Changes

Average [[Earth]] surface air temperature has risen about 1° F since 1970.  

Average [[Earth]] surface air temperature has risen about 1° F since 1970.  

<ref>Hansen's group at the Goddard Institute wrote, "Global warming is now 0.6&nbsp;°C [1.0&nbsp;°F] in the past three decades and 0.8&nbsp;°C [1.4&nbsp;°F] in the past century." http://data.giss.nasa.gov/gistemp/2005/</ref> How much of this is due to contamination of the temperature record from the [[urban heat island]] effect is hard to assess.  Efforts are currently underway to detect and remove this bias. Spurious warming trends that might be considered as global warming can occur almost anywhere. <ref name="col">http://climatesci.colorado.edu/2006/01/29/do-urban-areas-have-larger-long-term-temperature-trends-than-other-locations/feed/</ref>

<ref>Hansen's group at the Goddard Institute wrote, "Global warming is now 0.6&nbsp;°C [1.0&nbsp;°F] in the past three decades and 0.8&nbsp;°C [1.4&nbsp;°F] in the past century." http://data.giss.nasa.gov/gistemp/2005/</ref> How much of this is due to contamination of the temperature record from the [[urban heat island]] effect is hard to assess.  Efforts are currently underway to detect and remove this bias; however, it seems unlikely that this effect has a significant, or even moderate effect on the statistics quoted by environmentalists<ref>http://gristmill.grist.org/story/2006/10/26/224634/48</ref>. Spurious warming trends that might be considered as global warming can occur almost anywhere. <ref name="col">http://climatesci.colorado.edu/2006/01/29/do-urban-areas-have-larger-long-term-temperature-trends-than-other-locations/feed/</ref>

Nonetheless, controversy has persisted over the influence of urban warming on reported large-scale surface-air temperature trends. <ref name="col" />

Nonetheless, controversy has persisted over the influence of urban warming on reported large-scale surface-air temperature trends. <ref name="col" />