Hot Summer, Maybe the Hottest

Global Land-Ocean Temperature Index

The July 2010 global map of surfacetemperature anomalies was more than 10°F warmer than climatology in theeastern European region including Moscow. There was an area in easternAsia that was similarly unusually hot. The eastern part of the UnitedStates was unusually warm, although not to the degree of the hot spotsin Eurasia.

There were also substantial areas cooler than climatology, including a region in central Asia and the southern part of South America. Theemerging La Niña is now moderately strong, as evidenced by the regioncooler than climatology along the equator in the eastern and centralPacific Ocean. The global average July 2010 temperature was 0.55°Cwarmer than climatology in the GISS analysis, which puts 2010 inpractically a three way tie for third warmest July. July 1998 was thewarmest in the GISS analysis, at 0.68°C.

The 12-month running mean of global temperature achieved a recordhigh level during the past few months. Because the current La Niña willcontinue at least several months, and likely strengthen somewhat, the12-month running mean temperature is expected to decline during thesecond half of 2010.

Climatology Temperature Anomalies


The first seven months 2010 is warmer than prior warm years. Thedifference of +0.08°C compared with 2005, the prior warmest year, islarge enough that 2010 is likely, but not certain, to be the warmestyear in the GISS record. However, because of the cooling effect of LaNiña in the remainder of the year, there is a strong possibility thatthe 2005 and 2010 global temperatures will be sufficiently close thatthey will be practically indistinguishable.

Climate anomalies in the Northern Hemisphere summer of 2010,including the heat in Eastern Europe and unusually heavy rainfall andfloods in several regions, have received much attention. Are theseclimate anomalies an example of what we can expect global warming tolook like? Maps of temperature anomalies, such as Figure 1, are usefulfor helping people understand the role of global warming in extremeevents.

The location of extreme events in any particular month depends onspecific weather patterns, which are unpredictable except on short timescales. The weather patterns next summer will be different than thisyear. It could be a cooler than average summer in Moscow in 2011.

What we can say is that global warming has an effect on theprobability and intensity of extreme events. This is true forprecipitation as well as temperature, because the amount of water vaporthat the air carries is a strong function of temperature. So thefrequency of extremely heavy rain and floods increases as global warming increases. But at times and places of drought, global warming canincrease the extremity of temperature and associated events such asforest fires.

The paper describing the GISS analysis of global temperature has been revised in response to reviewer suggestions and has been accepted forpublication in Reviews of Geophysics. The biggest change in the paper is inclusion of an additional analysis is which global temperature changeis based only on stations located in “pitch dark” regions, i.e., regions with satellite-observed brightness below the satellite’s detectionlimit (1 ?W/m2/sr/?m). Our standard analysis uses stations withsatellite-observed brightness below 32 ?W/m2/sr/?m. This more strictbrightness limitation has no significant effect on analyzed globaltemperature change, providing additional confirmation that any urbaneffect on the GISS analysis of global temperature change is small.


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