When was weather first recorded

The dates and times had to be recalculated, since the old Florentine calendar began March 25 instead of January 1, and days started at twilight rather than midnight. Temperatures also had to be adapted from the Galileo scale used at the time to the Celsius scale. And there were other changes to consider: deforestation around weather stations, the construction of asphalt roads and buildings. A study showed that this switch in methodology exaggerated the global temperature dip seen in the s.

Temperatures have been officially recorded in almost all regions of the world since the early 20th century. By the s, records from individual temperature stations around the globe numbered in the millions. But using these records to unearth any long-term global trends involves pooling several different data sets, collected with very different methodologies across wide expanses of time and space. Unavoidably, there are gaps.

In some cases, technological breakthroughs have made it impossible to directly compare readings separated by a few decades. And temperature records from many places are scattered and fragmented: Historical events often disrupt data collection during World War II, for example, recordings from Pacific Island thermometers dropped sharply , and some areas have sparser coverage than others.

The England and Wales Precipitation series, which measures rainfall and snow, goes back to , and the Central England Temperature series, which covers the temperature from the south Midlands to Lancashire, is the longest-running record in the world, dating from Many don't just record the weather, they also record the effects on wildlife and plants.

It takes years to quality-control them and put the data on to a computer. Statisticians work out whether the entries are reliable, which is why the record going back to - when observation stations became more uniform in the way they collected data - is almost always the one used.

Temperature data showing rapid warming in the past few decades, the latest data going up to According to NASA, and are tied for the hottest year since , continuing a long-term trend of rising global temperatures.

The 10 hottest years in the year record have occurred since , with the seven most recent years being the hottest.