NASA: Human Activity, Not Solar Activity, Drives Global Warming and Returning to 350 ppm Is Needed to Stop It

Earth’s Energy Budget Remained Out of Balance Despite Unusually Low Solar Activity

Adam Voiland, NASA’s Earth Science News Team, in a repostThe research brief by Hansen et al is here.

A new NASA study underscores the fact that greenhouse gases generated by human activity — not changes in solar activity — are the primary force driving global warming.

The study offers an updated calculation of the Earth’s energy imbalance, the difference between the amount of solar energy absorbed by Earth’s surface and the amount returned to space as heat. The researchers’ calculations show that, despite unusually low solar activity between 2005 and 2010, the planet continued to absorb more energy than it returned to space.

graph of the sun's total solar irradiance

A graph of the sun’s total solar irradiance shows that in recent years irradiance dipped to the lowest levels recorded during the satellite era. The resulting reduction in the amount of solar energy available to affect Earth’s climate was about .25 Watts per square meter, less than half of Earth’s total energy imbalance. (Credit: NASA/James Hansen)

Total solar irradiance, the amount of energy produced by the sun that reaches the top of each square meter of the Earth’s atmosphere, typically declines by about a tenth of a percent during cyclical lulls in solar activity caused by shifts in the sun’s magnetic field. Usually solar minimums occur about every eleven years and last a year or so, but the most recent minimum persisted more than two years longer than normal, making it the longest minimum recorded during the satellite era.

Pinpointing the magnitude of Earth’s energy imbalance is fundamental to climate science because it offers a direct measure of the state of the climate. Energy imbalance calculations also serve as the foundation for projections of future climate change. If the imbalance is positive and more energy enters the system than exits, Earth grows warmer. If the imbalance is negative, the planet grows cooler.

James Hansen, director of NASA’s Goddard Institute for Space Studies (GISS) in New York City, led the research. Atmospheric Chemistry and Physics published the study last December.

Hansen’s team concluded that Earth has absorbed more than half a Watt more solar energy per square meter than it let off throughout the six year study period. The calculated value of the imbalance (0.58 Watts of excess energy per square meter) is more than twice as much as the reduction in the amount of solar energy supplied to the planet between maximum and minimum solar activity (0.25 Watts per square meter).

The fact that we still see a positive imbalance despite the prolonged solar minimum isn’t a surprise given what we’ve learned about the climate system, but it’s worth noting because this provides unequivocal evidence that the sun is not the dominant driver of global warming,” Hansen said.

According to calculations conducted by Hansen and his colleagues, the 0.58 Watts per square meter imbalance implies that carbon dioxide levels need to be reduced to about 350 parts per million to restore the energy budget to equilibrium. The most recent measurements show that carbon dioxide levels are currently 392 parts per million and scientists expect that concentration to continue to rise in the future.

A prolonged solar minimum left the sun’s surface nearly free of sunspots and accompanying bright areas called faculae between 2005 and 2010. Total solar irradiance declined slightly as a result, but the Earth continued to absorb more energy than it emit throughout the minimum. An animation of a full solar cycle is available here. (Credit: NASA Goddard’s Scientific Visualization Studio)

Climate scientists have been refining calculations of the Earth’s energy imbalance for many years, but this newest estimate is an improvement over previous attempts because the scientists had access to better measurements of ocean temperature than researchers have had in the past.

Argo float and shipThe improved measurements came from free-floating instruments that directly monitor the temperature, pressure and salinity of the upper ocean to a depth of 2,000 meters (6,560 feet). The network of instruments, known collectively as Argo, has grown dramatically in recent years since researchers first began deploying the floats a decade ago. Today, more than 3,400 Argo floats actively take measurements and provide data to the public, mostly within 24 hours.

Hansen’s analysis of the information collected by Argo, along with other ground-based and satellite data, show the upper ocean has absorbed 71 percent of the excess energy and the Southern Ocean, where there are few Argo floats, has absorbed 12 percent. The abyssal zone of the ocean, between about 3,000 and 6,000 meters (9,800 and 20,000 feet) below the surface, absorbed five percent, while ice absorbed eight percent and land four percent. 

The updated energy imbalance calculation has important implications for climate modeling. Its value, which is slightly lower than previous estimates, suggests that most climate models overestimate how readily heat mixes deeply into the ocean and significantly underestimates the cooling effect of small airborne particles called aerosols, which along with greenhouse gases and solar irradiance are critical factors in energy imbalance calculations.

“Climate models simulate observed changes in global temperatures quite accurately, so if the models mix heat into the deep ocean too aggressively, it follows that they underestimate the magnitude of the aerosol cooling effect,” Hansen said.

