A: Yes, it is an unequivocal fact that the Earth’s average temperature continues to rise, despite some natural year-to-year fluctuations. Each of the past several decades has been substantially warmer than the decade prior to it. The hottest five years on record are the last five years, 2014-2018.
All analyses of all surface temperature data sets compiled by major climate centers around the world show a clear warming trend. Besides these thousands of thermometer readings from weather stations around the world, there are many other clear indicators of global warming such as rising ocean temperatures, sea level, and atmospheric humidity, and declining snow cover, glacier mass, and sea ice.
Because temperatures vary from year to year, scientists measure trends in running averages and analyze trends over decades rather than expecting every year to be hotter than the previous year. Some years have particular factors that make them hotter than those just before and after. For example, a major El Niño event combined with the persistent rise in heat-trapping gases made 1998 one of the hottest years on record. That has caused some people to claim that Earth has been “cooling” since then. But as the data clearly show, this claim is false.
One common misunderstanding about climate is the difference between short-term noise and long-term signal. The animation below shows how the same temperature data that is used to determine the long-term global warming trend can be used inappropriately to “cherrypick” short time periods that show a cooling trend simply because the endpoints are chosen to mislead. (Source: Skeptical Science)