During the little ice age the earth was significantly colder than today, but there was special factors that led to this: The Maunder solar minimum and two super novas, one discovered in 1572 by Tycho Brave and the other in 1604 by Kepler.
I will beginthe time of industrialization with the invention of the steam engine 1775 by James Watt. While not the original inventor he improved it so much that it became common use for power generation. Up to that time people had depended on water and wind power and in a few cases tidal power. This increased the use of coal, which up to that point had been used exclusively for heating.
Since 1765 the global temperature of the earth has increased by about 1.4C and is expected to increase another tenth of a degree by 2050.
When global temperature increases 1.5 degrees and relative humidity stays the same there will be 10% more water vapor in the air. How much of the temperature rise is attributable to a 10% increase in water vapor?
To answer that we must take a look at the greenhouse effect. Without it the earth would be an ice ball with an average temperature about 33C cooler than today. The earth can be considered a black body that obeys laws for black body radiation, the Stefan–Boltzmann law that states that the total energy radiation is proportional to the fourth power of the absolute temperature (Kelvin), so an increase in global temp from 13C t0 14.5C results in an increase of 2.11% in the total greenhouse effect (a smaller increase in the atmospheric window).
To sum it up: Since water vapor is fundamental I will count it first, and the effect of all the other greenhouse gases will be additional, remembering that the total absorption in any frequency band can never exceed 100% of available energy.The increase of absorption occurs in the atmospheric window, and in some bands of the incoming sunlight in the near infrared region. The bands are 0.7, 0.8, 0.9, 1.1, 1.4 and 1.9 μm. Together, they make up 90% of the greenhouse gas temperature rise, or 29.9 degree C. When global temperatures increase by 1,5 C there will be 10% more water water vapor assuming relative humidity will stay constant, there will be an additional 0.31 C temperature rise.
Total greenhouse effect 33 C, Greenhouse effect from water vapor is 29.9C
Increased water vapor greenhouse effect from 2.11 % increased black body emissions: 0.52C
Increased greenhouse effect from 10 % water vapor increase 0.31C
Len Bilén's blog, a blog about faith, politics and the environment. 