We talked a week ago about the climate crisis, and the fact that the ratio of carbon emissions in the atmosphere "flirting with" 400 parts per million -- an alarming threshold climate scientists have long hoped to avoid.

It appears that flirtatious period is over.

The proportion of carbon dioxide in the atmosphere broke 400 parts per million Thursday, according to one of the best climate records available.

The Keeling Curve, a daily record of atmospheric carbon dioxide, has been running continuously since March 1958, when a carbon dioxide monitor was installed at Mauna Loa in Hawaii. On the first day, the observatory measured a carbon dioxide concentration of 313 parts per million (ppm). The number means there were 313 molecules of carbon dioxide in the air per every million air molecules.

Now, the Keeling Curve has reached 400 ppm for the first time in human history, with a new measure of 400.03 ppm. The data are preliminary, pending quality control checks, according to the National Oceanic and Atmospheric Administration (NOAA).

The last time the planet topped 400 ppm, there were no humans. What's more, there has never been an increase comparable to the accelerated increases we're seeing now.

The crisis, which many of today's U.S. conservatives perceive as a "hoax" cooked up by liberals to undermine capitalism, is only going to get worse without concerted efforts from policymakers here and around the globe.

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This week, in particular, the Republican approach to environmental policy came into sharp focus. GOP senators are blocking President Obama's nominee to head the Environmental Protection Agency, boycotting Gina McCarthy's confirmation hearing and instead holding fundraisers with energy-industry lobbyists.

But what about the other end of Pennsylvania Avenue?

The conventional wisdom certainly has merit -- Obama has set worthwhile environmental goals, but progress has been slow, in part because congressional Republicans have made it impossible to pass legislation, even a cap-and-trade policy that GOP leaders championed as recently as 2008. Carbon emissions have sharply improved, but there's no credible reason to give administration policies too much credit, since the reductions are largely the result of the recession and the fracking boom.

Jonathan Chait, however, this week challenges some of the assumptions in an interesting piece and gives Obama more credit for "amassing an impressive record" than he usually receives.

He has done quite a bit, probably far more than you think, and not all of it advertised as climate legislation, or advertised as much of anything at all. The American Recovery and Reinvestment Act was many things -- primarily, a desperate bid to shove money into enough Americans' pockets to prevent another Great Depression -- but one of them was a major piece of environmental reform. The law contained upwards of $90 billion in subsidies for green energy, which had a catalyzing effect on burgeoning industries. American wind-power generation has doubled, and solar power has increased more than six times over.... [T]he wave of innovation -- new fuels, plus turbines, energy meters, and other futuristic devices -- will reverberate for years. [...]

The administration has also carried out an ambitious program of regulation, having imposed or announced higher standards for gas mileage in cars, fuel cleanliness, energy efficiency in appliances, and emissions from new power plants. In aggregate, they amount to a major assault on climate change. Some environmentalists judge them to be insufficient -- a fair critique -- but many more Obama supporters aren't even aware that they exist.

Fair enough, but what about looking ahead? Chait's thesis is slightly more provocative on what the Obama White House might yet do in its second term. Cap and trade appears to be dead, at least without an unexpected Democratic wave in the 2014 midterms, but there is another opportunity for the president to combat climate change in a sweeping way without Congress.

[A] few weeks after last year's election, the Natural Resources Defense Council published a plan for the EPA to regulate existing power plants in a way that was neither ineffectual nor draconian. The proposal would set state-by-state limits on emissions. It sounds simple, but this was a conceptual breakthrough. Much like a cap-and-trade bill, it would allow market signals to indicate the most efficient ways for states to hit their targets -- instead of shutting coal plants down, some utilities might pay consumers to weatherize their homes, while others might switch some of their generators over to cleaner fuels. The flexibility of the scheme would, in turn, reduce the costs passed on to consumers. Here is a way for Obama to use his powers -- his own powers, unencumbered by the morass of a dysfunctional Congress -- in such a way that is neither as ineffectual as a firecracker nor as devastating as a nuke: The NRDC calculates its plan would reduce our reliance on coal by about a quarter and national carbon emissions by 10 percent.

This is the last best chance to deal with global warming in the Obama era. The prospect, for environmentalists, is exhilarating but also harrowing. The struggle will be lengthy, waged largely behind closed doors, and its outcome won't be known until the Obama presidency is nearly over.

Is this something the president is serious about pursuing? It's hard to say with confidence either way, though it's worth noting that Obama's State of the Union address included an implicit threat that Republicans probably recognized: "If Congress won't act soon to protect future generations, I will."

For now, it's a story well worth watching. I rather doubt we'll see officials committing to any specific course, but this regulatory approach has the benefit of (a) being entirely legal; (b) not needing congressional approval; and (c) efficacy in dealing with a genuine global crisis.

