The physics of greenhouse gases support the hypothesis that a significant part of that warming is anthropogenic, though attempting to parse the proportions gets one into the deep weeds.
Without question, industrialization has increased carbon-dioxide emissions—but are human emissions significant enough to accelerate warming?
Have they already done so?
Both the Earth’s average temperature and global carbon-dioxide emissions increased during the twentieth century.
But what should we make of research showing recent warming on Mars and Pluto, planets without power plants or automobiles?
Is planetary warming simply a natural cycle?
According to David J. C. MacKay, the burning of fossil fuels sends seven gigatons (only 3.27 percent) of
carbon dioxide into the atmosphere each year, while the biosphere and oceans account for 440 (55.28 percent) and 330 (41.46 percent) gigatons, respectively. (David John Cameron MacKay, FRS FInstP FICE, is the Regius Professor of Engineering in the Department of Engineering at the University of Cambridge and from 2009 to 2014 was Chief Scientific Adviser to the UK Department of Energy and Climate Change.)
Just how much of the "Greenhouse Effect" is caused by human activity? (All greenhouse gases, not just CO2.)
It is about 0.28%, if water vapor is taken into account-- about 5.53%, if not.
This point is so crucial to the debate over global warming that how water vapor is or isn't factored into an analysis of Earth's greenhouse gases makes the difference between describing a significant human contribution to the greenhouse effect, or a negligible one.
Water vapor constitutes Earth's most significant greenhouse gas, accounting for about 95% of Earth's greenhouse effect. Interestingly, many "facts and figures' regarding global warming completely ignore the powerful effects of water vapor in the greenhouse system, carelessly (perhaps, deliberately) overstating human impacts as much as 20-fold.
Water vapor is 99.999% of natural origin. Other atmospheric greenhouse gases, carbon dioxide (CO2), methane (CH4), nitrous oxide (N2O), and miscellaneous other gases (CFC's, etc.), are also mostly of natural origin (except for the latter, which is mostly anthropogenic).
Human activities contribute slightly to greenhouse gas concentrations through farming, manufacturing, power generation, and transportation. However, these emissions are so dwarfed in comparison to emissions from natural sources we can do nothing about, that even the most costly efforts to limit human emissions would have an undetectable effect on global climate. (Department of Environmental and Geographical Sciences, Manchester Metropolitan University, Manchester, United Kingdom)
