An Introduction to Satellite-Based Applications and Research for Understanding Climate Change - Satellite-based Applications on Climate Change - page 9

While the calibration is improving for the core measurements, Cao et al. ( 2009 )
pointed out there are still significant uncertainties in determining the long-term
climate trends using indices such as the Normalized Difference Vegetation Index
(NDVI). This is partly due to the lack of stability in measurements required for
climate change detection and partly due to the nonphysical derivation of the NDVI
from measured radiances. Using calibrated AVHRR (Advanced Very High Reso-
lution Radiometer) data from 1982 to 2007, complex trends in both the growing
season amplitude and seasonally integrated vegetation greenness in southwestern
North America can be observed. Zhang et al. ( 2010 ) show greenness measurements
from 1982 to 2007 with an increasing trend in grasslands but a decreasing trend in
shrublands. Also, vegetation growth appears to be a function of both the rainfall
amount and the dry season length. The average global temperature over the past
100 years increased 0.74 C according to the 2007 Intergovernmental Panel on
Climate Change Report. The period after 2000 was the warmest and includes the
two warmest years (2007 and 2010) since the 1880s. A warmer world is expected to
have tendencies toward higher temperature variability increasing the risk of sum-
mer droughts, which should affect larger areas, last longer, be more intense and
produce more devastating impacts on the environment and economy. Due to data
sparse ground observing stations, the assessment of agricultural impacts has been
performed using satellite data. Drought affects the largest number of people in the
world and has the largest economic impacts. The Vegetation Health Index has both
a temperature and moisture component to distinguish the effects of the dominant
variables (temperature and moisture/rainfall) for a particular region. Using the new
indices, drought intensity and the area covered appear to be increasing as the
temperature warms (Kogan et al. 2013 ). During the most recent decade, the global
drought analysis indicates that 17-35% of the world experienced droughts from
moderate to exceptional intensity, 7-15% severe to exceptional, and 2-6% the most
exceptional droughts, an increase over earlier periods. Two droughts, 2010 in
Russia and 2011 in the USA, stand out by their intensity, affected area, and
substantial economic consequences (Kogan et al. 2013 ).
Climate products will continue to evolve with time. They will incorporate a
greater variety of both satellite and in situ data. The combined use of the most
modern measurements to understand current trends while leveraging our knowl-
edge and understanding of the older in situ observations combined with modeled
physics to allow an improved assessment of past climate changes is the future trend.
An example of this type of project is the monthly reconstruction of precipitation
project (Smith et al. 2010 ) which covers 1900 until the present. This reconstruction
attempts to resolve interannual and longer time scales as well as spatial scales larger
than 5 over the entire globe using both direct and indirect correlations. A key
advantage for this type reconstruction is that it evaluates global precipitation
variations for periods much longer than the satellite period of record, which begins
in 1979 for routine use in NOAA operational models. In the future, the multisource
fusion of the in situ observations with remotely sensed measurements and detailed
model physics will allow the investigation of climate change to a level well beyond
today's capability. However, the unfolding debate over whether the model physics is