There has been a definite, palpable impact on the Earth’s climate by global warming. The unusual high frequency of heatwaves indicate that there has to be a human influence. As much of the USA sizzles through another scorching summer and the Midwest endures a historic drought, NASA’s climatologist James Hansen states that the future he predicted in 1988 has finally arrived.
Hansen and his colleagues have published a paper entitled Perceptions of Climate Change in the journal PNAS. They used seasonal temperature records form 1951-80, which was a relatively stable period, as a baseline. Then, they analyzed the frequency and scale of subsequent temperature anomalies. They conclude that on average, the Earth’s temperature has warmed by 0.5-0.6 °C. Since then, the shift has impacted many parts of the world. Extremely hot summers, with a 3.5°C warmer temperature, have affected 10% of the world since 2006, which is an order of magnitude higher than the period of 1951-80.
The likelihood that these events would have occurred without global warming is minuscule, states Hansen. The study is purely statistical and doesn’t try to explain how climate changes have affected extremely hot summers. It should help people understand global warming and the profound effect humans have on the climate system, states Kevin Trenberth, a climatologist at the US National Center for Atmospheric Research in Boulder, Colorado.
Reference: “Perception of climate change” by James Hansen, Makiko Sato and Reto Ruedy, 6 August 2012, Proceedings of the National Academy of Sciences.