The world average air temperature has been basically rising in this one hundred and several ten years (Fig. 1). The temperature rise looks stagnated between 1945 and 1964. The difference before and after the stagnation (between lines A and B) is approx. 0.5K. The stagnation is neither well simulated in IPCC AR4 (2008) nor explained by solar activity which showed a maximum around 1950. There is no giant eruptions in this period.
Fig. 1 Temperature anomaly by NASA (2009) between 1880 and 2008 with the biggest eruptions whose VEI (volcanic explosivity index) is 6 (Wikipedia, "VEI") and TNT equivalent mass (Wikipedia Ja, "Nuclear Weapons Testing") of nuclear explosions (only historic known ones).
It can be noted that the stagnation began with the atomic bomb attacks against Nagasaki and Hiroshima in 1945 and lasted for the period in which the succeeding atmospheric nuclear weapons testing were carried out. It began to rise again at the almost the same rate soon after PTBT (Partial Test Ban Treaty) prohibited atmospheric nuclear weapons testing in 1963. Hishida (2001) also pointed out that the bombing in World War II and atmospheric nuclear testing might have influenced the regime shift between 1940 and 1975. However, the author would like to concentrate on the stagnation in air temperature between 1945 and 1964 and the atmospheric nuclear explosions.
It is well known that nuclear wars can induce "nuclear winter" (Ehrlich et al., 1985). The smoke from nuclear war can reach the upper troposphere and rapidly spread with the jet streams. It can also reach the stratosphere to stay there for several months to years reflecting insolation. Temperature drop for a 3000 Mt nuclear war without smoke from cities is 10K and lasts for approx. a year in the simulation (Ehrlich et al., 1985). On the other hand, temperature drop for a 100 Mt nuclear war with smoke from cities is simulated as 32K and lasts for several months. The climate model used in Ehrlich et al. (1985) was a simple one. However, recently, Robock et al. (2007) obtained similar results for only cases with smoke from cities by using a modern climate model. Temperature drop by Nagasaki, Hiroshima and the 423 times nuclear weapons testing of total 545 Mt is estimated as between 0.11K and 1.3K based on Ehrlich et al. (1985) and Robock et al. (2007). The 0.5K stagnation is in this estimated range.
Ehrlich et al. (1985) also pointed out the possibility of nuclear summer which is gradual global warming by CO2 concentration increase after the temporary nuclear winter. There is a possibility that we are suffering a petit nuclear summer if the stagnation was a petit nuclear winter. Those countries which have responsibilities on the atmospheric nuclear explosions should recognize that they might have significantly influenced the world climate. It can also be pointed out that there is a possibility that human beings can control and lower air temperature by, for example, sprinkling detoxified fly ash by transport planes in the upper troposphere and the stratosphere. Deliberate considerations are required before the execution of course.
Extended Abstract (376K)