Many people cite the latest National Climate Assessment report as an authority that proves human carbon dioxide emissions are the main cause of recent warming. But reading the report shows a different story.
The 2014 National Climate Assessment (NCA) claims on page 7: “Multiple lines of independent evidence confirm that human activities are the primary cause of the global warming of the past 50 years.”
What physical evidence does the NCA give as proof that human carbon dioxide emissions play a significant role in global temperature? In my opinion they present no unequivocal evidence.
NCA cites three main lines of “evidence” in the report (pages 23 & 24):
NCA: “The first line of evidence is our fundamental understanding of how certain gases trap heat, how the climate system responds to increases in these gases, and how other human and natural factors influence climate.”
My response: That’s a claim, not evidence. If their “fundamental understanding” is so good, why then do modeled atmospheric temperature projections diverge so widely from actual measurements? (Graph source)
NCA: “The second line of evidence is from reconstructions of past climates using evidence such as tree rings, ice cores, and corals. These show that global surface temperatures over the last several decades are clearly unusual, with the last decade (2000-2009) warmer than any time in at least the last 1300 years and perhaps much longer.”
My response: First, evidence of warming does not constitute evidence of the cause of warming. Second, physical evidence shows that current warming is not unusual.
The temperature reconstruction below using tree ring data shows current temperatures are not unusual, and, in fact cooler than the past.
A closer look at the reconstructed temperature shows the current warming is nothing unusual.
NCA: “The third line of evidence comes from using climate models to simulate the climate of the past century, separating the human and natural factors that influence climate.”
My response: Again, computer model simulations are not physical evidence, they are merely speculations that depend on input assumptions. The computer simulations were exercises in curve fitting, massaging the data until it produced the desired result. To show how ridiculous this is, an Australian science writer produced a “tongue-in-cheek” correlation between U.S. First Class postal rates and temperature. (Source) The correlation of postal rates with temperature is better than that of CO2. The graph runs from 1880 to 2009. This demonstrates that correlation does not prove causation.
NCA also claims additional “evidence” in Appendix 3 which begins on page 735. Let’s take a look.
NCA Supplemental message 1:
“…the natural greenhouse effect is being artificially intensified by human activities.”
My response: If the greenhouse effect has been intensified, then we should see a decrease in outgoing long-wave infrared radiation. However, satellite measurements from NOAA show a slight increase. (See discussion here).
While more infrared radiation is escaping to space, there has been a decrease in down-welling infrared radiation from greenhouse gases, that is radiation from the atmosphere to the surface. An independent study, published in the Journal of Climate, based on 800,000 observations, find there has been a significant decrease in long-wave infrared radiation from increasing greenhouse gases over the 14 year period 1996-2010 in the US Great Plains. CO2 levels increased about 7% over this period and according to AGW theory, down-welling long-wave infrared radiation should have increased over this period with buildup of carbon dioxide.
Two independent measures of the “greenhouse effect” show that it is weakening even though we are putting more CO2 in the atmosphere. Why is this happening? In my opinion it is happening because a much stronger greenhouse gas, water vapor, is decreasing. That alone shows that CO2 has very little influence on global temperature. The graph below shows how relative humidity has been decreasing since 1948 (humidity data from NOAA).
NCA Supplemental Message 2:
“Global trends in temperature and many other climate variables provide consistent evidence of a warming planet.”
My response: As stated above, evidence of warming does not speak to cause.
NCA Supplemental Message 3:
“Natural variability, including El Niño events and other recurring patterns of ocean-atmosphere
interactions, influences global and regional temperature and precipitation over timescales ranging from months up to a decade or more.”
My response: I agree.
NCA Supplemental Message 4:
“Human-induced increases in atmospheric levels of heat-trapping gases are the main cause of observed climate change over the past 50 years. The ‘fingerprints’ of human-induced change also have been identified in many other aspects of the climate system, including changes in ocean heat content, precipitation, atmospheric moisture, and Arctic sea ice.”
My response: According to climate models, the rate of warming should increase by 200-300% with altitude in the tropics, peaking at around 10 kilometers – a characteristic “fingerprint” for greenhouse warming. However, measurements by weather balloons and satellites show the opposite result: no increasing temperature trend with altitude. In the graphic below, the computer predicted temperature distribution is on the left; measured observations, i.e., reality is on the right.
The remainder of the “messages” deal with computer modeling and some propaganda, not evidence.
Bottom Line: NCA presents no unequivocal evidence that supports their contention of significant human induced warming.
P.S. It should be noted also that the UN’s IPCC, in the thousands of pages that constitute five major reports, similarly fails to provide any physical or observational evidence supporting the contention that human carbon dioxide emissions play a significant role in global climate change.