We have pushed atmospheric CO2 levels to 400 parts per million (ppm) for the first time in human existence.

At the same time, a truly remarkably set of paleoclimate data shows the climate is much more sensitive to CO2 than we thought. And that means returning as quickly as possible back to 350 ppm is a vastly more rational course of action for a non-suicidal civilization, than, say continuing our unrestrained march toward 600 ppm, then 800, and then 1000.

NOAA reported Friday that the daily mean concentration of CO2 in the air around Mauna Loa, Hawaii, surpassed 400 parts per million this week:

At the same time, a major new Science study of paleoclimate temperatures — based on ”the longest sediment core ever collected on land in the Arctic” – revealed what happened the last time we had similar CO2 levels:

“One of our major findings is that the Arctic was very warm in the Pliocene [~ 5.3 to 2.6 million years ago] when others have suggested atmospheric CO2 was very much like levels we see today. This could tell us where we are going in the near future. In other words, the Earth system response to small changes in carbon dioxide is bigger than suggested by earlier models,” the authors state.

Yes, contrary to one or two (misreported) models suggesting a climate sensitivity on the low side, this study joins the myriad analyses of data that find it is likely to prove on the high side. For instance, recent observations of relative humidity in the tropics and subtropics found that “Future warming likely to be on high side of climate projections,” according to a November paper in Science.

How sensitive is the climate to increases in CO2, according to this “absolutely new knowledge” of paleoclimate temperatures?

Another significant finding to emerge from this first continuous, high-resolution record of the Middle Pliocene is documentation of sustained warmth with summer temperatures of about 59 to 61 degrees F [15 to 16 degrees C], about 8 degrees C [14 F] warmer than today.

This period of Arctic warmth “coincides, in part with a long interval of 1.2 million years when the West Antarctic Ice sheet did not exist.” Indeed, sea levels during the mid-Pliocine were about 25 m [82 feet] higher than today!

It is worth noting that a 2009 analysis in Science found that when CO2 levels were this high 15 to 20 million years ago, it was 5° to 10°F warmer globally and seas were also 75 to 120 feet higher.

The risks of failing to sharply curtail carbon pollution are enormous if the climate sensitivity is on the low side (see “Memo To Media: ‘Climate Sensitivity’ Is NOT The Same As Projected Future Warming, World Faces 10°F Rise“). But the risks of inaction are beyond incalculable if climate sensitivity is in the middle end of the range, let alone the high end suggested by the paleoclimate data:

Science (1/11) study — On our current emissions path, CO2 levels in 2100 will hit levels last seen when the Earth was 29°F (16°C) hotter: Paleoclimate data suggests CO2 “may have at least twice the effect on global temperatures than currently projected by computer models”

As I explained in Nature online back in 2008 (here), once you factor in carbon-cycle feedbacks, even the uber-cautious Fourth Assessment report (AR4) of the IPCC makes clear we are headed toward 1000 ppm (the A1FI scenario). That conclusion has been supported by just about every major independent analysis, including a recent report by PricewaterhouseCoopers (see Study: We’re Headed To 11°F Warming And Even 7°F Requires “Nearly Quadrupling The Current Rate Of Decarbonisation“).

This new paper is just the latest to suggest the Arctic will warm much faster than the models have suggested. For instance, back in 2006, scientists analyzed deep marine sediments to understand the Paleocene Eocene thermal maximum, a brief period some 55 million years ago of “widespread, extreme climatic warming that was associated with massive atmospheric greenhouse gas input.” That Nature study (subs. req’d) found Arctic temperatures almost beyond imagination–above 23°C (74°F)–temperatures more than 18°F warmer than climate models had predicted when applied to this period. The three dozen authors conclude that existing climate models are missing crucial feedbacks that can significantly amplify polar warming.

Clearly our climate models don’t do a good job of explaining what’s happening in the Arctic right now:

Arctic sea ice is melting much, much faster than even the best climate models had projected (actual observations in red). The reason is most likely unmodeled amplifying feedbacks. The image (from Climate Crocks via Arctic Sea Ice Blog) comes from a 2007 GRL research paper by Stroeve et al.

And this underestimation of polar amplification in turn leads the authors of the new study — and many other scientists — to conclude that the climate’s overall sensitivity is on the high side. As the UK Guardian reports:

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Last week, I wrote a piece “Extending Current Energy Policies Would Keep U.S. Carbon Pollution Emissions Flat Through 2040.” It was based on the latest report from the U.S. Energy Information Administration (EIA), summed up in this chart:

But EIA has modeled other cases than just one that extends tax credits for renewables and the like.

In fact, EIA has a chart-creating website that allows you to pick different scenarios. Here’s one that compares the reference case (i.e. no new policies) with the extended policies case with a carbon dioxide price scenario:

Figure: Energy-related CO2 emissions (in green) assuming a $25 per metric ton CO2 price starting in 2013, rising 5% per year through 2040 — compared to business as usual (in purple) and extended energy policies (in blue).

This CO2 price leaves emissions in 2040 one third lower than current (2012) levels — and 40% lower than 2005 levels. It is a pretty modest price for carbon pollution. The actual social cost of carbon today (and in 2040) is probably considerably higher (see here).

