Dr. James Hansen
Climate models indicate that an El Nino, probably a weak one, will begin this (Northern Hemisphere) winter and observations show that warming in the tropical Pacific has begun. Current global temperature (12-month running-mean) has thus reached its minimum and will begin to rise during the next few months. The global temperature minima associated with La Ninas are more uniform in depth than El Nino maxima. This provides an excellent opportunity to check whether the global warming rate is accelerating.
Global temperature appears to increase almost linearly over the past fifty years (green line on graph); the 1970-to-present rate of change is 0.17°C per decade. Investment strategist, Jeremy Grantham, pointed out that the rate of warming inferred by connecting the peak temperatures of the last two El Nino maxima (0.21°C per decade, see graph) exceeds this longer term rate, and he infers that global warming is accelerating. La Nina minima probably provide a better estimate, and they provide a more recent rate. As the figure shows, the most recent two La Ninas imply a warming rate of 0.38°C per decade, at least double the longer term rate! Acceleration is predicted by climate models for continued high fossil fuel emissions as a result of amplifying climate feedbacks and is a cause for concern. We expect global temperature to rise in the next few months and confirm that the global warming rate has accelerated.
Read more at http://www.columbia.edu/~jeh1/.
James Hansen, former director of the NASA Goddard Institute for Space Studies, is director of the Climate Science, Awareness and Solutions program at the Columbia University Earth Institute.