ILLUSTRATED FLORA OF EAST TEXAS - Brit - Botanical Research ...

FIG. 39/CO2 AND TEMPERATURE RECORDS FOR THE PAST 160,000 YEARS,
FROM ANTARCTIC ICE CORES AND RECENT ATMOSPHERIC MEASUREMENTS.
REPRINTED FROM HANSEN ET AL. 1993, NATIONAL GEOGRAPHIC SOCIETY,
©1993.
CLIMATE OF EAST TEXAS/INTRODUCTION 73
almost orange color—the next day
there will be a coating of dust on cars
and other objects. An example is the
“mammoth dust storm of January
25–26, 1965, which limited visibilities
to one or two miles in such disparate
locations as El Paso, San Angelo,
Dallas, San Antonio, and Houston”
(Bomar 1995). While irritating to the
residents of East Texas, the loss of topsoil
and its ecological and agricultural
implications are serious issues for the
western part of the state.
Pollen, plant macrofossils, packrat
middens, and other types of evidence
demonstrate that the climate of Texas
has changed substantially over the past
15,000 years since the end of the last
glacial period. At 15,000 years ago, the
mean annual air temperature was 5° C
(9° F) less than at present, and there
was a more widespread forest mosaic
over most of Texas, with boreal species
such as Picea glauca (white spruce) in
specialized microhabitats (Bryant
1977; Stahle & Cleaveland 1995).
Certain present-day plant distributions,
such as the rare western occur-
rence of plants normally found predominantly in eastern Texas, may thus reflect these past
climatic conditions (see page 209). While past long-term climate change is well-documented,
attention has focused recently on the possibility of future climate change in Texas due to
human-induced modifications of the atmosphere (e.g., increased CO2 concentrations) and
the resulting increased greenhouse effect and global warming (see e.g., Norwine et al. 1995;
North et al. 1995a). While considerable controversy exists over details, there is solid evidence
that global atmospheric CO2 concentrations have increased by about 31% since pre-industrial
times and that this trend can be attributed primarily to human activities (e.g., fossil fuel use,
land-use changes, and agriculture) (Houghton et al. 1995, 2001). In addition, over the past
160,000 years there has been a strong correlation between global atmospheric CO2 concentrations
and average global temperatures (Fig. 39) (Graham 1999). However, there is
controversy over whether CO2 concentrations can be characterized as the cause of these previous
temperature changes.
Since at least 1995, scientific consensus has existed that there is “…a discernible
human influence on climate” (Houghton et al. 1995). More recently, Houghton et al. (2001)
have indicated that “There is new and stronger evidence that most of the warming observed
over the last 50 years is attributable to human activities.” Further, Houghton et al. (2001)
note that the increase in temperature during the twentieth century is probably the largest
to have occurred during the past 1,000 years, and that taken together, a number of trends
“illustrate a collective picture of a warming world.” However, while the data clearly show a
global warming trend, there is still uncertainty about the actual cause—some authorities
believe the observed warming is at least partly the result of natural climatic fluctuations
rather than human activities (e.g., Grossman 2001; Lindzen 2001).