Thursday, January 12th 2012, 10:59 AM EST
As 2011 comes to a close, climate science celebrates an important landmark. It has now been 33 years, or a third of a century, since sensors aboard NASA and NOAA satellites began measuring temperatures throughout the earth’s lower atmosphere.
For 33 years, we have had precise, objective temperature data that do not require guesswork corrections to compensate for uneven thermometer placement and non-climate surface temperature biases such as expanding urban heat islands and land-use changes. The satellite data, moreover, tell us the earth is warming at a more modest, gradual, and reassuring pace than was foretold by United Nations computer models.
The satellite sensors became operational at a time that is very convenient for those who believe humans are causing a global warming crisis. Global temperatures declined from the mid-1940s through the late 1970s. As a result, the sensors coincidentally began measuring global temperatures at the very beginning of our most recent global warming trend. Had the sensors been in place 33 years earlier, during the 1940s, the overall pace of warming shown by the satellite sensors would be less than half what is shown by the post-1978 temperature data.
Even so, the measured temperature trend is quite modest. John Christy, who along with Roy Spencer oversees the NASA satellite sensor program, reports temperatures have warmed at an average pace of 0.14 degrees Celsius per decade since the satellite sensors became operational. This is merely half the pace predicted by computer models utilized by the United Nations Intergovernmental Panel on Climate Change (IPCC).
Christy appears to be making a generous concession regarding the warming that has occurred. The temperature data seem to show warming closer to 0.3 degrees over the 33 year period, or 0.09 degrees Celsius per decade. But why quibble over the difference? A warming of 0.14 degrees per decade, or 1.4 degrees per century, is still significantly less than predicted by UN climate models and far from an impending global warming crisis.
Importantly, the satellite sensors show less warming in the lower troposphere (approximately 10,000 feet above the earth’s surface) than is reported by surface temperature readings. Global warming theory holds that one of the fingerprints of human-induced global warming is more rapid warming in the lower troposphere than at the surface. The reason for this is carbon dioxide molecules reside in the lower troposphere and have their greatest heat-trapping effect there.
As a result, if global temperatures are rising as a result of human carbon dioxide emissions, the satellite sensors should report more warming in the lower troposphere than is actually occurring at the surface. In essence the satellite sensors should report a warming trend somewhat more severe than is actually occurring at the surface of the earth.
Surface temperature measurements, however, indicate more rapid warming at the surface of the earth than in the lower troposphere. According to James Hansen of NASA’s Goddard Institute, temperatures at the surface of the earth rose twice as fast during the past 33 years as the satellite data show. Surface temperatures compiled by the UK’s University of East Anglia Climate Research Unit reflect a similar warming trend.
With temperature data indicating more warming at the earth’s surface than in the earth’s lower troposphere, one of the following must be true: (1) the surface temperature data is more corrupted by heat biases such as expanding urban heat islands and localized land-use changes than the IPCC admits, (2) the warming of the past 33 years is primarily the result of factors other than greenhouse gas emissions, or (3) longstanding, widely believed assumptions about greenhouse gas theory are wrong.
Regardless of which one or more of the three options are true, the satellite sensors have contributed greatly to our scientific understanding of the earth’s ever-changing climate. Thirty-three years and counting, we rightly celebrate the scientific advances provided by satellite temperature sensors.