The following represents an effort to summarize the consensus emerging from climate science that identifies our current understanding of that science in 12 points.
- Much of the incoming radiation from the sun (particularly short-wave radiation) passes through the atmosphere to reach the Earth’s surface. Upon reaching the earth’s surface, this radiation transforms into longer wave infra-red radiation (heat) which radiates outwards. Some of this outwardly radiating heat energy is trapped by gases in the atmosphere thus causing warming that, absent these gases, otherwise would not occur.
- The properties of atmospheric gases in terms of retaining outwardly radiating heat was initially described nearly 200 years ago and has been elucidated and confirmed since.
- Without these gases, the earth’s atmospheric temperature would average about 0°F or -18°C and the planet would be largely uninhabitable for humans.
- The atmospheric gases responsible for retaining this outwardly radiating heat are primarily the naturally occurring gases carbon dioxide, methane, water vapor, and nitrous oxide augmented by man-made gases with a fluorocarbon base (chlorofluorocarbons, hydrochlorofluorocarbons, perfluorocarbons and sulfur hexafluoride, for example).
- When the Global Warming Potential (GWP – also designated the carbon dioxide equivalent CO2e) of carbon dioxide is designated as 1, the other gases have a greater capacity to absorb heat energy, when compared to an equal weight of carbon dioxide. Because it is short-lived in the atmosphere, methane is assigned a 20-year GWP of 86 in addition to the more standard 100-year GWP, which is 34. Meanwhile, nitrous oxide has a 100-year GWP of 298, CF4 is over 7,000, CFC – 11 is over 5,000, and HFC – 134a is assigned 15,500).
- While some of the outwardly radiating heat that is retained on Earth and contributes to warming of the atmosphere, by far the majority (in fact, 93.4%) increases the heat energy content of the oceans while only 2.3% (1/40th of that retained by oceans) warms the atmosphere. Indeed, if it were not for the capacity of the oceans to absorb vast amounts of this heat energy, the average global lower atmospheric temperature could be as much as 122°F – over 60°F warmer than 2019 global average of 58.7°F – the second hottest year on record.
- Since the industrial revolution, when fossil fuels were introduced into industry to be burned to drive machines, but also as a result of human-induced land transformation, greenhouse gas emissions have increased. Prior to the industrial revolution the atmospheric carbon dioxide equivalent concentration of these gases was about 285 parts per million (ppm), the same as the carbon dioxide concentration since the other gases contributed only a trivial amount. The atmospheric carbon dioxide equivalent has since risen to nearly 500 ppm (a rise of 215 ppm). Among the greenhouse gases, carbon dioxide contributes about 65% of the warming while the other gases contribute the remaining 35%. This explains why it is crucial that we reduce emissions of all greenhouse gases not just carbon dioxide.
- From the beginning of the industrial revolution to now, the average global temperature has risen about 1°C (1.8°F).
- To test the credibility of climate models, they have been run over the history for which we have temperature data – meaning from the late 1800s. Climate models applied to the historical global warming trend produce a curve very similar to that actually experienced when human-induced greenhouse gas emissions are included, but produce a trend much lower than actually observed when human emissions are excluded. This test of the credibility of climate models suggests that they produce values closely resembling what we have historically seen, and are thus credible as projections for future conditions.
- Although the models simulate historical temperature very closely, rather than producing projections that exaggerate the global warming trends and other consequences of warming, we find the actual historic trends fall either at the extreme high end of projections or the severity of actual patterns was slightly underestimated by the model projections.
- Rather than following the projections of models that are based on assumptions that we limit the trend of increasing greenhouse gas emissions, actual warming has continued at the high end of the so-called ‘worst case scenario (Representative Concentration Pathway or RCP 8.5) set of projections where it is assumed no efforts are undertaken to reduce emissions.
- This pattern, if followed, would result in global warming of some 4°C (7.2°F) by 2100 and if continued through 2300, warming of 8°C (14.4°F) compared to the 1986-2005 global average.
Global warming of the dimensions projected on item 12 which assume we follow the RCP 8.5 trend, would induce climate changes sufficient to destroy natural ecosystems across the planet, and totally undermine our agriculture, forestry and fisheries long before 2300, possibly by 2100.
Those who do not accept the climate science consensus regarding global warming and its climate change consequences, have a huge body of science to challenge. However, what is clear is that not everyone balks at the same conclusion emerging from climate scientists. One approach when communicating with climate consensus skeptics is to identify where, in the following sequence, they break from the current climate consensus: