President Barack Obama’s by turns tearful and triumphant unveiling of the Clean Power Plan Monday seemed like a turning point in the fight against global warming.

If it survives legal challenges, it could remake the way America generates electricity, accelerate a shift away from coal-fired power plants – the chief source of the greenhouse gas emissions that scientists blame for global warming—and cement Obama’s legacy as the greatest environmental president.

“I don’t want my grand-kids to not be able to swim in Hawaii or not be able to climb a mountain and see a glacier because we didn’t do something about it,” Obama said in the emotional conclusion to his speech. “That’d be shameful of us.”

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But for some who study climate change the only shame is this: Obama’s plan does not go nearly far enough. It’s meek and dangerously self-congratulatory, sapping the movement of urgency while doing almost nothing to maintain the future habitability of the earth.

“The actions are practically worthless,” said James Hansen, a climate researcher who headed NASA’s Goddard’s Institute for Space Studies for over 30 years and first warned congress of global warming in 1988. “They do nothing to attack the fundamental problem.”

“You’ve got to be kidding,” he wrote, when asked if the plan would make continued climate activism unnecessary. Obama’s plan, and for that matter the proposed plan Democratic front-runner Hillary Clinton, he continued, “is like the fellow who walks to work instead of driving, and thinks he is saving the world.”

Hansen suggested a gradually rising fee for fossil fuel extraction, collected at the port of entry or, in domestic cases, the place where the material actually comes out of the ground. “As long as fossil fuels are allowed to (appear to be) the cheapest energy, someone will burn them,” he wrote in an email to msnbc. “It is not so much a matter of how far you go. It is a matter of whether you are going in the right direction.”

The right direction is away from a global temperature rise of 2 degrees Celsius above pre-industrial times. If that grim milestone is reached the Intergovernmental Panel on Climate Change predicts that irreversible damage to society would be the likely result.

In Copenhagen in 2009, world leaders agreed to work together to keep global temperatures below that mark. In Paris this coming November and December, climate ministers will gather again in hopes of negotiating a new agreement, one that puts the world on a path for less than 2 degrees of warming.

Unfortunately, the current plans don’t go far enough, according to Climate Action Tracker, a group of research organizations dedicated to analyzing the world’s progress. In comments this spring and summer, the group criticized the plans out of Europe and other advanced economies, calling them “inadequate” and “insufficient.” They rated the U.S. plan in particular as about halfway to what’s needed, and hoped “urgent revisions” would arrive in the months ahead.

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In an analysis released Tuesday, CAT reported some good news, noting that Obama’s plan “makes a difference,” and will likely reduce America’s economy-wide emissions by “roughly 10%” beyond the current pace. However, researcher Hanna Fekete told msnbc in an email, “the targets are not sufficient for 2°C” and more will be needed for the U.S. to reach its goals. She reiterated the group’s early warning of “large gap” between the current pace of carbon emissions, and what’s considered safe.

Even with Obama’s Clean Power Plan, and the recent plans announced by China and Brazil and others, the world is on pace for about 3 degrees of warming by 2100. The most vulnerable countries of the world, including many small island nations, believe they can sustain about half that rate. Some climate scientists say a “war-like” mobilization is needed to cut emissions by 80% by 2030, with full decarbonization shortly thereafter–or not even the wealthier countries of the world will be safe.

While Republicans have pounced on Obama’s plan, calling it “lawless” and comparing it to a “crusade,” commentators on the left agree with Hansen. Vox’s Brad Palmer pointed out that U.S. emissions declines have little to do with policy and, in any case, have recently begun to creep upward again. Slate’s Eric Holthaus, meanwhile, is a a meteorologist who recently estimated that Obama’s plan cuts emissions only about a third of what researchers like Hansen say is necessary.

Even more worrying: In July, Hansen and 16 colleagues published a persuasive – and already hotly contest – paper, arguing that the Intergovernmental Panel on Climate Change is too conservative on sea level rise.

The study concludes that glaciers in Greenland and Antarctica will melt 10 times faster than the IPCC estimates, resulting in sea level rise of at least 10 feet in as little as 50 years. If true, coastal cities like New York and New Orleans have but a few decades of habitability left.

The White House is reviewing the criticisms and told msnbc that it would respond shortly.