Chapter 6: Alternate Explanations of Warming (Skeptics Guide to Global Warming)
The table of contents for the rest of this paper, A Layman's Guide to Anthropogenic Global Warming (AGW) is here. Free pdf of this Climate Skepticism paper is here and print version is sold at cost here
Solar Irradiance
If you walked into a room and found that it was too hot,
would you, as a first step:
- Measure the air to find anomalies in the mix of gasses
- Count the number of people in the room, to assess the effect
of body heat on the room's temperature - Check the thermostat on the furnace
If you answered #3, sorry, but you can't join the
IPCC. If you really want to irritate an AGW supporter, ask about the
sun. To AGW supporters, only a Luddite would check the sun's output when
they could instead be obsessing over the increase in CO2 by 0.009% of the
atmosphere.
When they looked at the problem, the IPCC decided that over
the last 50 years, the sun has been irrelevant to warming. Note that the
blue band in this chart (described in more detail in the last section), the
IPCC thinks that without man, the world would have cooled over the last 50
years:
Further, when they detailed different climate forcings, the
forcing from changing solar irradiance was a trivial rounding error (though
they had the good grace to mark their understanding of this as "low") meaning
the sun has very little effect vs. what the sun had in 1850 (in the Little Ice
Age!)
But it turns out, interestingly, that solar irradiance may be close to its
highest point in centuries. Al Gore says that current global temperatures
are the highest they have been in 1000 years. A new study by
the Institute of Astronomy in Zurich says that the "sun is more active now
than it has been at anytime in the previous 1,000 years." Related?
Sunspots have been monitored on the Sun since 1610,
shortly after the invention of the telescope. They provide the longest-running direct
measurement of our star's activity.
The variation in sunspot numbers has revealed the
Sun's 11-year cycle of activity as well as other, longer-term changes.
In particular, it has been noted that between about
1645 and 1715, few sunspots were seen on the Sun's surface.
This period is called the Maunder Minimum after the
English astronomer who studied it.
It coincided with a spell of prolonged cold weather
often referred to as the "Little Ice Age". Solar scientists strongly
suspect there is a link between the two events - but the exact mechanism
remains elusive....
But the most striking feature, he says, is that
looking at the past 1,150 years the Sun has never been as active as it has been
during the past 60 years.
Over the past few hundred years, there has been a
steady increase in the numbers of sunspots, a trend that has accelerated in the
past century, just at the time when the Earth has been getting warmer.
The data suggests that changing solar activity is
influencing in some way the global climate causing the world to get warmer.
We can look at solar output over large time frames by
looking at the production of carbon-14 (less is produced in years of high solar
activity, and vice versa). The analysis below used the ratio of oxygen
isotopes in the stalagmites to estimate the water temperature at the time they
were formed. The result is an interesting correlation between solar
activity and a global temperature proxy over a long time-scale (Graph from Neff et al., 2001):
Over the last 1000 years, we see that (again using a
reversed scale of C14 as a proxy) solar activity is highly correlated with long
term temperature trends (I have used the pre-Mann chart, because while it may
over-emphasize the Medieval Warm Period, I still think such a period existed).
Solar Output
Anomaly
Temperature Anomaly
Look at the following reconstruction data by Judith Lean of
the Naval Research Library and charted from her data at NOAA by Junkscience.com
shows that interestingly, the sun's output does appear to be higher today than
they have been in many, perhaps hundreds of years
Would such increased activity be expected to result in
higher Earth temperatures? I don't know, and there are some issues one
has to be careful with on this chart. Most importantly the scaling:
While the shape of the curve looks a lot like the temperature trend over the
last 400 years, note that the entire variation from the low to the high point
is only about 0.25% "“ the scaling makes it look more dramatic. Of course,
the same could be said for global temperature, where a half degree C
temperature increase on an absolute Kelvin scale would only be about 0.17%, so
an argument can be made that on a percentage basis, this change in irradiance
is about the same order of magnitude as our change in temperature. A more
sophisticated comparison might say that since black body radiation is related
to absolute temperature to the fourth power, .25% increase in irradiance would
be expected to heat the Earth by .06%.
The chart on the above left compares the recent temperature
anomaly to solar irradiance, while the chart on the right compares it to CO2
concentrations. Neither is a beautiful fit (and one may have to include
aerosols in either scenario to account for 1970's cooling) but solar irradiance
seems at least as good as that of CO2. Remember, the IPCC shows
the world cooling due to solar effects during the same time the red solar
irradiance line is peaking.
Recently Alexander et. al. in have done some very comprehensive
work relating solar irradiance and rainfall. The study posits that one of
the reasons for less than perfect fit of sunspot and irradiance data with
temperature is that the Sun actually works on a 21 year cycle when the sunspot
cycle is combined with the cyclical wobble of the Suns motion through
space. The study concluded:
The
Intergovernmental Panel on Climate Change (IPCC) (2001) dismisses the view that
solar activity has a meaningful influence on global climate. The basis for this
view is that variations in the receipt of solar activity are too small to
account for variations in the climatic responses. These variations were
determined from satellite and other observations. What the IPCC scientists
failed to appreciate is that changes in the level of solar radiation received
on earth are amenable to precise calculation. The variations are well in excess
of the IPCC value of +0,3 Wm"“2 quoted earlier.
One of the interesting things about solar output is that, if
it is really higher, we should see effects on other planets, not just on
Earth. And, in fact, a lot of evidence has been pouring in over the last
5 years from astronomers (not climate guys) that the rest of the solar system
has been warming dramatically.