By Dr. Jonathan G. Koomey, via koomey.com

If we don’t change our direction, we’ll end up where we’re headed

Climate Progress did a great service for climate communications on March 8th, 2013 by publishing this graph of historical and projected global temperatures:

Figure 1: Historical and projected global average surface temperatures on our current trajectory for fossil fuel emissions

The historical data in the graph came from a recently published article in Science, and the projected data came from the “no-policy” case developed by the folks at MIT back in 2009. The MIT case showed about a 5 Celsius degree increase in global average surface temperatures by 2100, equivalent to about a 9 Fahrenheit degree increase.

I like this graph because it combines what we know about historical temperatures with what is our most likely future — one where we continue to consume fossil fuels at increasing rates. I realized after seeing Joe’s graph that I could easily add additional context to it, because I have both historical data on carbon dioxide concentrations in the atmosphere, as well as the detailed projections from the MIT researchers (which I obtained from them while working on my most recent book, Cold Cash, Cool Climate: Science-based Advice for Ecological Entrepreneurs).

Here’s Figure 2-3 from Cold Cash, Cool Climate, updated to include CO2 concentrations through 2012. It shows historical carbon dioxide concentrations for the past 450,000 years, including the strikingly rapid increase since the 1800s. The early historical data come from the Vostok and Lawdome ice cores, while the more recent data (post 1959) come from direct measurements. We’ve pushed carbon dioxide concentrations well outside the range that has prevailed over the past 450 millennia.

Figure 2: Carbon dioxide concentrations for the past 450,000 years

The data for the past 12,000 years, the period over which human civilization developed, shows a picture similar to Romm’s graph of temperatures. Carbon dioxide concentrations were relatively stable for the entirety of this period, slightly increasing over time, with the most rapid increase only happening as the industrial revolution accelerated in the 1800s:

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This video produced by the Climate Reality Project featuring Reggie Watts demonstrates the argument that because carbon pollution costs us money, the world should put a price on carbon.

It’s important to remind viewers that it should be the polluters paying for what their products cost all of us — that they should not simply pass on the costs to everyone else. These companies already know carbon emissions will affect their bottom lines. But it’s difficult to ask consumers to pay double for fossil fuel addiction when these large companies and utilities slow-walk toward renewable energy. Especially when polluters’ products cause so many dangerous and expensive impacts.

So what’s the answer? The Center for American Progress has a report detailing what a carbon tax should look like, including ways to “minimizing harm to vulnerable consumers and businesses, growing the economy with investments in clean energy infrastructure and other infrastructure that makes communities more resilient in the face of climate change, and reducing the deficit burden on future generations.”

What do you think a price on carbon should look like?

Climate change could cause pollen counts to more than double over the next 30 years, according to an ongoing Rutgers University study.

The research, presented at the American College of Allergy, Asthma and Immunology conference in November, tested how allergenic plants respond to conditions that mimic those of a warming world, including changing weather patterns and increases in temperature and carbon dioxide.

Based on these tests, the researchers predict pollen counts could reach 21,735 particles of pollen per cubic meter by 2040 — a drastic spike from 2000’s average of 8,455. An “extremely high” pollen count for trees — which account for most of spring pollen — is 1,500. The research also predicts that, as spring arrives earlier due to climate change, pollen seasons will begin earlier as well. In 2000, pollen production began April 14 and peaked May 1, but by 2040, the researchers predict production will start more than a month earlier, peaking by April 8.

Though the research is not yet published, it lines up with what scientists already know about plants’ reactions to increased carbon dioxide and temperature. A 2002 study in the Annals of Allergy, Asthma and Immunology found that ragweed, which causes most fall allergies, produces 61 percent more pollen when grown in an atmosphere with double the normal amount of carbon dioxide. A 2006 study on the same plant produced similar results. Pollen produced under high CO₂ conditions may even be more highly allergenic, as Clifford Bassett, an allergist and ACAAI fellow, told CNN:

As you increase CO₂, it tells the allergenic plants to produce more pollen to the tune of three to four times more, and the pollen itself, we think, may actually be more potent.

Pollen records have been off the charts over the last few years, as warm weather arrived early in many states. Last year, pollen season began early due to a mild winter and early onset of warm weather, and pollen counts across the U.S. were extremely high. In Atlanta, the pollen count reached 9,369 particles per cubic meter of air, shattering the city’s 1999 record of 6,013. Vanderbilt University in Nashville recorded a pollen count of 11,000, the highest count recorded since the university began counting 12 years ago. Many places saw similarly high counts and early pollen releases in 2010 and 2011. This year has already seen early spikes and dips in the pollen count, due to temperatures rising and falling — some places, like Gainesville, Fla., logged high pollen counts as early as January.

Higher pollen counts aren’t just uncomfortable for allergy sufferers — since allergies can trigger asthma attacks, higher pollen counts and earlier pollen releases can have serious implications for those suffering from asthma, and could even be connected to the global rise of asthma cases.

As the climate warms and springs and summers become longer, allergy seasons in fall, spring and summer could extend as well, exacerbating allergy symptoms. When allergy sufferers have no respite from symptoms, it makes them more prone to serious allergy attacks than if they had had a break between seasons.