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The atmospheric temperature discussed as
dangerous has been common in many parts of
the earth for many years and is not nearly
new. The real threat discussed is from
heavy consideration of

"business-as-usual RCP8.5 emissions
scenario"

and that is based on climate models
evaluating the future, 2050+, effects of
human sources of CO2 on temperature and
climate.

We have a long history of such models.
Apparently they are usually based on the
fact that CO2 is a greenhouse gas.

The main question about CO2 is how much
warming will be caused by a given quantity
of CO2 from human activities.

Yes, CO2 is a greenhouse gas, but maybe
surprisingly so far from either
observations or models, we have no
credible evidence that human sources of
CO2 have caused, are causing, or will
cause significant warming.

Okay, let's look at the observational
data:

There was a movie, An Inconvenient
Truth. With data from Antarctic ice
cores, the movie showed, for the
atmosphere, a graph of temperature and CO2
concentrations going back about 800,000
years.

As I watched the movie, it appeared that
the claim was that the graph showed
temperature and CO2 concentrations going
up and down together. Then the movie
concluded that the higher concentrations
of CO2 caused the higher temperatures.
Then there was a claim that currently more
CO2 from human activities would rapidly
cause significantly higher temperatures.

But, we could look at that graph more
closely, and doing that we will see three
situations:

(1) When temperature started to increase,
CO2 (concentration, here and below) was
low, not high. So, something caused the
warming, but it was not high CO2.

(2) About 800 years later, CO2 had
increased. Presumably the cause was more
biological activity from the higher
temperatures.

(3) Some thousands of years later, while
CO2 was high, the temperatures fell again.
There was a cause, but it was not low CO2.
Indeed, the high CO2 did not keep
temperatures from falling.

Net, from that 800,000 years of data,
there is no evidence that high CO2 caused
high temperatures. It would be more
accurate (though of course still wrong) to
say that the data supported that CO2
caused LOWER temperatures.

For some more recent data, there was some
significant warming during the time of the
Roman Empire and during the Medieval Warm
Period, and there is no evidence that the
cause was high CO2. There was some
significant cooling during the Little Ice
Age from roughly 1300 to 1900, but there
is no evidence that the cause was low CO2.
There was some cooling from 1940 to 1970
and concerns in the media about another
ice age, and those years were when there
was more CO2 from human activity from WWII
and the post-war economic boom. So, in
those years, with more CO2, we got some
cooling instead of warming.

Again it would be more accurate (though of
course still wrong) to say that the data
supported that CO2 caused COOLING.

For some details, can start with "Global
Cooling" at

https://en.wikipedia.org/wiki/Global_cooling#1974_Time_magaz...

which discusses the two famous magazine
stories, the 1974 <i>Time</i> story and
the 1975 <i>Newsweek</i> story, worrying
about "global cooling" and asking if we
were entering a new ice age. For more on
these magazine stories, at

https://longreads.com/2017/04/13/in-1975-newsweek-predicted-...

can see the April 28, 1975,
<i>Newsweek</i> article “The Cooling
World”.

So, net, there is no data on temperature
and CO2 from the past that says that CO2
will cause warming.

Yes, CO2 is a <i>greenhouse</i> gas. This
means that it absorbs some light in the
infrared but not the visible. In the case
of CO2, it absorbs light out in the
infrared in three narrow bands. The
absorption spectrum is given at

https://webbook.nist.gov/cgi/cbook.cgi?Spec=C124389&Index=0&...

Part of the mechanism is Planck black body
radiation.

We have had some warming since the Little
Ice Age. It may be that we are still
pulling out of the Little Ice Age, e.g.,
it can take a long time for the oceans to
warm up. But even with this warming, it's
cooler than in the Medieval Warm period
and the Roman times when the polar bears
didn't go extinct, the ice in Greenland
and the Antarctic didn't melt, the oceans
didn't rise and flood the coasts, and
apparently humans didn't suffer.
Apparently the main effects were greater
agricultural productivity, e.g., in
England, grapes were grown for wine.

Could the warming since the Little Ice Age
be due to CO2? No: The warming is at the
surface, and CO2 absorbs high in the
troposphere with definition at Google:

<blockquote>the lowest region of the
atmosphere, extending from the earth's
surface to a height of about 3.7–6.2 miles
(6–10 km), which is the lower boundary of
the stratosphere. </blockquote>

which, from MIT climate scientist Richard
Lindzen, Alfred P Sloan Professor of
Atmospheric Sciences, Emeritus, at
Massachusetts Institute of Technology, has
gotten cooler, not warmer.

Several attempts were made to model the
atmosphere and calculate and predict the
effects of human sources of CO2 on
temperature. Nearly all the efforts
predicted temperature increases that were
rapid and significant.

It has now been some years since the times
of the predictions, and the predictions
and reality are compared in the graph at

http://www.energyadvocate.com/gc1.jpg

Summary: Nearly all the predictions were
way too high.

Science: So, so far climate modeling has
no predictive value and, thus, is not good
science.

Result: The predictions have no
meaningful credibility.

Current Summary: There is no credible
evidence from either the 800,000 years of
the earth or the climate models that human
sources of CO2 have had, are having, or
will have significant effects on
temperature or climate.

As a result of this lack of evidence,
there is no scientific reason to attempt
to lower human sources of CO2.