David Archibald has given us this very detailed paper on historical global climate and focuses on the role of solar activity. This is as complete a workout of the issues as I have so far seen.
http://www.lavoisier.com.au/papers/Conf2007/Archibald2007.pdf
Although he goes back through geologic time and produces the appropriate graphs, most of the data is hardly settled and certainly subject to and has been subject to ongoing debate and access to new proxies.
It is unfortunate but any proxy that can be projected to directly reflect temperatures, can also be modified almost randomly by other factors and we have no way to properly correct for this. The second problem is that once one draws a line between two points it is impossible to avoid thinking that this is a continuous process that is been measured. Yet climate is famously discontinuous
In any event, this is still a nice presentation, but do not get comfortable that any of this is all settled. More importantly, the Pleistocene Nonconformity has changed everything that has gone before inasmuch as the variation range of global temperature has been hugely narrowed. Therefore a look at the implied variation range for the past millions of years is misleading in the context of the Holocene.
What has been in fact remarkable has been the implied two degree range maintained for the past ten thousand years.
Archibald lays out the argument for the direct involvement of solar activity in driving the heat content of the atmosphere. He also spells out the nature of the current apparent slow onset of solar cycle number 24. His work is well done, and he argues forcefully for a major two degree drop over the next twenty years very similar to the Dalton minimum.
He also puts the contribution of CO2 to global warming into complete perspective and the result is negligible, largely because any response is logarithmic rather than linear and at best is good for a tenth of a degree. Solar variation appears to be able to produce variation over two degrees, several times any Anthropogenic effect.
This paper is well worth the read as it pulls together the total argument for the importance of solar variation and attempts to place it all in a continuous narrative that may be full of gaping holes but is at least making the attempt. This is much better than the many studies that usually focus on a narrow window of results and assume a position outside that window.
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This short item gives the accepted opinion on solar variation.
Solar Variability: Striking a Balance with Climate Change
http://www.lavoisier.com.au/papers/Conf2007/Archibald2007.pdf
Although he goes back through geologic time and produces the appropriate graphs, most of the data is hardly settled and certainly subject to and has been subject to ongoing debate and access to new proxies.
It is unfortunate but any proxy that can be projected to directly reflect temperatures, can also be modified almost randomly by other factors and we have no way to properly correct for this. The second problem is that once one draws a line between two points it is impossible to avoid thinking that this is a continuous process that is been measured. Yet climate is famously discontinuous
In any event, this is still a nice presentation, but do not get comfortable that any of this is all settled. More importantly, the Pleistocene Nonconformity has changed everything that has gone before inasmuch as the variation range of global temperature has been hugely narrowed. Therefore a look at the implied variation range for the past millions of years is misleading in the context of the Holocene.
What has been in fact remarkable has been the implied two degree range maintained for the past ten thousand years.
Archibald lays out the argument for the direct involvement of solar activity in driving the heat content of the atmosphere. He also spells out the nature of the current apparent slow onset of solar cycle number 24. His work is well done, and he argues forcefully for a major two degree drop over the next twenty years very similar to the Dalton minimum.
He also puts the contribution of CO2 to global warming into complete perspective and the result is negligible, largely because any response is logarithmic rather than linear and at best is good for a tenth of a degree. Solar variation appears to be able to produce variation over two degrees, several times any Anthropogenic effect.
This paper is well worth the read as it pulls together the total argument for the importance of solar variation and attempts to place it all in a continuous narrative that may be full of gaping holes but is at least making the attempt. This is much better than the many studies that usually focus on a narrow window of results and assume a position outside that window.
______________________________________
This short item gives the accepted opinion on solar variation.
Solar Variability: Striking a Balance with Climate Change
05.07.08
Credit: NASA Goddard Space Flight Center The sun has powered almost everything on Earth since life began, including its climate. The sun also delivers an annual and seasonal impact, changing the character of each hemisphere as Earth's orientation shifts through the year. Since the Industrial Revolution, however, new forces have begun to exert significant influence on Earth's climate.
"For the last 20 to 30 years, we believe greenhouse gases have been the dominant influence on recent climate change," said Robert Cahalan, climatologist at NASA’s Goddard Space Flight Center in Greenbelt, Md.
For the past three decades NASA scientists have investigated the unique relationship between the sun and Earth. Using space-based tools, like the Solar Radiation and Climate Experiment (SORCE), they have studied how much solar energy illuminates Earth, and explored what happens to that energy once it penetrates the atmosphere. The amount of energy that reaches Earth's outer atmosphere is called the total solar irradiance. Total solar irradiance is variable over many different timescales, ranging from seconds to centuries due to changes in solar activity.
