The UN Intergovernmental Panel on Climate Change (IPCC) has been making highly confident statements since the late 1980s.
They tell us that man made carbon dioxide (CO2) is the chief cause of the global warming trend since 1975.
The current level of atmospheric CO2 is about 400 parts per million by volume (ppmv), or 0.040 % by volume of the atmosphere, and in 1900 was about 300 ppmv.
Earth receives about 342 watts per square meter (W/m2) of incoming solar energy.
All of this incoming solar energy eventually finds its way back out into space.
CO2 and other greenhouse gasses, mostly water vapor, absorb some of the outgoing infrared energy and warm the atmosphere.
This is called the greenhouse effect.
Without it, Earth’s average surface temperature would a very cold -19°C (-2.2 F) -- with it, the surface warms to about +14°C (+57 F).
All the man made greenhouse gasses added to the atmosphere since 1900, including CO2, add up to only an extra 2.7 W/m2 of energy absorption by the atmosphere.
The minor greenhouse warming produced by CO2 is said to cause additional “enhanced water vapor feedback”.
The unproven claim is that as CO2 warms the atmosphere, more water vapor is produced.
The extra water vapor amplifies the warming caused by CO2 alone, by up to three times.
There is no scientific evidence, however, that enhanced water vapor feedback has ever happened in the past, or will ever happen in the future.
The average energy impact of clouds on Earth climate is about -27.6 W/m2
That means ±10% error produces almost ±2.8 W/m2 uncertainty in GCM climate projections.
This uncertainty for clouds is slightly more than 100% of the alleged changes caused by adding man made greenhouse gasses to the atmosphere!
After 100 years, the accumulated physical cloud uncertainty in temperature is ±111 degrees!
General Circulation Models are used to project the global average temperature.
The resolution limits of the GCMs is huge compared to what they are trying to project.
The error due to uncertainties in greenhouse gas effects add up too (~1% for CO2, ~10% for methane, ~5% for nitrous oxide).
Small uncertainties expand during 100 years of climate projections.
After 100 years, the uncertainty in predicted global average temperature is ±17 degrees, just from uncertainties about the effects of the three man made greenhouse gasses.
The rapid growth of uncertainty means that Earth 100 years in the future is a mystery -- the planet could be a winter wonderland, or a tropical paradise.
No one knows which, because climate change physics are not well understood.
GCMs have “parameters,” which are guesses of how certain climate processes work.
There are dozens of parameters, and up to one million variables.
No one has ever assessed the reliability of a GCM by adding up all parameter uncertainties.
That type of analysis is required in other (real) physical sciences.
Apparently not required in modern climate "science" !
In the ever changing climate on Earth:
(1) The causes of past warming and cooling are still guesses, and
(2) The future climate is impossible to predict.
People who pontificate about "climate change", while ignoring (1) and (2), are committing the biggest hoax in history.