[Vision2020] NASA GISS: 2011: "Earth's energy imbalance and implications" Atmos. Chem. Phys.

[Ted Moffett]

Some may recall the scientific nonsense presented to Vision2020 in the past
few years regarding solar forcing of climate being the dominant variable
causing the well documented rise in global average surface temperature
revealed in the instrumental record since the late 1800s, rather than human
sourced CO2 emissions.  Just why this theory is nonsense can be understood
in part by the data explored in the following recent peer reviewed climate
science article, revealing a continued Earth energy imbalance despite an
unusually low recent solar minimum, and negative feedback of human sourced
aerosols, which are masking anthropogenic global warming to some extent:
http://pubs.giss.nasa.gov/abs/ha06510a.html
Hansen et al. 2011

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.

Improving observations of ocean heat content show that Earth is absorbing
more energy from the Sun than it is radiating to space as heat, even during
the recent solar minimum. The inferred planetary energy imbalance,
0.58±0.15 W/m2 during the 6-yr period 2005-2010, confirms the dominant role
of the human-made greenhouse effect in driving global climate change.
Observed surface temperature change and ocean heat gain together constrain
the net climate forcing and ocean mixing rates. We conclude that most
climate models mix heat too efficiently into the deep ocean and as a result
underestimate the negative forcing by human-made aerosols. Aerosol climate
forcing today is inferred to be -1.6±0.3 W/m2, implying substantial aerosol
indirect climate forcing via cloud changes. Continued failure to quantify
the specific origins of this large forcing is untenable, as knowledge of
changing aerosol effects is needed to understand future climate change. We
conclude that recent slowdown of ocean heat uptake was caused by a delayed
rebound effect from Mount Pinatubo aerosols and a deep prolonged solar
minimum. Observed sea level rise during the Argo float era is readily
accounted for by ice melt and ocean thermal expansion, but the ascendency
of ice melt leads us to anticipate acceleration of the rate of sea level
rise this decade.

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Important graphs, regarding the peer reviewed paper referenced above,
removed from text below, can be viewed at website below:

http://pubs.giss.nasa.gov/abs/ha06510a.html
Earth's Energy Budget Remained Out of Balance Despite Unusually Low Solar
Activity

Jan. 30, 2012

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

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.

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.

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.

The 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.

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.
Reference

Hansen, J., Mki. Sato, P. Kharecha, and K. von Schuckmann, 2011: Earth's
energy imbalance and implications<http://pubs.giss.nasa.gov/abs/ha06510a.html>.
Atmos. Chem. Phys., *11*, 13421-13449, doi:10.5194/acp-11-13421-2011.

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Vision2020 Post: Ted Moffett
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