34 Years of Satellite Temperature Data Show Global Warming Is on a Plateau

University
of Alabama climatologists John Christy and Roy Spencer have
released their monthly statistics on global warming trends detected
by National Oceanic and Atmospheric Agency satellites. In the press
release accompanying the data, Christy notes that the rise in
global average temperatures has been largely stalled since the big
El Nino event in 1998:

The lowest level of the global atmosphere has warmed almost one
half of a degree Celsius (0.48 C or 0.86 degrees Fahrenheit) during
the 34 years since instruments aboard NOAA and NASA satellites
started collecting data on global temperatures in late November
1978, according to Dr. John Christy, a professor of atmospheric
science and director of the Earth System Science Center at The
University of Alabama in Huntsville. While the atmosphere has
warmed over the full 34-year time span, it has not warmed
noticeably since the major El Niño of 1997-98 — giving us about a
decade and a half of generally stable temperatures.

Since 2002, there has been a plateau of relatively warmer
temperatures with only 12 months when the global average
temperature was cooler than the long-term seasonal norm. In fact,
compared to the 30-year temperature baseline, the most recent five
years (12/07-11/12) averaged only 0.003 C (0.173 to 0.176 above
seasonal norms) warmer than the preceding five years (12/02-11/07).
…

The long term 0.14 C per decade warming trend measured by
microwave sounding units on a series of satellites is consistent
with the low-end of global climate change predictions made by some
climate models; it is also within the potential range of natural
climate variability, especially since most of the warming happened
over such a short period of time.

Based on the empirical data gathered by the NOAA satellites,
Christy remains skeptical of climate models that predict future
catastrophic warming:

“There are so many natural variations and
oscillations that we just can’t say that this looks like a human
fingerprint on the lower atmosphere’s climate,” said Christy. “We
know that some human activities must have an impact on the climate
system. But one has considerable difficulty in looking at what has
happened over the past 34 years and reasonably or with scientific
accuracy saying whether or by how much the change has been natural
or caused by us.

“Changes of this amount over these time scales could be
essentially natural. Such a hypothesis has not been proven false.
Scientists would love to have these types of measurements from the
past 2,000 years to see to what extent Mother Nature can cause
changes over decades on her own. But the thorny question of how
sensitive the climate is to extra greenhouse gases we are putting
into the atmosphere is still up in the air.”

In any case, the November global temperature trend update
notes:

Global climate trend since Nov. 16, 1978: +0.14 C per
decade

November temperatures (preliminary)

Global composite temp.: +0.28 C (about 0.50 degrees Fahrenheit)
above 30-year average for November.

Northern Hemisphere: +0.30 C (about 0.54 degrees Fahrenheit)
above 30-year average for November.

Southern Hemisphere: +0.26 C (about 0.47 degrees Fahrenheit)
above 30-year average for November.

Tropics: +0.17 C (about 0.31 degrees Fahrenheit) above 30-year
average for November.

Go
here to see my October 15 blogpost that looked at what other
datasets suggest about global temperature trends and various
critiques of those data.

2012-12-26 10:15:06

Source: http://reason.com/blog/2012/12/26/34-years-of-satellite-temperature-data-s