President Obama spoke to students in Mexico City this morning about a variety of subjects, but I was especially glad to hear this line: "Climate change is happening. The science is undeniable."

It really is.

The ratio of carbon dioxide in Earth's atmosphere is flirting with 400 parts per million, a level last seen about 2.5 million to 5 million years ago, according to the Scripps Institution of Oceanography at the University of California, San Diego. [...]

Isolated measurements have peaked at above 400 parts per million in the Arctic, but scientists are more alarmed at steady readings from Mauna Loa, Hawaii, far from major pollution sources. Those measurements, considered to be the most reliable indicators of Earth's atmospheric content, could breach the 400 level this month, according to Scripps. [...]

For the previous 800,000 years, CO2 levels never exceeded 300 parts per million, and there is no known geologic period in which rates of increase have been so sharp. The level was about 280 parts per million at the advent of the Industrial Revolution in the 18th century, when the burning of fossil fuels began to soar.

You've probably heard of 350.org, a group/movement founded Bill McKibben, which works on combating the climate crisis. The name of the organization has a specific meaning -- it refers to the goal of 350 parts per million for carbon emissions, a level scientists tell us is necessary to avoid climate catastrophes.

We're now "flirting with 400 parts per million," and moving in the wrong direction.

Making matters slightly worse, the United States will struggle to play a leadership role in addressing the crisis because many in Congress are convinced the totality of climate science is a communist conspiracy and a hoax perpetrated by greedy scientists who hate the American way of life.

Associated Press

Sen. James Inhofe (R-Okla.) and Admiral Samuel Locklear

Admiral Samuel Locklear, one of the nation's top military leaders and the head of the U.S. Pacific Command, was on Capitol Hill yesterday, answering questions about the scope of the threat posed by North Korea. His responses were important, but there was an unrelated part of his testimony that struck me as noteworthy.

When it comes to North Korea, Locklear told the Senate Armed Services Committee that the U.S. military is prepared to address a possible North Korean offensive, including intercepting a missile launch should there be one. The admiral added that North Korea does not yet have the ability to threaten the mainland United States or Hawaii, but Guam may be at risk, and the U.S. has "capability in place" to protect the island.

But then Sen. James Inhofe (R-Okla.), one of the nation's more strident opponents of climate science, wanted to talk about global warming.

Locklear argued last month that while there are important and ongoing threats in Pacific region, the biggest long-term security threat in the Pacific region is climate change. He spoke at length on the issue, telling the Boston Globe that significant upheaval related to the warming planet "is probably the most likely thing that is going to happen ... that will cripple the security environment, probably more likely than the other scenarios we all often talk about.''

Inhofe hoped Locklear would, if given a chance during yesterday's hearing, walk that back. The admiral did the opposite.

Inhofe pressed Locklear to say his view has been misrepresented by "environmental extremists" who "think we're spending too much money on defense." The admiral did anything but that.

About 280,000 people died in natural disasters in his Pacific area of responsibility from 2008 to 2012, Locklear said.

"Now, they weren't all climate change or weather-related, but a lot of them were," he said. And that will only get worse as the population soars and even more people move toward "the economic centers, which are near the ports and facilities that support globalization," according to the admiral.

The far-right senator then interrupted the head of the U.S. Pacific Command, complaining that Locklear had taken up too much of Inhofe's allotted time.

I can appreciate why it's best not to sound alarmist while reporting on global warming. I can also say there's a climate crisis and it's genuinely insane to ignore the increasingly terrifying evidence.

New research suggests average global temperatures were higher in the past decade than over most of the previous 11,300 years, a finding that offers a long-term context for assessing modern-day climate change.

The study, published Thursday in the journal Science, aims to give a global overview of Earth's temperatures over the past 11,300 years -- a relatively balmy period known as the Holocene that began after the last major ice age ended and encompasses all of recorded human civilization.

Consider this chart from the researchers' report:

As NBC News' science team explained, similar climate studies have reached similar conclusions, but reports have generally focused on temperature trends over the last two millennia. This new report goes back to the last ice age, showing the trend over 11,000 years.

I suppose the right's response will be varied. Some will say there's a communist conspiracy to manipulate the data by those determined to destroy the free-enterprise system. Others might try to suggest there's a remarkable coincidence, and that the sharp, unprecedented spike occurred naturally.

And then there will be a third group of conservatives who'll concede that global warming is real and the science is credible, but to address the crisis might hurt our short-term economy, and therefore, it's better left ignored, consequences for humanity be damned.