Take
Mars, for example. Mar's ice caps have been melting and diminishing
since NASA's Mars Global Surveyor and Odyssey started to measure them around
2002.
Changes in the red spot on Jupiter
seem to be a sign of warming temperatures. And Neptunes moon Triton is
warming. We have to be careful with how we draw conclusions on these
outer planets, since their "year" is so long, seasonal changes can last
decades.
As seen in Figure 1, Neptune has been getting
brighter since around 1980; furthermore, infrared measurements of the planet
since 1980 show that the planet has been warming steadily from 1980 to 2004. As
they say on Neptune, global warming has become an inconvenient truth. But with
no one to blame, Hammel and Lockwood explored how variations in the output of
the Sun might control variations in the brightness of Neptune.
Figure 1 (a) represents the corrected visible light from Neptune from 1950 to
2006; (b) shows the temperature anomalies of the Earth; (c) shows the total
solar irradiance as a percent variation by year; (d) shows the ultraviolet emission
from the Sun (Source: Hammel and Lockwood (2007)).
What would seem so simple statistically is
complicated by the degrees of freedom in the various time series which is
related to the serial correlation in the data (e.g., next year's value is
highly dependent on this year's value). Nonetheless, they find that the
correlation coefficient between solar irradiance and Neptune's brightness is
near 0.90 (1.00 is perfect). The same relationship is found between the Earth's
temperature anomalies and the solar output. Hammel and Lockwood note "In other
words, the Earth temperature values are as well correlated with solar
irradiance (r = 0.89) as they are with Neptune's blue brightness (|r| >
0.90), assuming a 10-year lag of the Neptune values." The temporal lag is
needed to account for the large mass of Neptune that would require years to
adjust to any changes in solar output.
Hammel and Lockwood conclude that "In summary, if
Neptune's atmosphere is indeed responding to some variation in solar activity
in a manner similar to that of the Earth albeit with a temporal lag" then
"Neptune may provide an independent (and extraterrestrial) locale for studies
of solar effects on planetary atmospheres."
More on the sun's
variance and climate change here.
Cosmic Rays
One of the problems with irradiance as a driver for climate
change is that though the changes seem to be fairly well correlated with the
temperature anomaly, many scientists think the magnitude is too small to
totally account for temperature changes. It is ironic that AGW supporters
use this as a refutation of the sun's effect, since they have exactly the same
problem with CO2, and must posit huge positive feedback loops to justify their
forecasts.
A second, newer theory has emerged as to a potential second
warming effect of solar output. To understand it, we have to start with
clouds. For those that don't live in a hot climate like I do here in
Phoenix, I will give everyone a bit of background "“ clouds cool things
off. Ok, as with everything in climate, things are actually far more
complicated "“ high clouds can sometimes cause warming, and nighttime clouds can
actually slow cooling. Never-the-less, in general, cloudcover cools things
off by blocking out and reflecting the sun's energy.
Clouds are in fact such a strong cooling force that is has
been estimated by several sources (Theodor Landscheidt, 1998) that having
clouds cover 1% more of the Earth's surface would cancel the heating effect of
a doubling of CO2. In fact, it was one of my criticisms earlier
that AGW theory seems overly intent on finding positive feedback loops, while
not considering negative feedbacks seriously enough "“ one such potential
negative feedback is that on a warmer Earth, more water is evaporated into
clouds, in turn cooling things back off.
But recently, an interesting new theory on cloud formation
has emerged. In short, it holds that cosmic rays, which are the high
energy particles that arrive at Earth from supernovas, spur cloud formation by
ionizing air molecules that act as seeds for water condensation and cloud
formation. This sounds wild, but really no wilder than warming by a gas
(CO2) that makes up a near trivial portion of the atmosphere. Like CO2 warming,
this effect has been observed in various laboratory chambers. But is it
really a measurable driver of climate?
Henrik
Svensmark and Eigil Fris-Christensen looked at historic data on cloud cover
and cosmic ray incidence, from various measuring points. Their data was
extended and refined by Shiva in 2005.
So what changes cosmic ray flux to the Earth? The
biggest influence is the sun. When the sun's output is high, cosmic rays are
prevented from hitting the Earth, and vice versa. So high solar activity
corresponds to low cosmic ray flux and therefore lower cloud formation and
higher temperatures.
While the link between solar irradiance levels and warming
is pretty straight forward, the cosmic ray cloud formation proposition is still
in its infancy. Those of us who criticize AGW supporters for running past
the evidence on CO2 should not make the same mistake on cosmic rays, and movies
such as The Global Warming Swindle have gone too far in portraying this
alternate theory as fact.
Man's Land Use
Recently, Roger Pielke has done a substantial amount of
research on a different type of anthropogenic forcing. Specifically, he
has hypothesized that man's changing patterns of land use can be a substantial
driver of regional climate, including temperature and even more particularly,
precipitation. For example, clearing relatively dry land and
replacing it with irrigated agriculture substantially changes to the local heat
balance, not the least by increasing humidity. Dr. Pielke explains
summarizes the consequences on his web site:
Humans are significantly altering
the global climate, but in a variety of diverse ways beyond the radiative
effect of carbon dioxide. The IPCC assessments have been too conservative in
recognizing the importance of these human climate forcings as they alter
regional and global climate. These assessments have also not communicated the
inability of the models to accurately forecast the spread of possibilities of
future climate. The forecasts, therefore, do not provide any skill in
quantifying the impact of different mitigation strategies on the actual climate
response
that would occur.
The table of contents for the rest of this paper, A Layman's Guide to Anthropogenic Global Warming (AGW) is here. Free pdf of this Climate Skepticism paper is here and print version is sold at cost here
