Where there are cold or warm ocean currents and the winds blow onshore, temperatures may be unusually moderate for the latitude. For example, San Francisco has a cold current offshore in summer and is colder in July than Vancouver, Canada, a thousand miles north. London, England is warmer in winter than Newfoundland at the same latitude because onshore winds pass over the Gulf Stream Drift, a warm current. Places at high elevations are generally colder than low elevations because the atmosphere is heated from below and there are fewer heat-absorbing gases at higher altitudes to absorb the earth s radiation. This is called the environmental lapse rate .
Cities are usually warmer than the surrounding countryside winter and summer, and day and night.
Cities form heat islands due to increased carbon dioxide, artificial energy, heat retentive masonry, reduced transpiration and greater surface area. They are also cloudier and foggier due to the amount of dust in the air. Global climate is impacted by the same factors. Worldwide temperatures have been rising which suggests a global warming . The positions of the isotherms are influenced by latitude, winds, ocean currents, distribution of land and sea, and altitude.