Pushing back in the other direction will be President Obama's newest administration nominees: Gina McCarthy, an expert on federal air quality law who's been nominated to lead the Environmental Protection Agency, and physicist Ernest Moniz, who's been tapped to lead the Department of Energy. If both can overcome Republican opposition in the Senate, they'll have major responsibilities in shaping a climate policy, including regulatory powers that can combat the crisis without congressional input.

Brad Plumer made the case this week that McCarthy may Obama's "most significant" second-term nominee, and Rebecca Leber had a good item detailing Moniz's background.

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One of the exciting aspects of John Kerry serving as Secretary of State is the fact that Kerry hopes to use this prestigious post to elevate the climate crisis on the international stage. Indeed, this came up during his confirmation hearing yesterday, explaining, "I'll be a passionate advocate, but not based on ideology, based on fact, based on science."

One high-profile Republican was unimpressed.

That's too much effort to put on climate change, according to Sen. Marco Rubio of Florida, a leading early contender for the Republican presidential nomination in 2016.

"I don't think it's the most pressing foreign policy issue facing America," Rubio told POLITICO outside Kerry's confirmation hearing on Thursday. "There's a lot of things government can do but changing the weather isn't one of them."

I'm reminded of an interview Rubio did with GQ a few months ago, in which he was asked how old he thinks the Earth is. The Republican responded, "I'm not a scientist, man," before immediately shifting to a theological discussion, and concluding that the age of the planet may simply be unknowable. "It's one of the great mysteries," Rubio said.

And yesterday, Mr. I'm Not A Scientist, Man suggested that, as far as he's concerned, combating global warming is an impossible effort to "change the weather."

Why does the political establishment consider the far-right Floridian a rising star with limitless potential? It's one of the great mysteries.

Australia's Bureau of Meteorology

We talked yesterday about 2012 being the warmest on record in the United States, and if you thought that was alarming, consider conditions in Australia (thanks to Cory Gnazzo for the heads-up).

As a record-breaking heatwave hovers over many regions and territories (which are in their summer months now), the continent's Bureau of Meteorology has added two new colors to the weather map to reflect the rising mercury.

The map currently shows the weather in orange tones at the top, which indicate temperatures 40 to 48 degrees Celsius. But forecasts are predicting off-the-charts weather. As a result, pink and purple will now cover temperatures over 50 degrees Celsius -- should it climb that high.

For those rusty on the temperature conversion, that is a sweat-inducing 122 degrees Fahrenheit.

David Jones, head of the bureau's climate monitoring and prediction unit, said the projected forecasts show temperatures "in excess of" 122 Fahrenheit.

MSNBC's Chris Hayes noted on Twitter earlier that he's noticed "a marked shift in climate denialist rhetoric" lately. Climate deniers have gone from saying, "It's not getting warmer!" to saying, "Of course it's getting warmer, we don't know the cause."

At this point, I'm almost inclined to consider this a breakthrough.

Kevin Drum had a piece a year ago that always stuck in my head.

Originally, climate denial went through three stages:

1. The world isn't warming.

2. OK, it's warming, but it's not man-made. It's just natural climate variability.

3. Fine, people are responsible. But it's not economically worth it to do anything about it.

But as the right grew more radical, and conservatives' discomfort with reality became more intense, we saw deniers regress quickly. Indeed, they not only started over, they went even further back, insisting that climate science itself is a communistic conspiracy which must be rejected in its entirety.

If the right is open to the reality of a warming planet, perhaps that's a step in the right direction?

Associated Press

One either wants to reduce carbon emissions or not.

About a year ago, Mitt Romney, to his credit, broke with Republican orthodoxy and acknowledged the climate crisis. "I believe the world is getting warmer, and I believe that humans have contributed to that," he told a New Hampshire audience. "It's important for us to reduce our emissions of pollutants and greenhouse gases that may be significant contributors."

Soon after, as is his habit, Romney reversed course and announced he no longer believes what he said he believes. The Republican told a different New Hampshire audience he "thinks" the world's getting hotter, but added, "I don't know that ... [and] I don't know if it's mostly caused by humans."

As of this week, he's rolling out an even murkier stance. Here's what Romney told Scientific American and ScienceDebate.org (via Carl Franzen).

"I am not a scientist myself, but my best assessment of the data is that the world is getting warmer, that human activity contributes to that warming, and that policymakers should therefore consider the risk of negative consequences. However, there remains a lack of scientific consensus on the issue -- on the extent of the warming, the extent of the human contribution, and the severity of the risk -- and I believe we must support continued debate and investigation within the scientific community.

"Ultimately, the science is an input to the public policy decision; it does not dictate a particular policy response. President Obama has taken the view that if global warming is occurring, the American response must be to slash carbon dioxide emissions by imposing enormous costs on the U.S. economy. First he tried a massive cap-and-trade bill that would have devastated U.S. industry. When that approach was rejected by Congress, he declared his intention to pursue the same course on his own and proceeded through his EPA to impose rules that will bankrupt the coal industry."

