Climate Sensitivity

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.