By the end of the 1990s, average temperatures in Los Angeles had risen to almost 4 degrees Fahrenheit warmer than in the 1940s. This was believed to be due to the dramatic loss of Los Angeles County orchards and farmland in favor of buildings and roads. The increased concrete and asphalt served to absorb more solar heat and heat up the surrounding atmosphere, causing a massive "urban heat island." Studies suggest that a massive planting of trees in the San Fernando Valley alone might lower average temperatures as much as 9 degrees Fahrenheit. After the 1990s, there was a drop in average monthly temperatures, although these continued to be higher than those in the 1940s and have again continued to climb.
|Decade Beginning:||Average Monthly Temperature During Decade|
* Decade through March 2017
Source: Western Regional Climate Center