San José State University
Thayer Watkins
Silicon Valley
& Tornado Alley

What Is the Evidence
of Climate Change?

A Google search on "evidence of climate change" brings up the webpage of NASA at the top of the list. That would seem to be an appropriate place to start.

The webpage starts with the graph below of carbon dioxide levels in the atmosphere over the past four hundred thousand years based upon ice core samples and recent direct measurements.

This is very interesting but it is not climate change, per se. It might be a signal of coming climate change but that is something that must be established. Intellectually there are a few other things that need to be established. It must be shown that the ice-cores at Vostok, Antarctica give the same level of CO2 measurements as the measuring devices located on the north slope of Mauna Loa on the island Hawaii which is subject to air pollution from the west coast urban areas of Hawaii.

But the much bigger failing of this presentation is that the total of all greenhouse gases is not given. Of course it is not just CO2 concentration per se which is important. In such a total of all greenhouse gases the concentrations of the various gases, of which water vapor is by far the most important, should be weighted according to their relative effectiveness in absorbing the relevant thermal radiation. A molecule of H2O is 50% more effective in absorbing thermal radiation than a molecule of CO2. I

The concentration of water vapor varies widely over the surface of the Earth, supposedly from 0.04 percent in the deserts to 4 percent in the tropics. But supposedly the average concentration is stable over time. There seems to be a great reluctance to specify what that average concentration of H2O in the air is, but 0.5 of 1 percent would be of the right order of magnitude. That is a concentration of 5000 parts per million. If a molecule of H2O is 50% more effective at absorbing thermal radiation than a molecule of CO2 then the X parts per million of CO2 is equivalent an additional (2/3)X parts per million of water vapor. The record of greenhouse gas (H2O+CO2) concentration, expressed as equivalent H2O concentration, for the period 1996 to 2015 appears as follows.

Although it is inappropriate deal with an average global concentration of H2O the above was presented just to illustrate that the increase in CO2 does not amount to an explosive expansion of the greenhouse effect for the Earth. The concentration of CO2 increased from an estimated 280 parts per million in pre-industrial times to a measured 407 parts per million in 2016. That is an increase of slightly over 45 percent. But in terms total greenhouse gas concentration expressed in terms of equivalent H2O concentration it is an increase from 5187 parts per million to 5271 parts per million; an increase of 1.63 percent over a two century period. This is hardly an explosive increase.

It is to be noted that there were several estimates of the concentration of CO2 in pre-industrial times besides the 280 parts per million and they differed from it substantially. The 280 parts per million figure was selected because it best fit to story that the alarmists wanted to tell. See CO2 history.

However the relationship between greenhouse gas concentration and the proportion of thermal radiation absorbed is nonlinear. The increase due to anthropogenic CO2 depends upon the natural concentration of greenhouse gases. In the graph below, C denotes the natural concentration, primarily of water vapor, which results in some proportion being absorbed. The anthropogenic CO2 increases the concentration of greenhouse gases to D and raises the proportion of thermal radiation absorbed.

In the graph Point A represents a desert condition. Point B represents the condition after CO2 raises the level of greenhouse gas. There is a much bigger impact from A→B than from C→D even though the increase from C to D is as large or larger than the increase from A to B.

The concentration of water vapor in the atmosphere varies greatly around the Earth and therefore the effect of anthropogenic CO2 varies with it. In deserts and the polar regions anthropogenic CO2 may have a substantial effect but almost no effect in the humid regions. This is why such a high proportion of the detected global warming occurred at night in the winter in places like Siberia. The air in the polar regions is as dry as the Sahara. Note that deserts like the Sahara have very little greenhouse gas (water vapor) in the atmosphere above them yet they are quite hot! It is a lack of cloud cover at a latitude of intense solar radiation rather than the greenhouse effect that makes them hot.

The NASA webpage makes the following statement:

There is no question that increased levels of greenhouse gases must cause the Earth to warm in response.

Yes, but the change in the total greenhouse gas concentration cannot be determined by just looking at the concentration of just one minor constituent. A major decline in the H20 concentration can wipe out entirely the effect of increased CO2. NASA did not present a graph of the total weighted concentration of greenhouse gases because they simply do not have it. Despite the public concern about global warming such a key bit of relevant information has not been established.

The second display by the NASA webpage on the evidence of climate change is a super-large quotation from the Intergovernmental Panel on Climate Change (IPCC)

Scientific evidence for the warming of the climate system is unequivocal.

Note that NASA in this is not presenting evidence of climate change. It is presenting another organization's judgement. And that judgement is not about climate change; it is about warming but it does not say "global warming." It says "warming of the climate system." It does not say anything about The magnitude of the warming and whether it is catastrophic or not. The IPCC is not noted for the sagacity of its judgements in matters of global climatology. It was the IPCC that perpetrated the infamous "hockeystick graph" that founded erroneous arithmetic.

The NASA webpage goes on to a major section entitled

The evidence for rapid climate change is compelling.