It’s kind of amazing to me that it took so long for there to be a direct experimental measurement of CO2 forcing in the field.   Spoiler alert:  Their observations were fully consistent with what theory predicts.

The effects of CO2 on radiative transfer are well-understood but apparently there’s never been direct measurement of radiative forcing at the Earth’s surface.   What’s novel (I think, having read just the Abstract of the paper not the full text) is that they directly measured heat transfer rather than inferring it from a network of temperature sensors (or satellite measurements) and independently verified radiative transfer models.  In short, their measurements are an additional test of things we believed to be true based on other measurements.   Had their measurements not been consistent with model predictions that would have been a big surprise and would merit further investigation.  Bottom line:  The CO2 contribution to net radiative forcing is well-understood.  Anthropogenic CO2 emissions have caused the Earth to retain (and it will continue to retain) a significant amount of heat above what it would without them.   The specifics of where that excess heat ends up – atmosphere near the surface?  oceans? – is a subject of ongoing investigation but make no mistake we’re retaining a massive amount of excess heat.   And bear in mind average surface temperature changes, however small they may seem, are really proxies for much more significant climatological effects.

From Lawrence Berkeley Lab’s press release, “First Direct Observation of Carbon Dioxide’s Increasing Greenhouse Effect at the Earth’s Surface”:

Scientists have observed an increase in carbon dioxide’s greenhouse effect at the Earth’s surface for the first time. The researchers, led by scientists from the US Department of Energy’s Lawrence Berkeley National Laboratory (Berkeley Lab), measured atmospheric carbon dioxide’s increasing capacity to absorb thermal radiation emitted from the Earth’s surface over an eleven-year period at two locations in North America. They attributed this upward trend to rising CO₂ levels from fossil fuel emissions.

The influence of atmospheric CO₂ on the balance between incoming energy from the Sun and outgoing heat from the Earth (also called the planet’s energy balance) is well established. But this effect has not been experimentally confirmed outside the laboratory until now. The research is reported Wednesday, Feb. 25, in the advance online publication of the journal Nature.

The results agree with theoretical predictions of the greenhouse effect due to human activity. The research also provides further confirmation that the calculations used in today’s climate models are on track when it comes to representing the impact of CO₂.

Read or download the paper here.  (It’s $5 to rent and $32 (!!) to buy a copy.   At those prices I recommend visiting your local college or university science library and reading the copy of Nature they have on the shelf.)