Aerosols, which can either warm or cool the atmosphere depending on their composition and how they interact with clouds, are thought to have a net cooling effect. But estimates of their overall impact on climate are quite uncertain given how difficult it is to measure the distribution of the particles on a broad scale. The new study suggests that the overall cooling effect from aerosols could be about twice as strong as current climate models suggest, largely because few models account for how the particles affect clouds.

map showing global reach of Argo floats
A chart shows the global reach of the network of Argo floats. (Credit: Argo Project Office)

“Unfortunately, aerosols remain poorly measured from space,” said Michael Mishchenko, a scientist also based at GISS and the project scientist for Glory, a satellite mission designed to measure aerosols in unprecedented detail that was lost after a launch failure in early 2011. “We must have a much better understanding of the global distribution of detailed aerosol properties in order to perfect calculations of Earth’s energy imbalance,” said Mishchenko.

Adam Voiland, NASA’s Earth Science News Team, in a repost.


Hansen, J., Mki. Sato, P. Kharecha, and K. von Schuckmann, 2011: Earth’s energy imbalance and implications. Atmos. Chem. Phys., 11, 13421-13449, doi:10.5194/acp-11-13421-2011.

Related Links

+ Science Brief: Earth’s Energy Imbalance

+ James Hansen Biography

+ Argo Project Office

+ NASA-led Study Solves Case of Earth’s ‘Missing Energy’

+ World of Change: Solar Activity

14 Responses to NASA: Human Activity, Not Solar Activity, Drives Global Warming and Returning to 350 ppm Is Needed to Stop It

  1. Lou Grinzo says:

    Two observations:

    1. The text highlighted above by Joe, the part where Hansen talks about what the prolonged solar minimum really tells us, can’t be repeated too often. This is, not coincidentally, a point deniers are so adamant in refusing to see (or admit they see), as they consistently cherry pick and shun an overall systems view of climate science. It’s obvious why they do it — they have no choice if they are to reach their desired, wholly incorrect conclusion that delays or stops action to reduce our use of fossil fuels. It’s also a subtle enough point that it doesn’t fit well on a bumper sticker, making it that much tougher to explain to newcomers.

    2. My hunch is that aerosols are about to bite us in the nether regions, big time. The evidence seems to be growing that their cooling influence is toward the high end of current estimates, and we’re entering a time when China, in particular, is getting serious about putting sulfur scrubbers on coal plants, even as they and India appear to be in a race to see who can build the most coal plants by 2030. This means lots more CO2 pumped into the atmosphere with comparatively less counterbalancing aerosols added, and therefore accelerated warming. This is very, very nasty, and it’s why Hansen has referred to this as our “Faustian bargain with aerosols” and I call it “aerosol whiplash”.

  2. Leif says:

    Very informative, Thank you yet again.

  3. fencepostman says:

    The publicity for this paper emphasizes that the latest ocean heat storage measurements are the strongest evidence that the planetary system continues to warm up. This appears to be aimed at deniers and people duped by them. But people who believe the observed changes in solar output were actually cooling the planet aren’t likely to be convinced by actual analysis of evidence. No one else believed the system was cooling down.

    For the rest of us, note that the title includes the word “implications”.

    Hansen brought in von Schuckmann as a co-author. He is saying if the von Schuckmann analysis of ARGO float data proves to be an accurate picture of what’s happening in the oceans, one implication is that “most” climate models need to be revised. The total of human caused climate forcing agents already in the atmosphere are more dangerous than most have believed, because aerosols emitted along with CO2 that mask its full effect look like they are more powerful than most thought. It looks like climate responds faster to a given forcing than was thought. And there never was any “missing energy”.

    Hansen is, yet again, issuing an urgent call that the actual aerosol effect be measured accurately by ongoing satellite observations: “continued failure to quantify the specific origins of this large climate forcing is untenable, as knowledge of changing aerosol effects is needed to understand future climate change”.

    The main caveat with the von Schuckmann analysis, Hansen notes, is that their error estimate “does not include an estimate for any remaining systematic calibration errors that may exist” in the ARGO network. But he was confident enough in their analysis to write the paper.

    There is a lot of detail in the paper about aerosols. Hansen says most models used by IPCC (2007) had a value for aerosol forcing of “about -1 W/m2”. If this latest ocean heat content analysis is correct, Hansen says it implies aerosol forcing is actually around -1.6 W/m2.

    This is a significant increase in the “Faustian bargain” he’s warned about in the past. Aerosols emitted as fossil fuels are burned mask the full effect of CO2 and consequently have contributed to the lack of concern civilization has about climate change. But, Hansen says: “aerosols remain airborne only several days”, consequently, “they must be pumped into the air faster and faster to keep pace with increasing long-lived GHGs. However, concern about health effects of particulate air pollution is likely to lead to eventual reduction of human-made aerosols. Thereupon the Faustian payment will come due.”

    If the IPCC (2007) typical model value of -1 W/m2 for aerosol is correct, Hansen says: “a major effort to clean up aerosols, say by half, increases the net forcing only 25%”.

    But if the new value of -1.6 W/m2 is correct, a similar sized global cleanup of aerosol emission would increase net climate forcing, caused by gases already in the atmosphere, by 57%.

