Signals of Human-induced Climate Warning, USGCRP Seminar, 10 October 1995. Page: 1
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USGCRP Seminar: Signals of Human-induced Climate Warming
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F~ Signals of Human-induced Climate Warning
USGCRP Seminar, 10 October 1995
Updated 13 August, 2004 .
How is the global climate changing? How is climate
changing in the United States? Does climate
warming mean we will see more weather variations
SPEAKER: Thomas Karl, NOAA National Climate
Data Center, Asheville, NC
INTRODUCTION: Michael MacCracken, Director,
Office of the USGCRP
There is increasing evidence that the global climate
is changingfglobal temperatures have risen about
1 F over the past century, mountain glaciers are
melting back, sea level is rising. But how is the
climate of the United States changing? Are these
changes like others being experienced around the
world? Is the US climate becoming more or less
variable? Are we having more or fewer climatic
extremes? This seminar will address these questions
in the context of the anthropogenic influences on
atmospheric composition and climate.
An increasing number of studies are tying the global
warming of the last 100 years to human influences.
These studies do so by analyzing the global
patterns of change, drawing on new analyses from
around the world. One very important study has
focused on climate changes in the United States.
Based on an analysis of national weather-related
trends since 1910, Thomas Karl and his colleagues
at the National Climate Data Center have found, with
high statistical confidence (typically 19 chances out
of 20) that trends of climate in the United States are
consistent with projected trends due to a human-
induced warming effect resulting from increased
concentrations of heat-trapping greenhouse gases.
To help better define how these changes in climate
will affect people in their day to day lives, Tom Karl
and his colleagues have looked very closely at
nearly nine decades of weather and temperature
trends. They have devised two climate change
indices: (1) a Climate Extremes Index, which takes
into account extreme heat, extreme cold, extreme
drought, and extreme wetness; and (2) a
Greenhouse Climate Response Index, which is a set
of measures that permit a comparison between
model predictions of climate change due to
increases of anthropogenic greenhouse gases, and
Climate models make a number of predictions about
how the climate will change due to the rising
concentrations of greenhouse gases. These include:
(1) an increase of mean surface temperature,
somewhat more pronounced during the night; (2) an
increase in precipitation, especially during the cold
season; (3) more severe and longer lasting droughts
during the warm season; (4) a greater portion of
warm season precipitation derived from heavy
convective rainfall (showers or thunderstorms)
compared with gentler, longer-lasting rainfalls; and
(5) a decrease in the day-to-day variability of
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Karl, Thomas. Signals of Human-induced Climate Warning, USGCRP Seminar, 10 October 1995., text, October 10, 1995; Pennsylvania Ave., Washington, D.C.. (digital.library.unt.edu/ark:/67531/metadc11840/m1/1/: accessed January 23, 2017), University of North Texas Libraries, Digital Library, digital.library.unt.edu; .