“It may seem impossible to imagine that a technologically advanced society could choose, in essence, to destroy itself, but that is what we are now in the process of doing.”
Climate scientists have been consistently downplaying and underestimating the risks for three main reasons. First, their models tended to ignore the myriad amplifying carbon cycle feedbacks that we now know are kicking in (such as the defrosting tundra).
Second, they never imagined that the nations of the world would completely ignore their warnings, that we would knowingly choose catastrophe. So until recently they hardly ever seriously considered or modeled the do-nothing scenario, which is a tripling (820 ppm) or quadrupling (1100 ppm) of preindustrial levels of carbon dioxide over the next hundred years or so. In the last 2 or 3 years, however, the literature in this area has exploded and the picture it paints is not pretty (see “An Illustrated Guide to the Science of Global Warming Impacts: How We Know Inaction Is the Gravest Threat Humanity Faces“).
Third, as Blakemore (and others) have noted, the overwhelming majority of climate scientists are generally reticent and cautious in stating results — all the more so in this case out of the mistaken fear that an accurate diagnosis would somehow make action less likely. Yes, it’d be like a doctor telling a two-pack-a-day patient with early-stage emphysema that their cough is really not that big a deal, but would they please quit smoking anyway. We live in a world, however, where anyone who tries to explain what the science suggests is likely to happen if we keep doing nothing is attacked as an alarmist by conservatives, disinformers, and their enablers in the media.