Climate researchers can now detect the fingerprint of global warming in daily weather observations at the global scale.

In October this year, weather researchers in Utah measured the lowest temperature ever recorded in the month of October in the US (excluding Alaska): -37.1°C (-34.78°F). The previous low-temperature record for October was -35°C (-31°F), and people wondered what had happened to climate change.

Until now, climate researchers have said that climate is not the same thing as weather. Climate is what we expect in the long term, whereas weather is what we get in the short term. Since local weather conditions are highly variable, it can be very cold in one location for a short time despite long-term global warming. In short, the variability of local weather masks long-term trends in global climate.

Now, however, a group led by Reto Knutti, a professor in the environmental systems sciences department at ETH Zurich, has conducted a new analysis of temperature measurements and models. The scientists concluded that the weather-is-not-climate paradigm is no longer applicable in that form.

According to the researchers, they can actually discern the climate signal—that is, the long-term warming trend—in daily weather data, such as surface air temperature and humidity, provided that global spatial patterns are taken into account.

In plain English, this means that—despite global warming—there may well be a record low temperature in October in the US. If it is simultaneously warmer than average in other regions, however, this deviation is almost completely eliminated.

“Uncovering the climate change signal in daily weather conditions calls for a global perspective, not a regional one,” says lead author Sebastian Sippel, a postdoc working in Knutti’s research group.

The findings could have broad implications for climate science. “Weather at the global level carries important information about climate,” says Knutti. “This information could, for example, be used for further studies that quantify changes in the probability of extreme weather events, such as regional cold spells. These studies are based on model calculations, and our approach could then provide a global context of the climate change fingerprint in observations made during regional cold spells of this kind. This gives rise to new opportunities for the communication of regional weather events against the backdrop of global warming.”

Read the full article about climate change and daily weather by Peter Rüegg at Futurity.