    It was concern over what will happen if aerosols are cleaned up that originally caused Paul Crutzen to write his famous paper on geoengineering that brought discussion of that topic out of the shadows. See: It is not generally realized that Crutzen proposed aerosol injection into the stratosphere as an emergency way to offset the possible catastrophic consequences of reducing tropospheric aerosol emissions such as what Hansen is discussing here. Reducing tropospheric aerosol could have an immediate effect on planetary temperature and only geoengineering could offset that effect quickly enough if it proved to be so large civilization could not stand it. You’d either have to take the filters off the smokestacks or start injecting aerosols into the stratosphere.

  4. Solar Jim says:

    According to my simple calculations:

    Total forcing = .58 W/m2

    Ice = 8% = 0.0464 W/m2

    multiply by earth area: 5.1 x 10 to the 14 m2

    gives 23,000 GIGAWATTS into icemelt (via man)

    We are “really cooking now” boys and girls!

    (would someone please confirm?)

  5. Roger S says:

    We, and especially our ‘leaders’ in Washington, need to learn to listen more closely to what NASA scientists, such as Jim Hansen, say. Here’s an example of why—another lesson from the past if you will:

    Some twenty six years ago, on January 28, 1986, NASA scientists warned against launching the Challenger because of possible O-ring failure due to the unusually cold temperatures that morning. As I’m certain Jim Hansen recalls, probably with some despair, NASA management decided to overrule their own experts for various reasons, including the fact that there had been a series of earlier delays.

    Sadly, ignoring the expert advice led to the death of seven brave American astronauts, and more.

    As is often done following an unacceptable disaster, a commission was formed to look into what caused the problem. Red flags were rampant regarding the potential for the O-ring to fail at low temperature. It wasn’t as if there weren’t clear warnings; it was that management chose to ignore the warnings.

    Here’s my point: As smart as we humans are in some areas (e.g., developing space travel), we seem to be strangely limited in our ability to learn, except by experience. Similarly, management (read government) tends to dismiss the warnings of experts with regard to predictions of future problems. (Notice how we generally pass laws to prevent bad things from happening only after they’ve happened numerous times. This may explain why our current legal system doesn’t seem to be working vs. AGW.)

    As further evidence of this human frailty, note that the Space Shuttle Columbia met a similar fate nine years ago, in 2003, when, according to the inevitable new commission set up to investigate that accident, management downplayed the concerns of the experts regarding the dangers of foam insulation breaking off the shuttle during launch. But seven more lives were lost in that accident.

    My question is, with perhaps as many, ultimately, as seven billion lives at stake, how can we get ‘management’ to pay attention to expert warnings from NASA where a livable climate is the issue? Could world leaders be locked into a sort of groupthink that allows them to essentially say to themselves, “Well it can’t be that bad if so and so isn’t doing more about it; why should we take action here?”

    Humans evolved (if you will) successfully by focusing their concern on short-term needs such as having enough food and shelter to survive from year to year. Later, we developed customs, markets, laws and other ‘systems’ to deal with an ever-more-complex society. Never before have we had to deal with a slow, insidious, almost-invisible, global problem such as climate change in order to survive.

    It took several costly and deadly failures to remind NASA management of the importance of expert opinion. Will America’s ‘management’ (or any of us) be able to make the right choices in dealing with the ongoing, growing threat of AGW, without our going through the painful “school of hard knocks?”

    One can hope that at some point, before the climate tipping points, we can get the huge numbers of people who will suffer the most from climate change to work in unison to thwart the efforts of the relative handful of humans who are working to protect their own selfish interests, and the status quo.

    Enjoy the game,

  6. Raul M. says:

    Certainly many may be expected to realize that they have finally made it in life

  7. Dr.A.Jagadeesh says:

    Good post. Yes. Human activity is contributing to much of Global warming and subsequent Climate Change.
    Dr.A.Jagadeesh Nellore(AP),India

  8. Doug Bostrom says:

    NASA says “Data! Data! Data! Conclusion!”

    To heck with NASA; they’re just pushing an agenda. Same as when my wife said we needed to buy more toilet paper; she just wanted to go shopping, spend our money. Toilet paper had nothing to do with it.

    I’m kind of lonely now, but by gosh I didn’t let myself be conned into going to the store and spending my money!

  9. Chris Winter says:

    Amen to that, Roger S. And I note just in passing that you share a first name with one of the men who warned against launching Challenger during those cold conditions — Roger Boisjoly, who died in January of this year.

  10. J.C. Moore says:

    Thanks for the accurate information. This site was nominated for a Hall of Fame Award at

  11. The y-axis of the chart seems to show the change between solar min and max as about 1 W/m2, but the chart label and the text say it’s about 0.25 W/m2.

    Can anyone clarify?

  12. Solar Jim says:

    Brian, the answer seems to be straightforward. The difference between the area of a circle and that of a sphere of the same diameter is a factor of four. So the intercepted radiation from the sun (a circle) is averaged over the earth’s surface (a sphere).

    The article could use a brief note for clarity.