evidence: Other scientists, starting in the 19th century, had already demonstrated that carbon dioxide was what we now call a "greenhouse gas". By the 1950s, scientists were predicting warming of several degrees from the burning of fossil fuels. In 1972 John Sawyer, the head of research at the UK Meteorological Office, wrote a four-page paper published in Nature summarising what was known at the time, and predicting warming of about 0.6°C by the end of the 20th century. [...] In this case, their very specific prediction was that warming of between 1.5°C and 4.5°C would accompany a doubling of atmospheric CO₂. At the time, global temperatures, in the absence of their hypothesis and science, might have been expected to stay pretty much the same over the ensuing 40 years, cooled a bit, possibly even cooled a lot, or warmed a lot (or a little). In the absence of global warming science any of these outcomes could have been feasible, so their very specific prediction made for a very stringent test of their science.