| December 10, 2003
Scientists “Reconstruct” Earth’s Climate Over
Past Millennia
Using the perspective of the last few centuries and millennia, speakers
in a press conference at the Fall Meeting of the American Geophysical
Union in San Francisco will discuss the latest research involving climate
reconstructions and different climate models.
The press conference features Caspar Ammann of the National Center for
Atmospheric Research (NCAR), Boulder, Colo.; Drew Shindell of NASA’s
Goddard Institute for Space Studies, New York; and Tom Crowley of Duke
University, Durham, N.C. The press conference is at 5 p.m. EST, Thursday,
December 11 in the Moscone Convention Center West, Room 2012.
Changes in the sun’s activity have been considered responsible
for some part of past climatic variations. Although useful measurements
of solar energy are limited to the last 25 years of satellite data, this
record is not long enough to confirm potential trends in solar energy
changes over time. Tentative connections between the measured solar activity,
with sunspots or the production of specific particles in the Earth’s
atmosphere (such as carbon-14 and beryllium-10), have been used to estimate
past solar energy.
Ammann will discuss how he used a set of irradiance estimates with the
NCAR coupled Ocean-Atmosphere General Circulation computer model to show
the climate system contains a clearly detectable signal from the sun.
Ammann’s work with the model also demonstrates that smaller, rather
than larger, background trends in the sun’s emitted energy are
in better agreement with the long-term climate record, as obtained from
proxy climate records, such as tree-ring data.
Shindell will discuss how he used a climate model that included solar
radiation changes, volcanic eruptions, and natural internal variability
to arrive at a more accurate look at Earth’s changing climate today.
Shindell said that while solar radiation changes and volcanoes exert
a similar influence on global or hemispheric average-temperature changes,
the solar component has the biggest regional effect over time scales
of decades to centuries, while volcanoes cause the largest year-to-year
changes.
Crowley will discuss one of the goals of climate modeling, to test whether
moderately reliable predictions of regional climate change can be made
under global warming scenarios. Using paleoclimate data, scientists can
in some cases test computer climate-model performance. This testing would
occur for a time period in which models accurately predict the larger
(hemispheric-scale) response to changes in the Earth’s radiation
balance.
NASA’s Earth Science Enterprise is dedicated to understanding
the Earth as an integrated system and applying Earth System Science to
improve prediction of climate, weather and natural hazards using the
unique vantage point of space.
NCAR is a research laboratory operated by the University Corporation
for Atmospheric Research, a consortium of 67 universities offering doctoral
programs in the atmospheric and related sciences. NCAR’s primary
sponsor is the National Science Foundation.
###
Contacts:
Elvia Thompson
Headquarters, Washington
Phone: 202/358-1696
Rob Gutro
Goddard Space Flight Center, Greenbelt, Md.
Phone: 301/286-4044; at AGU: 415/905-1007 |
|
The ‘Little Ice Age’
Unusually low solar activity between 1645-1715 likely triggered the ‘Little
Ice Age’ in regions like Europe and North America. A lag time of
arguably 10-30 years allowed for the climate system to be affected by
an increased ozone layer that altered the heating of the oceans. According
to the model, diminished jet stream winds caused by a dimmer sun created
cold land temperatures by reducing the transport of warm Pacific air
to America and warm Atlantic air to Europe. During this shift, winter
temperatures cooled as much as 2 to 4 degrees F - enough to freeze rivers
and alter agriculture, economy, disease, etc.
Pictured is the climate model used by researchers to watch temperature
anomalies. As such, 1780 was used as an arbitrary baseline; the ice age
period, then, is colder/bluer and 1780 is white or neutral. Redder colors
in more modern times reflect warmer temperatures. Credit: NASA
Movie of North America
Movie of flat world map
Solar Activity
The Sun shows signs of variability, such as its eleven-year sunspot cycle.
In that time, it goes from a minimum (seen here in 1996) to a maximum
(2000) period of activity that affects us everyday. When particularly
active, solar storms can spew tons of radiation to Earth in the form
of Coronal Mass Ejections (CMEs) that can affect power grids, spacecraft,
and communication systems. Credit: NASA / ESA
Carbon Trends
The lack of activity on the Sun was strongly felt during the Little Ice
Age, yet scientists credit greenhouse gases and global warming with having
such an impact on us today. Most experts point to 1850, start of the
industrial age, to when the major influence of climate started to shift
from the Sun to ourselves. Click on the image for an animation. In the
first graph on the animation, a flat line reflects steady carbon measurements
prior to 1850. The other graphs show a stable increase of ambient carbon
dioxide oscillating as a general trend, but still rising and falling
with seasonal change. Credit: NASA / ORBIMAGE
MPEG Animation
Volcanic Plumes
This computer model shows the dispersion of the volcanic plume from the
Mt. Pinatubo volcano. The 1991 Pinatubo eruption was sulfur-rich, producing
volcanic clouds that lasted a number of years in the stratosphere. The
Pinatubo eruption widely expanded the area of ozone loss over the Arctic
and Antarctic. Red colors indicate higher elevations and blue colors
indicate lower elevations for the plume. Credit: NASA
High-Resolution
Image
Mt. Pinatubo’s Sulfur Cloud
The eruption of Mt. Pinatubo blasted a huge cloud of sulfur dioxide,
shown in red, into the stratosphere. This data taken from NASA“s
Total Ozone Mapping Spectrometer (TOMS) instrument shows that initial
burst of sulfur dioxide and its international path in the days following
the eruption, from June 16th to June 30th. The
sulfur gas cloud dissipates as the gas turns into droplets of sulfuric
acid. Both the gas and subsequent acid were contributors to the overall
dust cloud that cooled the global climate. Image Credit: NASA
MPEG Animation
High-Resolution
Image
Decreasing Ozone Levels
During the year and a half after the eruption, global stratospheric ozone
levels decreased as a result of chemical reactions with the ozone and
the sulfur dioxide gases released by the volcano. However, the initial
effect of the injection of sulfur dioxide into the atmosphere was so
strong, that a small hole was created in the ozone layer, (from June
15th, 1991 through June 30, 1991) as seen here, in blue, using
TOMS data. This visualization shows global ozone levels before and after
the eruption. After the hole dissipates, continued low levels of ozone,
in very light blue, can be seen around the tropics. Credit: NASA
MPEG Animation
High-Resolution
Image
The Ozone “Hole”
The Arctic Ozone “Hole” The blue colors in this sequence
depict the depleted region of ozone over the North Pole that occurred
in the winter of 2000. Though ozone “holes” appear each year
over the South Pole, low levels of ozone only occasionally form over
the northern polar regions during very cold winters. Scientists say the
northern ozone hole may reappear for several consecutive years after
a period of high volcanic activity. A northern ozone hole could be significant
because more people live in Arctic regions than near the South Pole.
The data for these images were collected by the Total Ozone Mapping Spectrometer
(TOMS) satellite.Credit: NASA
MPEG Animation |
