Today, when global warming denial and vaccination denial are alarmingly prevalent, it is crucial to understand that throughout history, science denial at the state level has cost scores of millions of lives. In the Soviet Union under Stalin, Lysenko's denial of genetics led to disastrous agricultural policies, resulting in the persecution and execution of dissenting scientists and widespread famine. A similar tragedy unfolded in Mao's China, where the wholesale adoption of Lysenkoism contributed to a famine that claimed an estimated 45 million lives. In Germany starting in the 1930s, Adolf Hitler made state policy of Nazi eugenics, a twisted theory which held that some races are superior to others. This led first to the murder of disabled persons, including children, and then to the smoking chimneys of the Holocaust. President Mbeki of South Africa conducted his own internet research and rejected a virtually unanimous scientific consensus to conclude that HIV does not cause AIDS and that folk remedies are preferable to anti-retroviral drugs, costing an estimated 330,000 deaths. In this century, in Brazil and the United States, Presidents Jair Bolsonaro and Donald Trump rejected medical advice to downplay the danger of the COVID-19 virus and discourage protective measures, causing many unnecessary deaths. The two of them and today's Republican party reject the consensus among scientists that manmade global warming is true, thus choosing to deny and ignore the greatest threat that humanity has ever faced. Doomsday has not yet arrived, but we can see it from here and time is running out.