6+ statements summarizing why the vast majority of climate scientists think human burning of fossil fuels is causing contemporary global warming. (1/10) #SJSU #Metr12 #GlobalWarming
1) Fundamental physics tells us that increasing greenhouse gas concentrations in the atmosphere should warm the surface, all else equal. This is so fundamental that the greenhouse effect was 1st proposed way back in 1824 (by Joseph Fourier). (2/10)
2) Through burning fossil fuels, humans have increased the concentrations of greenhouse gasses in the atmosphere. CO2 concentrations were nearly constant for thousands of years but have increased by almost 50% since the industrial revolution. (3/10)
3) We have observed an increase in global average surface temperature in line with what we would expect given the increase in greenhouse gas concentrations and the 1st law of thermodynamics (and also considering negative forcings from e.g., sulfate aerosols). (4/10)
4) The spatial uniformity of the warming is what we would expect from a spatially uniform forcing like increases in the concentrations of well-mixed greenhouse gasses like CO2. (5/10)
5) We can directly measure the enhanced greenhouse effect through satellite observations of reduced outgoing longwave radiation at wavelengths absorbed by CO2 and through observed increases in longwave “back radiation” at the surface. (6/10)
6) There is no satisfactory natural explanation for the observed warming. (7/10)
6.1) Many previous climate changes were actually affected by CO2 changes but the causes themselves (e.g., changes in the Earth’s orbit) are too slow to be responsible for pronounced warming on decade to century timescales. (8/10)
6.2) Changes in volcanic activity (via changes in stratospheric sulfate aerosol concentration) and changes in incoming solar radiation can indeed cause global temperature change on decade to century timescales but ... (9/10)
...these natural climate forcings have not been changing in a way that would explain contemporary warming. If anything, solar radiation changes and volcanic activity changes should have caused cooling in recent decades when warming has been observed. (10/10)