The response, which appears to have been a written answer provided by the Romney campaign, is a bit of a mess. He believes there's no scientific "consensus," for example, though there's ample evidence to the contrary. Romney also scoffs at the prospect of a "massive cap-and-trade bill," overlooking a minor detail: this massive cap-and-trade bill was a Republican idea, in line with what McCain/Palin proposed just four years ago.

That said, the answer isn't a total disaster -- Romney at least believes the planet is warming and that human activity "contributes" to the problem. The follow-up question is, what does he intend to do about it?

His written response touches on this, too. After explaining all the effective policies he's against, Romney presents what he calls a "No Regrets" policy.

"For instance, I support robust government funding for research on efficient, low-emissions technologies that will maintain American leadership in emerging industries."

That's nice, I suppose, but it's more of a wish than a policy. By Romney's reasoning, he'll support increased taxpayer spending on scientific research -- the Ryan budget plan, which Romney endorsed, cuts taxpayer spending on scientific research -- and researchers will create new technologies.

In other words, Romney's plan for global warming is to wait for scientists to come up with a solution to global warming. Take that, Al Gore.

Romney's energy plan doesn't make so much as a passing reference to the climate crisis, and as of his convention speech, he was using rising sea levels as a cheap punch-line. As we talked about last month, there are basically three categories of politicians when it comes to the global warming: (1) those who deny the problem; (2) those who recognize the problem; and (3) those who support taking concrete steps to mitigate the problem.
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Romney wants folks to know he's in Group #2, and while it's marginally better than Group #1, as a practical matter, there's no real difference -- either policymakers will work to address the crisis or they won't.

Romney believes "the world is getting warmer." I'm glad. But unless he's prepared to actually do something about it, his beliefs are largely meaningless.

We talked earlier about Mitt Romney's convention speech and its shortcomings, but I'd be remiss if I neglected to mention this 39-second portion that was genuinely painful.

For those who can't watch clips online, Romney said, "President Obama promised to begin to slow the rise of the oceans and to heal the planet. My promise is to help you and your family."

That's great news for those of us who don't have families on this planet.

Now, as a factual matter, Romney's promise is itself rather strange. How "you and your family" will benefit from less access to affordable health care, less access to education, and fewer investments in roads and infrastructure is something of a mystery.

But even putting that aside, the aspect of Romney's comments that was simply astounding was the ignorance. The Republican treated rising sea levels as a punch-line, as if the very idea of addressing the climate crisis is ridiculous and those who take this seriously are fools worthy of mockery.

Indeed, the Republican audience took their cues, literally laughing at Obama's efforts to address global warming.

Also notice that, in Romney's mind, there's a distinction -- the nation can deal with the climate crisis or we can help families, as if the two have nothing to do with one another.

When people in the future look back at Romney's contempt for the idea of "slowing the rise of the oceans," and his party's willingness to bury their hands in the sand, history will not be kind.

The Business Roundtable hosted a debate on energy policy today, with representatives of President Obama and Mitt Romney on hand to make their case. Speaking for the Republican was Linda Stuntz, a lawyer who worked at the Energy Department under Bush/Quayle, who assured attendees that Romney is "certainly not a denier" of global warming.

That's true, he's not. In fact, a year ago, the former governor was willing to admit, "I believe the world is getting warmer, and I believe that humans have contributed to that."

And while that's likely reassuring to those who hope Romney would be a sane president, the key detail here is easy to overlook: it doesn't matter what Romney "believes." The only thing that matters is what he intends to do as a matter of public policy, and in this case, his surrogate made clear he doesn't intend to do much of anything.

[Stuntz] said Environmental Protection Agency regulations will "hamstring" the economy, and made the case that greenhouse gases should not be regulated under the Clean Air Act.

"The notion that the U.S. can act unilaterally on carbon emissions and make a material difference in global greenhouse gases is not realistic," said Stuntz, speaking at a debate on energy hosted by The Business Roundtable. "It will only hamstring our economy."

So what would a Romney administration do to address the climate crisis? According to his surrogate this morning, there's no real need for action because greenhouse gas emissions are already declining.

I've long believed there are basically three categories of politicians when it comes to the climate crisis: (1) those who deny the problem; (2) those who recognize the problem; and (3) those who support taking concrete steps to mitigate the problem.

Romney wants folks to know he's in Group #2. While it's marginally better than Group #1, as a practical matter, there's no real difference -- either policymakers will work to address the crisis or they won't.

Romney is "certainly not a denier" of global warming? Great. But unless he's prepared to actually do something about it, I don't know why anyone should give him credit.