Uppsala is now defined as a warm-temperate climate

Uppsala has on average become 1.5 degrees warmer in the last 30 years and can now be considered a mild-temperate climate.

“This is an enormous temperature increase and it means a movement of the climate zone,” according to Cecilia Johansson, Associate professor in meteorology.

(Image removed) Uppsala has one of the world's longest sustained weather statistics. Measuring weather and temperature statistics began in 1722 in Uppsala and this is the first time in almost 300 years that the measurements show such a sharp deviation. "0.1 or 0.2 degrees fluctuation in the average temperature would have been remarkable, but 1.5 degrees warmer is something huge. This will impact society and community planning,” says Cecilia Johansson, Associate professor in meteorology.

The latest statistics show that Uppsala now has a mild-temperate climate.

Global warming has made Uppsala on average 1.5 degrees warmer over the past 30 years, which means that Uppsala can now be redefined from a cold climate to a mild-temperate climate. SMHI statistics show exactly the same thing.

Uppsala has among the oldest ongoing weather analysis in the world. Anders Celsius was among those who began meteorological observations in Uppsala in 1722. The measurements are still taken daily at the Department of Earth Sciences, Uppsala University.

Weather measurements are presented in 30-year series to describe climate, in periods such as 1961-1990, 1991-2020 etc. When the coldest monthly temperature is below minus 3 on average it is defined as a cold climate, if the temperature is above it is known as a mild-temperate climate. Uppsala has been considered a cold climate since the middle of the 18th century, but the latest survey changes things.

“During the most recent measurement period, the temperature has risen one and a half degrees, compared with the period before. That is a significant increase. We meteorologists would have reacted if it had been a 0.1-0.2 degree increase, but 1.5 degrees is so much that we actually change climate zones. Sadly, this was not completely unexpected; we have noticed that it has become warmer and this is exactly what the climate models have said could happen. We also know that this is due to greenhouse gas emissions. We humans are interfering with the climate which has consequences: it gets warmer and wetter; we get more water vapor in the air because hot air contains more steam. It is no longer possible to question that we have global warming, these are facts. The IPCC calls it indisputable, and now we have it in black and white here in Uppsala as well,” says Cecilia Johansson.

(Image removed) Both the Uppsala area and the highlands of Småland have been cold climates, but the Småland highlands have now likely also become mild-temperate, as can be seen in the image of the SMHI map above. The map shows that the yellow, indicating a cold area, shrinks over time in the south.

In addition to the warmer climate in Uppsala, the highlands in Småland have also undergone a change and large parts are now classified as a mild-temperate climate. It is usually colder in areas higher up from sea-level, but warming of the Småland highlands moves as expected in line with both climate models developed by the IPCC and the climate models used by meteorologists at Uppsala University.

Effects of a warmer climate

But what is the significance of a shift in climate zones towards a warmer climate? What do we know?

Cecilia Johansson points towards some effects:

• More precipitation and greater risk of heavy showers and heavy rainfall;
• The statistics and data show a greater risk of longer dry periods with extreme drought;
• A consequence of longer dry periods can also increase risk for forest fires;
• Longer dry periods with higher average temperatures also have an impact on agriculture.

Most municipalities in Sweden are already working with SMHI to prepare for possible crises.

“There is now a shift in northern European conditions, which means that we will have warmer summers. If we look at Uppsala, the wettest months are now June and August, which means that it is dry in the middle of summer. This affects agriculture as precipitation for crops has decreased by an average of 25-30 mm in July. Previously we would have had, on average, 14 really hot days every summer, i.e. days with average temperatures above 25 degrees. This has now increased by a further 9 extreme-heat days per year. In 2018, we had 59 days with temperatures over 25 degrees. These changes do not happen suddenly in one year but occur over several years. Most things will be affected, but it is creeping up on us. This may be why some do not really take on board the changes, but it is undoubtedly climate change that we are seeing.

The rainstorms that recently hit Gävle, can they hit Uppsala?

“No, it is not so likely because north and northeast winds make Gävle more exposed while Uppsala is a little further in from the coast. Not so long ago the Fyrisån river flooded, which put  at risk local streets, homes and, particularly, houses with basements. Some ways to mitigate this is to build discrete water levels under pedestrian streets in order to absorb water in the event of floods and to develop more floodplains. We can also use flood alarms. That said, even if we anticipate these possibilities, we still can not prepare for the really big extreme weather events. What can be said is that we should avoid development in low-lying places: the higher up the better.”

For more information contact Cecilia Johansson, Associate professor in meteorology at the Department of Earth Sciences.
Email: Cecilia.Johansson@met.uu.se
Phone: 018-471 7185

Link to the weather measurements.

Facts:
When measurements began these were taken manually. Today weather measurements are mainly digital. Every second the temperature, air pressure, relative humidity, precipitation, ground temperature and solar radiation levels are measured. In addition to this data manual measurements are made every morning at the observation farm in Uppsala. The weather statistics are used in order to create climate models, among other things. Climate modeling is about picking up all the knowledge we have from the past and the present and using different tools to develop models for the future. This is important not least for societal development and planning.