1) What proportion of the girls born today (in the developed world) will live through the entire 21st century?
2) In studies of the Bighorn Basin, Wyoming, ecologists are finding that the largest environmental changes may be caused by climate changes spanning how many years?
3) Changes in the total solar irradiance of +/- what percent over a century could explain every type of climate change that the Earth has seen within the last one million years?
a) +/- 50
What on Earth, or really what in space, do these apparently unrelated questions have to do with each other?
In the late 1960s and the decade of the 1970s, scientists
at the Jet Propulsion Laboratory (JPL),
working to perfect an instrument capable of measuring the total energy
delivered to Earth, were not worrying about such global issues. Just
being able to measure solar variability was a dream in those
yearsa dream which came to fruition with the flight of the Active
Cavity Radiometer Irradiance Monitor I (ACRIM I) instrument on the Solar
Maximum Mission spacecraft launched in 1980. Data returned from the
ACRIM I instrument demonstrated that the energy output of the sun was
variable on the scale of seconds to years. In fact, ACRIM I could
measure the suns energy in fine enough detail to demonstrate that
sun spots cause temporary decreases in the total irradiance output of
the sun when sunspots are visible from Earth.
The measurement of the total solar irradiance is key for
climatologists who need to perform the energy accounting for
the Earths climate system. Total solar irradiance is the light
energy coming to the Earth, most being in the wavelengths from 200 to
2000 nanometers. To calculate the suns heating of Earths
climate system, the first thing a researcher needs to know is the amount
of energy that reaches the Earth from the sun. Separate instruments
measure the amount of light that is reflected from the Earth. The
difference between the incoming and the reflected total solar irradiance
is the amount of energy that is absorbed by the Earthin the air,
in the clouds, in the ocean, and on the land. This absorbed energy
determines the Earths average temperature. The differences in the
absorption at equatorial versus polar latitudes, and at the surface
versus in the clouds, are responsible for driving the fluid motions that
control weather and climate.
|Continuous measurements of solar irradiance go back just over 20 years. Much longer-term monitoring is necessary to fully understand the effect of solar variability on climate. Several instruments collected the data used in the graph at leftthe Hickey-Frieden radiometer aboard Nimbus 7 (HF), ACRIM I, ACRIM II, and Variability of Solar Irradiance and Gravity Oscillations (Virgo). (Graph by the World Radiation Center)|
An important consideration in the solar irradiance measurement is that it must be made for a very long time. Climate models show that changes as small as 0.5 percent of full scale over a century could produce equivalents of the most extreme periods of warm or cold climate that the Earth has experienced within the period humans have lived here. In real terms, this means total irradiance data gathered over a few decades is just beginning to scratch the surface of what we can understand about the suns behavior and its impact on the Earths climate.
The Recent Launch of ACRIM III
Given that girls born this year stand a good chance of living to the 22nd century, one can only imagine that they, their brothers, and eventually their sons and daughters will be the scientists who will continue the long-term database to help unravel the secrets of the suns contribution to the Earths climate. And this understanding will provide the basis for predicting the Earths climate as part of humankinds stewardship of the Earth for the decades and centuries to come.
Answers to the questions at the beginning:
Half of the girls born today [in the developed world] will live through the entire 21st century.James Vaupel, executive director of the Max Planck Institute for Demographic Research in Rostock, Germany.
In studies of the Bighorn Basin, Wyoming, ecologists are finding that the largest environmental changes may be caused by climate changes spanning 5000 years (Kloor 2000).
Changes in the total solar irradiance of +/- 0.5 percent over a century could explain every type of climate change that the Earth has seen within the last one million years (R.C. Willson, et al. 1986).
Kloor, Keith, 2000: "Returning America's Forests to Their Natural Roots," Science, Volume 287, p. 573-75.
Willson, R.C., H.S. Hudson, C. Frohlick, and R.W. Brusa, 1986: "Long-Term Downward Trend in Total Solar Irradiance," Science, Volume 234, p. 1114.
For more information:
Sunspots & the Solar Max
Climate change is at least partially responsible for the encroachment of Utah junipers into the Bighorn Basin in Wyoming. This pair of photographs were taken from the same spot 76 years apart. Junipers appear in the foreground of the later image, and are packed more densely on the slopes of the mountain in the background. (Photographs courtesy Utah Juniper Project, USGS)