Making Temperature Count

Global Historical Climatology Network

Number of active temperature stations over time

Global Historical Climatology Network

Present-day global coverage of temperature stations

Galileo made one of the earliest attempts to invent a thermometer in the 1500s. But it was Daniel Fahrenheit, in 1714, who invented the first mercury thermometer. The introduction of a scientific instrument meant temperature could be measured and quantified with a number to tell us more accurately just how much warming or cooling is occurring.

Our confidence in the calculation of Earth’s temperature really begins to grow in the mid 1800s when networks of weather stations started to develop, taking systematic and more reliable measurements over about 80 percent of the planet’s surface. This is considered the beginning of the modern instrumental record.

Another leap forward came in the 1960s with NASA launching satellites into space that carried advanced instruments to collect even more global measurements, marking the beginning of a new era of space observations of Earth. We now have more than 50 years of satellite instrument measurements of global land and ocean temperatures. Millions of ocean temperature measurements are also collected from ships and buoys that measure sea surface temperature (SST).

Space-based instruments and thousands of ground stations form massive global networks that collect billions of continuous measurements about our planet’s temperature. From the modern instrumental record of temperature spanning more than 150 years, GISS scientists created one of the world's best sources for global temperature data, GISTEMP. Today, GISS scientists and scientists around the world use this data set, and many others that tell us about Earth's climate vital signs to piece together the temperature puzzle. We now have a definitive answer to one of the most fiercely debated science questions of our time – Are human activities changing Earth’s climate? Yes.

There’s always an interest in the annual temperature numbers and on a given year’s ranking, but usually that misses the point... But when we average temperature over five or ten years to minimize that variability, we find that global warming is continuing unabated. James Hansen, GISS Director