and improving America's global reputation. And turning the tide on climate change.

His success on most of those is debatable (and hotly debated). But of those four, it's almost certainly the fourth point that he would today have the hardest time defending.

Right now, world leaders and corporate executives are meeting in New York to try and figure out ways in which the threat of climate change can be addressed. Obama is scheduled to speak on Tuesday afternoon and, in advance, released an executive order of planned actions on the climate.

President Obama told leaders at the United Nations summit on climate change that "nobody can stand on the sidelines on this issue," insisting that an "ambitious" agreement is needed to protect the world from environmental dangers. (AP)

The timing of the event is remarkable. This week we learned that the amount of carbon dioxide released into the atmosphere in 2013 increased by 2.3 percent. We learned, too, that this summer was the hottest summer in recorded history; this August, the hottest month on record. Far from slowing the rise of the oceans, sea levels are rising faster now, according to Obama's own National Oceanic and Atmospheric Administration.

If climate change is to be part of Obama's legacy, he faces two separate -- and only lightly-overlapping -- challenges. First, he faces stiff domestic political pressure on any and all efforts to trim America's greenhouse gas emissions and energy efficiency. (In 2013, for the first time in years, carbon dioxide emissions in the United States rose.) And, second, he faces the reality of climate change: That it requires international attention and commitments.


Activists march through Columbus Circle during the People's Climate March in Manhattan this week. (Yana Paskova/For The Washington Post)

For decades, the United Nations has tried to put together a binding commitment from its members aimed at reducing greenhouse gas emissions -- particularly carbon dioxide. In 1992, 165 countries signed the United Nations Framework Convention on Climate Change in Rio de Janeiro, with that goal. More famously, at the UNFCCC's 1997 meeting in Kyoto, a protocol for doing so was agreed to, setting firm goals and legal obligations. The United States never ratified the treaty; Canada withdrew in 2011.

Subsequent attempts to broker a deal have fallen apart. In 2009, the UNFCCC held a Conference of Parties in Copenhagen, Denmark, aimed at developing a new binding treaty. Instead, the conference fractured, in part due to the divisive issue of whether or not developing countries would be held to similar criteria.

What's happening right now in New York, in the wake of the largest climate rally in history, is something different. Instead of parties coming together to develop a binding agreement, it's an attempt to self-regulate, to encourage countries and companies to establish individual goals for reduction that, in the aggregate, will hopefully have a global effect.

Mashable is tracking those commitments: a European Union pledge to reduce emissions up to 95 percent by 2050, financial commitments from France and Switzerland, Costa Rica's switch to clean energy. All of these things could have an effect, and particularly that E.U. pledge. But none will have a huge impact in the absence of other efforts.

What remains to be seen is what the largest emitters will do: China and India, whose emissions were the main reason for 2013's global CO2 increase, and the United States, which has the highest per-capita emissions (although China just moved into second place). China has already proposed a carbon dioxide market -- similar in some ways to a proposal that died in the U.S. Senate in 2010 -- and the EPA has announced a regulation that would drop power plant carbon dioxide emissions by 30 percent. Neither of these steps alone is going to heal the planet. So what else?

Obama's response is heavy on information. Mandated consideration of the effects of climate resilience in development work, an emphasis on tracking and predicting climate change's effects, enrollment in international efforts. It's not a world-healer, either.

This week's gathering is not his last chance to rise to a position of global leadership on climate change. And some steps, like increasing fuel efficiency, will have significant long-term benefits for the environment. But he's hobbled on other large measures by a Republican Party which largely considers climate change to be an undue economic encumbrance, if it thinks about climate change at all. That means the administration is left in this moment -- a moment of activist energy and perhaps a slight move toward acceptance of climate change by the general public -- to rely on the tools of executive action.

Earlier this year, riffing off of Obama's pledge to take more executive actions to work around Congress, CNN's Jake Tapper asked the president, "I remember during the campaign when you talked about your presidency being a moment when the rise of the oceans would slow and the nation and the world would heal. Now you're talking about pen and phone and executive orders and executive actions. Do you think you were naive back then, or have you recalibrated your expectations and your ambitions?"

Obama's response? "We got a lot of that stuff done." He pointed to health-care reform first -- understandably -- and then previewed the EPA action on climate change mentioned above. (It was announced in June.)

When he's asked similar questions on Jan. 21, 2017, he certainly hopes to have a stronger answer. There's still a chance that he'll point to an announcement made or an agreement brokered in September 2014.