Dr. Volkmar said it is possible there was in fact an increase in the rate of autism over the long run, because of changes over time such as a greater prevalence of older fathers contributing sperm with small genetic abnormalities.
In 2003 Hansen wrote a widely distributed (but not peer reviewed) paper called Can We Defuse the Global Warming Time Bomb? in which he argues that human-caused forcings on the climate are now greater than the natural ones, and that this, over a longtime period, can cause large climate changes.