Detailed measurements show that the average temperature of the Earth is increasing. Glaciers and snow pack are melting, while ice melt in the Arctic increases the extent of open water during the summer months, a process which may produce significant climate change over time. Sea levels are undergoing a modest thermal expansion as surface temperatures increase. Organisms large and small are on the move to adjust to climate changes already underway.
Many claim that warming of the Earth is due primarily to burning of fossil fuels, a process which has notably increased since the beginning of the Industrial Revolution. Slightly more than a century ago, Svante Arrhenius suggested that atmospheric carbon dioxide was a major reason for the warming of the Earth. Indeed, he calculated that without carbon dioxide in the atmosphere, the Earth would be much cooler (by about 60 degrees Fahrenheit), and not nearly as receptive to humans and other living creatures. He also noted that a doubling of carbon dioxide concentrations from about 300 to 600 parts per million would be expected to increase atmospheric temperatures about 4-5 degrees centigrade. However, as the Industrial Revolution was, in a sense just getting up a full head of steam, he vastly underestimated how long it would take to double atmospheric concentrations of carbon dioxide. He estimated it would take thousands of years–yet after just a little over a century we are a little over a third of the way there.
Of course, we’ve been adding carbon dioxide to the atmosphere first by burning wood, and then for most of the Industrial revolution we burned coal and later oil, but oil did not take over from coal until 1951. But still, to this day, considerable coal continues to be burned. Aerosol pollution in the form of particulates from coal produces smog, dust and many contaminants that have a cooling effect. These may have had the most pronounced effect just as coal burning was reduced to an extent in favor of oil. From 1945 to 1968 mean global temperatures appear to have dropped by about 0.5 degrees Fahrenheit. This cooling trend has stopped and in the last 30 years more significant warming has occurred. While we still burn coal and oil, we also burn natural gas, and increasingly generate power and warmth from renewable forms of energy: wind, solar, geothermal, and nuclear. Still, carbon dioxide levels increase while global warming continues apparently unabated.
A modern understanding of thermal physics tends to deny altogether the idea of a global warming as a greenhouse effect associated with carbon dioxide or any other so-called greenhouse gas. Modern ideas about the trapping of heat and atmospheric physics were not available to Arrhenius, and in retrospect his analysis is rendered suspect even though elevated surface temperatures on the Earth for the past hundred years or so have been approximately in line with is predictions. If not a carbon dioxide greenhouse effect, what then?
With the gradual conversion of coal to oil and natural gas, and with increasing attention to renewable forms of energy, particulates are not being added to the atmosphere at the same rate even while carbon dioxide concentrations are not yet diminishing. Thus, provided there are no major continuing volcanic eruptions adding significant cooling aerosols to the atmosphere warming may continue even though we may gradually replace coal with a combination of oil, natural gas and renewable sources of energy. Subsequently, if we should replace oil and gas with renewable forms of energy and actually begin to observe reductions in atmospheric carbon dioxide while still observing global warming, we shall have to conclude that the Earth is in a warming trend we do not understand.
Not withstanding this possibility we should continue on the path to ridding ourselves of dependence on fossil fuels. We are running low. Indeed, various estimates have us running out of easily extracted fossil fuel reserves over the next century or two. Clearly as we get closer and closer to the end of fossil fuels, we either have to extract from newly discovered sources or mine those last few remaining very difficult sources and sell them to users at perhaps 100 time current costs. No one will be pleased to pay the freight.
In addition, oil and coal products are currently used as starting materials for the synthesis of many drugs, important fine chemicals as well as for making materials for textiles, rubber & polymers, fertilizers and many chemical processes. Many of these uses can likely be replaced with alternative natural non-petroleum natural products, but it might be a better idea to save the last billion or so barrels of petroleum until replacement strategies are perfected.