The sun goes through roughly an 11-year cycle of activity, from stormy to quiet and back again. Solar activity often occurs near sunspots, dark regions on the sun caused by concentrated magnetic fields. The solar irradiance measurement is much higher during solar maximum, when sunspot cycle and solar activity is high, versus solar minimum, when the sun is quiet and there are usually no sunspots.
The sun radiates huge amounts of electromagnetic energy in all directions. Earth is only one small recipient of the sun's energy; the sun's rays extend far out into the solar system, illuminating all the other planets. Credit: NASA
"The fluctuations in the solar cycle impacts Earth's global temperature by about 0.1 degree Celsius, slightly hotter during solar maximum and cooler during solar minimum," said Thomas Woods, solar scientist at the University of Colorado in Boulder. "The sun is currently at its minimum, and the next solar maximum is expected in 2012."
Using SORCE, scientists have learned that about 1,361 watts per square meter of solar energy reaches Earth's outermost atmosphere during the sun's quietest period. But when the sun is active, 1.3 watts per square meter (0.1 percent) more energy reaches Earth. "This TSI measurement is very important to climate models that are trying to assess Earth-based forces on climate change," said Cahalan.
Over the past century, Earth's average temperature has increased by approximately 0.6 degrees Celsius (1.1 degrees Fahrenheit). Solar heating accounts for about 0.15 C, or 25 percent, of this change, according to computer modeling results published by NASA Goddard Institute for Space Studies researcher David Rind in 2004. Earth's climate depends on the delicate balance between incoming solar radiation, outgoing thermal radiation and the composition of Earth's atmosphere. Even small changes in these parameters can affect climate. Around 30 percent of the solar energy that strikes Earth is reflected back into space. Clouds, atmospheric aerosols, snow, ice, sand, ocean surface and even rooftops play a role in deflecting the incoming rays. The remaining 70 percent of solar energy is absorbed by land, ocean, and atmosphere.
"Greenhouse gases block about 40 percent of outgoing thermal radiation that emanates from Earth," Woods said. The resulting imbalance between incoming solar radiation and outgoing thermal radiation will likely cause Earth to heat up over the next century, accelerating the melting polar ice caps, causing sea levels to rise and increasing the probability of more violent global weather patterns.
Non-Human Influences on Climate Change
Before the Industrial Age, the sun and volcanic eruptions were the major influences on Earth's climate change. Earth warmed and cooled in cycles. Major cool periods were ice ages, with the most recent ending about 11,000 years ago.
"Right now, we are in between major ice ages, in a period that has been called the Holocene,” said Cahalan. “Over recent decades, however, we have moved into a human-dominated climate that some have termed the Anthropocene. The major change in Earth's climate is now really dominated by human activity, which has never happened before."
The sun is relatively calm compared to other stars. "We don't know what the sun is going to do a hundred years from now," said Doug Rabin, a solar physicist at Goddard. "It could be considerably more active and therefore have more influence on Earth's climate."Or, it could be calmer, creating a cooler climate on Earth similar to what happened in the late 17th century. Almost no sunspots were observed on the sun's surface during the period from 1650 to 1715. This extended absence of solar activity may have been partly responsible for the Little Ice Age in Europe and may reflect cyclic or irregular changes in the sun's output over hundreds of years. During this period, winters in Europe were longer and colder by about 1 C than they are today.
Since then, there seems to have been on average a slow increase in solar activity. Unless we find a way to reduce the amount of greenhouse gases we put into the atmosphere, such as carbon dioxide from fossil fuel burning, the solar influence is not expected to dominate climate change. But the solar variations are expected to continue to modulate both warming and cooling trends at the level of 0.1 to 0.2 degrees Celsius (0.18 to 0.26 Fahrenheit) over many years.
Future Measurements of Solar Variability
For three decades, a suite of NASA and European Space Agency satellites have provided scientists with critical measurements of total solar irradiance. The Total Irradiance Monitor, also known as the TIM instrument, was launched in 2003 as part of the NASA’s SORCE mission, and provides irradiance measurements with state-of-the-art accuracy. TIM has been rebuilt as part of the Glory mission, scheduled to launch in 2009. Glory's TIM instrument will continue an uninterrupted 30-year record of solar irradiance measurements and will help researchers better understand the sun's direct and indirect effects on climate. Glory will also collect data on aerosols, one of the least understood pieces of the climate puzzle.
